Control of coating properties by tailored particle interactions: relation between suspension rheology and film structure - Peukert, Wolfgang; Günther, Lydia (Colloids and Surfaces, 2003)
The microstructure of dip-coated particulate thin films is studied by varying the stability of an aqueous silica sol used as coating bath. Different stability conditions are adjusted by changing electrolyte concentration and pH-value. The sol is characterized by acoustic and electroacoustic spectroscopy to obtain particle size distribution (PSD) and ζ-potentials. Furthermore, photometric measurements supplement the studies of stability behavior giving clear evidence of a non-DLVO contribution that is attributed to hydration forces. The structure of coatings, defined as the order of particles within the layer, was found to vary with stability parameters. It is observed that the surface roughness scanned by atomic force microscope (AFM) increased with increasing electrolyte concentration. Moreover, the structural evolution of the particulate network as a function of solid concentration and stability parameters is studied. For these purposes the sol is accumulated by dialysis against polyethylenglycol (PEG) and evaluated in terms of the viscosity as a function of shear rate. Finally, the influence of coating structures on the UV-light transmission properties is determined. Especially in case of LaCl3 a strong dependency between sol stability and the optical transmission property of the thin film is observed. The results explicitly confirm a correlation between microscopic structure and macroscopic propert
UnivIS-Import:2015-03-09:Pub.2003.tech.ITC.mechve.struct
Keywords: Dip-coating; Particles; Stability; Rheology; Particle arrangement

Control of Crystallization of PBT-PC Blends by Anisotropic SiO2 and GeO2 Glass Flakes - Düsenberg, Björn; Esper, Julian Duane; Maussner, Felix; Mayerhofer, Magdalena; Schmidt, Jochen; Peukert, Wolfgang; Bück, Andreas (Polymers, 2022)
Polymer composites and blend systems are of increasing importance, due to the combination of unique and different material properties. Blending polybutylene terephthalate (PBT) with polycarbonate (PC) has been the focus of attention for some time in order to combine thermo-chemical with mechanical resistance. The right compounding of the two polymers is a particular challenge, since phase boundaries between PBT and PC lead to coalescence during melting, and thus to unwanted segregation within the composite material. Amorphization of the semi-crystalline PBT would significantly improve the blending of the two polymers, which is why specific miscibility aids are needed for this purpose. Recent research has focused on the functionalization of polymers with shape-anisotropic glass particles. The advantage of those results from their two-dimensional shape, which not only improves the mechanical properties but are also suspected to act as miscibility aids, as they could catalyze transesterification or act as crystallization modifier. This work presents a process route for the production of PBT-PC blends via co-comminution and an in-situ additivation of the polymer blend particles with anisotropic glass flakes to adjust the crystallinity and therefore enhance the miscibility of the polymers.
CRIS-Team Scopus Importer:2022-11-25
Keywords: anisotropic particles; co-comminution; crystallization modifiers; functional filler; glass flakes; polymer-blends

Control of particle interfaces - the critical issue in nanoparticle technology - Peukert, Wolfgang; Günther, Lydia; Götzinger, Martin; Schwarzer, Hans-Christoph; Stenger, Frank (Advanced Powder Technology, 2003)
In the field of particle technology, processes cannot yet be designed from a basic molecular understanding. Nanotechnology, however, begins to bridge this gap between molecules and particles, and may thus not only open new ways for the production and handling of particulate matter, but also for the engineered design of advanced material properties. The visions and applications in nanoparticle technology cover a broad range, e.g. quantum dots in information technology, refractory particles for advanced ceramics, highly active substances in pharmacy, catalysts and micro- and mesoporous adsorbents to name only a few applications. Starting from the concept of product engineering we investigate the basic preconditions for tailoring nanoparticulate properties, i.e. the control of the particle interactions. This concept is then applied to precipitation as an example for particle synthesis and to particulate thin film formation as an example for structure formation.
UnivIS-Import:2015-03-09:Pub.2003.tech.ITC.mechve.contro_7
Keywords: Nanoparticles; Precipitation; Product engineering; Surface forces; Thin films

Control of Particle Properties in Thermally-Induced Precipitation of Polyetherimide - Unger, Laura; Fischer, Sybille; Sesseg, Jens P.W.; Pfister, Andreas; Schmidt, Jochen; Bück, Andreas (Polymers, 2023)
The feasibility of thermally-induced phase separation and crystallization for the production of semi-crystalline polyetherimide (PEI) microparticles from an amorphous feedstock has been reported recently. Here, we investigate process parameter dependencies for designing and control of particle properties. A stirred autoclave was used to extend the process controllability, as the applied process parameters, e.g., stirring speed and cooling rate, were adjusted. By increasing the stirring speed, the particle size distribution was shifted to larger values (correlation factor ρ = 0.77). Although, the enhanced droplet breakup, induced by the higher stirring speed, led to the formation of smaller particles (ρ = −0.68), broadening the particle size distribution. The cooling rate showed a significant influence on the melting temperature, reducing it with a correlation factor of ρ = −0.77, as confirmed by differential scanning calorimetry. Lower cooling rates led to larger crystalline structures and enhanced the degree of crystallinity. The polymer concentration mainly affected the resulting enthalpy of fusion, as an increased polymer fraction enhanced the latter (correlation factor ρ = 0.96). In addition, the circularity of the particles was positively correlated to the polymer fraction (ρ = 0.88). The structure assessed via X-ray diffraction, was not affecte
Keywords: process control; microparticles; precipitation; liquid–liquid phase separation; high-performance thermoplast

Control of Particle Size and Porosity in Continuous Fluidized-Bed Layering Granulation Processes - Neugebauer, Christoph; Bück, Andreas; Kienle, Achim (Chemical Engineering & Technology, 2020)
Particle formulation processes such as continuous fluidized-bed layering granulation (FBLG) are widely applied in chemical, food, and pharmaceutical industries. Particle size and particle porosity are important product properties in FBLG. In this paper, a new concept is presented for the simultaneous control of both properties. The new concept allows stable process operation, automatic adjustment of the desired product properties, and rejection of unforseen disturbances.
CRIS-Team Scopus Importer:2020-03-27
Keywords: Continuous operation; Fluidized-bed layering granulation; Particle porosity; Particle size; Process stability

Correlation between product purity and process parameters for the synthesis of Cu2ZnSnS4 nanoparticles using microwave irradiation - Ahmad, Rameez; Nicholson, K. S.; Nawaz, Qaisar; Peukert, Wolfgang; Distaso, Monica (Journal of Nanoparticle Research, 2017)
Kesterites (CZT(S,Se)4) emerged as a favourable photovoltaic material, leading to solar cell efficiencies as high as 12.7%. The development of sustainable roll-to-roll printing processes that make use of Cu2ZnSnS4 (CZTS) nanoparticle inks requires the proper design of synthetic approaches and the understanding of the relation between process parameters and product purity. In the current paper, we developed this relationship by calculating a specific energy factor. A microwave-assisted synthetic method that operates at atmospheric pressure and makes use of eco-friendly solvents is established. Four solvents, i.e. ethylene glycol (EG), diethylene glycol (di-EG), triethylene glycol (tri-EG) and tetraethylene glycol (tet-EG) are compared and the temperature during the reaction is assessed by two different methods. In particular, two by-products have been identified, i.e. Cu2-x S and a hexagonal phase. We show that the variation of reaction parameters such as power irradiation, type of solvent and precursor concentration influences the nanoparticles' sizes (from 12 to 6 nm) and also the temperature-time profile of reaction which, in turn, can be related to phase purity of CZTS nanoparticles. The results suggest that the product purity scales with the specific energy factor providing a useful tool to a rational design of high-quality CZTS nanoparticles.
Keywords: Disordered CZTS; Energy conversion; Cubic CZTS; Photovoltaics; Solar cells; Green chemistry; Kesterite

Correlation between shape, evaporation mode and mobility of small water droplets on nanorough fibres - Funk, Christine; Winzer, Bettina; Peukert, Wolfgang (Journal of Colloid and Interface Science, 2014)
The dynamic wetting behaviour and the mobility of droplets on fibres is a very important factor in coating processes, textile fabrication, in self-cleaning processes and in the filtration of fluids. In principal, filter regeneration depends on the mobility of the droplets on the fibre surface. Mobile droplets tend to coalesce which greatly simplifies their removal from the filter. In this contribution mobility analyses of water droplets on monofilaments in air are performed. Studies of droplet evaporation on pure PET fibres and on nanorough fibres coated with SiO2 nanoparticles of diameters between 6 nm and 50 nm in a hydrophilic binder system were done. We show that the mobility of water droplets correlates with the droplet conformation which in turn is determined by the droplet-fibre interface. We demonstrate that fibre coatings can be used to tailor the conformation and mobility of water droplets. The smaller the nanoparticle diameters in the coating are, the smaller are the contact angles between water droplets and fibre and the better is the mobility of the droplets on the fibre. Our results allow a fast optimization of the fibre surface properties which are directly influencing the contact angle, the mobility and the coalescence of water droplets and thus filter regeneration.
Keywords: Silica; Three phase contact line; Fibre surface energy; Nanoparticle coating; Wettability of fibres; Coalescing media; Droplet conformation; Contact angle; Evaporation mode; Droplet mobility

Correlation of Enhanced Strength and Internal Structure for Heat-Treated Submicron Stöber Silica Particles - Romeis, Stefan; Paul, Jonas; Hanisch, Mathias; Marthala, Venkata; Hartmann, Martin; Klupp Taylor, Robin; Schmidt, Jochen; Peukert, Wolfgang (Particle & Particle Systems Characterization, 2014)
The Stöber–Fink–Bohn (SFB) method allows the synthesis of spherical silica particles over a wide size range. Owing to the complex formation mechanism, the internal structure and related mechanical properties are not well understood. Within this account, the internal structure of synthesized SFB particles is changed systematically by heat treatments. Characterization by colloid titration, infrared spectroscopy, and solid-state nuclear magnetic resonance spectroscopy and the assessment of mechanical properties for single particles by in situ micromanipulation shed light on structure–property relations. Over the course of heat treatment, SFB particles become denser and owing to condensation of internal hydroxyl groups, the cross-linking of the silica network is enhanced. The observed chemical and structural changes are reflected by the mechanical properties of the particles: starting from a low Young’s modulus and hardness, clearly below the bulk properties of fused silica, both values are increasing over the course of the thermal treatment. Hardness for fused silica is approached after a treatment at 800 °C and exceeded after a treatment at 1000 °C. Young’s modulus approaches the bulk value. Furthermore, a significant plasticity is found: the sustained deformations are extremely high, and thus silica spheres with enhanced strength have been obtained by the thermal treatment.

Correlation of surface Volta potential with galvanic corrosion initiation sites in solid-state welded Ti-Cu bimetal using AFM-SKPFM - Rahimi, Ehsan; Rafsanjani-Abbasi, Ali; Imani, Amin; Hosseinpour, Saman; Davoodi, Ali (Corrosion Science, 2018)
Keywords: Local melted zone; SKPFM; Dissimilar welding; Galvanic corrosion

Corrosion Inhibition of Two Brass Alloys by Octadecanethiol in Humidified Air with Formic Acid - Hosseinpour, Saman; et al. (Corrosion, 2015)

Covalent Immobilization of Imidazolium Cations Inside a Silica Support: Palladium-Catalyzed Olefin Hydrogenation - Wang, Lei; Shylesh, Sankaranarayanapillai; Dehe, Daniel; Philippi, Thomas; Doerr, Gunder; Seifert, Andreas; Zhou, Zhou; Hartmann, Martin; Klupp Taylor, Robin; Jia, Mingjun; Ernst, Stefan; Thiel, Werner R. (ChemCatChem, 2012)
Mesoporous organosilica materials with different contents of bistrialkoxysilyl imidazolium salts in the framework were synthesized by a one-step synthesis. Textural characterization of the materials confirmed that the morphology and surface properties of the imidazolium-bridged organosilicas depended critically on the amount of organic groups in the framework, whereas solid-state NMR characterization showed that the imidazolium fragments were integrated covalently into the framework. Further reaction of these materials with Pd(OAc)(2), followed by reduction with NaBH4 yielded palladium nanoparticles stabilized in the mesoporous organosilicas. The stabilizing effect of the imidazolium cations and the mesostructure contributed to the high activity, selectivity, and stability of the palladium nanoparticles and allowed olefin hydrogenation under mild reaction conditions.
Keywords: heterogeneous catalysis; hydrogenation; immobilization; organic-inorganic hybrid composites; palladium

Critical Solids Transport Velocity in Horizontal Pipelines - Wirth, Karl-Ernst; Molerus, Otto (Preprints "Pneumatech II", 1984)
A new critical velocity equation, derived for horizontal pneumatic conveying, is compared with relations described in the literature. The comparison shows that the new dimensionless velocity group, which describes the ratio of momentum of the strand to its resistance, correctly defines conditions resulting in plugging of the pipeline. The new equation for critical velocity is a generalization of known empirical correlations which are valid only for particular regimes of variables. The blower characteristics exert a strong influence on measured critical velocities. Therefore installations designed for proving pipeline characteristics should be equipped either with a blower with a steep characteristic or with air supply controlled by a Laval nozzle. (A)
UnivIS-Import:2015-04-16:Pub.1984.tech.ITC.mechve.critic_6

Critical Solids Transport Velocity in Horizontal Pipelines - Wirth, Karl-Ernst; Molerus, Otto (Encyclopedia of Fluid Mechanics, 1986)
UnivIS-Import:2015-04-17:Pub.1986.tech.ITC.mechve.critic
Keywords: transport; pneumatik; fluidisation

Critical Solids Transport Velocity with Horizontal Pneumatic Conveying - Wirth, Karl-Ernst; Molerus, Otto (Powder and Bulk Engineering, 1985)
Comparison of a new critical velocity Vcrit equation, derived for horizontal pneumatic conveying, with literature equations shows that the new dimensionless velocity group, which describes the ratio of momentum of the strand to its resistance, correctly defines conditions that result in plugging of the pipeline. This equation for Vcrit is a generalization of known empirical correlations which are valid only for particular regimes of variables. The blower characteristics exert a strong influence on measured Vcrit and installations designed to prove pipeline characteristics should be equipped with either a blower with a steep characteristic or an air supply controlled by a Laval nozzle.
UnivIS-Import:2015-03-05:Pub.1985.tech.ITC.mechve.critic_1
Keywords: PNEUMATISCHES FOERDERN; STROEMUNG; GAS-SOLID FLOW; PNEUMATIC CONVEYING

Critical Velocity and Pressure Drop for Horizontal Pneumatic Conveying in Non-circular Pipes - Wirth, Karl-Ernst; Molerus, Otto (German Chemical Engineering, 1986)
Starting from the calculation of additional pressure drop for horizontal pneumatic strand-type conveying in circular pipes, the additional pressure drop and critical velocity for different pipe cross-sections were calculated. The relationships derived for horizontal pneumatic conveying in non-circular pipes were compared with measurements in non-circular pipes during hydraulic conveying. The comparison shows that there is a qualitative agreement between theory and measurement. It follows from the calculations and measurements that, in general, pipes with low cross-sectional profiles can be operated at lower fluid velocities than circular pipes with identical cross-sectional areas.
UnivIS-Import:2015-03-05:Pub.1986.tech.ITC.mechve.critic_40

Critical Velocity of Solids Transport through Horizontal Circular Pipelines - Wirth, Karl-Ernst (German Chemical Engineering, 1983)
Critical velocity, derived for horizontal pneumatic conveying, is compared with equations of other authors. The comparison shows that the theoretical dimensionless velocity group, which describes the ratio of momentum of the strand to its resistance, correctly reproduces conditions resulting in plugging of the pipeline. The theoretical equation for critical velocity differs from empirical correlations only by a constant. The characteristic of the employed blower exerts a strong influence on the measured critical velocities. Therefore, experimental installations should be either equipped with blowers with steep characteristics or the air supply should be controlled by Laval nozzles. The comparison between the theoretical equation for critical velocity in horizontal pneumatic conveying and the frequently applied equation of Durand for determination of critical velocity in horizontal hydraulic transport shows that the two differ only by a constant.
UnivIS-Import:2015-03-05:Pub.1983.tech.ITC.mechve.critic_37
Keywords: velocity; solid; transport; pneumatic

Crystallinity and internal structure of photonic balls prepared by colloidal crystallization in the confinement of an emulsion droplet - Vogel, Nicolas; et al. (2013)

Crystal Shape Engineering of Silicon Nanoparticles in a Thermal Aerosol Reactor - Koermer, Richard; Butz, Benjamin; Spiecker, Erdmann; Peukert, Wolfgang (Crystal Growth & Design, 2012)
In this work, the capability of gas phase synthesis for crystal shape engineering of silicon nanoparticles (SiNP) in a hot wall reactor is demonstrated. Therefore, the necessary boundary conditions for the formation of monodisperse spherical SiNP as well as octahedral shaped particles from silane pyrolysis are systematically deduced. The different shapes of the SiNP are ascribed to different growth regimes (reaction limitation, diffusion limitation) depending on the global process parameters. Single crystalline, defect-free, spherical particles with a mean diameter of 30 nm (geometric standard deviation below 1.1) and octahedra with a mean edge length of about 100 nm could be obtained solely by process parameter adjustment. Particle size and shape as well as crystallinity were characterized by scanning electron microscopy and X-ray diffraction. The inner structure and faceting of the particles was analyzed in detail by high resolution transmission electron microscopy. A model which elucidates the orientation relation between inner silicon structure and the particle shape is derived for the octahedra.

Cubes to Cubes: Organization of MgO Particles into One-Dimensional and Two-Dimensional Nanostructures - Thomele, Daniel; Baumann, Stefan O.; Schneider, Johannes; Sternig, Andreas; Shulda, Sarah; Richards, Ryan M.; Schwab, Thomas; Zickler, Gregor A.; Bourret, Gilles R.; Diwald, Oliver (Crystal Growth and Design, 2021)
Developing simple, inexpensive, and environmentally benign approaches to integrate morphologically well-defined nanoscale building blocks into larger high surface area materials is a key challenge in materials design and processing. In this work, we investigate the fundamental surface phenomena between MgO and water (both adsorption and desorption) with particles prepared via a vapor-phase process (MgO nanocubes) and a modified aerogel process (MgO(111) nanosheets). Through these studies, we unravel a strategy to assemble individual MgO nanoparticles into extended faceted single-crystalline MgO nanosheets and nanorods with well-defined exposed surfaces and edges. This reorganization can be triggered by the presence of H2O vapor or bulk liquid water. Water adsorption and the progressive conversion of vapor-phase grown oxide particles into hydroxides give rise to either one-dimensional or two-dimensional (1D or 2D) structures of high dispersion and surface area. The resulting Mg(OH)2 lamella with a predominant (001) surface termination are well-suited precursor structures for their topotactic conversion into laterally extended and uniform MgO(111) grain surface configurations. To understand the potential of polar (111) surfaces for faceting and surface reconstruction effects associated with water desorption, we investigated the stability of MgO(111) nanosheets during vacuum annealing and electron beam exposure. The significant surface reconstruction of the MgO(111) surfaces observed shows that adsorbate-free (111)-terminated surfaces of unsupported MgO nanostructures reconstruct rather than remain as charged planes of either three-fold coordinated O2- ion or Mg2+ ions. Thus, here we demonstrate the role water can play in surface formation and reconstruction by bridging wet chemical and surface science inspired approaches.
CRIS-Team Scopus Importer:2021-08-06

Cu, Zn doped borate bioactive glasses: antibacterial efficacy and dose-dependent in vitro modulation of murine dendritic cells - Schuhladen, Katharina; Stich, Lena; Schmidt, Jochen; Steinkasserer, Alexander; Boccaccini, Aldo R.; Zinser, Elisabeth (Biomaterials Science, 2020)
Among emerging biomaterials, bioactive glasses (BGs) are being widely explored for various applications in tissue engineering. However, the effects of BGs (in particular BG ionic dissolution products) on immune cells and specifically on dendritic cells (DCs), which are the most potent antigen-presenting cells of the immune system, have not been previously investigated in detail. Such interactions between BGs and DCs must be assessed as a novel biocompatibility criterion for biomaterials, since, with the increased application possibilities of BGs, the modulation of the immune system may induce potential complications and undesired side effects. Indeed, the effects of BG exposure on specific immune cells are not well understood. Thus, in this study we investigated, for the first time, the effect of borate BGs doped with biologically active ions on specific immune cells, such as DCs and we further investigated the antibacterial properties of these borate BGs. The compositions of the borate BGs (B3) were based on the well-known 13-93 (silicate) composition by replacing silica with boron trioxide and by adding copper (3 wt%) and/or zinc (1 wt%). By performing an agar diffusion test, the antibacterial effect depending on the compositions of the borate BGs could be proved. Furthermore we found a dose-dependent immune modulation of DCs after treatment with borate BGs, especially when the borate BGs contained Zn and/or Cu. Depending on the ion concentration and the rise in pH, the phenotype and function of DCs were modified. While at low doses B3 and Zn-doped B3 BGs had no impact on DC viability, Cu containing BGs strongly affected cell viability. Furthermore, the surface expression of DC-specific activation markers, such as the major histocompatibility complex (MHC)-II, CD86 and CD80, was modulated. In addition, also DC mediated T-cell proliferation was remarkably reduced when treated with high doses of B3-Cu and B3-Cu-Zn BGs. Interestingly, the release of inflammatory cytokines increased after incubation with B3 and B3-Zn BGs compared to mock-treated DCs. Considering the essential role of DCs in the modulation and regulation of immune responses, these findings provide first evidence of phenotypic and functional consequences regarding the exposure of DCs to BGs in vitro.
CRIS-Team Scopus Importer:2020-04-28

Deciphering the Role of Impurities in Methylammonium Iodide and Their Impact on the Performance of Perovskite Solar Cells - Levchuk, Ievgen; Hou, Yi; Gruber, Marco; Brandl, Marco; Herre, Patrick; Tang, Xiaofeng; Högl, Florian; Batentschuk, Miroslaw; Osvet, Andres; Hock, Rainer; Peukert, Wolfgang; Tykwinski, Rik; et al. (Advanced Materials Interfaces, 2016)
Solution-based perovskite solar cell fabrication typically involves rather complex processing sequences to yield highest performance. While most studies concentrate on the exploration of processing conditions, the purity levels of common perovskite precursor solutions have been investigated and a number of impurities that are critically important toward controlling the crystallization of perovskites are found. In this study, an in-depth chemical study of the possible impurities formed during CHNHI preparation is presented and their relevance on solar cell processing is revealed. A primary consideration is the chemical transformation of hypophosphorous acid, which plays the role of the stabilizer for HI. The detrimental role of the impurities is best demonstrated by comparing perovskite solar cell devices fabricated from impurity-free precursors versus precursors containing different concentrations of impurities. Most interestingly, it is revealed that a certain concentration of impurities is detrimental to the growth of large-grained crystals. PbHPO nanoparticles, which are formed after hypophosphorous acid transformation, actually cause crystal domain growth through serving as a nucleation center. This study gives valuable insight into the rate determining steps of perovskite crystal growth and further provides the basis for developing reliable and reproducible high-performance recipes for perovskite solar cell processing.
Keywords: Grain size; Impurities; Perovskites; Seed growth; Solar cells

Defects in oxygen-depleted titanate nanostructures - Vittadini, Andrea; Schirmer, Michael; Walz, Marie-Madeleine; Vollnhals, Florian; Lukasczyk, Thomas; Steinrück, Hans-Peter; Marbach, Hubertus; Riss, Alexander; Elser, Michael J.; Schürer, Benedikt; Diwald, Oliver (Langmuir, 2012)
The identification of defects and their controlled generation in titanate nanostructures is a key to their successful application in photoelectronic devices. We comprehensively explored the effect of vacuum annealing on morphology and composition of Na Ti O nanowires and protonated H Ti O nanoscrolls using a combination of scanning electron microscopy, Auger and Fourier-transform infrared (FT-IR) spectroscopy, as well as ab initio density functional theory (DFT) calculations. The observation that H Ti O nanoscrolls are more susceptible to electronic reduction and annealing-induced n-type doping than Na Ti O nanowires is attributed to the position of the conduction band minimum. It is close to the vacuum level and, thus, favors the Fermi level-induced compensation of donor states by cation vacancies. In agreement with theoretical predictions that suggest similar formation energies for oxygen and sodium vacancies, we experimentally observed the annealing induced depletion of sodium from the surface of the nanowires. © 2012 American Chemical Society.

Defined core–shell particles as the key to complex interfacial self-assembly - Menath, Johannes; Eatson, Jack; Brilmayer, Robert; Andrieu-Brunsen, Annette; Martin, D.; Vogel, Nicolas (Proceedings of the National Academy of Sciences of the United States of America, 2021)
The two-dimensional self-assembly of colloidal particles serves as a model system for fundamental studies of structure formation and as a powerful tool to fabricate functional materials and surfaces. However, the prevalence of hexagonal symmetries in such self-assembling systems limits its structural versatility. More than two decades ago, Jagla demonstrated that core–shell particles with two interaction length scales can form complex, nonhexagonal minimum energy configurations. Based on such Jagla potentials, a wide variety of phases including cluster lattices, chains, and quasicrystals have been theoretically discovered. Despite the elegance of this approach, its experimental realization has remained largely elusive. Here, we capitalize on the distinct interfacial morphology of soft particles to design two-dimensional assemblies with structural complexity. We find that core–shell particles consisting of a silica core surface functionalized with a noncrosslinked polymer shell efficiently spread at a liquid interface to form a two-dimensional polymer corona surrounding the core. We controllably grow such shells by iniferter-type controlled radical polymerization. Upon interfacial compression, the resulting core–shell particles arrange in well-defined dimer, trimer, and tetramer lattices before transitioning into complex chain and cluster phases. The experimental phase behavior is accurately reproduced by Monte Carlo simulations and minimum energy calculations, suggesting that the interfacial assembly interacts via a pairwise-additive Jagla-type potential. By comparing theory, simulation, and experiment, we narrow the Jagla g-parameter of the system to between 0.9 and 2. The possibility to control the interaction potential via the interfacial morphology provides a framework to realize structural features with unprecedented complexity from a simple, one-component syste
Keywords: Interfaces; Microgels; Colloids; Interactions; Self-assembly

Deformation behavior of micron-sized polycrystalline gold particles studied by in situ compression experiments and frictional finite element simulation - Paul, Jonas; Romeis, Stefan; Herre, Patrick; Peukert, Wolfgang (Powder Technology, 2015)
We present a combined experimental and finite element study on the deformation behavior of micron-sized polycrystalline gold particles. This study enables detailed insights into the underlying deformation mechanisms of the particles. Scanning electron microscope supported in situ uniaxial compression experiments of the single spherical polycrystalline gold particles were performed in the size range of 1. μm by using a custom built manipulation device. By testing a large number of particles stress-strain data and information on the particle morphology were obtained with statistical significance. The experimentally observed stress-strain behavior and the geometric shape of the stressed particles were found to be in excellent agreement with the elastic-perfectly plastic finite element model accounting for frictional effects at the contact interfaces. A significantly increased yield strength compared to bulk gold was found - grain size strengthening according to the Hall-Petch relation was identified as the main hardening mechanism. Hardness was found to vary with strain - an effect related to the altering geometric shape of the particles during compression. Comparison to a frictionless finite element model revealed the necessity of considering the effect of friction. These findings are not restricted to gold particles, but should be applicable to a wide range of elastic-perfectly plastic materials.
Keywords: FEM; Friction; Gold particles; In situ SEM; Mechanical properties

Deformation behavior of nanocrystalline titania particles accessed by complementary in situ electron microscopy techniques - Herre, Patrick; Romeis, Stefan; Mackovic, Mirza; Przybilla, Thomas; Paul, Jonas; Schwenger, Jan; Torun, Boray; Grundmaier, Guido; Spiecker, Erdmann; Peukert, Wolfgang (Journal of the American Ceramic Society, 2017)
The mechanical behavior of nanostructured spherical submicrometer titania parti- cles was studied by in situ uniaxial compression experiments in the scanning and transmission electron microscope (SEM and TEM). Mesoporous and amorphous titania particles were prepared by a wet chemical sol-gel approach. To obtain nanocrystalline (nc) single-phase anatase and rutile particles the amorphous parti- cles were cryst allized by high-temperature annealing. For each sample the defor- mation behavior of at least 50 particles was investigated by in situ compression experiments in the SEM. In all cases an elastic – predominantly plastic deforma- tion behavior accompanied by crack initiation at exceptionally high engineering strain values of several percent were observed. Crack propagation presumably along grain boundaries and a Weibull distributed fracture stress was shown for all nc particles. Complementary in situ TEM experiment s and ex situ analysis of focused ion beam prepared particle cross-sections were carried out to identify the underlying deformati on mechanisms. Grain rotations and grain sliding are observed for nc anatase particles during in situ compr ession and are further identi- fied to be linked to a densification of the mesoporous particle structure. Our dedi- cated prepar ation and quanti tative in situ characterization methodology provides an excellent basis for a better understanding of the mechanical behavior of advanced ceramics.
Keywords: mechanical properties; nanoparticles; scanning electron microscopy; titanium oxide; transmission electron microscopy

Deformation behavior of nanocrystalline titania particles accessed by complementary in situ electron microscopy techniques - Herre, Patrick; Romeis, Stefan; Mackovic, Mirza; Przybilla, Thomas; Paul, Jonas; Schwenger, Jan; Torun, Boray; Grundmeier, Guido; Spiecker, Erdmann; Peukert, Wolfgang (Journal of the American Ceramic Society, 2017)
Keywords: mechanical properties; titanium oxide; transmission electron microscopy; nanoparticles; scanning electron microscopy

Delamination and Dissolution of Titanate Nanowires: A Combined Structure and in Situ Second Harmonic Generation Study - Schürer, Benedikt; Elser, Michael J.; Sternig, Andreas; Peukert, Wolfgang; Diwald, Oliver (Journal of Physical Chemistry C, 2011)
Mechanistic insights into shape and structure transformation of metal oxide nanostructures are critical to our understanding of how synthesis parameters and chemical environment affect their properties. Na2Ti3O7 nanowires, which are composed of titanate nanosheets and which contain sodium ions in the interlayer region, are thermodynamically unstable in acid solutions. At room temperature nanosheet delamination along the nanowire length axis leads to coiled-up nanoscrolls. At 373 K, a dissolution and TiO2 recrystallization process gives rise to colloidal anatase nanoparticles. The impact of temperature on different reaction pathways is attributed to differences in the energy barriers associated with the two transformation channels. We comprehensively investigated these reactions with X-ray diffraction and electron microscopy and for the first time tracked processes at the solid–liquid interface such as nanosheet delamination by time-resolved second harmonic generation (SHG) measurements. The applicability of the SHG method for in situ studies which address the transformation of layered nanostructures in aqueous solution even at high electrolyte concentrations is demonstrated.

Delamination of graphite in a high pressure homogenizer - Nacken, Thomas; Damm, Cornelia; Walter, Johannes; Rüger, Andreas; Peukert, Wolfgang (RSC Advances, 2015)
A scalable industrial method for graphene and Few-Layer-Graphene (FLG) production by graphite delamination in N-methylpyrrolidone and water-surfactant mixtures using a high pressure homogenizer is presented. This paper is focused on processing conditions and extensive subsequent analysis of the delaminated products by a combination of analytical ultracentrifugation, UV/Vis and statistical Raman spectroscopies including co-localization with atomic force microscopy. In this way quantitative processing-structure-property correlations showing how suspension properties and processing parameters governing yield, quality and lateral dimension of the produced graphene are obtained. It is found that a high pressure homogenizer can be used to obtain sufficiently high concentrated FLG suspensions with low defect concentration.

Delamination of graphite sheets in stirred media mills - Knieke, Catharina; Peukert, Wolfgang (2008 AIChE Annual Meeting, AIChE 100, 2008)

Delamination of hexagonal boron nitride in a stirred media mill - Damm, Cornelia; Peukert, Wolfgang; Körner, Julia (Journal of Nanoparticle Research, 2013)
A scalable process for delamination of hexagonal boron nitride in an aqueous solution of the non-ionic surfactant TWEEN85 using a stirred media mill is presented. The size of the ZrO beads used as grinding media governs the dimensions of the ground boron nitride particles as atomic force microscopic investigations (AFM) reveal: the mean flakes thickness decreases from 3.5 to 1.5 nm and the ratio between mean flake area and mean flake thickness increases from 2,200 to 5,800 nm if the grinding media size is reduced from 0.8 to 0.1 mm. This result shows that a high number of stress events in combination with low stress energy (small grinding media) facilitate delamination of the layered material whereas at high stress energies in combination with a low number of stress events (large grinding media) breakage of the layers dominates over delamination. The results of particle height analyses by AFM show that few-layer structures have been formed by stirred media milling. This result is in agreement with the layer thickness dependence of the delamination energy for hexagonal boron nitride. The concentration of nanoparticles remaining dispersed after centrifugation of the ground suspension increases with grinding time and with decreasing grinding media size. After 5 h of grinding using 0.1 mm ZrO grinding media the yield of nanoparticle formation is about 5 wt%. The nanoparticles exhibit the typical Raman peak for hexagonal boron nitride at 1,366 cm showing that the in-plane order in the milled platelets is remained. © 2013 Springer Science+Business Media Dordrecht.
Keywords: Delamination; Hexagonal boron nitride; Stirred media mill

Design and scale-up of a semi-industrial downer-reactor for the rounding of irregular polymer particles - Peukert, Wolfgang; Sachs, Marius; Schmidt, Jochen; Wirth, Karl-Ernst (AIP Conference Proceedings 1713, 2016)
The recent development of rapid prototyping technologies towards additive manufacturing reveals some major drawbacks of processes such as laser beam melting (LBM). This contribution focuses on the lack of suitable polymer material with a fine particle size and good flowability. Polymer particles obtained by a wet grinding process 1 are treated in a heated downer reactor. This treatment changes the particles' morphology from a chiselled state towards a spherical form by surface tension forces in a molten state 2 and leads to an improved flowability. To reach the required amount of rounded polymer powder, a downer reactor in semi-industrial scale has been established and will be characterized in this article. For the purpose of particle rounding it is necessary to avoid contact of molten particles with each other and with the hot reactor walls. Furthermore, the heat distribution has been investigated as one of the key parameters of the process. Finally, a proof of concept by rounding wet grinded PBT material was successfully conducted. The product was examined to obtain data about a change in particle size and flowability.
Keywords: additive manufacturing; downer reactor; particle rounding; polymers

Design of a new invertible polymer coating on a solid surface and its effect on dispersion colloidal stability - Peukert, Wolfgang; Kohut, Ananiy; Ranjan, Sodhi; Voronov, Andriy; Tokarev, Victor; Bednarska, O.; Gevus, O.; et al. (Langmuir, 2006)
This article presents a new approach to building up self-adjustable invertible polymer coatings at solid surfaces. The approach is based on a two-step process. In the first step, the surface of dispersed TiO or silicon wafers was functionalized with the aid of a reactive copolymer, viz., poly(styrene-alt-maleic anhydride) (PSM), to which, in the second step, the chains of amphiphilic oligoester have been tethered. The latter contains both hydrophilic poly(ethylene glycol) and hydrophobic aliphatic dibasic acid moieties being alternately distributed along the oligomer chains. It is shown that the titania modified in this way can form stable suspensions in both polar (water) and nonpolar (toluene) media. Moreover, multiple drying/redispersion cycles demonstrate the ability of the modified titania particles, after their removal from one type of dispersion and consequent drying, to be redispersed in dispersing media strongly differing by polarity from that of the previous medium. An environmentally induced switching of the surface properties has been observed via the measurement of the wetting contact angles and scanning force microscopy (SFM) of silicon wafers covered by PSM with tethered oligoester chains. These experiments give strong support for the predicted capability of such polymer coatings to switch their environmental appearance (i.e., to behave as a self-adjustable invertible interface because of the ability of the tethered amphiphilic oligoester chains to change their conformations in response to environmental changes in such a manner so as to adapt and enhance their compatibility with the surrounding media). © 2006 American Chemical Society.
Keywords: surfaces; polymer; titan; oxide; dispersion

Desulfurization of natural gas condensate using polyethylene glycol and water intercalated activated γ-bauxite - Behmadi, Reza; Mokhtarian, Mahsa; Davoodi, Ali; Hosseinpour, Saman (Journal of Cleaner Production, 2022)
Three different active γ-bauxite were developed from a low-grade raw boehmite ore, as a cheap and efficient adsorbent for the desulfurization of gas condensates. The first adsorbent (RBa) was developed directly through a two-stage thermochemical activation (thermal activation process followed by an acid treatment) of the boehmite ore. The other two adsorbents (PBa and WBa) were initially intercalated with polyethylene glycol (PEG) solution or water, respectively, at the optimum temperature and pressure followed by thermochemical activation to modify the pore size and active surface area. The process parameters such as pulp density and leaching time were optimized using response surface methodology (RSM) based on central composite design (CCD). Comparing the performance of prepared adsorbents to remove sulfur-containing compounds from natural gas condensate indicated the superior sulfur removal efficiency of PBa compared to WBa and non-intercalated adsorbents. Using PBa, the sulfur content was significantly reduced from 2821 ppm to <35 ppm. Characterization of the developed adsorbents indicated that after thermal activation, the pore size of the non-intercalated adsorbent was significantly reduced, which negatively affects its desulfurization efficiency. Nevertheless, the pore diameter of PBa was maintained similar to that of raw bauxite while its surface area was approximately 12-fold larger, which confirms the successful role of PEG as a lattice expansion element, improving its desulfurization efficiency.
CRIS-Team Scopus Importer:2022-10-14
Keywords: Average pore diameter; Bauxite adsorbent; Desulfurization; Intercalation

Detailed Analysis of the Growth Kinetics of ZnO Nanorods in Methanol - Voigt, Michael; Klaumünzer, Martin; Thiem, Heiko; Peukert, Wolfgang (Journal of Physical Chemistry C, 2010)
The growth kinetics of ZnO nanorods in methanol is studied by a combination of scanning and high-resolution transmission electron microscopy and X-ray diffraction analysis. In the early stage of growth oriented attachment of 2−3 spheroidal crystallites to rod-like structures occurs. Later, rods of up to 90 nm in length with a hexagonal cross-section up to 18 nm in diameter form by ripening. Our main finding is that the growth follows a power law as a function of the ripening time with exponents of 0.32 to 0.39 for the length and 0.17 to 0.21 for the diameter. In contrast to previous studies on the growth of ZnO rods in alcohols our results indicate that the growth is dominated by anisotropic Ostwald ripening that is limited by volume diffusion.

Detailed investigations of ZnO photoelectrodes preparation for dye sensitized solar cells - Marczak, Renata; Werner, Fabian; Ahmad, Rameez; Lobaz, Volodymyr; Guldi, Dirk Michael; Peukert, Wolfgang (Langmuir, 2011)
Wurtzite ZnO hexagonal nanopyramids were successfully synthesized in the liquid phase from homogeneous methanolic solutions of zinc acetate and tetramethylammonium hydroxide at an excess of zinc ions. The formation and properties of the nanocrystals were examined as a function of synthesis conditions. No significant influence of the [Zn ]/[OH ] ratio was noticed on the final particle size, in spite of increased amounts of OH ions, which tend to accelerate the particle nucleation and growth. Nevertheless, the reactant concentration ratio influences the surface properties of the ZnO nanocrystals. Mesoporous ZnO films were prepared by doctor blading ethanolic pastes containing ZnO nanoparticles and ethyl cellulose onto FTO conductive glass substrate followed by calcination. Additionally, the influence of a plasticizer (triacetin)-used during the paste preparation-on the film quality was investigated. A higher content of ZnO nanoparticles and plasticizer in the pastes improved the film quality. Four different temperatures (i.e., 400, 425, 450, and 475 °C) were used for the film calcination and their influence on the structural properties of the films was characterized. In principle, increasing the calcination temperature goes hand in hand with an increase of particle size, as well as the pore diameter and reduction of the surface area. Suitable mesoporous films were employed as photoanodes in dye sensitized solar cells (DSSCs). In order to assess the effect of the varied parameters on complete DSSC devices-using cis-diisothiocyanato-bis(2,2′- bipyridyl-4,4′-dicarboxylato) ruthenium(II)bis(tetrabutylammonium (N719) as a sensitizer-incident photon to current efficiency (IPCE) and current voltage measurements were carried out. The IPCE measurements confirmed photoinduced electron injection from the dye, reaching IPCE values up to 76%. Furthermore, current-voltage characteristics of complete cells emphasized the importance of the proper preparation methods and temperatures. These features are important assets for the preparation of nanocrystalline ZnO based photoelectrodes and for improving the DSSC performance. © 2011 American Chemical Society.

Determination of 2D Particle Size Distributions in Plasmonic Nanoparticle Colloids via Analytical Ultracentrifugation: Application to Gold Bipyramids. - Frank, Uwe; Drobek, Dominik; Sánchez-Iglesias, Ana; Wawra, Simon; Nees, Nico; Walter, Johannes; Pflug, Lukas; Apeleo Zubiri, Benjamin; Spiecker, Erdmann; Liz-Marzan, Luis M.; Peukert, Wolfgang (ACS nano, 2023)
Multidimensional particle properties determine the product properties in numerous advanced applications. Accurate and statistically meaningful measurements of complex particles and their multidimensional distributions are highly challenging but strongly needed. 2D particle size distributions of plasmonic nanoparticles of complex regular shape can be obtained from analytical ultracentrifugation experiments via the optical back coupling method. A workflow for the calculation of frictional properties of arbitrarily shaped nanoparticles was developed based on bead shell models and applied to gold bipyramids with a pentagonal cross-section. The obtained 2D particle length-diameter distributions and the reduced cumulative 1D length and diameter distributions were compared to transmission electron microscopy measurements. While we find very good agreement for most measurements, the obtained length and diameter distributions were shifted by a few nanometers for some samples. Transmission electron microscopy, energy-dispersive X-ray spectroscopy, electron tomography, and finite element modeling indicate that the shift originated from a slight mismatch between the assumed shape of the simulated perfect bipyramids and the real particle shape and composition due to the presence of silver in the particles. This study demonstrates the feasibility of the applied techniques for complex shape analysis of nanoparticle ensembles with unmatched particle count numbers.
Keywords: analytical ultracentrifugation; bead modeling; electron tomography; extinction cross section; gold bipyramids; optical back coupling; particle shape distribution

Determination of Hansen parameters for particles: A standardized routine based on analytical centrifugation - Süß, Sebastian; Sobisch, Titus; Peukert, Wolfgang; Lerche, Dietmar; Segets, Doris (Advanced Powder Technology, 2018)
Keywords: Particle interactions; Formulation; Dispersibility; Nanoparticles; Hansen solubility parameter

Determination of material properties relevant to grinding by practicable labscale milling tests - Peukert, Wolfgang; Vogel, Lutz (European Congress on Comminution, 2002)
The breakage probability of different materials can be described well by a single mastercurve comprising the breakage performance of various materials. The function which is obtained when the Weibull statistics is applied to particle breakage depends on the mass-specific impact energy, a minimum energy required to cause any particle fracture at all, the initial particle size and a material parameter which describes the material-specific breakage behaviour. The material parameters are determined by single particle experiments. This procedure under well known stressing conditions gives reproducible results. A second approach to determine the material parameters from more practicable and less time consuming labscale milling tests is presented.
UnivIS-Import:2015-04-16:Pub.2002.tech.ITC.mechve.determ
Keywords: grinding; labscale milling tests; weibull statistics

Determination of quantitative structure-property and structure-process relationships for graphene production in water - Nacken, Thomas; Damm, Cornelia; Xing, Haichen; Rüger, Andreas; Peukert, Wolfgang (Nano Research, 2015)
A scalable method for graphene and few-layer graphene (FLG) production by graphite delamination in aqueous solutions of the nonionic surfactant TWEEN®80 (TW80) using stirred-media mills is presented. Delaminated product analysis using statistical Raman spectroscopy yielded extensive processing-structure-property relationships that revealed how stress intensity and specific energy input, i.e., the process parameters, govern the yield of graphene production and defect formation. The dispersed carbon concentration increased but the content and the quality of the FLG product decreased sharply with higher specific energy input. The FLG content of the product was up to 90%, especially for low specific energy input. Moreover, Raman analyses revealed that stress intensities greater than about 1 nJ were related to significant defect formation in the product particles. Another key parameter for graphene production is solvent viscosity. The FLG concentration in the product increased by a factor of 10 when the solvent’s viscosity was increased from 1 to 6 mPa·s because shear- and friction-induced delamination was enhanced and in-plane fracture was reduced due to dampening of bead motion. Based on the processing-structure-property relationships found, we propose that the delamination process can be designed in such way that the product consists, almost totally, of FLG and that single-layer graphene is produced. The scalability of graphene production by stirred-media delamination was demonstrated when an increase in the batch size from 0.2 to 2 L had no significant effect on product quality. [Figure not available: see fulltext.]
Keywords: few-layer graphene; graphene; graphite delamination; process parameters; statistical Raman spectroscopy; stirred-media mill

Determination of specific and non-specific protein-protein interactions for beta-lactoglobulin by analytical ultracentrifugation and membrane osmometry experiments - Uttinger, Maximilian; Hundschell, Christoph S.; Lautenbach, Vanessa; Pusara, Srdjan; Bather, Simon; Heyn, Timon R.; Keppler, Julia K.; Wenzel, Wolfgang; Walter, Johannes; Kozlowska, Magdalena; Wagemans, Anja M.; Peukert, Wolfgang (Soft Matter, 2022)
Protein-protein interactions are essential for the understanding of biological processes. Specific protein aggregation is an important aspect for many biological systems. In particular, electrostatic interactions play the key role for protein-protein interactions, as many amino acids have pH-dependent charge states. Moreover, protein dissociation is directly related to the solution pH, ionic strength, temperature and protein concentration. The subtle interplay between different specific and non-specific interactions is demonstrated for beta-lactoglobulin (BLG) with a focus on low salt concentrations, thus mimicking technically relevant processing conditions. BLG is a well-characterized model system, proven to attain its monomer-dimer equilibrium strongly dependent upon the pH of the solution. In this manuscript, we present a unique combination of analytical ultracentrifugation and membrane osmometry experiments, which quantifies specific and non-specific interactions, i.e. in terms of the dimer dissociation constants and the second osmotic virial coefficient, at pH 3 and 7 and sodium chloride concentrations of 10 mM and 100 mM. This provides direct insight to protein-protein interactions for a system with a concentration-dependent monomer-dimer equilibrium. Moreover, using a coarse-grained extended DLVO model in combination with molecular dynamics simulations, we quantify non-specific monomer-monomer, monomer-dimer and dimer-dimer interactions as well as the binding free energy of BLG dimerization from theoretical calculations. The experimentally determined interactions are shown to be mainly governed by electrostatic interactions and further agree with free energy calculations. Our experimental protocol aims to determine non-specific and specific interactions for a dynamically interacting system and provides an understanding of protein-protein interactions for BLG at low salt concentrations.
Keywords: 2nd virial-coefficient; molecular-dynamics; sedimentation-velocity; aqueous-solutions; salt; equilibrium; stability; systems; range; solubility

Determination of specific and non-specific protein-protein interactions for beta-lactoglobulin by analytical ultracentrifugation and membrane osmometry experiments - Uttinger, Maximilian; Hundschell, C. S.; Lautenbach, Vanessa; Pusara, Srdjan; Bather, S.; Heyn, T. R.; Keppler, J. K.; Wenzel, W.; Walter, Johannes; Kozlowska, Mariana; Wagemans, A. M.; Peukert, Wolfgang (Soft Matter, 2022)
Protein-protein interactions are essential for the understanding of biological processes. Specific protein aggregation is an important aspect for many biological systems. In particular, electrostatic interactions play the key role for protein-protein interactions, as many amino acids have pH-dependent charge states. Moreover, protein dissociation is directly related to the solution pH, ionic strength, temperature and protein concentration. The subtle interplay between different specific and non-specific interactions is demonstrated for beta-lactoglobulin (BLG) with a focus on low salt concentrations, thus mimicking technically relevant processing conditions. BLG is a well-characterized model system, proven to attain its monomer-dimer equilibrium strongly dependent upon the pH of the solution. In this manuscript, we present a unique combination of analytical ultracentrifugation and membrane osmometry experiments, which quantifies specific and non-specific interactions, i.e. in terms of the dimer dissociation constants and the second osmotic virial coefficient, at pH 3 and 7 and sodium chloride concentrations of 10 mM and 100 mM. This provides direct insight to protein-protein interactions for a system with a concentration-dependent monomer-dimer equilibrium. Moreover, using a coarse-grained extended DLVO model in combination with molecular dynamics simulations, we quantify non-specific monomer-monomer, monomer-dimer and dimer-dimer interactions as well as the binding free energy of BLG dimerization from theoretical calculations. The experimentally determined interactions are shown to be mainly governed by electrostatic interactions and further agree with free energy calculations. Our experimental protocol aims to determine non-specific and specific interactions for a dynamically interacting system and provides an understanding of protein-protein interactions for BLG at low salt concentrations.
CRIS-Team WoS Importer:2022-09-09

Determination of the Lateral Dimension of Graphene Oxide Nanosheets Using Analytical Ultracentrifugation - Walter, Johannes; Nacken, Thomas; Damm, Cornelia; Thajudeen, Thaseem; Eigler, Siegfried; Peukert, Wolfgang (Small, 2014)
In this paper, a method to determine the lateral dimensions of 2D nanosheets directly in suspension by analytical ultracentrifugation (AUC) is shown. The basis for this study is a well-characterized and stable dispersion of graphene oxide (GO) monolayers in water. A methodology is developed to correlate the sedimentation coefficient distribution measured by AUC with the lateral size distribution of the 2D GO nanosheets obtained from atomic force microscopy (AFM). A very high accuracy can be obtained by virtue of counting several thousand sheets, thereby minimizing any coating effects or statistical uncertainties. The AFM statistics are further used to fit the lateral size distribution obtained from the AUC to determine the unknown hydrodynamic sheet thickness or density. It is found that AUC can derive nanosheet diameter distributions with a relative error of the mean sheet diameter of just 0.25% as compared to the AFM analysis for 90 mass% of the particles in the distribution. The standard deviation of the size-dependent error for the total distribution is found to be 3.25%. Based on these considerations, an expression is given to calculate the cut size of 2D nanosheets in preparative centrifugation experiments.

Determination of the length and diameter of nanorods by a combination of analytical ultracentrifugation and scanning mobility particle sizer - Thajudeen, Thaseem; Walter, Johannes; Srikantharajah, Rubitha; Lübbert, Christian; Peukert, Wolfgang (Nanoscale Horizons, 2017)
A combination of orthogonal measurement techniques is utilized in this study to predict the average lengths and diameters of colloidal nanorods. Sedimentation coefficient distributions and electrical mobility distributions obtained from analytical ultracentrifugation and a scanning mobility particle sizer, respectively, are used for the hydrodynamic correlation. The method is validated theoretically and application to Au and ZnO nanorod samples is shown. The results demonstrate that the combination of both measurement techniques is an excellent method for the two-dimensional characterization of nanorods.

Determination of the quantum dot band gap dependence on particle size from optical absorbance and transmission electron microscopy measurements - Segets, Doris; Lukas, Matthew; Klupp Taylor, Robin; Scheele, Marcus; Zheng, Haimei; Alivisatos, Pa; Peukert, Wolfgang (Acs Nano, 2012)
This work addresses the determination of arbitrarily shaped particle size distributions (PSDs) from PbS and PbSe quantum dot (QD) optical absorbance spectra in order to arrive at a relationship between band gap energy and particle size over a large size range. Using a modified algorithm which was previously developed for ZnO, we take only bulk absorption data from the literature and match the PSDs derived from QD absorbance spectra with those from transmission electron microscopical (TEM) image analysis in order to arrive at the functional dependence of the band gap on particle size. Additional samples sized solely from their absorbance spectra with our algorithm show excellent agreement with TEM results. We investigate the influence of parameters of the TEM image analysis such as threshold value on the final result. The band gap versus size relationship developed from analysis of just two samples lies well within the bounds of a number of published data sets. We believe that our methodology provides an attractive shortcut for the study of various novel quantum-confined direct band gap semiconductor systems as it permits the band gap energies of a broad size range of QDs to be probed with relatively few synthetic experiments and without quantum mechanical simulations. © 2012 American Chemical Societ
Keywords: absorbance spectra; automated TEM image analysis; optical properties; particle size distribution; PbS(e); quantum dot

Determination of the two-dimensional distributions of gold nanorods by multiwavelength analytical ultracentrifugation - Wawra, Simon; Pflug, Lukas; Thajudeen, Thaseem; Kryschi, Carola; Stingl, Michael; Peukert, Wolfgang (Nature Communications, 2018)
Properties of nanoparticles are influenced by various parameters like size, shape or composition. Comprehensive high throughput characterization techniques are urgently needed to improve synthesis, scale up to production and make way for new applications of multidimensional particulate systems. In this study, we present a method for measuring two-dimensional size distributions of plasmonic nanorods in a single experiment. Analytical ultracentrifuge equipped with a multiwavelength extinction detector is used to record the optical and sedimentation properties of gold nanorods simultaneously. A combination of sedimentation and extinction properties, both depending on diameter and length of the dispersed nanorods, is used to measure two-dimensional distributions of gold nanorod samples. The length, diameter, aspect ratio, volume, surface and cross-sectional distributions can be readily obtained from these results. As the technique can be extended to other non-spherical plasmonic particles and can be used for determining relative amounts of particles of different shapes it provides complete and quantitative insights into particulate systems.
EAM Import::2019-03-13

Determination of the yield, mass and structure of silver patches on colloidal silica using multiwavelength analytical ultracentrifugation - Meincke, Thomas; Walter, Johannes; Pflug, Lukas; Thajudeen, Thaseem; Völkl, Andreas; Cardenas Lopez, Paola; Uttinger, Maximilian; Stingl, Michael; Watanabe, Satoshi; Peukert, Wolfgang; Klupp Taylor, Robin (Journal of Colloid and Interface Science, 2022)
Anisotropic nanoparticles offer considerable promise for applications but also present significant challenges in terms of their characterization. Recent developments in the electroless deposition of silver patches directly onto colloidal silica particles have opened up a simple and scalable synthesis method for patchy particles with tunable optical properties. Due to the reliance on patch nucleation and growth, however, the resulting coatings are distributed in coverage and thickness and some core particles remain uncoated. To support process optimization, new methods are required to rapidly determine patch yield, thickness and coverage. Here we present a novel approach based on multiwavelength analytical ultracentrifugation (MWL-AUC) which permits simultaneous hydrodynamic and spectroscopic characterization. The patchy particle colloids are produced in a continuous flow mixing process that makes use of a KM-type micromixer. By varying the process flow rate or metal precursor concentration we show how the silver to silica mass ratio distribution derived from the AUC-measured sedimentation coefficient distribution can be influenced. Moreover, through reasoned assumptions we arrive at an estimation of the patch yield that is close to that determined by arduous analysis of scanning electron microscopy (SEM) images. Finally, combining MWL-AUC, electrodynamic simulations and SEM image analysis we establish a procedure to estimate the patch thickness and coverag
Keywords: ultracentrifugation; localized surface plasmon resonance; patchy particles; continuous flow synthesis; multidimensional characterization

Development and characterization of niobium-releasing silicate bioactive glasses for tissue engineering applications - Miguez-Pacheco, Valentina; de Ligny, Dominique; Schmidt, Jochen; Detsch, Rainer; Boccaccini, Aldo R. (Journal of the European Ceramic Society, 2018)
Novel niobium-containing bioactive glass formulations (Nb-BGs) were designed, produced and used to fabricate sintered glass-ceramic granules to examine their in vitro bioactivity and angiogenic potential. Nb-BGs were prepared by melting and quenching. Afterwards, the glasses were crushed and milled into fine powders. These powders were used to make aqueous slurries which were poured into molds, dried and sintered to produce pellets, from which granules of 0.5-0.85 mm in size were obtained. In vitro bioactivity was tested by immersing the granules in simulated body fluid for up to 14 days. Cell biology tests were carried out by indirect culture of bone marrow stromal cells (ST-2) with supernatants resulting from incubation of BG granules in cell culture medium. The effect of dissolution products from Nb-BGs on the secretion of vascular endothelial growth factor (VEGF) was assessed to characterize the angiogenic potential of the new Nb-containing BG compositions.
Keywords: Bioactive glasses; Scaffolds; Tissue engineering; Niobium; Angiogenesis

Development of a low-cost activated mesoporous bauxite for the reclamation of used transformer oil - Behmadi, Reza; Mokhtarian, Mahsa; Ghadrian, Kazem; Davoodi, Ali; Hosseinpour, Saman (Separation and Purification Technology, 2021)
Regeneration/reclamation of used oil using active adsorbents with high surface area is considered as one of the most efficient methods for the waste management and treatment of oil pollutants. In this work, we developed a mesoporous active γ-bauxite (DABa) from a low-grade raw boehmite ore (RBa) through a two-stage thermal activation process followed by an acid treatment. Acid leaching in hydrochloric acid resulted in the high specific surface area and optimum pore distribution in γ-bauxite. The surface area of the mesoporous γ-bauxite was as high as 130.66 m2/gr, approximately 11-fold larger than its parent ore. The regeneration performance of developed adsorbents to remove contaminants from used transformer oil was compared with three high-performance commercial adsorbents; Brazilian activated bauxite (BABa), Japanese activated bentonite (JABe), and Iranian activated alumina (IAA). The results showed DABa has the best oil reclamation performance and significantly improves the used oil characteristics such as its color, acidity, interfacial tension, dielectric dissipation factor, dibenzyl disulfide (DBDS) content, and corrosive sulfur.
Keywords: Waste management; Transformer oil reclamation; Oil regeneration; Active adsorbent

Development of an advanced multiwavelength emission detector for the analytical ultracentrifuge - Lautenbach, Vanessa; Onishchukov, Georgy; Wawra, Simon; Frank, Uwe; Hartmann, Lukas; Peukert, Wolfgang; Walter, Johannes (Nanoscale Advances, 2024)
An advanced design of the analytical ultracentrifuge with multiwavelength emission detection (MWE-AUC) is presented which offers outstanding performance concerning the spectral resolution and range flexibility as well as the quality of the data acquired. The excitation by a 520 nm laser is complemented with a 405 nm laser. An external spectrograph with three switchable tunable gratings permits optimisation of the spectral resolution in an order of magnitude range while keeping the spectral region broad. The new system design leads also to a significant reduction of systematic signal noise and allows the assessment and control of inner filter effects. Details regarding the very large signal dynamic range are presented, an important aspect when studying samples in a broad concentration range of up to five orders of magnitude. Our system is validated by complementary studies on two biological systems, fluorescent BSA and GFP, using the commercial Optima AUC with absorbance detection for comparison. Finally, we demonstrate the capabilities of our second generation MWE-AUC with respect to multiwavelength characterisation of gold nanoclusters, which exhibit specific fluorescence depending on their structure. Overall, this work depicts an important stepping stone for the concept of multiwavelength emission detection in AUC. The MWE-AUC developed, being to our knowledge the first and sole one of its kind, has reached the development level suitable for the future in-depth studies of size-, shape- and composition-dependent emission properties of colloids.
CRIS-Team Scopus Importer:2024-03-22

Development of poly(L-lactide) (PLLA) microspheres precipitated from triacetin for application in powder bed fusion of polymers - Dechet, Maximilian; Demina, Anna; Römling, Lea; Gomez Bonilla, Juan Sebastian; Lanyi, Franz; Schubert, Dirk W.; Bück, Andreas; Peukert, Wolfgang; Schmidt, Jochen (Additive Manufacturing, 2020)
In this work, the development and processing behavior of poly(L-lactide) (PLLA) particles for powder bed fusion (PBF) of polymers obtained via a green and sustainable process route are thoroughly studied. Liquid-liquid phase separation and precipitation from triacetin, a non-toxic solvent, are applied for the production of highly spherical PLLA particles of excellent flowability. Starting from the measured cloud-point diagram of the PLLA-triacetin system, appropriate temperature profiles for the precipitation process are derived. The effect of process parameters on the product properties is addressed in detail; the PLLA particles are characterized regarding their size distribution and morphology. Furthermore, material properties including thermal behavior (c.f. processing window for powder bed fusion (PBF)) and powder flowability are assessed. The spherical PLLA particles of narrow size distribution display a wide sintering window of 59 K and an excellent flowability due to the intrinsic surface roughness of the particles. Thus, tensile test bars and complex porous gyroid specimens were successfully manufactured via PBF without the need for any additional surface functionalization of the particles with flow agents. The high potential of the newly developed PLLA powders produced via an environmentally friendly approach omitting the use of halogenated or toxic solvents, as well as flowing aids, is demonstrated by mechanical testing of the printed specimen

Development of polyoxymethylene particles via the solution-dissolution process and application to the powder bed fusion of polymers - Dechet, Maximilian; Baumeister, Ina; Schmidt, Jochen (Materials, 2020)
In this study, the development of a polyoxymethylene (POM) feedstock material for the powder bed fusion (PBF) of polymers is outlined. POM particles are obtained via liquid-liquid phase separation (LLPS) and precipitation, also known as the solution-dissolution process. In order to identify suitable POM solvent systems for LLPS and precipitation, in the first step, a solvent screening based on solubility parameters was performed, and acetophenone and triacetin were identified as the most promising suitable moderate solvents for POM. Cloud point curves were measured for both solvents to derive suitable temperature profiles and polymer concentrations for the solution-dissolution process. In the next step, important process parameters, namely POM concentration and stirring conditions, were studied to elucidate their effect on the product's properties. The product particles obtained from both aforementioned solvents were characterized with regard to their morphology and size distribution, as well as their thermal properties (cf. the PBF processing window) and compared to a cryo-milled POM PBF feedstock. Both solvents allowed for precipitation of POM particles of an appropriate size distribution for PBF for polymer concentrations of at least up to 20 wt. %. Finally, a larger powder batch for application in the PBF process was produced by precipitation from the preferred solvent acetophenone. This POM powder was further analyzed concerning its flowability, Hausner ratio, and mass-specific surface area. Finally, test specimens, namely a complex gyroid body and a detailed ornament, were successfully manufactured from this feedstock powder showing appropriate bulk solid and thermal properties to demonstrate PBF processability. In summary, a processable and suitable POM PBF feedstock could be developed based on the non-mechanical solution dissolution process, which, to the authors' best knowledge, has not been reported in previous studies.
CRIS-Team Scopus Importer:2020-04-17
Keywords: Additive manufacturing; Particle analysis; Polyoxymethylene (POM); Powder bed fusion; Precipitation; Solution-dissolution

Dewetted Au Nanoparticles on TiO2 Surfaces: Evidence of a Size-Independent Plasmonic Photoelectrochemical Response - Licklederer, Markus; Mohammadi, Reza; Nguyen, Nhat Truong; Park, Hyoungwon; Hejazi, Seyedsina; Halik, Marcus; Vogel, Nicolas; Altomare, Marco; Schmuki, Patrik (Journal of Physical Chemistry C, 2019)
We induce solid-state dewetting of thin Au films (nominal thickness of 0.5-10 nm) on flat TiO2 surfaces to produce Au nanoparticles with an average size tunable in the 3-200 nm range. Such Au-decorated TiO2 surfaces enable plasmonic photoelectrochemical water splitting under visible light illumination (450-750 nm), with a photon-to-current conversion efficiency that reaches a maximum for TiO2 surfaces decorated with similar to 30 nm sized Au particles. Optical measurements show, as expected, a red shift of the plasmon resonance with the increasing Au nanoparticle size. More interestingly, the photocurrent is found to peak for every photoanode at similar to 600 nm regardless of the Au nanoparticle size, i.e., the wavelength of maximum photocurrent is size-independent. Such a remarkable observation can be ascribed to a hot electron injection cutoff effect, i.e., can be explained in terms of the interband versus intraband transition scenario.
CRIS-Team WoS Importer:2019-07-30

Die Grundlagen der pneumatischen Förderung - Wirth, Karl-Ernst (Chemie Ingenieur Technik, 1983)
Principles of pneumatic conveying. The design of pneumatic conveying systems is critically dependent upon a knowledge of the pressure drop and the minimum necessary velocity of the conveying gas. Starting from the areas of application of pneumatic conveying systems, the conveying states occurring are discussed and appropriately assigned to the diagram of state. The pressure loss equation is reported for conveying in form of a fully suspended flow and strand-type conveying and the theoretically predicted pressure losses are compared with experimental values for the conveying of coarse and finegrained materials. After mentioning the calculation of the pressure drops due to acceleration and to pipe bends, the article discusses the problem of pipe enlargement for long conveying distances. Equations are also given for the calculation of the so-called blocking limit and of the conveying gas velocity at which the minimum pressure drop occurs. The influence of the compressor on the choice of the operating point is also discussed. New calculation equations are then given for horizontal and vertical conveying in form of a fully suspended flow conveying and for horizontal strandtype conveying which permit reliable scale-up. Moreover, a new equation is reported for the blocking limit in horizontal conveying.
UnivIS-Import:2015-04-17:Pub.1987.tech.ITC.mechve.diegru
Keywords: Sichten; Abscheiden; Fördern; Wirbelschichten

Die in-situ Adsorption als neuer Weg zur schonenden Gewinnung von Proteinen - Peukert, Wolfgang; Millitzer, Marcus; Wenzig, Edda (Chemie Ingenieur Technik, 2002)
UnivIS-Import:2015-03-09:Pub.2002.tech.ITC.mechve.dieins
Keywords: adsorption

Die kritische Geschwindigkeit feststoffbeladener horizontaler Kreisrohrströmungen - Wirth, Karl-Ernst (Chemie Ingenieur Technik, 1982)
Fur die Auslegung hydraulischer und pneumatischer Forderanlagen ist die kritische Geschwindigkeit, vielfach auch Stopfgrenze genannt, von entscheidender Bedeutung. Bei kleineren Fordergeschwindigkeiten wird die Forderung instationar, und die Gefahr der Anlagenverstopfung ist betrachtlich. Eine sichere stationare hydraulische  wie auch  pneumatische  Forderung, bei  der  keine  Verstopfungsgefahr besteht, mu0 somit immer bei einer etwas hoheren als der kritischen Geschwindigkeit betrieben werden. Fur die Dimensionierung einer Forderanlage sollte deshalb die kritische Geschwindigkeit so genau wie möglich berechenbar sein. Aufgrund von Stabilitatsbetrachtungen konnte aus dem Gleichungssystem fur den Zusatzdruckverlust  bei pneumatischer  Strahnenforderung die Grenze der stabijen pneumatischen Forderung berechnet werden [I]. Tragt man fur diese Grenze das Volumenstromverhaltnis uber  der  Fri-Zahl  auf, so erhalt  man  das  Diagramm  fur  die Stopfgrenze  bei  horizontaler  pneumatischer  Forderung  (Abb. 1), wobei  die Porositat der  am Rohrboden rutschenden  Strahne als Parameter auftritt. Die Betriebspunkte einer stabilen pneumatischen Forderung liegen zwischen Abszisse und  Stopfgrenze. Im  Bereich zwischen Ordinate und Stopfgrenze ist durchaus noch eine pneumatische Forderung bei einem instationaren  Forderzustand  oder einer Forderung mit zusatzlicher Hilfseinrichtung, wie z. B. der Pfropfen- forderung mit innenliegender Beluftungsleitung, moglich. Fur große Fri-Zahlen strebt die Stopfgrenze zum maximalen stabil als Strahne transportierbaren  Volumenstromverhaltnis.  Der uber die  Strahne fliegende Feststoff wird hierbei allerdings als vernachlassigbar klein betrachtet.  Der  Verlauf  der  Stopfgrenze  kann  in  einem  groRen Geschwindigkeitsbereich durch die Näherungsgleichung wiedergegeben werden.
UnivIS-Import:2015-03-05:Pub.1982.tech.ITC.mechve.diekri
Keywords: rohrströmung

Die Stopfgrenze der horizontalen pneumatischen Förderung - Wirth, Karl-Ernst; Molerus, Otto (Verfahrenstechnik, 1981)
Bei der Einphasenrohrströmung ist die Verwendung kreisförmiger Förderrohre optimal. Die Ursache hierfür ist, dass bei diesen Rohrquerschnitten wegen der Rotationssymmetrie des Strömungsfeldes das Verhältnis von benetztem Umfang zu Rohrquerschnittsfläche und damit der Druckverlust minimal ist. Die gleichen Überlegungen gelten auch für zweiphasige Gas/Feststoff Rohrströmungen, solange der Feststoff homogen über den Rohrquerschnitt verteilt ist. Sobald allerdings eine Entmischung der Zweiphasenströmung vorliegt, d.h. dass ein Teil des durchsetzten Feststoffmassenstromes als Strähne am Boden gleitet und der restliche Anteil des Feststoffmassenstromes in Form der Flugförderung über die Strähne transportiert wird, ist nicht mehr das Verhältnis von Rohrumfang zu Rohrquerschnittsfläche für den einstellenden Druckverlust von Bedeutung. In diesem Fall muss vielmehr die Geometrie der Strähne Auswirkungen auf das Druckverlustverhältnis und die minimale Fördergeschwindigkeit haben. Im besonderen stellt sich die Frage, ob durch Verwendung eines nichtkreisförmigen Rohrquerschnitts die Strähnengeometrie so beeinflusst werden kann, dass im Vergleich zum Kreisrohr eine Reduzierung der für eine sichere Förderung notwendigen minimalen Gaslerrrohrgeschwindigkeit erzielt wird.
UnivIS-Import:2015-03-05:Pub.1981.tech.ITC.mechve.diesto
Keywords: pneumatik; stofftransport; pulver

Diffusion of Gold Nanoparticles in Inverse Opals Probed by Heterodyne Dynamic Light Scattering - Giraudet, Cédric; Knoll, Matthias; Galvan, Yaraset; Süß, Sebastian; Segets, Doris; Vogel, Nicolas; Rausch, Michael Heinrich; Fröba, Andreas Paul (Transport in Porous Media, 2020)
The diffusive behavior of nanoparticles inside porous materials is attracting a lot of interest in the context of understanding, modeling, and optimization of many technical processes. A very powerful technique for characterizing the diffusive behavior of particles in free media is dynamic light scattering (DLS). The applicability of the method in porous media is considered, however, to be rather difficult due to the presence of multiple sources of scattering. In contrast to most of the previous approaches, the DLS method was applied without ensuring matching refractive indices of solvent and porous matrix in the present study. To test the capabilities of the method, the diffusion of spherical gold nanoparticles within the interconnected, periodic nanopores of inverse opals was analyzed. Despite the complexity of this system, which involves many interfaces and different refractive indices, a clear signal related to the motion of particles inside the porous media was obtained. As expected, the diffusive process inside the porous sample slowed down compared to the particle diffusion in free media. The obtained effective diffusion coefficients were found to be wave vector-dependent. They increased linearly with increasing spatial extension of the probed particle concentration fluctuations. On average, the slowing-down factor measured in this work agrees within combined uncertainties with literature data.
CRIS-Team WoS Importer:2019-11-26
Keywords: Particle diffusion; Gold nanoparticles; Inverse opals; Heterodyne dynamic light scattering; Confinement

Diffusion of gold nanoparticles in porous silica monoliths determined by dynamic light scattering - Wu, Wenchang; Cui, Junwei; Sultan, Umair; Gromotka, Lukas; Malgaretti, Paolo; Damm, Cornelia; Harting, Jens; Vogel, Nicolas; Peukert, Wolfgang; Inayat, Alexandra; Fröba, Andreas Paul (Journal of Colloid and Interface Science, 2023)
Hypothesis: The applicability of the dynamic light scattering method for the determination of particle diffusivity under confinement without applying refractive index matching was not adequately explored so far. The confinement effect on particle diffusion in a porous material which is relevant for particle chromatography has also not yet been fully characterized. Experiments: Dynamic light scattering experiments were performed for unimodal dispersions of 11-mercaptoundecanoic acid-capped gold nanoparticles. Diffusion coefficients of gold nanoparticles in porous silica monoliths were determined without limiting refractive index matching fluids. Comparative experiments were also performed with the same nanoparticles and porous silica monolith but applying refractive index matching. Findings: Two distinct diffusivities could be determined inside the porous silica monolith, both smaller than that in free media, showing a slowing-down of the diffusion processes of nanoparticles under confinement. While the larger diffusivity can be related to the slightly slowed-down diffusion of particles in the bulk of the pores and in the necks connecting individual pores, the smaller diffusivity might be related to the diffusion of particles near the pore walls. It shows that the dynamic light scattering method with a heterodyne detection scheme can be used as a reliable and competitive tool for determining particle diffusion under confinement.
CRIS-Team Scopus Importer:2023-03-29
Keywords: Confinement; Diffusion; Dynamic light scattering; Gold nanoparticles; Porous material

Directional wetting in anisotropic inverse opals - Vogel, Nicolas; et al. (Langmuir, 2014)

Direct numerical simulation of water–ethanol flows in a T-mixer - Schikarski, Tobias; Peukert, Wolfgang; Avila, Marc (Chemical Engineering Journal, 2017)
The efficient mixing of fluids is key in many applications, such as chemical reactions and nanoparticle precipitation. Detailed experimental measurements of the mixing dynamics are however difficult to obtain, and so predictive numerical tools are helpful in designing and optimizing many processes. If two different fluids are considered, the viscosity and density of the mixture depend often nonlinearly on the composition, which makes the modeling of the mixing process particularly challenging. Hence water-water mixtures in simple geometries such as T-mixers have been intensively investigated, but little is known about the dynamics of more complex mixtures, especially in the turbulent regime. We here present a numerical method allowing the accurate simulation of two-fluid mixtures. Using a high-performance implementation of this method we perform direct numerical simulations resolving the spatial and temporal dynamics of water-ethanol flows for Reynolds numbers from 100 to 2000. The flows states encountered during turbulence transition and their mixing properties are discussed in detail and compared to water-water mixtures.
Keywords: Mixing; T-mixer; Direct numerical simulation; Miscible fluids; Water–ethanol; Transition to turbulence; Turbulent flows

Direct Tape Casting of Nanosized Al2O3 Slurries Derived from Autogenous Nanomilling - Vozdecky, Pavel; Roosen, Andreas; Knieke, Catharina; Peukert, Wolfgang (Journal of the American Ceramic Society, 2010)
Nanoparticles offer many advantages in the manufacture of ceramic products concerning processing and final properties, but are still difficult to process, and not all ceramic powder compositions can be obtained commercially like, e.g., alpha-alumina. In this paper, the production of alpha-alumina nanosized particles with a median size < 60 nm by a wet grinding process in a highly concentrated suspension of up to 49 wt% solid content starting from a commercial microsized powder is presented. Furthermore, the subsequent direct processing of these suspensions to ceramic green tapes via tape casting is performed. The effect of nanosized alpha-Al2O3 powders on the viscosity of slurries, the casting process, binder burnout, and sintering behavior is characterized. Flat and crack-free sintered substrates with a density > 95%TD, a submicrometer microstructure, and a translucent appearance could be obtained. A decrease of the sintering temperature, an improvement of the mechanical strength, and a lower surface roughness were achieved through the use of nanoparticles compared with particles in the micrometer size range.

Direct visualization of the interfacial position of colloidal particles and their assemblies - Vogel, Nicolas; et al. (Nanoscale, 2014)

Disperse forces of particle - surface interactions: direct AFM measurements and modelling - Peukert, Wolfgang; Götzinger, Martin (Powder Technology, 2003)
Fundamentals of particle–particle interaction are of great interest in agglomeration processes. Particle adhesion depends on dispersive forces (van der Waals force), local chemical bindings, Coulomb force and capillary attractions. Additionally, surface properties like roughness, adsorption layers and surface chemistry strongly affect adhesion forces. van der Waals interactions are poorly understood because popular ab initio force calculations for molecules like density functional theory (DFT) often do not lead to proper results. van der Waals forces are difficult to measure directly. We present direct measurements of particle–particle and particle–surface interactions in the gas phase carried out with an atomic force microscope (AFM). Special emphasis is given to a proper statistical treatment of the data. For modelling of particle adhesion, we use computer-assisted empirical potential methods. Parameters like adsorbed water and surface roughness are considered. We extract parameters for weak interactions from the Lifshitz theory and gas adsorption data. Adsorbing molecules can be used as probes to measure dispersive forces. Studying surface and particle properties combined with computer-assisted modelling is a basic requisite to reach the aim of predicting particle–particle interactions in industrial processes.
UnivIS-Import:2015-03-09:Pub.2003.tech.ITC.mechve.disper
Keywords: AFM measurements; van der Waals forces; Adhesion; Adsorption; Alumina

Dispersing and stabilizing silicon nanoparticles in a low-epsilon medium - Reindl, Armin; Voronov, Andriy; Gorle, Prem Kumar; Rauscher, Martin; Roosen, Andreas; Peukert, Wolfgang (Colloids and Surfaces A-Physicochemical and Engineering Aspects, 2008)
One possible approach to prevent the oxidation of silicon nanoparticles during a dispersing process is to use a dispersing medium, which does not contain any oxygen atoms in its structure, e.g. toluene. However, dispersing nanoparticles in such a non-polar organic medium is a major challenge, because the particles tend to aggregate very easily. The attempt of wet-grinding non-stabilized SiNP in toluene with a stirred media mill results in mu m-sized aggregates that precipitate rapidly. In order to achieve stable suspensions with regard to aggregation a suitable additive, added during the process of dispersion, is necessary. The stabilizing efficiency of several different additives, mostly oligo- and polymeric compounds, was evaluated by investigating the aggregate formation via dynamic light scattering, complemented by scanning electron micrographs. This work demonstrates that the stability of the particulate system and therefore the formation of aggregates can be adjusted selectively by the choice of the additive towards well-dispersed or densified particles. The attachment of the additives upon the surface of the SiNP was examined by diffuse reflectance infrared Fourier transform spectroscopy and the surface coverage was quantified by a combination of thermogravimetric analysis and gas sorption experiments. (C) 2008 Elsevier B.V. All rights reserved.
Keywords: silicon nanoparticles; dispersing; steric stabilization; stirred media mill; additive

Dispersing nanoparticles in liquids - Müller, Frank; Peukert, Wolfgang; Polke, Reinhard F.; Stenger, Frank (International Journal of Mineral Processing, 2004)
Dispersing particles in liquids is a key requirement for a diversity of applications including pigments for coating applications, ceramic materials, fillers in polymers and tailored rheology of suspensions. Dispersing is especially demanding when the primary particle size is in the nanometer size range. In order to overcome the adhesion forces, high stress intensities are required. However, the high mobility of primary particles may lead to fast aggregation. which has to be prevented by adequate stabilisation of produced primary particles.The dispersion apparatuses and their influencing parameters are discussed. A special problem is the evaluation of the degree of defragmentation. The results of different purposes are presented and discussed. Unanswered questions should lend to further investigations including systematic fundamental studies on model systems, to understand the product behaviour better. (C) 2004 Elsevier B.V All rights reserved.
Keywords: dispersing; defragmentation; liquids

Dispersing nanoparticles in liquids - Peukert, Wolfgang; Müller, F.; Polke, R; Stenger, Frank (European Congress on Comminution, 2002)
Dispersing particles in liquids is a key requirement for a diversity of applications including pigments for coating applications, ceramic materials, fillers in polymers and tailored rheology of suspensions. Dispersing is especially demanding when the primary particle size is in the nanometer size range. In order to overcome the adhesion forces, high stress intensities are required. However, the high mobility of primary particles may lead to fast aggregation, which has to be prevented by adequate stabilisation of produced primary particles. The dispersion apparatuses and their influencing parameters are discussed. A special problem is the evaluation of the degree of defragmentation. The results of different purposes are presented and discussed. Unanswered questions should lead to further investigations including systematic fundamental studies on model systems, to understand the product behaviour better.
UnivIS-Import:2015-04-16:Pub.2002.tech.ITC.mechve.disper
Keywords: dispersing; defragmentation; liquids

Dispersing silicon nanoparticles in a stirred media mill - investigating the evolution of morphology, structure and oxide formation - Frank, Gerhard; Peukert, Wolfgang; Reindl, Armin; Altin, Ergün; Aldabergenova, Saule (physica status solidi (a), 2007)
Silicon nanoparticles were dispersed for 24 hours in 1-butanol using a stirred media mill. Via this process intrinsically stable suspensions (in regard to aggregation) of Si nanoparticles were produced after 6 hours of dispersing. The evolution of morphology, particle size and structure was investigated by dynamic light scattering, X-ray diffraction, Raman spectroscopy and high resolution transmission electron microscopy as a function of dispersing time. The average crystallite size decreased from about 18 nm down to about 10 nm within 24 hours of milling as determined by X-ray diffraction and Raman scattering measurements. In addition careful analysis of the Raman spectra revealed a decrease of the crystalline volume fraction from 75% down to 24% and a corresponding increase of the amorphous phase. The microstructural development with varying crystallite size and crystalline volume fraction was directly confirmed by transmission electron microscopy measurements. Elemental analysis showed an increase of oxygen content that was directly proportional to the increase in specific surface area of the silicon nanoparticles during the dispersing process. The surface chemistry of the Si nanoparticles was analyzed by diffuse reflectance infrared Fourier transform spectroscopy that indicated vibrational bands of HSi-Si 3-xO x, SiO x, and residual 1-butanol. The final product of the dispersing process seems to be a two-phase mixture of amorphous Si and Si nanocrystallites covered with SiO x on the surface. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.
UnivIS-Import:2015-03-09:Pub.2007.tech.IW.LM.disper
Keywords: nano; particle; dispersion

Dispersing silicon nanoparticles with a stirred media mill and subsequent functionalization with phenyl acetylene - Reindl, Armin; Cimpean, Carla Ramona; Bauer, Walter; Peukert, Wolfgang; Kryschi, Carola; Comanici, Radu; Ebbers, André (Colloids and Surfaces A-Physicochemical and Engineering Aspects, 2007)
Silicon particles were dispersed in 1-butanol using a stirred media mill. Morphology, size and bulk structure of untreated, ground and styrenyl-functionalized silicon nanoparticles (SiNP) were examined using high-resolution transmission electron microscopy (HRTEM), dynamic light scattering (DLS) and X-ray diffraction (XRD). The amorphous oxide shell of the SiNP was removed by hydrofluoric acid (HF) etching. The resulting hydride (H)-terminated SiNP surfaces were functionalized with styrene via hydrosilylation of phenyl acetylene. Evidences for the styrenyl termination of the SiNP through Sisingle bondC bonds were obtained from diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), solid-state C nuclear magnetic resonance (NMR) and HRTEM. © 2007 Elsevier B.V. All rights reserved.
Keywords: Silicon nanoparticles; Stirred media mill; Hydrosilylation; Nuclear magnetic resonance

Dispersion-based, scalable fabrication of repellent superhydrophobic and liquid-infused coatings under ambient conditions - Walter, Teresa; Hein, Tamara; Weichselgartner, Matthias; Wommer, Kirsten; Aust, Martin; Vogel, Nicolas (Green Chemistry, 2022)
Superhydrophobic and liquid-infused porous coatings provide effective repellency against contaminations and ensure efficient performance of surfaces in a wide range of applications. Conventional fabrication processes of such coatings typically require fluorinated components, toxic solvents, and elevated temperatures, and therefore contribute to environmental pollution. Here, we present a dispersion-based, fluorine-free coating system that produces highly repellent surface coatings at ambient conditions. Our system is based on aqueous dispersions of a polymeric binder and hydrophobic fumed silica particles, which upon drying self-organize into a micro- and nanostructured thin film with superhydrophobic properties, characterized by a water contact angle above 150 degrees and a contact angle hysteresis below 10 degrees. An additional dispersion-based coating step allows infusing these structures with silicone oil, thus producing a lubricant-infused repellent coating mimicking the pitcher plant. Water droplets on such coatings exhibit efficient repellency properties, characterized by low sliding angles (<5 degrees) and contact angle hysteresis of water droplets (<10 degrees). Our method provides a versatile, dispersion-based toolbox to create functional, repellent coatings in a simple, scalable and environmentally benign process.

Dispersion of aggregates in shear flow - Peukert, Wolfgang; et al. (2007 AIChE Annual Meeting, 2007)

Dissolution kinetics of oxidic nanoparticles: The observation of an unusual behaviour - Vogelsberger, Wolfram; Schmidt, Jochen; Roelofs, Frank (Colloids and Surfaces A-Physicochemical and Engineering Aspects, 2008)
The solubility of nanoparticles was measured in aqueous solution as a function of time, and oxides of aluminium, silicon, titanium, and zirconium were investigated. Our solubility results show a maximum at the beginning of the dissolution process, whereas over time, the solubility levels are shown to decrease. Depending on the special conditions the solubility maximum may exceed the long-time solubility of the nanoparticles by several orders of magnitude. This behaviour is called as kinetic size effect. The extent of the effect depends on the size, surface tension and mass of the particles exposed to dissolution. It will always be of practical interest if a larger quantity of nanoparticles is brought into contact with a solvent, even when the equilibrium solubility data appears negligible. A rigorous thermodynamic and kinetic analysis of a colloidal system, which includes nucleation, particle growth, Ostwald ripening, and dissolution of particles, shows at least a qualitative agreement between all the experimental results and model calculations. (C) 2008 Elsevier B.V. All rights reserved.
Keywords: dissolution kinetics; nanoparticles; Gibbs free energy of colloidal systems

Dissolution kinetics of titanium dioxide nanoparticles: The observation of an unusual kinetic size effect - Schmidt, Jochen; Vogelsberger, Wolfram (Journal of Physical Chemistry B, 2006)
Different types of industrially produced titanium dioxide nanoparticles and a precipitated titanium dioxide have been dissolved in aqueous NaCl solutions at temperatures of 25 and 37 degrees C. The titanium concentration in solution with regard to dependence on time has been determined up to 3000 h after starting the dissolution experiment. The effect of particle size, pH value, temperature, background electrolyte concentration, and mass concentration of titanium dioxide exposed to the liquid phase has been studied. The nanoparticles have been characterized by N-2 physisorption measurements and XRD. The total dissolved titanium in solution has been determined by adsorptive stripping voltammetry (AdSV) and inductively coupled plasma mass spectrometry (ICP-MS). A new kinetic size effect has been observed. It turns out that this effect can be explained by applying an already existing phenomenological thermodynamic and kinetic model. The model describes all possible phenomena in a colloidal dispersion, nucleation, growth of particles, Ostwald ripening, and dissolution of particles using a uniform concept.

Dissolution of commercial nanoscale silica particles in electrolyte solution: The importance of the solid-solvent-ratio to physical and chemical properties of the solid-liquid interface - Vogelsberger, Wolfram; Schmidt, Jochen (Colloids and Surfaces A-Physicochemical and Engineering Aspects, 2018)
Dissolution experiments of silica nanoparticles (NPs) were performed in an aqueous TRIS buffer system (pH = 7.6) at 25 degrees C and the effect of the particles to solvent ratio (PSR) was studied. Increasing the PSR distinctly promotes the kinetic size effect described previously, which leads to solute concentrations exceeding the thermodynamic saturation concentration under the respective conditions considerably. The striking experimental observations readily are rationalized by analysis of the Gibbs free energy (GFE) of the system. In the extended model approach the dissolution and Ostwald ripening is described using gradient curves of GFE, which have been calculated considering a variable interfacial tension of the solid-liquid-interface, gamma. The GFE analysis provides size, R-P, and concentration, Z(P), of NPs as a function of dissolution time. The variation of the interfacial tension with particle size, gamma(R-P), is a consequence of the properties of the electric double layer, surface charge and surface potential, around the NPs. Suggestions are made how to predict the dissolution process from properties of the initial system solid-solution. Any meaningful report of dissolution experiments should include the saturation concentration of the material that forms the NPs as thermodynamic criterion, and the time necessary to obtain half of the saturation concentration in the system considered as kinetic criterion. Both aforementioned criteria are accessible from experiments without any model considerations.
Keywords: Silica nanoparticle dissolution; Solid-solvent ratio; Kinetic size effect; Interfacial tension; Electrical double layer

Doppel-Energie Röntgen-Computer-Tomographie in der Verfahrenstechnik - Wirth, Karl-Ernst; Strabel, Michael (Technisches Messen, 2002)
Das tomographische Messverfahren unter Verwendung von Röntgenstrahlung wird schon seit vielen Jahren erfolgreich eingesetzt, um Strömungsstrukturen in zweiphasigen Gas/Feststoff-Strömungen zu untersuchen. Die Einführung der Doppel-Energie-Technik ermöglicht es, die Anwendbarkeit auch auf dreiphasige Systeme zu erweitern und Prozesse wie das Einspritzen von flüssigem Edukt in eine Gas/Feststoff-Wirbelschicht zu untersuchen oder den Reaktionsverlauf in dreiphasigen Blasensäulen besser zu verstehen. Messungen an statischen und dynamischen Testobjekten haben die Zuverlässigkeit des Messsystems bewiesen und demonstrieren die breite Anwendbarkeit der Doppel-Energie-Röntgen-Computer-Tomographie. Conventional X-ray tomography has been successfully used for many years to study twophase flow pattern of vertical gas/solid flows. Now, the implementation of the dual-energy technique allows it to understand three-phase systems like an injection of liquid educts in fluidized bed reactors or a reaction process in three-phase bubble columns. A number of static and dynamic test objects composed of different materials have been investigated to verify the technique and to demonstrate the broad range of possible applications.
UnivIS-Import:2015-03-09:Pub.2002.tech.ITC.mechve.doppel
Keywords: Tomographie; Doppel-Energie; Mehrphasenströmung

Dos and don'ts tutorial for sample alignment in sum frequency generation spectroscopy - Hosseinpour, Saman (Biointerphases, 2022)
This Tutorial aims to provide a concise yet practical guideline for different scenarios that one may face in a sum frequency generation (SFG) spectroscopy laboratory, especially when it comes to sample alignment. The effort is made to reconstruct the real and often challenging sample alignment conditions for a broad range of liquid or solid samples interfacing solid, liquid, or gas phases, with a pedagogical approach. Both newcomer operators of an SFG setup without a strong experience in nonlinear spectroscopy and the more experienced SFG users can utilize the approaches that are provided in this Tutorial for an easier and more reliable sample alignment in their SFG laboratories.& nbsp;& nbsp;Published under an exclusive license by AIP Publishing.& nbsp;
CRIS-Team WoS Importer:2022-05-27

Drag Force Simulation of Particle Agglomerates with the Lattice Boltzmann Method - Thürey, Nils; Rüde, Ulrich; Peukert, Wolfgang; Feichtinger, Christian; Binder, Christian; Schmid, Hans-Joachim (18th Symposium Simulationstechnique ASIM 2005 Proceedings, 2005)
In this work we show, that the Lattice Boltzmann method is capable of calculating the drag force on spheres with a sufficient accuracy. The main Interest lies on laminar flows around nano particle agglomerates. To give an overview over the simulated force accuracy the results are compared with analytical solutions. Thereby the benefit from curved boundary treatments such as [YD03] and [PL03] is taken into account. Through the use of curved boundary treatments the lattice radius of the spheres can be reduced and thus smaller domain sizes can be used with the same force accuracy. Further more, results for complex agglomerates are presented and compared to solutions of the Stokesian Dynamics approach [AS01]
UnivIS-Import:2015-04-16:Pub.2005.tech.IMMD.lsinfs.dragfo_7
Keywords: drag; stokkesian; simulation; lattice; boltzmann

Druckverlust bei der Strömung durch Schüttungen - Wirth, Karl-Ernst (VDI-Wärmeatlas, 1996)
Festbetten sind Feststoffanhäufungen, bestehend aus einzelnen Partikeln, die von einem Fluid (Flüssigkeit,Gas) durchströmt werden.Sie unterscheiden sich damit von Füllkörperschüttungen, die in aller Regel von einem Zweiphasengemisch aus Flüssigkeit und Gasdurchströmt werden. Im Gegensatz zu den einzelnen Elementen einer Füllkörperschüttung, wie z.B. Raschig-Ringe und Sattelkörper, die üblicherweise eine Oberfläche pro Volumender Schüttung bei gleichzeitiger in m Strömungsdruckverlust aufweisen sollen, sind die Partikeln in Festbetten von gedrungener Gestalt und werden vielfach als kugelförmig bezeichnet. Gegenstand dieses Abschnittes ist der Strömungsdruckverlust von Festbetten. Derjenigein Füllkörperschüttungen wird in Abschn. Lbf beschrieben. Die Beschreibungdes Strömungsdruckverlustes, imfolgenden Druckverlustgenannt, in Festbetten kann nach zwei völlig unterschiedlichen Modellvorstellungenerfolgen: Modelldeshydraulischen Durchmessers, ModellderEinzelpartikelumströmung.Die erste Modellvorstellung das Modelldeshydraulischen Durchmessers ist die ältere, die zu relativ einfach aufgebauten Druckverlustbeziehungen vom Typ der Ergun-Gleichungführt[1].Die zweite Modellvorstellung ist neueren Datums und wurde erstmals von Molerus[2]publiziert.
UnivIS-Import:2015-04-20:Pub.1996.tech.ITC.mechve.druckv
Keywords: Druckverlust; Schüttungen

Drying of sugarcane bagasse in a partially filled horizontal drum - Tada, E. F. R.; Bück, Andreas; Casciatori, F. P.; Thomeo, J. C. (IDS'2018: 21ST INTERNATIONAL DRYING SYMPOSIUM, 2018)
CRIS-Team WoS Importer:2019-08-16

Dry particle coating for tailor-made product properties: Coating and decoating processes - Blümel, Christina; Wirth, Karl-Ernst (PARTICLE TECHNOLOGY FORUM. 2013. CORE PROGRAMMING AREA AT THE 2013 AICHE ANNUAL MEETING: GLOBAL CHALLENGES FOR ENGINEERING A SUSTAINABLE FUTURE, 2013)

Dry particle coating of polymer particles for tailor-made product properties - Blümel, Christina; Schmidt, Jochen; Dielesen, Andrea; Sachs, Marius; Winzer, Bettina; Peukert, Wolfgang; Wirth, Karl-Ernst (AIP Conference Proceedings 1593, 2014)
Disperse polymer powders with tailor-made particle properties are of increasing interest in industrial applications such as Selective Laser Beam Melting processes (SLM). This study focuses on dry particle coating processes to improve the conductivity of the insulating polymer powder in order to assemble conductive devices. Therefore PP particles were coated with Carbon Black nanoparticles in a dry particle coating process. This process was investigated in dependence of process time and mass fraction of Carbon Black. The conductivity of the functionalized powders was measured by impedance spectroscopy. It was found that there is a dependence of process time, respectively coating ratio and conductivity. The powder shows higher conductivities with increasing number of guest particles per host particle surface area, i.e. there is a correlation between surface functionalization density and conductivity. The assembled composite particles open new possibilities for processing distinct polymers such as PP in SLM process. The fundamentals of the dry particle coating process of PP host particles with Carbon Black guest particles as well as the influence on the electrical conductivity will be discussed.<br
Keywords: agglomeration; dry particle coating; conductivity; percolation; impedance spectroscopy

Dry powder coating in additive manufacturing - Schmidt, Jochen; Peukert, Wolfgang (Frontiers of Chemical Science and Engineering, 2022)
Dry powder coating is used in many industries to tailor the bulk solid characteristics of cohesive powders. Within this paper, the state of the art of dry coating of feedstock materials for powder based additive manufacturing (AM) processes will be reviewed. The focus is on feedstock materials for powder bed fusion AM processes, such as powder bed fusion of polymers with a laser beam and powder bed fusion of metals with lasers or an electron beam. Powders of several microns to several ten microns in size are used and the feedstock’s bulk solid properties, especially the flowability and packing density are of immanent importance in different process steps in particular for powder dosing and spreading of powder layers onto the building area. All these properties can be tuned by dry particle coating. Moreover, possibilities to improve AM processability and to manipulate the resulting microstructure (c.f. grain refinement, dispersion strengthening) by adhering nanoparticles on the powders will be discussed. The efect of dry coating on the obtained powder properties along the whole AM process chain and the resulting part properties is assessed. Moreover, appropriate characterization methods for bulk solid properties of dry-coated AM powders are critically discussed<br

Dual-energy X-ray tomography in process engineering – A non-intrusive technique to characterise vertical multiphase flows - Graßler, Thomas; Wirth, Karl-Ernst (Proceedings of 2nd World Congress on Industrial Process Tomography, 2001)
Since years conventional x-ray tomography has been successfully used to study the flow structures of vertical gas-solids flows. Now, the additional implementation of a dual-energy technique makes it possible to investigate multiphase flows like an injection of liquid educts in a gas-solids fluidized bed or a reaction progress in a three-phase bubble column. The x-ray tomography system mainly consists of an 160 kV/640W x-ray source, which can be operated at different energy levels, and an x-ray linear detector with 1024 sensitive elements. With a dual-energy technique the dependence of the materials absorption coefficients on the x-ray energy is used. A number of static test objects composed of two different materials have been investigated to simulate technical applications like mixing or drying processes of granulated material. Additionally, the dual-energy x-ray tomography system has been applied to determine the solids, liquid and gas distribution in a three-phase bubble column in order to show the possibilities of this measuring technique. © 2014 International Society for Industrial Process Tomograph
Keywords: Multiphase Flow; Dual-Energy; X-Ray; Tomography

Dynamic range multiwavelength particle characterization using analytical ultracentrifugation. - Peukert, Wolfgang; Walter, Johannes (Nanoscale, 2016)
We demonstrate how a sophisticated data analysis methodology enables us to perform multiwavelength evaluations of dynamic rotor speed gradient experiments obtained by analytical ultracentrifugation equipped with a multiwavelength detector. Our data evaluation tool HDR-MULTIFIT allows for the accurate analysis of sedimentation coefficient distributions which can be converted to particle size distributions. By means of multiwavelength evaluation, species dependent extinction spectra can be determined even for complex mixtures. Moreover, optical and hydrodynamic properties can be correlated for spherical particles of known optical properties applying multiwavelength evaluation and Mie's theory leading to a significant increase in the dynamic range of the experiment. We provide the theoretical background about the operation principle of our methodology and compare the performance of the multiwavelength analysis to the conventional single wavelength analysis as it is applied in turbidity analysis. We validate our technique using NIST traceable reference particles and show that our technique is universally applicable to materials of known and unknown optical properties, thus clearly extending the possibilities of particle analysis.
Keywords: muliwavelength; ultracentrifugation; sedimentation; particle

Dynamics of fine grinding in a fluidized bed opposed jet mill - Köninger, Benedikt; Hensler, Timo; Romeis, Stefan; Peukert, Wolfgang; Wirth, Karl-Ernst (Powder Technology, 2018)
Keywords: Fine dry comminution; First order kinetics; Fluidized bed opposed jet mill; Process dynamics

Dynamics of spray granulation in continuously operated horizontal fluidized beds - Neugebauer, C.; Diez, E.; Mielke, L.; Palis, S.; Bück, Andreas; Tsotsas, E.; Kienle, A.; Heinrich, S. (Dynamic Flowsheet Simulation of Solids Processes, 2020)
This chapter presents new findings on process and product design in continuous spray layering granulation in horizontal fluidized beds. The results are achieved by a multi-scale approach, combining single-particle characterization of the influence of drying conditions on layer formation and properties with meso-scale information of particle flowand recirculation between process chambers separated by weirs. On the macro-scale, population balance modeling is used to describe the overall process dynamics taking into account apparatus design and process conditions. New process regime maps are presented along with control concepts to guarantee stable and safe operation as well as desired particle properties.
CRIS-Team Scopus Importer:2020-08-28

Early-stage bifurcation of crystallization in a sphere - Mbah, Chrameh Fru; Wang, Junwei; Englisch, Silvan; Bommineni, Praveen Kumar; Varela Rosales, Nydia Roxana; Spiecker, Erdmann; Vogel, Nicolas; Engel, Michael (Nature Communications, 2023)
Bifurcations in kinetic pathways decide the evolution of a system. An example is crystallization, in which the thermodynamically stable polymorph may not form due to kinetic hindrance. Here, we use confined self-assembly to investigate the interplay of thermodynamics and kinetics in the crystallization pathways of finite clusters. We report the observation of decahedral clusters from colloidal particles in emulsion droplets and show that these decahedral clusters can be thermodynamically stable, just like icosahedral clusters. Our hard sphere simulations reveal how the development of the early nucleus shape passes through a bifurcation that decides the cluster symmetry. A geometric argument explains why decahedral clusters are kinetically hindered and why icosahedral clusters can be dominant even if they are not in the thermodynamic ground state.
CRIS-Team Scopus Importer:2023-09-08

Early Stages of Oriented Attachment: Formation of Twin ZnO Nanorods under Microwave Irradiation - Distaso, Monica; Mackovic, Mirza; Spiecker, Erdmann; Peukert, Wolfgang (Chemistry - A European Journal, 2012)
Let’s become twins! Early stages of formation of twin ZnO nanorods under microwave irradiation have been studied. The coupling of facets with the same polarity was triggered by the rough surface and the defect-rich microstructure of the constituent ZnO building blocks. Oriented attachment was found to be the underlying mechanism of the twinning process (see scheme).

Early stages of particle formation by in-situ UV-vis and HRS - Peukert, Wolfgang; Segets, Doris; Schürer, Benedikt (technical proceedings of the 2010 NSTI Nanotechnology Conference and Expo, 2010)
We present a new approach for the study of early states of particle formation that can be applied for precipitation processes that occur on timescales from milliseconds to several minutes. A T-shaped micro-mixer is used to precipitate nanoparticles at steady state conditions. The nucleation and growth of the nanoparticles occurs along the path through a transparent quartz capillary. Hyper Rayleigh scattering (HRS) and UV/Vis absorbance spectra are recorded simultaneously. By changing the measurement position along the capillary, different reaction stages of the nanoparticle formation process can be studied in detail. As the precipitation is performed at steady state the integration time for recording signals is not limited by the kinetics of the precipitation process. The HRS intensities and the particle size information can be used to calculate the nucleation and growth rates of the particle formation process.
Keywords: Hyper Rayleigh Scattering; Nanoparticle; Precipitation; UV-Vis; ZnO

Easy Room Temperature Synthesis of High Surface Area Anatase Nanowires with Different Morphologies - Schneider, Christopher; Liu, Ning; Romeis, Stefan; Peukert, Wolfgang; Schmuki, Patrik (ChemistryOpen, 2019)
Anatase nanowires were synthesized in solution by using a simple mixing of titanium diisopropoxide bis(acetylacetonate), lactic acid and sodium hydroxide at room temperature. We discuss effects of reaction parameters and post treatment (annealing) on the nanowire morphology, surface area, and crystallinity, as well as the competing morphology directing effects of lactic acid and sodium hydroxide. Then the room temperature nanowires were directly grown onto fluoride doped tin oxide (FTO) glass to form photoanodes. Photoelectrochemical measurements of the different nanowires were performed and compared to conventional nanowires produced by high temperature synthesis. Clearly the nanowires introduced in this work show a significant increase in the maximum photocurrent, compared to classic hydrothermal nanowire layers.
CRIS-Team Scopus Importer:2019-05-02
Keywords: lactic acid; low temperature processes; nanowires; sodium hydroxide; titanium dioxide

Effective Ligand Engineering of the Cu2ZnSnS4 Nanocrystal Surface for Increasing Hole Transport Efficiency in Perovskite Solar Cells - Khanzada, Laraib Sarfraz; Levchuk, Ievgen; Hou, Yi; Azimi, Seyed Hamed; Osvet, Andres; Ahmad, Rameez; Brandl, Marco; Herre, Patrick; Distaso, Monica; Hock, Rainer; Peukert, Wolfgang; Batentschuk, Miroslaw; et al. (Advanced Functional Materials, 2016)
Effective engineering of surface ligands in semiconductor nanocrystals can facilitate the electronic interaction between the individual nanocrystals, making them promising for low-cost optoelectronic applications. Here, the use of high purity CuZnSnS (CZTS) nanocrystals as the photoactive layer and hole-transporting material is reported in low-temperature solution-processed solar cells. The high purity CZTS nanocrystals are prepared by engineering the surface ligands of CZTS nanocrystals, capped originally with the long-chain organic ligand oleylamine. After ligand removal, CZTS nanocrystals show substantial improvement in photoconductivity and mobility, displaying also an appreciable photoresponse in a simple heterojunction solar cell architecture. More notably, CZTS nanocrystals exhibit excellent hole-transporting properties as interface layer in perovskite solar cells, yielding power conversion efficiency (PCE) of 15.4% with excellent fill factor (FF) of 81%. These findings underscore the importance of removing undesired surface ligands in nanocrystalline optoelectronic devices, and demonstrate the great potential of CZTS nanocrystals as both active and passive material for the realization of low-cost efficient solar cells.
Keywords: CZTS solar cells; HTM; Inorganic nanocrystals; Ligand exchange; Perovskite

Effective Thermal Conductivity of Nanofluids: Measurement and Prediction - Bioucas, Francisco; Rausch, Michael Heinrich; Schmidt, Jochen; Bück, Andreas; Koller, Thomas Manfred; Fröba, Andreas Paul (International Journal of Thermophysics, 2020)
In the present study, the effective thermal conductivity of nanoparticle dispersions, so-called nanofluids, is investigated experimentally and theoretically. For probing the influence of the nanoparticles on the effective thermal conductivity of dispersions with water as liquid continuous phase, nearly spherical and monodisperse titanium dioxide (TiO2), silicon dioxide (SiO2), and polystyrene (PS) nanoparticles with strongly varying thermal conductivities were used as model systems. For the measurement of the effective thermal conductivity of the nanofluids with particle volume fractions up to 0.31, a steady-state guarded parallel-plate instrument was applied successfully at temperatures between (298 and 323) K. For the same systems, dynamic light scattering (DLS) was used to analyze the collective translational diffusion, which provided information on the dispersion stability and the distribution of the particle size as essential factors for the effective thermal conductivity. The measurement results for the effective thermal conductivity show no temperature dependency and only a moderate change as a function of particle volume fraction, which is positive or negative for particles with larger or smaller thermal conductivities than the base fluid. Based on these findings, our theoretical model for the effective thermal conductivity originally developed for nanofluids containing fully dispersed particles of large thermal conductivities was revisited and also applied for a reliable prediction in the case of particles of relatively low thermal conductivities.
CRIS-Team Scopus Importer:2020-03-20
Keywords: Dynamic light scattering; Effective thermal conductivity; Measurement; Nanofluids; Parallel-plate method; Prediction

Effect of Asymmetry on Plasmon Hybridization and Sensing Capacities of Hole-Disk Arrays - Mohammadi, Reza; Ochs, Maria; Andrieu-Brunsen, Annette; Vogel, Nicolas (Journal of Physical Chemistry C, 2020)
Plasmonic complementary structures are interesting model systems that combine propagating and localized surface plasmon resonances and allow the fundamental study of their hybridization. In the simplest form, such structures are formed by stacking arrays of nanodisks and nanoholes with matching dimensions. Here, we produce such hole-disk arrays in an experimentally easy and parallel colloidal lithography process with accurate control over vertical alignment and separation between the individual disks and holes. Importantly, our process readily enables symmetry breaking and the design of asymmetric hole-disk arrays with controlled lateral offset between each hole-disk pair. We investigate the coupling between the parental resonances of the two elements as a function of feature size and separation distance and provide a plasmon hybridization scheme to rationalize the resonances. We find that for the asymmetric hole-disk structure, a new, hybrid resonance arises as a peak in the transmission spectra, which is not found in their symmetric analogues. We demonstrate that this new resonance imparts a higher sensitivity in refractive index sensing as it features a pronounced near-field enhancement in between holes and disks. The near-field structure, paired with the accessibility of this separation region in the presented hole-disk structures, implies that this architecture should be sensitive to local changes in the refractive index at the surface of the dielectric layer separating the plasmonic elements. We demonstrate this sensitivity of the asymmetric hole-disk arrays by the detection of the binding of a silane monolayer at the walls of the dielectric silica spacer layer.
CRIS-Team WoS Importer:2020-02-18

Effect of Fast Annealing on Structural Characteristics and Optical Properties of Cu2ZnSnS4 Absorber Films Deposited by Doctor-Blade Technique - Hassanien, A. E.; Abdelhaleem, Soraya; Ahmad, Rameez; Schuster, Matthias; Moustafa, S. H.; Distaso, Monica; Peukert, Wolfgang; Wellmann, Peter (Journal of Nanoelectronics and Optoelectronics, 2019)
Cu2ZnSnS4 of kesterite structure is a non-toxic, earth-abundant and low-cost alternative for Cu (In, Ga)Se-2 compound due to its direct band gap of similar to 1.5 eV and absorption coefficient higher than 10(4) cm(-1). The thin CZTS films were prepared by the Doctor-Blade technique as a cheap, simple and suitable process for large-scale production. The ink of CZTS nanoparticles was synthesized by a solvothermal method and dispersed in chloroform before deposition on glass substrates. The effect of annealing conditions (temperature and time) on the structural characteristics (phase formation and grain size) and optical properties (band gap) of CZTS thin films was investigated. The elemental composition of the CZTS films was investigated by energy dispersive X-ray spectroscopy. The films, before and after annealing, are rich in sulfur, which decreases with the increase of annealing temperature as a result of its evaporation at high temperature. X-ray diffraction analysis and Raman scattering measurements confirm the formation of the crystalline tetragonal phase of CZTS. Values of the optical band gap were estimated using Tauc equation and optical transmission data. The band gap decreases from 2.10 eV to 1.23 eV and the grain grows from 4.6 nm to 38.8 nm as the annealing temperature ascends. The dependence of band gap energy on the grain size is verified, thus, the size of the grain can be used as a factor tuning the band-gap energy.
CRIS-Team WoS Importer:2019-08-30

Effect of Fluid Flow on the Corrosion Performance of as-Cast and Heat-Treated Nickel Aluminum Bronze Alloy (UNS C95800) in Saline Solution - Jafari, Hamid Reza; Davoodi, Ali; Hosseinpour, Saman (Corrosion and Materials Degradation, 2021)
In this work, the corrosion behavior and surface reactivity of as-cast and heat-treated nickel aluminum bronze casting alloy (UNS C95800) in 3.5 wt% NaCl solution is investigated under stagnant and flow conditions. Increasing flow rate conditions are simulated using a rotating disk electrode from 0 to 9000 revolutions per minute (rpm). Optical micrographs confirm the decrease in the phase fraction of corrosion-sensitive β phase in the microstructure of C95800 after annealing, which, in turn, enhances the corrosion resistance of the alloy. Electrochemical studies including open circuit potentiometry, potentiodynamic polarization, and electrochemical impedance spectroscopy are performed to assess the effect of flow rate and heat treatment on the corrosion of samples at 25 and 40 °C in 3.5 wt% NaCl solution. For both as-cast and heat-treated samples, increasing the flow rate (i.e., electrode rotating rate) linearly reduces the corrosion resistance, indicating that the metal dissolution rate is significantly affected by hydrodynamic flow. Increasing the solution temperature negatively impacts the corrosion behavior of the as-cast and heat-treated samples at all flow conditio
Keywords: nickel aluminum bronze; annealing; flow dynamics; rotating disc electrode; corrosion; electrochemistry

Effect of functionalization of colloidal gold on controlled flocculation by the ligand-receptor mechanism - Kogut, A.M.; Voronov, A.S.; Kislenko, V.N.; Peukert, Wolfgang (Russian Journal of Applied Chemistry, 2005)
Modification of colloidal gold particles with octadecanthiol and alkyl biotin, with the subsequent flocculation of these particles via introduction of a tetramer protein avidin, was studied.
Keywords: Gold; Biotin; Flocculation; Gold Particle; Colloidal Gold

Effect of grinding conditions on mechanochemical grafting of poly(1-vinyl-2-pyrrolidone) onto quartz particles - Damm, Cornelia; Mallembakam, Madhusudhan Rao; Peukert, Wolfgang (Advanced Powder Technology, 2010)
Grinding of quartz in an aqueous solution of 1-vinyl-2-pyrrolidone (VP) in a stirred media mill results in grafting of poly(1-vinyl-2-pyrrolidone) (PVP) onto the quartz particles as proven by FTIR-spectroscopy. The grinding kinetics, the particle size of the final product and the amount of PVP grafted onto the silica particles depend on grinding conditions like VP and quartz concentration, pH and size of grinding media. The grinding kinetics becomes slower in the presence of VP due to the damping effect of the forming PVP chains. The final particle size, however, is almost independent on VP concentration. The amount of PVP grafted onto the silica particles ground for 12 h increases with growing VP concentration because the amount of adsorbed VP and the polymerization rate increase with growing VP concentration. The primary particle size and the kinetics of particle breakage do not depend on the pH-value of the dispersing medium, whereas the degree of agglomeration of the particles decreases with increasing pH-value of the medium. Under alkaline conditions, however, less PVP is grafted onto the quartz particles than under neutral or strong acidic conditions. The reasons for these effects are pH-dependent interactions between the grafted PVP chains and the surface hydroxyl groups on the quartz particles. If the quartz concentration in the suspension decreases the grinding kinetics becomes much faster because the specific energy input increases with decreasing particle concentration if the other process parameters are kept constant. For a very low quartz concentration (1 wt.%), however, after 7 h of grinding the particle size measured by dynamic light scattering starts to increase with grinding time. SEM investigations reveal that grinding of 1 wt.% quartz in aqueous VP solution for longer than 7 h results in the formation of plate-like particles. © 2009 The Society of Powder Technology Japan.
Keywords: Mechanochemical polymerization; Quartz; Reactive grinding

Effect of hydrogen peroxide on bovine serum albumin adsorption on Ti6Al4V alloy: A scanning Kelvin probe force microscopy study - Rahimi, Ehsan; Offoiach, Ruben; Hosseinpour, Saman; Davoodi, Ali; Baert, Kitty; Lutz, Alexander; Terryn, Herman; Lekka, Maria; Fedrizzi, Lorenzo (Applied Surface Science, 2021)
Protein adsorption on the surface of implant materials greatly affects the performance of the implants, such as their stability as well as the release of metal ions from and the adhesion of cells to their surface. In addition, the production of extracellular H2O2 from the activation of inflammatory cells could interfere with protein–metal interactions and/or modify the conformation of adsorbed proteins. In this study, we utilised scanning Kelvin probe force microscopy (SKPFM) to visualise the impact of H2O2 on bovine serum albumin (BSA) adsorption on the positively polarised Ti6Al4V alloy in a phosphate-buffered saline (PBS) solution. We show that the negatively charged BSA adsorbs onto the surface of polished and anodically polarised Ti6Al4V in a dense layer with a continuous network-like morphology or cluster shape and reduces the variation in the total surface potential compared to that of blank Ti6Al4V. However, addition of H2O2 to the PBS solution interferes with the formation of the dense protein network, and only a thin and discontinuous protein layer adsorbs onto the surface of the Ti6Al4V alloy, lowering the total surface potential difference. The information presented in this work provides new insights into the adsorption distribution of proteins on metallic substrates in biomaterials fiel
Keywords: Protein surface potential; SKPFM; Albumin protein; Hydrogen peroxide; Ti6Al4V alloy

Effect of manganese, zinc, and copper on the biological and osteogenic properties of mesoporous bioactive glass nanoparticles - Westhauser, Fabian; Wilkesmann, Sebastian; Nawaz, Qaisar; Hohenbild, Frederike; Rehder, Felix; Saur, Merve; Fellenberg, Jörg; Moghaddam, Arash; Ali, Muhammad Saad; Peukert, Wolfgang; Boccaccini, Aldo R. (Journal of Biomedical Materials Research Part A, 2020)
Mesoporous bioactive glass nanoparticles (MBGNs) have demonstrated promising properties for the local delivery of therapeutically active ions with the aim to improve their osteogenic properties. Manganese (Mn), zinc (Zn), and copper (Cu) ions have already shown promising pro-osteogenic properties. Therefore, the concentration-dependent impact of MBGNs (composition in mol%: 70 SiO2, 30 CaO) and MBGNs containing 5 mol% of either Mn, Zn, or Cu (composition in mol%: 70 SiO2, 25 CaO, 5 MnO/ZnO/CuO) on the viability and osteogenic differentiation of human marrow-derived mesenchymal stromal cells (BMSCs) was assessed in this study. Mn-doped MBGNs (5Mn-MBGNs) showed a small “therapeutic window” with a dose-dependent negative impact on cell viability but increasing pro-osteogenic features alongside increasing Mn concentrations. Due to a constant release of Zn, 5Zn-MBGNs showed good cytocompatibility and upregulated the expression of genes encoding for relevant members of the osseous extracellular matrix during the later stages of cultivation. In contrast to all other groups, BMSC viability increased with increasing concentration of Cu-doped MBGNs (5Cu-MBGNs). Furthermore, 5Cu-MBGNs induced an increase in alkaline phosphatase activity. In conclusion, doping with Mn, Zn, or Cu can enhance the biological properties of MBGNs in different ways for their potential use in bone regeneration approaches.
CRIS-Team Scopus Importer:2020-12-25
Keywords: copper; manganese; mesoporous bioactive glass nanoparticles; osteogenic differentiation; zinc

Effect of particle presence on gas phase temperature in the flame spray pyrolysis - Peukert, Wolfgang; Engel, Sascha; Gao, Yi; Kögler, Andreas; Kilian, Daniel; Seeger, Thomas; Leipertz, Alfred (Nanotechnology 2012: Advanced Materials, CNTs, Particles, Films and composites (Volume 1), 2012)
For the production of manufactured nanoparticles at a commercial scale flame processes are most frequently used. An important basis for understanding the complexity of this process is the characterization of the combustion process in dependence of the operation conditions. As minor changes of process parameters have huge impact on the product, invasive classic methods would fail. Hence, there is a demand for non-invasive advanced optical measurement tools acquiring data regarding the flame and the particle formation without changing the product by the applied measuring technique. In this work, gas phase temperatures, significantly influencing product particle sizes, were acquired by O -based pure rotational CARS during flame spray pyrolysis (FSP) and were compared for a particle-free and a particle-laden flame. Furthermore, the influence of different precursor concentrations on the distribution of the liquid regime was investigated by Mie scattering.
Keywords: Flame spray pyrolysis; Nanoparticles; Rotational CARS; Spray combustion; Temperature measurement

Effect of particle rounding on the processability of polypropylene powder and the mechanical properties of selective laser sintering produced parts - Gomez Bonilla, Juan Sebastian; Kletcher, Robin; Lanyi, Franz; Schubert, Dirk W.; Bück, Andreas; Schmidt, Jochen; Peukert, Wolfgang (30th Annual International Solid Freeform Fabrication Symposium - An Additive Manufacturing Conference, SFF 2019, 2019)
Common techniques for the production of polymer powders for selective laser sintering (SLS) involve the comminution of polymers. Comminution of polymers often results in powders made of irregular shaped particles with a low bulk density and a bad flow behavior. With the aim to improve the flowability of grinded powders and, thus, the SLS processability, a thermal process for particle shape modification was developed. This has been applied successfully for a broad variety of thermoplasts. In this contribution, a modified design of a rounding reactor with direct heating and optimized geometry is presented. The performance of the new design is assessed by the rounding of commercially available polypropylene powders. The influence of the rounding process on the packing density, flowability and particle size and shape distributions of the powders is investigated. Test specimens produced by SLS were tested to assess the effect of the rounding process on the mechanical properties of the produced parts. © Solid Freeform Fabrication 2019: Proceedings of the 30th Annual International Solid Freeform Fabrication Symposium - An Additive Manufacturing Conference, SFF 2019. All rights reserve
Keywords: Additives; Comminution; Compressive strength; Laser heating; Particle size; Polypropylenes; Powders; Sintering; Modified designs; Optimized geometries; Packing density; Particle size and shape; Polymer powders; Selective laser sintering (SLS); Shaped particles; Thermal process

Effect of pH and urea on the proteins secondary structure at the water/air interface and in solution - Guckeisen, Tobias; Hosseinpour, Saman; Peukert, Wolfgang (Journal of Colloid and Interface Science, 2021)
Hypothesis: The secondary structure of proteins affects their functionality and performance in physiological environments or industrial applications. Change of the solution pH or the presence of protein denaturants are the main chemical means that can alter the secondary structure of proteins or lead to protein denaturation. Since proteins in the bulk solution and those residing at the solution/air interface experience different local environments, their response to chemical denaturation can be different. Experiments: We utilize circular dichroism and chiral/achiral sum frequency generation spectroscopy to study the secondary structure of selected proteins as a function of the solution pH or in the presence of 8 M urea in the bulk solution and at the solution/air interface, respectively. Findings: The liquid/air interface can enhance or decrease protein conformation stability. The change in the secondary structure of the surface adsorbed proteins in alkaline solutions occurs at pH values lower than those denaturing the studied proteins in the bulk solution. In contrast, while 8 M urea completely denatures the studied proteins in the bulk solution, the liquid/air interface prevents the urea-induced denaturation of the surface adsorbed proteins by limiting the access of urea to the hydrophobic side chains of proteins protruding to air.
CRIS-Team Scopus Importer:2021-02-05
Keywords: Circular dichroism (CD); Denaturation; Proteins secondary structure; Sum frequency generation (SFG) spectroscopy

Effect of polymer species and concentration on the production of mefenamic acid nanoparticles by media milling - Peukert, Wolfgang; Ito, A; Konnerth, Christoph-Günther; Schmidt, Jochen (European Journal of Pharmaceutics and Biopharmaceutics, 2016)
The effect of four structurally different polymer species (hydroxypropylcellulose, polyvinylpyrrolidone, vinylpyrrolidone-vinyl acetate copolymer and polyvinyl alcohol) on the production of mefenamic acid nanoparticles during media milling has been studied. It was found that product particle sizes are strongly determined by the type of polymeric stabiliser as well as by its concentration at constant process conditions. With respect to small product particle sizes an optimum excipient concentration was identified and adjusted for colloidal stability of the drug nanosuspensions. Furthermore, it was found that overdosing of excipients must be omitted to suppress ripening due to enhanced solubilisation phenomena. Hence, the smallest product particle sizes were obtained using a polymeric stabiliser which exhibits a high affinity to the model drug compound and a low solubilisation capacity. Affinities of each polymer species to mefenamic acid and corresponding surface concentrations were determined using straightforward and simple viscosity measurements of the supernatant. A relationship between polymer affinity, solubilisation capacity and limiting product particle size has been observed, which supports the hypothesis that final product particle sizes are rather determined by the solid-liquid equilibrium than by pure mechanical fracture.
Keywords: Active pharmaceutical ingredient; Formulation; Media milling; Mefenamic acid; Nanosuspension; Ripening; Solubilisation; Solubility; Surface concentration

Effect of process conditions on mechanical behavior of aluminium wrought alloy EN AW-2618 additively manufactured by Laser Beam Melting in powder bed - Karg, Michael; Ahuja, Bhrigu; Schaub, Adam; Schmidt, Jochen; Sachs, Marius; Mahr, Alexander; Wiesenmayer, Sebastian; Wigner, Leon; Wirth, Karl-Ernst; Peukert, Wolfgang; Merklein, Marion; Schmidt, Michael (Proceedings of Laser in Manfacturing Conference 2015, 2015)
Additive Manufacturing offers geometric freedom excellently suited for topology optimized light weight designs. Ideally these should be built from materials of high strength to weight ratio and high plastic formability- such as aluminium-copper wrought alloys. Al-Cu wrought alloys are considered much less suitable for welding without cracks, so processing them in Laser Beam Melting of Metals in powder bed (LBM) can be considered challenging. Today, the only class of aluminium alloys widely processed by LBM is that of aluminium-silicon cast alloys which are easily weldable. In this contribution, mechanical characteristics of LBM samples are presented and discussed. Tensile tests were conducted under variation of load direction relative to build-up direction and heat treatment. Pronounced anisotropy was observed. Remarkably, elongation at break of T6 heat treated samples pulled in build-up direction exceeds values from literature for conventionally manufactured EN AW-2618A. The chemical constitutions of both the powder and the LBM samples were analyzed and shown to be similar to the expected EN AW-2618A. For further interpretation, boundary conditions of sample production, metallographic microsections and fracture surfaces were considere
Keywords: Additive Manufacturing; high-strength Aluminium Copper Wrought Alloy EN AW-2618A; AlCuMgNi; 3.1924; Selective Laser Melting™; LaserCUSING™; Direct Metal-Laser-Sintering™

Effect of protein adsorption on the dissolution kinetics of silica nanoparticles - Ali, Muhammad Saad; Uttinger, Maximilian; Romeis, Stefan; Schmidt, Jochen; Peukert, Wolfgang (Colloids and Surfaces B-Biointerfaces, 2022)
Nanoparticulate systems in the presence of proteins are highly relevant for various biomedical applications such as photo-thermal therapy and targeted drug delivery. These involve a complex interplay between the charge state of nanoparticles and protein, the resulting protein conformation, adsorption equilibrium and adsorption kinetics, as well as particle dissolution. SiO2 is a common constituent of bioactive glasses used in biomedical applications. In this context, the dissolution behavior of silica particles in the presence of a model protein, bovine serum albumin (BSA), at physiologically relevant pH conditions was studied. Sedimentation analysis using an analytical ultracentrifuge showed that BSA in the supernatant solution is not affected by the presence of silica nanoparticles. However, zeta potential measurements revealed that the presence of the protein alters the particles' charge state. Adsorption and dissolution studies demonstrated that the presence of the protein significantly enhances the dissolution kinetics via interactions of positively charged amino acids in the protein with the negative silica surface and interaction of BSA with dissolved silicate species. Our study provides comprehensive insights into the complex interactions between proteins and oxide nanoparticles and establishes a reliable protocol paving the way for future investigations in more complex systems involving biological solutions as well as bioactive materials.

Effect of roughness on particle adhesion in aqueous solutions: A study of Saccharomyces cerevisiae and a silica particle - Götzinger, Martin; Weigl, Bernhard; Peukert, Wolfgang; Sommer, Karl (Colloids and Surfaces B: Biointerfaces, 2007)
An atomic force microscope (AFM) has been used to quantify the adhesion of living cells Saccharomyces cerevisiae on three different silica surfaces with defined roughness. The effects of support roughness on the adhesion forces of a smooth silica particle were studied in addition. A living single cell was immobilized at the apex of a tipless AFM cantilever using a key-lock mechanism. Adhesion was quantified from the force-distance data measured on a smooth silica substrate and two substrates coated with hydrophilic monodisperse silica particles with 110 and 240 nm in diameter to study the effect of roughness on particle adhesion. The AFM technique gives unique insight into the primary colonization event of biofilm formation. The new knowledge helps substantially to design surface coatings relevant for biotechnology, medicine and dentistry. (C) 2006 Elsevier B.V. All rights reserved.
Keywords: Saccharomyces cerevisiae; silica; adhesion; roughness; AFM

Effect of Stabilizing Particle Size on the Structure and Properties of Liquid Marbles - Asaumi, Yuta; Rey, Marcel; Oyama, Keigo; Vogel, Nicolas; Hirai, Tomoyasu; Nakamura, Yoshinobu; Fujii, Syuji (Langmuir, 2020)
A liquid marble (LM) describes a liquid droplet that is wrapped by nonwetting micro- or nanoparticles and therefore obtains characteristics of a solid powder particle. Here, we investigate the effect of the stabilizing particle size on the resulting structure and properties of the LM. We synthesize a series of polystyrene particles with ultrathin coatings of heptadecafluorooctanesulfonic acid-doped polypyrrole with diameters ranging between 1 and 1000 μm by an aqueous chemical oxidative seeded polymerization of pyrrole. The methodology produced a set of hydrophobic particles with similar surface characteristics to allow the formation of LMs and to probe size effects in the LM formation and stabilization efficiency. We found that particles with a size above 20 μm adsorb as a particle monolayer to the surface of the LM, while smaller particles are adsorbed as ill-defined, multilayered aggregates. These results indicate that the balance between particle-particle interaction and gravity is an important parameter to control the surface structure of the LMs. The assembly behavior and size of the particles also correlated with the mechanical integrity of the LM against fall impact. The mechanical resistance was affected by the gap distance between the inner liquid of the LM and supporting substrate, the capillary forces acting between the particles at the LM surface, and the potential energy that depended on the particle size. Last, we demonstrate that the broadband light-absorbing properties of the polypyrrole shell also allow manipulating the evaporation rate of the inner liquid.
CRIS-Team Scopus Importer:2020-11-20
Keywords: Polymer particles; Interfaces; Liquids; Nanoparticles; Particle size

Effect of Substrate Grain Size on Structural and Corrosion Properties of Electrodeposited Nickel Layer Protected with Self-Assembled Film of Stearic Acid - Noorbakhsh Nezhad, Amir Hossein; Rahimi, Ehsan; Arefinia, Reza; Davoodi, Ali; Hosseinpour, Saman (Materials, 2020)
In the present study, the impact of copper substrate grain size on the structure of the succeeding electrodeposited nickel film and its consequent corrosion resistance in 3.5% NaCl medium were evaluated before and after functionalization with stearic acid. Nickel layers were electrodeposited on two different copper sheets with average grain size of 12 and 25 µm, followed by deposition of stearic acid film through self-assembly. X-ray diffraction analysis of the electrodeposited nickel films revealed that the deposition of nickel film on the Cu substrate with small (12 µm) and large (25 µm) grains is predominantly governed by growth in the (220) and (111) planes, respectively. Both electrodeposited films initially exhibited a hydrophilic nature, with water-contact angles of 56° and <10°, respectively. After functionalization with stearic acid, superhydrophobic films with contact angles of 150° were obtained on both samples. In a 3.5% NaCl medium, the corrosion resistance of the nickel layer electrodeposited on the copper substrate with 25 µm grains was three times greater than that deposited on the copper substrate with 12 µm grains. After functionalization, the corrosion resistance of both films was greatly improved in both short and long immersion times in 3.5% NaCl medium.<br
Keywords: grain-size effect; electrodeposition; nickel coating; XRD; self-assembled layers

Effect of surfactants on the molecular structure of the buried oil/water interface - Hosseinpour, Saman; Götz, Vanessa; Peukert, Wolfgang (Angewandte Chemie International Edition, 2021)
The oil/water interface, for instance in emulsions, is often stabilized by surfactants. Hence, the co-existence of oil, water, and surfactant molecules at the buried oil/water interface determines macroscopic properties such as surface tension or emulsion stability. Utilizing an inherently surface sensitive spectroscopic method, sum frequency generation (SFG) spectroscopy, we show that adsorption of an anionic surfactant to the buried oil/water interface increases the magnitude of the interfacial electric field. Meanwhile, the degree of ordering of the interfacial oil molecules increases with the surfactant concentration due to the intercalation of aliphatic chains of interfacial oil and surfactant molecules. At sufficiently high surfactant concentrations, the interfacial charge reaches a maximum value and the interfacial oil molecules arrange in a fully ordered conformation, a state which coincides with the significant decrease in interfacial tension and increased emulsion stability.

Effect of the Counteranion on the Formation Pathway of Cu2ZnSnS4 (CZTS) Nanoparticles under Solvothermal Conditions - Ahmad, Rameez; Saddiqi, Naeem-ul-Hasan; Wu, Mingjian; Prato, Mirko; Spiecker, Erdmann; Peukert, Wolfgang; Distaso, Monica (Inorganic Chemistry, 2020)
Cu2ZnSnS4 and Cu2ZnSnSe4 (CZTS and CZTSe, respectively) and their mixed chalcogenide phase Cu2ZnSnSxSe4-x (CZTSS(e)) are benign and cheap photovoltaic absorber materials that represent a valuable alternative to the more expensive chalcogenide systems: i.e., Cu(In,Ga)SS(e)2 (CIGSS(e)). One of the main challenges related to the fabrication of CZTS(e) layers is the control over both the crystalline phase (tetragonal, cubic, or hexagonal) and the formation of binary (MS, M = Cu(II), Zn(II), Sn(II); M'2-xS, M'= Cu(I), x = 0, 0.2; M″S2, M″ = Sn(IV)) and ternary products (CTS phases, Cu2SnS3, Cu3SnS4) that hinder the performance of the corresponding devices. In the present work, we rationalize the formation pathway of the CZTS phase through binary and ternary products when salt precursors with chloride and acetate as counteranions, respectively, are employed. The results show that the counteranions have a remarkable influence on the formation pathway of CZTS nanoparticles. The use of chloride precursors leads to the predominant formation of CTSs ternary phases (Cu2SnS3, Cu3SnS4), whereas the formation of the CZTS phase is not observed even for higher temperature and longer reaction time (250 °C, 24 h). In the case of acetates the copresence of CZTS as the main product, together with binary and ternary phases, is observed in the early stages of the reaction even at lower temperature and shorter reaction time (200 °C, 2 h), while when the reaction time and temperature are increased, only the CZTS phase is observed. In addition to a careful microstructural characterization of the as-synthesized materials by Raman spectroscopy, X-ray diffraction (XRD), Energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM), we shed light on the reactivity among the metal precursors, the organic ligand oleylamine, and the sulfur precursor carbon disulfide (CS2) by 13C nuclear magnetic resonance (13C NMR) and investigate in depth the effect on particle surfaces by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and XPS. A rationale for the formation pathway of CZTS nanoparticles is proposed and supported by experimental evidence.
CRIS-Team Scopus Importer:2020-02-11
Keywords: Salts; Anions; Precursors; Nanoparticles; Organic compounds

Effects of an adhesive force of admixed particles on compressed packing fractions in a particle bed - Peukert, Wolfgang; Paul, Jonas; Koch, Thomas; Yoshida, Mikio; Sanagawa, Tomoya; Okano, Shun-ichiro; Oshitani, Jun; Yamamoto, Hiroaki; Gotoh, Kuniaki (Advanced Powder Technology, 2015)
One of the techniques for a reduction in particle cohesiveness is the admixing of nano-particles. However, the mechanism of cohesiveness reduction has not yet been clarified. In this study we focused on a compressed packing fraction as one of the values reflecting the cohesiveness and flowability in a compressed particle flow. In order to estimate the mechanism of the reduction, the effects of an adhesive force of admixed particles on the packing fraction were investigated experimentally. In the experiments, silica particles with 397 and 8 nm diameters were used as the main and the admixed particles, respectively. The surfaces of the admixed particles were modified chemically in order to vary their adhesive force with maintaining morphological and mechanical characteristics. At more than 2.0% mixing mass ratios, the decreasing rate with increasing the mass ratio in net difference value of packing fraction for modified admixed particles was smaller than that for the raw particles. A calculation of the packing fraction of the admixed particles in the voids of main particles revealed that difference of the decreasing rates could be attributed to the difference of cohesivenesses between raw and modified admixed particles. The maximum packing fraction achieved by the modified admixed particles was lower than that achieved by the raw admixed particles. However, when a mixture of main and admixed particles was packed by tapping, the packing fraction with modified admixed particles was higher than that with raw admixed particles. This implied that the adequate adhesive force of admixed particles is different by the applied compression force value.
Keywords: Admixture of nano-particles; Chemical surface modification; Compressed particle bed; Packing fraction

Effects of filter structure, flow velocity, particle concentration and fouling on the retention efficiency of ultrafiltration for sub-20 nm gold nanoparticles - Lee, Handol; Segets, Doris; Süß, Sebastian; Peukert, Wolfgang; Chen, Sheng Chieh; Pui, David Y.H. (Separation and Purification Technology, 2020)
Ultrafiltration techniques with membranes of pore sizes under 100 nm have been widely applied in drinking water, wastewater, semiconductor and pharmaceutical process water treatments for nanoparticle (NP) and pathogen removal. The most direct way to evaluate the membrane performance is to experimentally obtain the size fractional retention efficiency. However, the real-life performance of the membrane in terms of fouling (or loading) characteristics and the effects of the concentration of challenging particles and rate of flux (or filtration velocities) on the filtration efficiency during fouling have not been well understood. In this study, systematic filtration experiments for filtration efficiency at clean and loaded conditions were conducted for three different 50 nm rated membrane filters, including PTFE (Polytetrafluoroethylene), PCTE (Polycarbonate Track-Etched) and MCE (Mixed Cellulose Ester) membranes, against 5, 10 and 20 nm Au NPs at different feed concentrations and fluxes. The results showed that the effects of feed concentration and flux are significant. This study provides important insights of retention mechanisms and efficiency for different ultrafiltration membrane structures at varied filtration velocities and fouling characteristics giving clear directions of future NP ultrafiltration research.
CRIS-Team Scopus Importer:2020-03-06
Keywords: Concentration effects; Diffusion deposition; Fouling effects; Surface interactions; Ultrafiltration

Effects of Medium pH and Preconditioning Treatment on Protein Adsorption on 45S5 Bioactive Glass Surfaces - Höhn, Sarah; Zheng, Kai; Romeis, Stefan; Brehl, Martin; Peukert, Wolfgang; de Ligny, Dominique; Virtanen, Sannakaisa; Boccaccini, Aldo R. (Advanced Materials Interfaces, 2020)
Protein adsorption on 45S5 bioactive glass (BG, Bioglass) surfaces influences the biocompatibility of Bioglass and the cellular response to the material. The medium pH greatly affects protein adsorption behavior. However, the influence of pH variation on protein adsorption on Bioglass has not been investigated in detail before, although an acidifying pH has been observed in fractured or injured bone tissues. This study investigates how the medium pH (pH 7, 5, and 2) affects protein (serum albumin) adsorption on Bioglass with or without preconditioning in simulated body fluid (SBF). The results show that Bioglass can adsorb a larger amount of bovine serum albumin (BSA) than bioinert glasses at all tested pHs. The BSA adsorption on Bioglass surfaces is pH-dependent and a larger amount of adsorbed BSA is observed at lower pH (5 and 2). After preconditioning, BSA adsorption is significantly enhanced. However, the trend of pH-dependent adsorption is attenuated. No significant difference in BSA adsorption is observed at different pHs after preconditioning. The results reveal for the first time the influence of medium pH on protein adsorption on Bioglass with or without preconditioning treatment in SBF, which provides useful information for developing Bioglass based biomedical devices that will be in contact with protein-containing physiological fluids during applications.
CRIS-Team Scopus Importer:2020-05-29
Keywords: 45S5 Bioglass; bovine serum albumin; pH influence; preconditioning; surface reactivity

Effects of pH of processing-medium on re-dispersion of spray dried, crystalline nanoparticles of pure naproxen - Braig, Veronika; Konnerth, Christoph-Günther; Peukert, Wolfgang; Lee, Geoffrey (International Journal of Pharmaceutics, 2019)
Crystalline nanodispersions of naproxen stabilized with hydroxypropyl cellulose were prepared at different pHs both below and above the pK(a) of the drug. After spray drying together with lactose, the measured particle size of the rehydrated dispersions using laser light scattering/Mie analysis was found to depend strongly on the pH of the original, processed nanodispersion. The pH-dependent solubility of this weak acid resulted in formation of a dissolved fraction of drug in the nanodispersions, this being higher as the pH increases. There was therefore a loss of crystalline naproxen during processing at higher pH, with fewer and/or smaller nanoparticles in the nanodispersion after nanomilling. After spray drying, the dissolved naproxen fraction formed an amorphous solid, as shown by differential scanning calorimetry and X-ray powder diffraction. The amorphous fraction redissolves on re-hydration. An improved disaggregation and smaller particle size of the nanoparticles at higher pH was observed because of the lower amount of crystalline nanoparticles now present. If the pH of the nanodispersion during processing is kept below the pK(a) for a weak acid, then a high yield of nanoparticles should be expected with little formation of an amorphous phase of the drug.
CRIS-Team WoS Importer:2019-02-22

Effects of the Gas/Solids Distribution on the Local and Overall Solids Distribution in a Downer Reactor - Wirth, Karl-Ernst; Lehner, Peter (Canadian Journal of Chemical Engineering, 1999)
In the last few years, the downer has been proposed as a new reactor for gas/solids reactions. Compared to state-of-the-art riser reactors, the cocurrent downflow of gas and solids should lead to a more uniform flow structure, close to plug flow. Experimental studies showed, that the gas/solids distributor at the top of the reactor is significantly influencing the flow pattern in a downer reactor. Local information about the solids concentration is indispensable for a thorough characterization of the flow structure in gas/solids flows. To obtain this information, x-ray computed tomography has been used for the experimental investigations.
UnivIS-Import:2015-03-05:Pub.1999.tech.ITC.mechve.effect
Keywords: Circulating fluidized bed; Downer reactor; Gas/solids flow; Tomography

Effervescent atomization of polyvinylpyrrolidone solutions: Influence of liquid properties and atomizer geometry on liquid breakup and spray characteristics - Schroeder, Jewe; Günther, Astrid; Wirth, Karl-Ernst; Schuchmann, Heike P.; Gaukel, Volker (Atomization and Sprays, 2013)
An effervescent atomizer is a special type of internal mixing pneumatic atomizer with significantly reduced atomization gas consumption compared to conventional pneumatic atomizers. The influence of the mass fraction of polyvinylpyrrolidone (PVP) K30 in aqueous solutions and the influence of nozzle orifice length on the spray have been investigated. The breakup of PVP K30 solutions is changed significantly by their viscosity, which depends on the mass fraction. With increasing viscosity, the breakup changes from complete breakup into drops directly at the nozzle orifice outlet to an incomplete breakup with ligaments present. The corresponding Sauter mean diameter and the standard deviation s(2) (representing the width of the drop size distribution) increase with increasing viscosity as well. The air-to-liquid ratio by mass (ALR) has comparably less impact on the breakup at the nozzle orifice outlet. Nevertheless an increasing ALR results in decreasing Sauter mean diameters and standard deviations s(2). The atomizer geometry has minor impact on the breakup and the resulting drop size distribution. The unsteadiness of the spray was quantified by its pulsation frequency. Comparing Sauter mean diameters and standard deviations s(2) with the corresponding pulsation frequencies of the spray indicates that an increase in pulsation frequency correlates with a reduction of both characteristic values and leads accordingly to a steadier spray. The pulsation frequency can be slightly controlled by the atomizer geometry. The effect of the pulsation frequency on Sauter mean diameter and standard deviation s(2) is less distinct than the effect of ALR and mass fraction.
Keywords: polyvinylpyrrolidone solution; rheology; effervescent atomization; breakup; unsteadiness; pulsation; laser diffraction spectroscopy; shadowgraphy

Efficient drug-delivery using magnetic nanoparticles–biodistribution and therapeutic effects in tumour bearing rabbits. - Peukert, Wolfgang; Tietze, Rainer; Lyer, Stefan; Dürr, Stephan; Struffert, Tobias; Engelhorn, Tobias; Schwarz, Marc; Eckert, Elisabeth; Göen, Thomas; Vasylyev, Serhiy; Trahms, Lutz; Dörfler, Arnd; et al. (Nanomedicine : nanotechnology, biology, and medicine, 2013)
To treat tumours efficiently and spare normal tissues, targeted drug delivery is a promising alternative to conventional, systemic administered chemotherapy. Drug-carrying magnetic nanoparticles can be concentrated in tumours by external magnetic fields, preventing the nanomaterial from being cleared by metabolic burden before reaching the tumour. Therefore in Magnetic Drug Targeting (MDT) the favoured mode of application is believed to be intra-arterial. Here, we show that a simple yet versatile magnetic carrier-system (hydrodynamic particles diameter <200nm) accumulates the chemotherapeutic drug mitoxantrone efficiently in tumours. With MDT we observed the following drug accumulations relative to the recovery from all investigated tissues: tumour region: 57.2%, liver: 14.4%, kidneys: 15.2%. Systemic intra-venous application revealed different results: tumour region: 0.7%, liver: 14.4 % and kidneys: 77.8%. The therapeutic outcome was demonstrated by complete tumour remissions and a survival probability of 26.7% (P=0.0075). These results are confirming former pilot experiments and implying a milestone towards clinical studies. FROM THE CLINICAL EDITOR This team of investigators studied drug carrying nanoparticles for magnetic drug targeting (MDT), demonstrating the importance of intra-arterial administration resulting in improved clinical outcomes in the studied animal model compared with intra-venous.
Keywords: treatment; drug; delievery; magnetic; nanoparticles

Efficient quenching sheds light on early stages of gold nanoparticle formation - Biegel, Markus; Schikarski, Tobias; Cardenas Lopez, Paola; Gromotka, Lukas; Lübbert, Christian; Völkl, Andreas; Damm, Cornelia; Walter, Johannes; Peukert, Wolfgang (RSC Advances, 2023)
The formation mechanism of plasmonic gold nanoparticles (Au NPs) by fast NaBH4 induced reduction of the precursors is still under debate. In this work we introduce a simple method to access intermediate species of Au NPs by quenching the solid formation process at desired time periods. In this way, we take advantage of the covalent binding of glutathione on Au NPs to stop their growth. By applying a plethora of precise particle characterization techniques, we shed new light on the early stages of particle formation. The results of in situ UV/vis measurements, ex situ sedimentation coefficient analysis by analytical ultracentrifugation, size exclusion high performance liquid chromatography, electrospray ionization mass spectrometry supported by mobility classification and scanning transmission electron microscopy suggest an initial rapid formation of small non-plasmonic Au clusters with Au10 as the main species followed by their growth to plasmonic Au NPs by agglomeration. The fast reduction of gold salts by NaBH4 depends on mixing which is hard to control during the scale-up of batch processes. Thus, we transferred the Au NP synthesis to a continuous flow process with improved mixing. We observed that the mean volume particle sizes and the width of the particle size distribution decrease with increasing flow rate and thus higher energy input. Mixing- and reaction-controlled regimes are identified.
CRIS-Team Scopus Importer:2023-07-21

Efficient synthetic access to cationic dendrons and their application for ZnO nanoparticles surface functionalization: New building blocks for dye-sensitized solar cells - Gnichwitz, Jan-Frederik; Marczak, Renata; Werner, Fabian; Lang, Nina; Jux, Norbert; Guldi, Dirk Michael; Peukert, Wolfgang; Hirsch, Andreas (Journal of the American Chemical Society, 2010)
A new concept for the efficient synthesis of cationic dendrons, 4-tert-butyl-1-(3-(3,4-dihydroxybenzamido)benzyl)pyridinium bromide (17), 1,1′-(5-(3,4-dihydroxybenzamido)-1,3-phenylene)bis(methylene) bis(4-tert-butylpyridinium) bromide (18), N1,N7-bis(3-(4-tert-butyl-pyridium- methyl)phenyl)-4-(3-(3-(4-tert-butyl-pyridinium-methyl)phenyl-amino) -3-oxopropyl)-4-(3,4-dihydroxybenzamido)heptanediamide tribromide (19), and N1,N7-bis(3,5-bis(4-tert-butyl-pyridium-methyl)phenyl)-4-(3-(3, 5-bis(4-tert-butyl-pyridinium-methyl)phenylamino)-3-oxopropyl)-4-(3, 4-dihydroxybenzamido)heptanediamide hexabromide (20), and their facile binding to zinc oxide (ZnO) nanostructures is introduced. Dendrons containing highly reactive benzylic bromides reacted readily with 4-tert-butyl-pyridine and resulted in cationic dendrons. Furthermore, these permanently positively charged dendrons were equipped with a catechol anchor group. This enabled ZnO surface functionalization by simple immersion. The adsorption of 17, 18, 19, and 20 on the colloidal nanoparticles was monitored by Langmuir isotherms. The highest obtained experimental loadings correspond to 99.5%, 98.6%, 99.1%, and 42.5% of the particle surface for 17, 18, 19, and 20, respectively. These results indicate insufficient adsorption of the largest molecule 20 leading to reduced colloidal stability of the nanoparticles, while an enhanced stability after grafting with 17, 18, and 19 was observed. Mesoporous films suitable for the use as electrodes in dye-sensitized solar cells (DSSCs) were prepared. Subsequently, the films were functionalized with 18, 19, or 20 and sensitized with zinc-5,15-bis-[2′,6′-bis-2″,2″-bis-(carboxy)- ethyl-methyl-4′-tert-butyl-pheny]-10,20-bis-(4′-tert-butylphenyl) porphyrin-octasodium-salt. UV-vis absorption spectra confirmed that 18, 19, and 20 are suitable for the stable electrostatic attachment of the dye. Current-voltage characteristics of complete cells demonstrated that increasing positive functionalization of the ZnO surface leads to decreased open circuit voltages (V ). All V values were around 0.4 V with a maximum for the 18 functionalized ZnO film of 0.45 V. The maximum cell efficiency obtained (0.31%) is rather high, considering the narrow spectral absorption of the dye and the rather thin ZnO films used. Finally, incident photon to current efficiency (IPCE) measurements confirmed photoinduced electron injection from the dye. These features are important assets for applications in particle technology and even facilitated advanced devices like a supramolecular DSSC complete with a subsequent layer of negatively charged porphyrins. © 2010 American Chemical Society.

Ein Pulver lernt fließen - Wirth, Karl-Ernst; Linsenbühler, Markus (Farbe und Lack, 2002)
Die Nachfrage nach Pulverlacken mit immer feineren Partikeln wächst. Aber damit wachsen auch die Probleme bei der Handhabung solcher Pulver, insbesondere bei der Fluidisierung. Abhilfe verspricht die Beschichtung der Pulverlack-Partikel mit Nano-Abstandshaltern, welche die van-der-Waals-Kräfte zwischen den Partikeln verrringern. Hier wird ein innovativer Prozess für diese Partikelbeschichtung vorgestellt: Die Nanopartikel und Pulverlackpartikel werden in Flüssigstickstoff dispergiert, entgegengesetzt elektrostatisch aufgeladen und dann vermischt. Der Stickstoff verdampft anschließend rückstandslos. Das Verfahren ist auch allgemein zur Mischung feinkörniger Pulver von Intresse.
UnivIS-Import:2015-03-09:Pub.2002.tech.ITC.mechve.einpul
Keywords: powder; fine; particle; eletrostatic; force; van; der; waals

Ein verallgemeinertes Modellierungswerkzeug für die numerisch effiziente Beschreibung mehrphasiger Fällungsprozesse - Peukert, Wolfgang; Haderlein, Michael; Segets, Doris; Sterbak, Martin (Chemie Ingenieur Technik, 2016)
Die Fällung in T-Mischern ist ein wichtiges Verfahren zur Partikelsynthese in wässriger Phase. Mischintensität, Komplexbildung und verschiedene Feststoffbildungsprozesse wie Keimbildung und Wachstum bestimmen maßgeblich die späteren Eigenschaften Dispersität und Zusammensetzung. Um die äußerst komplexe Interaktion dieser Prozesse numerisch zu beschreiben, wurde ein allgemein einsetzbares Modellierungswerkzeug entwickelt. Ein überarbeitetes Mischmodell gewährleistet Recheneffizienz und Flexibilität. Die Bildung chemischer Komplexe spielt für die Berechnung der Übersättigung eine entscheidende Rolle. Die Berechnung des chemischen Gleichgewichts wird durch die analytische Herleitung der Jacobi-Matrix des entsprechenden Gleichungssystems stark beschleunigt. Die Bildung beliebig vieler Feststoffphasen wird durch gekoppelte Populationsbilanzgleichungen modelliert, wobei auch hier mit der direct quadrature method of moments (DQMOM) ein numerisch effizientes Verfahren genutzt wird. Abschließend wird die Anwendung dieser Methode an einem anspruchsvollen Beispiel mit komplexer Hydrochemie und zahlreichen Feststoffphasen gezeigt. Diese Arbeit ist ein Teil von Dynsim-FP (SPP 1679)
Keywords: simulation; fällung; populationsbilanz

Electrical properties of solution processed layers based on Ge-Si alloy nanoparticles - Meric, Zeynep; Mehringer, Christian; Jank, Michael. P. M.; Peukert, Wolfgang; Frey, Lothar (MRS Advances, 2016)
Ge-Si alloy nanoparticles (NPs) covering the full range of compositions were studied in regard to their suitability as semiconducting channel layer in thin-film transistors (TFTs). Special focus is given to the influence of annealing and encapsulation techniques on the contact and channel properties. Therefore, electrical characterization methods separating contact from channel characteristics are highlighted and applied. It is demonstrated that appropriate passivation of the nanoparticle surfaces can improve the Ion/Ioff ratios by modulation of the density of free charge carriers and also can suppress hysteresis effects. Ge-rich NP alloys can generally be passivated more effectively regardless if passivation is done with solution-processed poly(methyl methacrylate) (PMMA) or by aluminum oxide (Al2O3) from Atomic Layer Deposition (ALD). Sufficient annealing improves the contact formation between aluminum electrodes and Ge-Si particles by modification of charge injection. The presented analysis leads to a better understanding interface and surface effects in porous nanoparticle semiconductors for application in TFT devices.
Keywords: thin film; passivation; nanostructure

Electronic Reducibility Scales with Intergranular Interface Area in Consolidated In2O3 Nanoparticles Powders - Thomele, Daniel; Siedl, Nicolas; Bernardi, Johannes; Diwald, Oliver (Journal of Physical Chemistry C, 2016)
Interfaces between nanoparticles of reducible metal oxides play a critical role for stoichiometry changes and associated self-doping effects. We explored the susceptibility of consolidated In2O3 nanoparticle ensembles exhibiting enhanced concentrations of intergranular interfaces toward vacuum annealing induced lattice oxygen depletion. Dielectric loss effects observed for nonstoichiometric In2O3–x nanoparticles inside the cavity of an Electron Paramagnetic Resonance (EPR) spectrometer system were used to determine trends in oxygen deficiency and n-type doping level for differently consolidated nanoparticle powders. Moreover, interfacial electron transfer from the In2O3–x nanoparticles to O2 was utilized to evaluate the abundance of paramagnetic O2δ− adsorbates as a function of different levels of nanoparticle consolidation. Both particle aggregation inside aqueous nanoparticle dispersions, which is driven by capillary forces, and mechanical powder compaction were employed for the adjustment of intergranular interface area. For the first time, we observed a clear correlation between reducibility of In2O3–x nanoparticles achieved by vacuum annealing and the amount of intergranular interface area. This study clearly underlines the multiple role of intergranular interfaces. Inside ensembles of semiconducting oxide nanoparticles, they not only provide diffusion paths for charge carriers, but also offer a handle to adjust the n-type doping level via heat treatment in vacuum or other reducing gas atmosphere

Electron Microscopy of Self-Assembled Superparamagnetic Plasmon Resonant Colloidal Nanostructures - Klupp Taylor, Robin; et al. (Proceedings of the 15th International Congress on Electron Microscopy, 2002)
The development of techniques to form identical nanostructures in solution is of great importance to many applications. In recent years there has been a departure from the most simple of requirements – to produce identical pure nanoparticles. It is clear that such pure particles, whilst often displaying interesting and potentially useful properties have other drawbacks such as chemical and colloidal instability or undesirable surface properties. It is therefore becoming increasingly common to engineer such pure particles into identical nanostuctures, which retain or enhance the favourable properties whilst passivating against the unfavourable. As the toolkit of possible particle engineering strategies becomes more elaborate, it is clear that multi-functional structures also become possible. This means the combination of properties which would traditionally be mutually exclusive in pure materials or composites using traditional formation techniques, e.g. ceramic processing. This work aims to combine two classes of quite strongly functional nanoparticulate materials, namely those with magnetic and plasmon resonant properties. It is well known that below a certain size particles of ferro- or ferrimagnetic material can only support a single magnetic domain and that for very small particles thermally-activated rotation of the magnetisation gives rise to superparamagnetic behaviour at ambient conditions. A simple method for the formation of such small particles comprising of iron oxide (magnetite or maghemite) has been known for some time [1] . A controlled agglomeration of these nanoparticles onto larger monodisperse cores would retain the superparamagnetic behaviour whilst increasing the effective dipole per particle. Gold sols have long been known for their deep colours which are due to a collective optical frequency oscillation of conduction electrons. Furthermore, it has recently been confirmed that the formation of a thin gold shell around a dielectric core results in a similar resonance but with a far greater tunability, namely in the core diameter to shell thickness ratio [2]. The formation of nanostructures combining these components would allow for the magnetic modulation of optical properties and also provide individual building blocks for subsequent magnetic directed self-assembly of nanochains. These nanochains are expected to behave like tiny transmission lines, with particles connected through the near-field of their shell plasmon resonances. We have made use of a JEOL 4000EX transmission electron microscope to evaluate the various stages of nanostructure fabrication. The growth of superparamagnetic plasmon resonant nanostructures followed the general scheme: (i) Monodisperse 250nm silica spheres were produced by the well-known Stoeber process [3]. (ii) Iron oxide (maghemite) nanocrystals with an approximate size of 8nm were attached to the cores by the layer-by-layer (LbL) process [4]. (iii) A barrier layer of silica was then grown by a modified Stoeber process. (iv) A gold shell was finally grown around the structures using a successive gold colloid attachment gold reduction process This manufacturing process therefore is an example of how three distinct strategies (LbL, sol-gel and seeded growth) can be utilised on the same nanoscale workpiece. Figure 1(b) shows the result of magnetic directed assembly of the particles in Fig.1(a)(iv). Electron microscopy was essential to the optimisation of the silica barrier layer and to monitor attachment of the seed gold colloid. In the former case, a thin or broken silica layer would adversely effect the attachment of seed colloid whereas a thick layer would effectively shield the interparticle magnetic interaction which could ultimately be useful when performing magnetic directed assembly. Microscopy was also utilised to estimate the decrease in surface roughness as the silica thickness. In this contribution we will present recent work on the self-assembly of multi-functional colloidal nanostructures, making note particularly of the microscopical features of our analysis. References 1. Massart, R. (1981) IEEE Trans. Magn. (1981) 17, 1247. 2. Oldenburg S.J. et al. (1998) Chem. Phys. Lett. 288, 243. 3. Stober, W., Fink, A., Bohn, E. (1968) J. Colloid Interface Sci., 26, 62. 4. Caruso F. et al. (1999) Adv. Mater. 11(11), 950.<br

Electrophoretic Deposition of alpha-Fe2O3/Chitosan Nanocomposite Coatings for Functional and Biomedical Applications - Cabanas Polo, Sandra; Distaso, Monica; Peukert, Wolfgang; Boccaccini, Aldo R. (Journal of Nanoscience and Nanotechnology, 2015)
Promising composite coatings based on hematite (alpha-Fe2O3) mesocrystals of size 110 nm and chitosan (CHT) molecules for different biotechnological applications have been successfully obtained by electrophoretic deposition (EPD). Homogeneous and reproducible coatings have been obtained by studying and controlling the chemical interactions between both phases (alpha-Fe2O3 and CHT). A voltage of 25 V and a deposition time of 5 min were chosen as best deposition conditions, which resulted in highly homogeneous coatings with well-distributed alpha-Fe2O3 particles. According to TGA measurements, the content of alpha-Fe2O3 and chitosan in the final composite coating were found to be 74 and 26 wt%, respectively. The presence of both phases in the composite coating was determined by XRD analysis and the coatings microstructure was observed by SEM.
Keywords: Iron Oxide Nanoparticles; Chitosan; Composite Coating; Electrophoretic Deposition

Electrophoretic deposition of anisotropic α-Fe2O3/PVP/chitosan nanocomposites for biomedical applications - Ramos Rivera, Laura; Distaso, Monica; Peukert, Wolfgang; Boccaccini, Aldo R. (Materials Letters, 2017)
Electrophoretic deposition (EPD) has been used to fabricate composite coatings based on anisotropic hematite particles ( extgreeka-Fe2O3) comprising residual poly-N-vinyl-pyrrolidone (PVP) and chitosan (CHT) on stainless steel substrates. The experimental conditions towards homogeneous surface, non-delamination and good distribution of extgreeka-Fe2O3/PVP particles are described. The coatings were characterized by SEM, XRD and TGA. A molecular interaction between PVP adsorbed on the surface of the particles and CHT is identified.
EAM Import::2019-03-14
Keywords: Electrophoretic deposition; Hierarchical structures; Porous layers; PVP/Chitosan interaction

Electrophoretic Deposition of Out‐of‐Plane Oriented Active Material for Lithium‐Ion Batteries - Esper, Julian Duane; Helmer, Alexandra; Wu, Yanlin; Bachmann, Julien; Klupp Taylor, Robin (Energy Technology, 2021)
The performance of secondary batteries, of which the lithium‐ion battery is one of the most well known, depends not only on the active electrode materials but also on the electrode architecture. In particular, the reduction in electrode tortuosity is expected to enable batteries with high active material utilization and fast charging and discharging capabilities. Herein, it is shown how electrophoretic deposition can be used to produce electrodes comprising hybrid particles of cobalt(II,III) oxide‐coated rutile‐mica oriented in an out‐of‐plane fashion. Key to this process is a sacrificial anode which leads to charging of the flake‐shaped particles and formation of a holding layer cementing them perpendicular to the substrate. Moreover, the electrochemical performance of lithium‐ion battery anodes with out‐of‐plane and in‐plane oriented architectures is compared. The out‐of‐plane orientation of the flake‐like particles results in better utilization of active material, lower charge‐transfer impedance, and faster ion diffusion. Moreover, for a range of charge/discharge rates, the specific capacity is over three times higher in comparison to an electrode with the same material oriented in an in‐plane architecture. The approach to electrode structuring is both facile and scalable and can be readily applied in the future to produce other electrochemical energy storage device electrodes.<br
Keywords: electrode architectures; electrophoretic deposition; flake-like hybrid particles; lithium-ion batteries; mica

Electrophotographic Multilayer Powder Pattern Deposition for Additive Manufacturing - Stichel, Thomas; Brachmann, Clemens; Raths, Max; Dechet, Maximilian; Schmidt, Jochen; Peukert, Wolfgang; Frick, Thomas; Roth, Stephan (JOM Journal of the Minerals, Metals and Materials Society, 2019)
The use of electrophotographic polymer powder transfer for the preparation of patterned powder layers is discussed with respect to a possible multimaterial application in powder bed-based additive manufacturing technologies such as selective laser sintering (SLS). Therefore, an experimental setup with a two-chamber design was realized, enabling the electrophotographic transfer of SLS powder materials at typical process conditions. The powder development (pick-up) step was investigated thoroughly for different powder materials to provide deep understanding of the underlying electrostatic effects and the influence of distinct powder properties. While using two different development modes, differences in the development results were correlated to differences in their particle size distribution, bulk density, and relative permittivity. Moreover, a new strategy was invented, allowing the residual electrophotographic powder deposition to be in general independent from the already produced part height. This is known to be a huge challenge but is mandatory for the buildup of three-dimensional multimaterial components.
CRIS-Team Scopus Importer:2020-02-21

Electrostatically supported Mixing of Fine Grained Particles - Wirth, Karl-Ernst; Linsenbühler, Markus (Chemical Engineering & Technology, 2004)
Highly disperse powders are increasingly used in industrial applications. For example in the pharmaceutical industry fine and finest particles are of great interest, since particles with grain sizes of several microns can be inhaled and deposited into the alveoli of the lung. As further example for the industrial application of finest powders the powder coating technique can be mentioned, which enables the production of extreme thin lacquer films. Fine and finest particles show special physical properties. With decreasing particles size the influence of the van der Waals interaction in comparison to other forces like the gravity force increases significantly. Therefore the particles stick to each other. This leads to production problems, e.g., caking, agglomeration and a reduced flowability, since fine powders agglomerate and easily stick to surfaces. By means of appropriate conditioning processes the product properties of the powders to be treated can be considerably improved. If the particles are coated with even smaller nano-particles, the nanos act as spacer between the particles reducing their mutual attraction forces. Thereby on the one hand the solids handling is improved and on the other hand a stable solid mixture is generated. © 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim.
UnivIS-Import:2015-03-09:Pub.2004.tech.ITC.mechve.electr

Electrostatically supported surface coating of solid particles using liquid nitrogen - Wirth, Karl-Ernst; Bindl, Hubert Christian (Proceedings PARTEC 2001, 2001)
The homogenous coating of particles in the micrometer range with fine-grained particles in the nanometer range leads to increasing flowability of the powder. Experiments have been carried out concerning the selective charging and coating of solid particles in liquid nitrogen. Liquid nitrogen as a suspension medium for solid particles offers certain advantages in comparison to other liquids and especially to gases. The charging of the fine-grained particles was realized by triboelectric charging as well as contact charging at metal electrodes at which a certain high voltage is applied. With selective charging of fine-grained solid particles, the coating quality of a powder mixture can be improved significantly. With respect to the use of coated particles in Dry-Powder-Inhalers (DPIs), the share of respirable particles reaching the lung is very high.
UnivIS-Import:2015-04-16:Pub.2001.tech.ITC.mechve.electr
Keywords: Mixing; Coating; Electrostatic charge; Liquid nitrogen; Dry-Powder-Inhaler

Electrostatic and steric stabilization of precipitated nanoscaled barium sulphate - Peukert, Wolfgang; Gradl, Johannes; Schwarzer, Hans-Christoph (2006 AIChE Spring National Meeting - 5th World Congress on Particle Technology, 2006)
Aggregation plays an important role in synthesizing nanoscaled particles e.g. by a precipitation process in a T-mixer. The possibility to stabilize barium sulphate suspensions electrostatically as well as sterically by adding different polymers is studied experimentally. The influence of the initial molar ration of Ba /SO " ions on the resulting particle size distribution is shown. To investigate the influence of the chemical composition and of the conformation of the polymer on the potential of stabilizing colloidal suspensions, which is coupled directly to their adsorption behaviour on the particle surface, three different polymers (PVA80 poly vinyl alcohol - 80%-hydrolyzed, PVA98 poly vinyl alcohol - 98%-hydrolyzed and Dapral GE202) are used as capping agents. In this study operating conditions are searched, where stabilizing by polymers is possible. However, polymers do not only influence the surface properties of the precipitated nanoparticles but reduce the turbulence of the flow field and consequently damp the mixing intensity. This is reflected in larger mean particle sizes of the precipitate.
Keywords: Aggregation; Barium sulphate; Electrostatic and steric stabilization; Polymer adsorption; Precipitation; Turbulence reduction

Electrostatic grafting of a triphenylphosphine sulfonate on SBA-15: application in palladium catalyzed hydrogenation - Wang, Lei; Dehe, Daniel; Philippi, Thomas; Seifert, Andreas; Ernst, Stefan; Zhou, Zhou; Hartmann, Martin; Klupp Taylor, Robin; Singh, Anand Pal; Jia, Mingjun; Thiel, Werner R. (Catalysis: Science and Technology, 2012)
A novel strategy for the immobilization of a sulfonate functionalized triphenylphosphine ligand by ion-ion interactions on an imidazolium modified SBA-15 is presented. A support containing electrostatically grafted triphenylphosphine as the ligand was reacted with PdCl2( CNPh)(2) and the resulting hybrid material catalyzed olefin hydrogenation under mild conditions. The catalyst exhibits excellent activity, selectivity and stability and it can be reused for at least ten times without any loss of activity. An analogous but covalently grafted palladium system does not show any hydrogenation activity under the same conditions. TEM images of the used catalyst clearly prove the absence of palladium nanoparticles. Additionally, XPS investigations prove that palladium( 0) is formed and the phosphine is oxidized. By AAS no palladium contamination down to 0.5 X 10(-4) mmol could be detected in the products and further leaching tests verified the reaction to be truly heterogeneous. This concept of non-covalent immobilization guarantees a tight bonding of the catalytically active species to the surface in combination with a high mobility, which should be favorable for other catalyses, too.

Electrostatic Powder Coating as a Novel Process for High-Voltage Insulation Applications - Scholl, Moritz; Vogel, Nicolas; Lang, Steffen (Advanced Engineering Materials, 2023)
A novel strategy for manufacturing of the main insulation of high-voltage rotating machines is presented. The developed process is based on established electrostatic powder coating equipment. Using complete automation enables the precise and reproducible application of homogeneous powder coating layers. Individual layers can be stacked by process repetitions to achieve a desired layer thickness. This coating strategy alters the particle deposition process by introducing additional capillary bridges that significantly increase powder adhesion. A systematic parameter study is performed to provide process–structure relations connecting various process parameters with the resultant coating thickness and homogeneity. The parameters of the developed coating process are iteratively improved to maximize coating homogeneity and minimize defect density, the most critical parameters in high-voltage insulation applications. The obtained powder coatings with a target thickness of 1.5 mm are subjected to electrical testing to examine the partial discharge activity as a key criterion for a functional insulating coating. The measurements reveal no significant partial discharge activity up to an electric field strength of 10 kV mm−1, demonstrating that this novel strategy for the production of the main insulation of high-voltage rotating equipment surpasses the state-of-the-art process in terms of partial discharge activity.
CRIS-Team Scopus Importer:2023-07-28
Keywords: electrical insulation; high voltages; powder coating; process optimization

Elektrostatisch unterstütztes Mischen feinkörniger Partikel - Linsenbühler, Markus; Wirth, Karl-Ernst (Chemie Ingenieur Technik, 2003)
UnivIS-Import:2015-03-09:Pub.2003.tech.ITC.mechve.elektr

Elektrostatisch unterstütztes Mischen feinkörniger Partikel - Wirth, Karl-Ernst; Linsenbühler, Markus (Proceedings Symposium Partikeltechnologie, 2002)
HoHochdisperse Pulver werden zunehmend bei industriellen Applikationen eingesetzt. So sind zum Beispiel in der pharmazeutischen Industrie feine und feinste Pulver von großem Interesse ,da Partikel mit Korngrößen von wenigen Mikrometern durch Inhalation in die Alveolen der Lunge trtransportiert und dort abgeschieden werden. Als weiteres Beispiel sei die Pulverlackierung genannt ,die es ermöglicht ,extrem dünne Lackschichten herzustellen. Feine und feinste Partikel weisen besondere physikalische Eigenschaften auf. Mit sinkender Korngröûe nimmt der Einfluss der van-der-Waals-Wechselwirkung im Vergleich zur Gewichtskraft erheblich zu ,wodurch die Partikel aneinander haften bleiben. Dies führt zu Verarbeitungsproblemen ,wie Anbackungen ,Agglomeratbildung und eine verminderte Fließfähigkeit der Pulver ,da feinste Pulver verklumpen und leicht an Oberflächen haften bleiben. Mit Hilfe geeigneter Konditionierungsverfahren lassen sich jedoch die Produkteigenschaften der zu verarbeitenden Pulver erheblich verbessern. Beschichtet man beispielsweise die Partikel mit noch kleineren Nanopartikeln ,so wirken diese als Abstandshalter ,womit sich die Haftkräfte reduzieren lassen. Dadurch wird einerseits das Feststoff-Handling verbessert ,während andererseits eine stabile Mischung der Komponenten entsteht
UnivIS-Import:2015-04-16:Pub.2002.tech.ITC.mechve.elektr
Keywords: mischen; partikel; agglomeration; dispersion

Elucidation of the Formation Mechanism of Metal-Organic Frameworks via in-Situ Raman and FTIR Spectroscopy under Solvothermal Conditions - Embrechts, Heidemarie; Kriesten, Martin; Hoffmann, Kilian; Peukert, Wolfgang; Hartmann, Martin; Distaso, Monica (Journal of Physical Chemistry C, 2018)
The metal–organic framework MIL-53(Al) serves as a model system in this study. Its formation mechanism in N,N-dimethylformamide (DMF) is elucidated through simultaneous FTIR and Raman spectroscopy and turbidity measurements collected under in-situ synthesis conditions in a custom-designed solvothermal reactor coupled with reaction sampling. Different synthesis steps are followed over synthesis time including a prenucleation building unit (PNBU) consisting of one linker molecule and one aluminum atom, the assembly of the PNBUs to MIL-53 nuclei in solution, the decomposition of DMF to formic acid and dimethylammonium, and finally the precipitation of the crystalline MOF phase. The rearrangement of the PNBU to form MIL-53 is identified as the rate-limiting reaction step responsible for the long induction time at low temperatures (<80 °C). MOF nucleation and particle growth is followed directly in-situ through a novel method—comparison of the temporal evolution of the respective FTIR and Raman bands. Analysis of the particles isolated after various synthesis times indicates that MIL-53(H2BDC) of low crystalline long-range order is formed initially, which quickly rearranges to form more ordered, crystalline particles with DMF inside of the pores (MIL-53(DMF)). It is to be expected that the synthesis steps elucidated herein can be generalized to the solvothermal synthesis of other metal–organic framework structures from metal salts and organic acid li
Keywords: Organic acids; Fourier transform infrared spectroscopy; Chemical synthesis; Metal organic frameworks; Raman spectroscopy; Bis(1; 3; 5-Benzenetricarboxylate)Tricopper(Ii); MIL-101; Metalorganic Framework; Crystalline materials; Dimethylformamide; Metals: Organic polymers; Organic solvents; Organometallics; Synthesis (chemical); Crystalline particles; Formation mechanism; Metal organic framework; N; N-Dimethylformamide; Rate-limiting reaction; Solvothermal conditions; Solvothermal synthesis; Turbidity measurements

Emerging Organic Surface Chemistry for Si Anodes in Lithium-Ion Batteries: Advances, Prospects, and Beyond - Chen, Zidong; Soltani, Askar; Chen, Yungui; Zhang, Qiaobao; Davoodi, Ali; Hosseinpour, Saman; Peukert, Wolfgang; Liu, Wei (Advanced Energy Materials, 2022)
Due to its uniquely high specific capacity and natural abundance, silicon (Si) anode for lithium-ion batteries (LIBs) has reaped intensive research from both academic and industrial sectors. This review discusses the ongoing efforts in tailoring Si particle surfaces to minimize the cycle-induced changes to the integral structure of particles or electrodes. As an upgrade or alternative to conventional coatings (e.g., carbons), the emerging organic moieties on Si offer new avenues toward tuning the interactions with various battery components that are key to electrochemical performances. The recent progress on understanding Si surfaces is reviewed with an emphasis on newly emerged diagnostic tools, which increasingly points to the critical role of organic components in stabilizing Si. The detailed analysis on the chemistry-structure-performance relationships in Si surface are discussed and the successful cases demonstrating the functions of the organic layers are provided, that is, via tailored interactions toward electrolyte or binder or conductive agents, are recapped. Various synthetic strategies for designing the surface organic layers are discussed and compared, highlighting the versatility and tunability of surface organic chemistry. The holistic considerations and promising research directions are summarized, shedding light on in-depth understanding and engineering Si surface chemistry toward practical LIBs application.
CRIS-Team WoS Importer:2022-07-29

eMoM: Exact method of moments—Nucleation and size dependent growth of nanoparticles - Pflug, Lukas; Schikarski, Tobias; Keimer, Alexander; Peukert, Wolfgang; Stingl, Michael (Computers & Chemical Engineering, 2020)
In this study we present a reformulation for a broad class of population balance equations that model nucleation and size dependent growth. This formulation enables the definition of new numerical methods, which have two advantages compared to existing schemes in the literature (e.g. finite volume type methods and methods based on the evolution of moments): i) higher precision due to non-smoothing and ii) less run-time in comparison to finite volume algorithms of equivalent accuracy. The described formulation represents the solution of the considered balance equation in terms of the solution of a scalar integral equation, which can then be exploited to establish efficient numerical solvers. The computation of a solution of an initial boundary value problem in space-time is thus reduced to a scalar integral equation, which considerably reduces the computational effort required for its approximation. The integral equation describes the exact evolution of the third moment of the solution, justifying the name for this method: the exact method of moments (eMoM).
CRIS-Team Scopus Importer:2020-03-20
Keywords: Crystallization; Fixed point equation; Growth; Integral equation; Method of moments; Nanoparticle; Nonlocal conservation laws; Nucleation; Population balance equation

Enabling triboelectric charging as a powder charging method for electrophotographic powder application in laser-based powder bed fusion of polymers by triboelectric charge control - Kopp, Sebastian-Paul; Düsenberg, Björn; Eshun, Pius Marcellinus; Schmidt, Jochen; Bück, Andreas; Roth, Stephan; Schmidt, Michael; Kopp, Sebastian-Paul (Additive Manufacturing, 2023)
Substituting conventional doctor blade- or roller-based powder application methods for laser-based powder bed fusion of polymers (PBF-LB/P) by electrophotographic powder application (EPA) offers significant advantages. In particular, the selective powder deposition enabled by EPA allows high powder efficiency and the possibility to locally adjust part properties during their fabrication. However, defined charging of powder particles is crucial for achieving an accurate selective deposition of powder layers by means of electrophotography. This is the first comprehensive study on the specific triboelectric charge control of polymer particles for their subsequent use in electrophotographic powder application for PBF-LB/P. For this purpose, approaches for charge control of toner particles in the context of digital (2D) printing technologies are adapted and applied to polypropylene (PP) feedstocks for PBF-LB/P. In order to show transferability to other polymers, the charge control method developed in this paper is also applied to polyamide 12 (PA12) high density polyethylene (HDPE) and polystyrene (PS). For successful EPA, unipolar charging of polymer particles is crucial. However, non-functionalized PP shows a strongly bipolar triboelectric charging, which is unsuitable for EPA. The charge control method developed in this work shifts this strongly bipolar triboelectric charging to a unipolar charging. This is achieved by the synergy of both functionalizing the particle surface with charge control agents (CCAs) and choosing suitable carrier particles known from two-component toners. The developed method allows to control crucial parameters of triboelectric charging, namely polarity, amount of charge and resulting surface potential. Furthermore, the presented results provide new insights into the transfer behavior of charged PP particles in an external electric field. Finally, this enables the triboelectric charging mechanism to be used for electrophotographic powder application in PBF-LB/P.<br
Keywords: Charge control Electrophotography Triboelectric charging Laser powder bed fusion Polymer particles Powder application

Enduring liquid repellency through slippery ionic liquid-infused organogels - Salbaum, Tobias; Galvan, Yaraset; Haumann, Marco; Wasserscheid, Peter; Zarraga, Ramon; Vogel, Nicolas (Journal of Materials Chemistry A, 2021)
Lubricant-infused repellent coatings provide efficient repellency against contamination as the lubricant avoids direct contact between the surface and any contaminant to be repelled. Here, we address two mechanisms that potentially cause failure of the coating by loss of the liquid lubricant, and present a strategy for long-lasting coatings. We use ionic liquids as lubricants with extremely low vapor pressure. These are confined to the underlying substrate by means of functionalized polymeric gel that matches the chemical structure of the ionic liquids and thereby maximizes their molecular interactions. We use pentafluorophenol-based active ester polymers to provide a versatile platform that allows a convenient post-synthetic functionalization of the polymer network. The matching functional groups to efficiently bind a desired ionic liquid can thus be introduced via their amine-functionalized analogues, which we demonstrate for imidazole- and phosphonium-based molecules. We copolymerize benzophenone methacrylate for surface attachment and gel formation in one step. At 85 °C the surface and repellency properties remained constant for several months, outperforming thick, swollen PDMS films as the gold standard of lubricant-infused coatings.
CRIS-Team Scopus Importer:2021-02-26

Engineered disorder and light propagation in a planar photonic glass - Romanov, Sergey; Orlov, Sergej; Ploss, Daniel; Weiss, Clemens K.; Vogel, Nicolas; Peschel, Ulf (Scientific Reports, 2016)
The interaction of light with matter strongly depends on the structure of the latter at wavelength scale. Ordered systems interact with light via collective modes, giving rise to diffraction. In contrast, completely disordered systems are dominated by Mie resonances of individual particles and random scattering. However, less clear is the transition regime in between these two extremes, where diffraction, Mie resonances and near-field interaction between individual scatterers interplay. Here, we probe this transitional regime by creating colloidal crystals with controlled disorder from two-dimensional self-assembly of bidisperse spheres. Choosing the particle size in a way that the small particles are transparent in the spectral region of interest enables us to probe in detail the effect of increasing positional disorder on the optical properties of the large spheres. With increasing disorder a transition from a collective optical response characterized by diffractive resonances to single particles scattering represented by Mie resonances occurs. In between these extremes, we identify an intermediate, hopping-like light transport regime mediated by resonant interactions between individual spheres. These results suggest that different levels of disorder, characterized not only by absence of long range order but also by differences in short-range correlation and interparticle distance, exist in colloidal glasses.

Engineering the surface functionality of 45S5 bioactive glass-based scaffolds by the heterogeneous nucleation and growth of silver particles - Meincke, Thomas; Miguez Pacheco, Valentina; Hoffmann, Daniel; Boccaccini, Aldo R.; Klupp Taylor, Robin (Journal of Materials Science, 2017)

Enhanced Crystallization of Lysozyme Mediated by the Aggregation of Inorganic Seed Particles - Weichsel, Ulrike; Segets, Doris; Thajudeen, Thaseem; Maier, Eva-Maria; Peukert, Wolfgang (Crystal Growth and Design, 2017)
We show that aggregation plays a major role in seeded growth of protein crystals. The seeded batch approach provides the opportunity to set the starting conditions for protein crystallization by adding a defined amount of well-characterized seed particles. The experimental observations for tetragonal hen egg-white lysozyme (LSZ) confirm the concept of the oriented aggregation of larger building blocks to form a protein crystal. It was shown that the aggregation of the seed particles/bioconjugates is advantageous for the product quality in terms of larger and more defined LSZ crystals and in terms of accelerated reaction kinetics. We present a population balance (PB) model for the seeded batch crystallization of LSZ considering the aggregation of growth units to form protein crystals. For the modeling of crystal growth, evolving particle size distributions (PSDs) of agglomerating LSZ molecules were measured by dynamic light scattering (DLS). Moreover, the aggregation of seed particles in LSZ solutions under crystallization conditions was investigated by DLS. In line with our expectations, the number of seeds was found to be important as it strongly affects the collision frequency in the aggregation term of our PB model. Finally, the applied model gives trends of the supersaturation depletion curves and orders of magnitude of the measured CSDs in particle size correctly, ranging from only a few nanometers up to micrometer-sized particles/crystals. Thus, by the combination of PB modeling and experimentally determined crystallization parameters, insights into the crystal formation mechanism were obtained. To the best of our knowledge, this is the first attempt to model growth within a crystal population by an aggregation mechanism induced by seeding with foreign particles.

Enhanced dissolution of naproxen from pure-drug, crystalline nanoparticles: A case study formulated into spray-dried granules and compressed tablets - Konnerth, Christoph-Günther; Peukert, Wolfgang; Braig, Veronika; Lee, Geoffrey (International Journal of Pharmaceutics, 2019)
This is a case study of the use of rapidly-dissolving naproxen crystalline nanoparticles to prepare compressed tablets. The dissolution rates of different formulations were determined: the crystalline pure-drug nanodispersion, a pure-drug microsuspension, a granule prepared by spray drying the nanodispersion with mannitol, and a tablet prepared by compressing the granule with a bulking agent and a disintegrant. The goal was to determine the influence of each of the process steps on the rapid dissolution of the nanodispersion. A procedure was developed to allow sampling during the first 120 s of dissolution. Dissolution of the nanodispersion was completed after 60 s under both sink and non-sink conditions. Spray drying with mannitol delayed dissolution slightly under both sink and non-sink conditions. Under sink conditions a microsuspension (volume median size 11 µm) showed similar rapid dissolution to the nanodispersion. We propose this to be a result of rapid shrinkage of the microparticles on dissolution under sink conditions. This nullifies any effects of specific surface on dissolution rate. Under non-sink conditions the microparticles retain their lower specific surface for a longer time during dissolution and dissolve therefore more slowly. When compressed into tablets, the dissolution rates of nanoparticles or microparticles were determined primarily by the tablet disintegration time; the influence of sink or non-sink conditions was only observable after disintegration.
UnivIS-Import:2019-08-15:Pub.2019.nat.dchph.lphte.enhanc
Keywords: Low-soluble drug; Dissolution; Spray-drying; Nanosuspension; Tablet

Enhanced Electrochemical Performance of Graphite Anodes for Lithium-Ion Batteries by Dry Coating with Hydrophobic Fumed Silica - Lux, S. F.; Placke, Tobias; Engelhardt, C.; Nowak, Sascha; Bieker, P.; Wirth, Karl-Ernst; Passerini, Stefano; Winter, M.; Meyer, H-W (Journal of The Electrochemical Society, 2012)
Coating of electrode materials for lithium-ion batteries is usually performed in order to improve performance, safety and the processability of the raw material. Here, we apply a dry coating method of graphite with hydrophobic fumed silica particles. This method excludes the use of any harmful solvents and the nano-scale particles cover and stick to the graphite substrate by only adhesive forces. Furthermore, this dry coating method is easily mass-scalable and a high throughput can be obtained in a short processing time. The nanoparticle coating reduces the van-der-Waals forces between the graphite particles and leads in this way to better flowability of the graphite powder which is important for further processing and the production of electrode tapes. Furthermore, these core-shell particles were processed to composite negative graphite electrodes in combination with the water soluble binder sodium carboxy-methylcellulose. Electrodes obtained with the coated material displayed a smooth surface, a high mechanical stability and outperformed the unmodified ones in the electrochemical investigations.

Enhanced Figure of Merit via Hybridized Guided-Mode Resonances in 2D-Metallic Photonic Crystal Slabs - Sarkar, Swagato; Ghosh, Anik Kumar; Adnan, Mohammad; Aftenieva, Olha; Gupta, Vaibhav; Fery, Andreas; Joseph, Joby; Koenig, Tobias A. F. (Advanced Optical Materials, 2022)
Metallic nanostructures are highly attractive for refractive index sensing, as the evanescent field from the associated plasmonic resonances resides in close proximity to the adjacent analyte media. However, this benefit is often reduced due to broad plasmonic lineshapes producing poor quality factors. The rational design provides strategies for narrowing the plasmonic modes by incorporating photonic diffraction, which promotes surface lattice resonances . Due to the stringent parametric dependencies, these resonances in metallic lattices are not always feasible, particularly when a straightforward fabrication route with fewer process steps is desired. Herein, hybridized guided-mode resonance in a 2D-metallic photonic crystal slab (2D-mPhCs) is introduced that ensures high-quality hybrid modes while maintaining a simple fabrication methodology. In direct comparison to its constituent plasmonic and photonic modes, this concept is discussed for sensing applications. The "figure of merit (FOM)" is frequently regarded as a valid metric for measuring sensing performanceensuring high-quality modes with an improved detection limit. The experimental results confirm enhanced FOM (three to six times) for the hybrid modes, in contrast to the constituent counterparts. For optoelectronic applications, such as photodetection and photocatalysis, these hybrid structures with high-quality modes offer a promising platform to harvest light at the metal-semiconductor interfaces.
CRIS-Team WoS Importer:2022-08-19

Enhanced Nucleation of Lysozyme Using Inorganic Silica Seed Particles of Different Sizes - Weichsel, Ulrike; Segets, Doris; Janeke, Stefanie; Peukert, Wolfgang (Crystal Growth and Design, 2015)
In this work we investigate the impact of differently sized plain silica nanoparticles (NPs) between 10 and 200 nm on the crystallization of lysozyme (LSZ). In the first part of our work we investigate the electrostatic interactions between LSZ and NPs by zeta potential measurements and place special emphasis on the adsorption behavior of LSZ@SiO2. The determined adsorption isotherms - derived from UV-vis spectroscopy - indicate that with increasing particle size more LSZ is adsorbed per NP surface area probably due to a size-dependent surface chemistry and the variation of surface curvature. Second, seeded crystallization experiments both at the microliter and milliliter scale and thus close to a technically relevant scale were performed. A clearly extended crystallization window upon the addition of seed particles toward lower protein and salt concentrations was found. Moreover, induction times of crystal formation and crystallization times were considerably reduced. These effects were intensified with the addition of larger seed particles. In general, with the addition of silica seed particles, a shift of the final crystal size distribution to larger structures is observed.

Enhancement of polyamide laser sinter powder reusability by acid catalyzed hydrolysis - Hesse, Nicolas; Peukert, Wolfgang; Schmidt, Jochen (Procedia CIRP, 2020)
This contribution introduces a method to reverse the deterioration in melt rheological behaviour (‘ageing’) of polyamide 12 that has previously been used in powder bed fusion processing by reduction of the polymers molecular weight via acid catalysed hydrolysis. Chosen hydrolysis conditions allow for a reconditioning below melting temperature and therefore leave the particulate nature of the powder intact while significantly improving the polymers rheological properties. The influences of different temperatures, acids and pH-values are investigated and the processability of recycled powders is assessed by melt rheological, optical and thermal characteristics.
Keywords: powder bed fusion; selective laser sintering; polyamide 12; powder reusability; hydrolysis; molecular chain length; zero shear viscosity

Enhancing In Vitro Bioactivity of Melt-Derived 45S5 Bioglass® by Comminution in a Stirred Media Mill - Romeis, Stefan; Hoppe, Alexander; Eisermann, Claudia; Schneider, Nadine; Boccaccini, Aldo R.; Schmidt, Jochen; Peukert, Wolfgang (Journal of the American Ceramic Society, 2014)
45S5 Bioglassâ (45S5 BG) is a frequently applied Type A bioactive material, capable of forming an inherent bond to bone and soft tissue. Currently, applied melt-derived bioactive glass powders (BG) exhibit particle sizes between a few to several hundred micrometers. Recent studies on nanometer-sized bioactive glasses (nBGs), produced by bottom-up methods like sol– gel processing or flame spray pyrolysis, have indicated their great potential for several biomedical applications. In this study, the feasibility of top-down processing starting from bulk 45S5 BG by wet comminution in a stirred media mill was investigated. The products were assessed by in vitro hydroxycarbonate apatite (HCAp) formation in simulated body fluid, which is a marker for bioactive behavior. The study reveals the paramount influence of the used solvent for a successful topdown processing: In comparison with the as-received material bioactivity is lost for powders processed in water, preserved for comminution in ethanol and increased for powders processed using the alcohols n-butanol, n-pentanol, and n-hexanol. It was also found that only for the latter solvents, the chemical composition of the glass is maintained during comminution. Flakelike, slightly porous particles with specific surface areas of  25–30 m2/g are obtained. Thus, the presented comminution approach offers a convenient technique to process 45S5 BG with enhanced bioactivity.
UnivIS-Import:2015-03-09:Pub.2013.tech.IW.LM.enhanc

Enhancing Photoelectric Powder Deposition of Polymers by Charge Control Substances - Düsenberg, Björn; Kopp, Sebastian-Paul; Tischer, Florentin; Schrüfer, Stefan; Schmidt, Jochen; Schmidt, Michael; Schubert, Dirk W.; Peukert, Wolfgang; Bück, Andreas; Roth, Stephan (Polymers, 2022)
Charge control substances (CCS) as additives for polymer powders are investigated to make polymer powders suitable for the electrophotographic powder deposition in powder-based additive manufacturing. The use of CCS unifies the occurring charge of a powder, which is crucial for this novel deposition method. Therefore, commercially available polymer powder is functionalized via dry coating in a shaker mixer with two different CCS and analyzed afterwards. The flowability and the degree of coverage of additives on the surface are used to evaluate the coating process. The thermal properties are analyzed by use of differential scanning calorimetry. Most important, the influence of the CCS on the powder charge is shown by measurements of the electrostatic surface potential at first and the powder deposition itself is performed and analyzed with selected formulations afterwards to show the potential of this method. Finally, tensile strength specimens are produced with the conventional deposition method in order to show the usability of the CCS for current machines.<br
Keywords: additive manufacturing; charge control substances; photoelectric powder deposition; polypropylene; dry coating

En route towards a comprehensive dimensionless representation of precipitation processes - Schikarski, Tobias; Avila, Marc; Peukert, Wolfgang (Chemical Engineering Journal, 2022)
Precipitation of (nano-) particles is a unit operation for the preparation of suspensions. Despite its widespread use, no general understanding is established of how different operating conditions, such as mixing rates or reactant concentrations, affect the precipitation outcome (e.g. the particle size distribution). We obtain overarching relations between the operating conditions and the precipitation outcome by deriving dimensionless numbers governing the precipitation process. In particular, we consider the interdiffusion of two chemical compounds reacting to a sparingly soluble salt by coupling the reaction–diffusion equations for the solute concentrations, to a population balance equation for the evolution of the dispersed phase including nucleation and growth. We vary the relevant process parameters for different chemical systems and uncover three dimensionless numbers, which fully determine the precipitation outcome under the assumption of fast chemical reactions. Two of these dimensionless numbers are Damköhler numbers, which put the relevant mixing kinetics in relation to the relevant time scales for the nucleation and the growth kinetics, respectively. The third dimensionless number corresponds to a dimensionless solid concentration. Simple functional expressions for the Damköhler numbers valid for any chemical system allow estimating whether the precipitation product is controlled by mixing, or solely by the kinetics of solid formation. In the mixing-controlled regime, scaling laws relate the mean particle sizes and the number of particles to the Damköhler number.
Keywords: Reactive precipitation; Nanoparticles; Nucleation; Growth; Damköhler number; Population balance equation

EPR investigations of non-oxidized silicon nanoparticles from thermal pyrolysis of silane - Jank, Michael; Frey, Lothar; Peukert, Wolfgang; Körmer, Richard; Wu, Jia; Otto, Michael (Physica Status Solidi, 2011)
Electron paramagnetic resonance (EPR) investigations of non-oxidized crystalline silicon nanoparticles (SiNP) from thermal silane pyrolysis revealed that the dangling bond (db) concentration strongly depends on the synthesis temperature. For SiNP synthesized at 1000-1200 °C and processed entirely in inert atmosphere, approximately 1013 cm-2 dbs were found which is at least one order of magnitude higher than the values previously reported for oxidized SiNP. After the synthesis, the dbs can be quenched by the addition of bromine (Br2) that proves their location at the particle surface. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
UnivIS-Import:2015-03-09:Pub.2011.tech.IE.LEB.eprinv
Keywords: Electron paramagnetic resonance; Nanoparticles; Pyrolysis; Silicon

Erratum: A self-assembled metamaterial for Lamb waves (Applied Physics Letters (2015) 107 (071903) DOI: 10.1063/1.4928564) - Khanolkar, A.; Wallen, S.; Ghanem, M. Abi; Jenks, J.; Vogel, Nicolas; Boechler, N. (Applied Physics Letters, 2019)
In the original article,1 the quality factors were calculated incorrectly. In the second full paragraph on page 071903-4, the corrected relevant statements are as follows: “We also observe the lowest quality factors (Q 7) for peaks near the microsphere contact resonance, despite low group velocities.” and “In contrast, the quality factors for the observed spheroidal resonances are higher, with Q 16.” No results or conclusions are affected by this error.
CRIS-Team Scopus Importer:2019-05-02

Erratum: Radiation induced corrosion of copper in anoxic aqueous solution(Electrochemical and Solid-State Letters (2012) 15 (C5)) - Hosseinpour, Saman; et al. (Electrochemical and Solid State Letters, 2012)

Establishing High Photocatalytic H-2 Evolution from Multiwalled Titanate Nanotubes - Yoo, Jeong Eun; Alshehri, Abdulmohsen Ali; Qin, Shanshan; Bawaked, Salem Mohamed; Mostafa, Mohamed Mokhtar M.; Katabathini, Narasimharao; Fehn, Dominik; Schmidt, Jochen; Mazare, Anca Valentina; Denisov, Nikita; Cha, Gi; Meyer, Karsten; et al. (ChemCatChem, 2020)
Black TiO2 in various forms has been investigated for numerous photochemical applications. In photocatalytic water splitting, "grey" titania forms have been reported to reach considerable H-2 generation rates without using a noble metal co-catalyst. Up to now, a variety of anatase powders or other morphologies has been investigated in grey and black forms. Here we describe that hydrothermal titanate/anatase nanotubes can show a strong noble metal free photocatalytic activity. For optimized "blackening" conditions, a drastically higher photocatalytic H-2 production can be obtained than for other nanoscale morphologies. This effect can further be improved with a very mild Pt doping that again shows a clearly stronger photocatalytic H-2 production than comparably loaded nanopowders.
CRIS-Team WoS Importer:2020-05-15

Estimation of bivariate probability distributions of nanoparticle characteristics, based on univariate measurements - Furat, Orkun; Frank, Uwe; Weber, Matthias; Wawra, Simon; Peukert, Wolfgang; Schmidt, Volker (Inverse Problems in Science and Engineering, 2020)
The properties of complex particle systems typically depend on multivariate distributions of particle properties, like size and shape characteristics. Multidimensional particle property distributions can be a powerful tool to describe these systems. However, only few techniques exist which are able to simultaneously measure more than one property of individual particles in fast and efficient ways. It is shown how two-dimensional property spaces can be constructed by the combination of two univariate measurements to obtain bivariate particle size distributions. The proposed method is a general approach, which can be applied to a wide spectrum of particle systems and measurement devices. In this paper, the results of a case study are presented, which allow the estimation of bivariate distributions of length and diameter of nanorods, solely using univariate distributions of their particle mass and extinction-weighted sedimentation coefficient distributions. These quantities contain joint information about the particle lengths and diameters, which is used for the reconstruction. The method is validated in a simulation study in which the bivariate distribution to be reconstructed and the reconstruction parameters are varied. In addition, regularization techniques are introduced to reduce methodical errors. This approach can be transferred to other particle systems and measurement techniques, for which functional relationships between particle properties and measured quantities are well describe
Keywords: particle size distributions; reconstruction; inverse problem; Multidimensional characterization; copulas

Estimation of the dominant size enlargement mechanism in spray fluidized bed processes - Rieck, Christian; Bück, Andreas; Tsotsas, Evangelos (Aiche Journal, 2020)
This work deals with estimating the dominant size enlargement mechanism in spray fluidized beds. A new process model is presented, which consists of population balances and a heat- and mass-transfer model. New methods to incorporate the wet surface fraction and the Stokes criterion are proposed, which allow for the probability of wet collisions and the probability of successful wet collisions to be calculated. The product of these parameters, the probability of successful collisions, is linked to the dominant size enlargement mechanism. Simulation studies were performed to investigate the influence of inlet gas temperature, viscosity, droplet size, and contact angle on the probability of successful collisions. Further simulation results based on experiments available in literature suggest that exceeding a probability of successful collisions of 0.001 is sufficient for agglomeration to become dominant. Otherwise, layering will be the dominant size enlargement mechanism. Finally, regime maps of layering and agglomeration are constructed.
CRIS-Team Scopus Importer:2020-02-14
Keywords: agglomeration; layering; size enlargement mechanism; spray fluidized bed

Eulerian Multiphase Simulation of the Particle Dynamics in a Fluidized Bed Opposed Gas Jet Mill - Dyrney, Araujo dos Santos; Baluni, Shivam; Bück, Andreas (Processes, 2020)
The compressible and turbulent gas-solid multiphase flow inside a fluidized bed opposed jet mill was systematically investigated through numerical simulations using the Euler-Euler approach along with the kinetic theory of granular flow and frictional models. The solid holdup and nozzle inlet air velocity effects on the gas-solid dynamics were assessed through a detailed analysis of the time-averaged volume fraction, the time-averaged velocity, the time-averaged streamlines, and the time-averaged vector field distributions of both phases. The simulated results were compared with the experimental observations available in the literature. The numerical simulations contributed to a better understanding of the particle-flow dynamics in a fluidized bed opposed gas jet mill which are of fundamental importance for the milling process performance.
CRIS-Team WoS Importer:2021-01-15
Keywords: granular temperature; OpenFOAM; particle velocity; compressible flow; turbulent flow; comminution

Evaluation of the film formation and the charge transport mechanism of indium tin oxide nanoparticle films - Mahajeri, Mahdi; Voigt, Michael; Klupp Taylor, Robin; Reindl, Armin; Peukert, Wolfgang (Thin Solid Films, 2010)
The structure formation and charge transfer of thin nanoparticulate indium tin oxide (ITO) films prepared by dip-coating was studied as a function of stabilizer before and after annealing at different temperatures. The analysis of the film structure by optical methods revealed that it is a function of the stability. Suspensions containing an optimum stabilizer concentration of 0.1 mol/l resulted in densely packed films with a peak specific conductivity of 8.3 S cm− 1 after annealing at 550 °C for 1 h in air and 121 S cm− 1 after annealing in forming gas at 250 °C for 1 h, respectively. Furthermore, for the densely packed films fluctuation-induced tunnelling was found to be the dominant charge transport mechanism, whereas for the low density films a thermally activated charge transport was observed. That the films of maximum density showed a metallic charge transport behaviour at temperatures above 300 K indicated the optimal contact between ITO particles had been achieve
Keywords: Indium tin oxide; Nanoparticles; Dispersion; Stability; Transmittance; Conductance; Charge transport

Evaporation phenomena in superheated atomization and its impact on the generated spray - Wirth, Karl-Ernst; Günther, Astrid (International Journal of Heat and Mass Transfer, 2013)
Applying the process of superheated atomization (flash atomization) finely dispersed sprays with moderate droplet velocities can be obtained, without the necessity of high pressure or an additional gas phase. In this paper occurring evaporation phenomena inside a nozzle capillary and their impact on the generated spray are analyzed. Evaporation is enhanced for increasing superheating. An intensified evaporation induces a considerably extended spray and smaller droplet sizes are generated. Furthermore a reduced mass flux and decreased velocity of the droplets are to be expected. By increasing the amount of vapor spray pulsation, triggered by bubble bursting, is increased. This is shown in acoustic measurements, which also demonstrate a simple way to monitor, or even control the atomization of superheated liquids.
Keywords: Evaporation; Spray; Superheated; Optic; Acoustic

Evidence of Spatially Inhomogeneous Electron Temperature in a Resonantly Excited Array of Bow-Tie Nanoantennas - Lehr, Martin; Bley, Karina; Vogel, Nicolas; Rethfeld, Bärbel; Schönhense, Gerd; Elmers, Hans Joachim (Journal of Physical Chemistry C, 2019)
We studied the excitation of large-area Au bow-tie nanoantenna arrays, which we have fabricated on indium-tin-oxide (ITO)-coated glass substrates using colloidal lithography with nanoscale polystyrene colloidal particles. Ultrashort (100 fs, 800 nm) laser pulses of a Ti-Sapphire laser resonantly excite electron emission from a few tens of nanometer wide-gap regions of the array. We investigated the near-field enhanced photoemission using time-of-flight momentum microscopy. The variation of the electron emission intensity as a function of kinetic energy, parallel momentum, power density, and polarization of the laser beam reveals two distinct emission mechanisms: a coherent multiphoton photoemission process from the optically heated electron gas and a field emission process resulting from the optical near-field enhancement at the nanoantenna tips. The analysis of the momentum-resolved kinetic energy spectra indicates a spatially inhomogeneous distribution of the electron gas temperature within the bow-tie resonators.
CRIS-Team Scopus Importer:2019-05-28

Evolution of the fractal dimension for simultaneous coagulation and sintering - Schmid, Hans-Joachim; Al Zaitone, Belal; Artelt, Christian; Peukert, Wolfgang (Chemical Engineering Science, 2006)
Simulation results on the evolution of aggregate structure in aerosol processes with coagulation and sintering as the dominant mechanisms are presented. A model for simulation of the three-dimensional morphology of nano-structured aggregates formed by concurrent coagulation and sintering is applied. The model is based on a stochastic diffusion controlled cluster–cluster aggregation algorithm and sintering is modeled as a successive overlapping of spherical primary particles, which are allowed to grow in order to maintain mass conservation. This leads to computer simulated structured aggregates which are then subject to evaluation. Two different methods to determine the fractal dimension are presented which give comparable results. It is shown that even very small particles show the same fractal behavior. Furthermore, equilibrium structures assuming a constant ratio of the characteristic collision time to the characteristic fusion time are considered as well as the kinetics of structural changes due to a change in the ambient condition
Keywords: Simulation; Sintering; Fractals; Coagulation; Particle formation; Nanostructure

Evolution of the Ligand Shell Around Small ZnO Nanoparticles During the Exchange of Acetate by Catechol: A Small Angle Scattering Study - Schindler, Torben; Lin, Wei; Schmutzler, Tilo; Lindner, Peter; Peukert, Wolfgang; Segets, Doris; Unruh, Tobias (ChemNanoMat, 2018)
The core‐shell structure of colloids surrounded by ligands is of great importance for their later application as it can significantly alter the chemical and physical properties of the nanoparticles (NPs). A combination of small angle X‐ray and neutron scattering (SAXS/SANS) in the native solution with additional ex situ measurements (titration‐UV) was applied to study the NP/ligand interface of ZnO NPs after functionalization with catechol derivatives. Based on SAXS data, it was found that within the multimodal particle size distribution the fraction of agglomerates is shifted to smaller sizes and nearly disappeared upon the binding of ethyl 3,4‐dihydroxybenzoate (CAT) molecules. This is ascribed to improved stabilization at the primary particle level by CAT molecules. By combining the neutron scattering contrast with the input of bound CAT molecules from a previously developed titration‐UV method, the heterogeneous composition of the ligand shell became accessible for the first tim
Keywords: quantum dots; Raman spectroscopy; core-shell; nanoparticles; small angle scattering

Excited-state relaxation dynamics of 3-vinylthiophene-terminated silicon quantum dots - Groenewegen, Vincent; Kuntermann, Volker; Haarer, Dietrich; Kunz, Michael; Kryschi, Carola (Journal of Physical Chemistry C, 2010)
In theory, silicon quantum dots (SiQDs) emit enhanced photoluminescence with a size-tunable spectrum in the visible range. In practice, surface states originating from oxide defect structures or organic ligands are strongly involved in exciton relaxation dynamics because the amplitudes of hole and electron wave functions are nonzero at the SiQD surface. In this study, SiQDs with well-defined surface properties were obtained through a wet-chemistry procedure providing SiQDs with adjustable sizes and oxide-free, 3-vinylthiophene-terminated surfaces. The 3-vinylthiophene-terminated SiQDs have a crystalline spherical 2 nm core and were observed to exhibit blue photoluminescence (∼460 nm) with a quantum yield and lifetime of ca. 23% and 1.3 ns, respectively. The interplay between electronically excited molecular states and conduction band states was examined upon direct monitoring of photoexcited carrier dynamics with femtosecond transient absorption spectroscopy. The 3-vinylthiophene ligands were found to act as surface-bound antennae that mediate ultrafast electron transfer or excitation energy transfer across the SiQD interface. © 2010 American Chemical Society.

Exciton Formation at Solid-Solid Interfaces: a systematic experimental and ab initio Study on compressed MgO Nanopowders - Sternig, Andreas; Koller, David; Siedl, Nicolas; Diwald, Oliver; Mckenna, Keith (Journal of Physical Chemistry C, 2012)
An important and so far neglected class of structural elements affecting the overall properties of metal oxide nanopowders are interfaces between individual nanocrystals. In this work we show experimentally that these defects inside a powder of compressed MgO nanocubes are subject to photoexcitation in the UV light range. In particular, we identify a so far unobserved photoluminescence emission process at 2.5 eV. First principles calculations of the optical properties of nanocrystal interfaces provide plausible candidates for both light absorbing and emitting sites which involve different types of interface features. It was found that edge dislocations that arise from interfaces between nanocube edges and terraces induce a significant electrostatic perturbation of the interfacial electronic states. This leads to exciton generation and luminescence at even lower energies than those related to corners and edges of MgO nanocubes
EAM Import::2019-03-14

Experimental and computational chemistry studies of two imidazole-based compounds as corrosion inhibitors for mild steel in HCl solution - Talari, Mahla; Mozafari Nezhad, Siavosh; Alavi, Seyed Jamal; Mohtashamipour, Mostafa; Davoodi, Ali; Hosseinpour, Saman (Journal of Molecular Liquids, 2019)
Two imidazole-based corrosion inhibitors, namely thiazole-4-carboxylic acid (TCA) and 2-methyl-1,3-thiazole-4-carboxylic acid (MTCA), were synthesized and their corrosion inhibition performance on mild steel in 0.1 mol·L−1 HCl solution at 25 °C was investigated using electrochemical measurements. Corrosion inhibition efficiency increased with increasing inhibitor concentration in solution and at a concentration of 150 ppm, both MTCA and TCA exhibited similar corrosion inhibition efficiencies of 90%. Adsorption of both inhibitors on steel followed the Langmuir adsorption isotherm. Theoretical quantum chemical calculation and Monte Carlo simulation were employed to determine the most stable configuration, the adsorption sites, and the interaction energies of TCA and MTCA on the steel surface. The simulation results demonstrated that the competitive adsorption of inhibitors and water molecules, proton, and chloride ions has a large impact on the adsorption configuration of inhibitor
Keywords: Thiazole-based compounds Electrochemical impedance spectroscopy Monte Carlo simulation Density functional theory

Experimental and numerical investigations of the influence of fluid dynamics on the precipitation of nanoscaled particles - Gradl, Johannes; Peukert, Wolfgang (4, 2007)
Continuous precipitation in a T-mixer is a promising way for the economic production of commercial amounts of nanoscaled particles. The challenge is to tailor the product properties of the precipitated particles, i.e. to control the particle size distribution (PSD). The coupling of all relevant subprocesses is the key for predicting the PSD. In this work the influence of the flow field conditions in a mixer on the precipitation process is investigated experimentally as well as numericall
Keywords: Mixing; Precipitation; Population balance equation

Experimental and Theoretical Studies of the Colloidal Stability of Nanoparticles−A General Interpretation Based on Stability Maps - Segets, Doris; Marczak, Renata; Schäfer, Stefan; Paula, Carolin; Gnichwitz, Jan-Frederik; Hirsch, Andreas; Peukert, Wolfgang (Acs Nano, 2011)
The current work addresses the understanding of the stabilization of nanoparticles in suspension. Specifically, we study ZnO in ethanol for which the Influence of particle size and reactant ratio as well as surface coverage on colloidal stability in dependence of the purification progress was investigated. The results revealed that the well-known zeta-potential determines not only the colloidal stability but also the surface coverage of acetate groups bound to the particle surface. The acetate groups act as molecular spacers between the nanoparticles and prevent agglomeration. Next to DLVO calculations based on the theory of Derjaguin, Landau, Verwey and Overbeek using a core shell model we find that the stability is better understood in terms of dimensionless numbers which represent attractive forces as well as electrostatic repulsion, steric effects, transport properties, and particle concentration. Evaluating the colloidal stability in dependence of time by means of UV-vis absorption measurements a stability map for ZnO is derived. From this map it becomes clear that the dimensionless steric contribution to colloidal stability scales with a stability parameter including dimensionless repulsion and attraction as well as particle concentration and diffusivity of the particles according to a power law with an exponent of -0.5. Finally, we show that our approach is valid for other stabilizing molecules like cationic dendrons and is generally applicable for a wide range of other material systems within the limitations of vanishing van der Weals forces in refractive index matched situations, vanishing zeta-potential and systems without a stabilizing shell around the particle surface.
Keywords: nanoparticles; stabilization; particle size; electrostatic; repulsion

Experimental investigation of process behaviour of continuous fluidized bed spray agglomeration with internal classification - Strenzke, Gerd; Dürr, Robert; Bück, Andreas; Kienle, Achim; Tsotsas, Evangelos (13th International Conference on Fluidized Bed Technology, CFB 2021, 2021)

Experimental investigation of the morphology of salt deposits from drying sessile droplets by white-light interferometry - Sondej, Franziska; Peglow, Mirko; Bück, Andreas; Tsotsas, Evangelos (AIChE Journal, 2018)
This study presents a new approach to investigate the drying behavior and the structure of deposit resulting from drying of solid containing micro droplets. It is shown that deposit structure (porosity and “footprint”) depends on drying conditions. This dependency may contribute to better understanding of particle‐forming processes, such as fluidized bed coating. In the framework of this study, sessile droplets containing sodium benzoate dissolved in water were dried on thin glass plates in a small drying chamber. The drying conditions (temperature, moisture content and flow rate of drying gas) and material parameters (solid content of solution) were systematically varied. The drying rate of droplets was determined from the moisture balance of the drying gas. The final three‐dimensional shape of dried sessile droplets was measured using white‐light interferometry and transformed into a two‐dimensional profile using a Monte Carlo method. Moreover the mean porosity of dried droplets was calculated. By comparison of structural information and process conditions it is shown that the drying process may have a large influence on deposit structur
Keywords: Monte Carlo evaluation; salt solutions; drying chamber; structural analysis; white-light interferometry; sessile droplet drying; solid deposit

Experimental study of metal nanoparticle synthesis by an arc evaporation/condensation process - Förster, Henning; Wolfrum, Christian; Peukert, Wolfgang (Journal of Nanoparticle Research, 2012)
The generation of copper nanoparticles in an arc furnace by the evaporation/condensation method is systematically investigated. The evaporation/condensation process is advantageous because it allows direct synthesis using pure metals as starting materials avoiding reactions of expensive and potentially poisonous precursors. In the presented system, a transferred direct current arc provides the energy for evaporation of the metal target. In order to prevent an oxidation of the particles in the process, the synthesis is conducted in an atmosphere of inert gases (purity grade 5.0). The arc stability and its effect on particle synthesis are investigated. The experiments reveal excellent long-term arc stability for at least 8 h continuous operation delivering aerosols with high reproducibility (+/- 10% of average particle size). The influences of the arc current and length, the flow rates of the applied gases and the injection of hydrogen in the plasma zone on the particle size distributions and the agglomerate structure are studied. The produced copper nanoparticles are characterized by scanning mobility particle sizing and scanning electron microscopy. The average particle size could be well controlled in a size range 4-50 nm by selecting appropriate operating parameters.
Keywords: Metal nanoparticles; Synthesis; Arc evaporation/condensation; Aerosol

Experimentelle und theoretische Untersuchungen der Bildungskinetik diffusions- sowie reaktionslimitierter Systeme am Beispiel der Nanopartikelfällung von Bariumsulfat und Zinkoxid - Gradl, Johannes (Friedrich-Alexander-Universität Erlangen-Nürnberg, 2010)
In dieser Arbeit wird die nasschemische Synthese nanoskaliger Bariumsulfat- sowie Zinkoxidpartikel experimentell und theoretisch untersucht. Abhängig von den materialspezifischen Eigenschaften und den gewählten Versuchsbedingungen dominieren einzelne Teilprozesse, deren Kinetiken die dispersen und optischen Produkteigenschaften bestimmen. Im ersten Teil der Arbeit wird auf die Fällung von Bariumsulfatpartikeln im wässrigen Medium als Vertreter eines durch Mikromischeffekte dominierten Partikelbildungsprozesses eingegangen. Mittels laseroptischer Messmethoden wird das Strömungsbild des verwendeten T-Mischers untersucht. Den Schwerpunkt bildet dabei die Quantifizierung des Mischens auf kleinsten Längenskalen mit Hilfe hochauflösender laserinduzierter Fluoreszenz. Die experimentellen Ergebnisse bestätigen die Notwendigkeit einer aufwändigen Strömungssimulation inklusive der Betrachtung räumlicher und zeitlicher Fluktuationen für eine genaue und prädiktive Berechnung des Partikelbildungsprozesses. Aufbauend auf den gewonnenen Erkenntnissen wird ein Modell vorgestellt, das alle relevanten Teilprozesse (Makro- und Mikromischen, homogene Keimbildung, transportlimitiertes Wachstum, Aggregation sowie elektrostatische Stabilisierung) berücksichtigt, und das somit ermöglicht, die komplette Partikelgrößenverteilung (PGV) für unterschiedliche Versuchsbedingungen prädiktiv zu bestimmen. Die Ergebnisse der Simulation liefern aufschlussreiche Erkenntnisse über den im Mischer ablaufenden Partikelbildungs-prozess. Im Anschluss daran werden mehrere Ansätze zur Reduktion der Komplexität des Modells unter unterschiedlichen fluiddynamischen Bedingungen untersucht und diskutiert. Den Mittelpunkt der Untersuchungen des zweiten Teils der Arbeit stellt die Synthese von Zinkoxid Quanten Punkten (QDs) in ethanolischer Lösung dar. Dabei ist eine chemische Reaktion des Precursors zu kolloidalem Zinkoxid der Keimbildung vorge-lagert, die den primären Partikelbildungsprozess entscheidend beeinflusst. Aus diesem Grund spielt hier im Gegensatz zur Bariumsulfatfällung der Mischprozess eine untergeordnete Rolle. Zu Beginn werden auf der DLVO-Theorie basierende Rechnungen vorgestellt, die eine intrinsische Stabilität der untersuchten QDs gegen Aggregation erklären. Des Weiteren wird ein Ansatz zur simultanen Bestimmung der PGV sowie der Partikelanzahlkonzentration einer Suspension aus ihren optischen Eigenschaften für QDs kleiner als 15 nm vorgestellt. Dieser Ansatz ermöglicht eine schnelle und effektive Auswertung der durchgeführten Experimente mittels UV/Vis Spektroskopie. Die Kombination aus linearen und nichtlinearen spektroskopischen Messmethoden bildet den auf unterschiedlichen Zeitskalen ablaufenden Partikelbil-dungsprozess vollständig ab. Aus den daraus gewonnenen Erkenntnissen wird ein numerisches Modell der Zinkoxidfällung entwickelt. Dieses auf Populationsbilanzen basierende Modell berücksichtigt die Reaktion des Precursors zu kolloidalem Zink-oxid, den durch orientiertes Aggregationsverhalten limitierten Wachstumsprozess sowie die im Anschluss einsetzende stark temperaturabhängige Ostwald-Reifung. Durch eine modellbasierte Auswertung der experimentellen Arbeiten ist es zusätzlich möglich, schwer messbare Größen wie die Grenzflächenenergie und die Löslichkeit des Systems zu bestimme

Experiments in micro-patterned model membranes support the narrow escape theory - Meiser, Elisabeth; Mohammadi Eslami, Reza; Vogel, Nicolas; Holcman, David; Fenz, Susanne F. (Communications Physics, 2023)
The narrow escape theory (NET) predicts the escape time distribution of Brownian particles confined to a domain with reflecting borders except for one small window. Applications include molecular activation events in cell biology and biophysics. Specifically, the mean first passage time τ¯ can be analytically calculated from the size of the domain, the escape window, and the diffusion coefficient of the particles. In this study, we systematically tested the NET in a disc by variation of the escape opening. Our model system consisted of micro-patterned lipid bilayers. For the measurement of τ¯ , we imaged diffusing fluorescently-labeled lipids using single-molecule fluorescence microscopy. We overcame the lifetime limitation of fluorescent probes by re-scaling the measured time with the fraction of escaped particles. Experiments were complemented by matching stochastic numerical simulations. To conclude, we confirmed the NET prediction in vitro and in silico for the disc geometry in the limit of small escape openings, and we provide a straightforward solution to determine τ¯ from incomplete experimental trace
Keywords: Cytology; Fluorescence; Fluorescence microscopy; Micromachining; Stochastic systems; Brownian particles; Cell biology; Cell biophysics; Escape time; Mean first passage time; Membrane supports; Micropatterned; Model membranes; Molecular activation; Time distribution; Lipid bilayers

Exploring mechano-bactericidal nature of Psalmocharias cicadas wings: an analytical nanotopology investigation based on atomic force microscopy characterization - Dehghani, Shahrzad; Mashreghi, Mansour; Noorbakhsh Nezhad, Amir Hossein; Karimi, Javad; Hosseinpour, Saman; Davoodi, Ali (Surfaces and Interfaces, 2021)
In this study, the bactericidal properties of the wing surface of two different Psalmocharias cicada species, Psalmocharias querula (PQ) and Psalmocharias akesensis (PA), are examined based on the organization and nano-topographical characteristics of the wing nanostructure. The bacterial killing capacity of the wings was assessed by counting the colony-forming units (CFU). Atomic force microscopy (AFM), scanning electron microscopy (SEM), and contact angle measurements were utilized to reveal wings nano-topographical structures and their impact on bacterial contact-killing efficiency. The role of surface roughness parameters on bacterial cell attachments and bactericidal properties of the wings was evaluated by analysis of topography results using histogram height distribution and power spectral density (PSD) methods. It was found that the skewness and kurtosis values of the cicada wing nanopillars significantly correlate with their shear-inducing capacity, confirming the higher bactericidal activity for PQ wing surface compared to PA wing surface.
Keywords: Cicada wing; Bio-inspiration; Bactericidal activity; Atomic force microscopy

Exploring Plasmonic Resonances Toward "Large-Scale" Flexible Optical Sensors with Deformation Stability - Ghosh, Anik Kumar; Sarkar, Swagato; Nebel, Lisa Julia; Aftenieva, Olha; Gupta, Vaibhav; Sander, Oliver; Das, Amit; Joseph, Joby; Wiessner, Sven; Koenig, Tobias A. F.; Fery, Andreas (Advanced Functional Materials, 2021)
The next generation of sensors requires a simple yet compact lab on chip-based precise optical detection mechanism where data interpretation can be achieved with minimum effort. Hereby, cost-efficient strategies of manufacturing both propagating surface plasmon polariton (SPP) and localized surface plasmon resonance (LSPR) sensors on flexible platforms are explored via mechanical instabilities and oblique-angled metal evaporation. Centimeter scaled dielectric grating structures produced by plasma oxidation of pre-stressed polydimethylsiloxane film have comprised the substrates, thus imparting inherent flexibility. Subsequently, both continuous and discontinuous 1D-metallic lattices are obtained via vapor deposition of gold at different angles. The optical isotropy (gold surface-grating) and anisotropy (gold edge-grating) are distinctly observed as a difference between forward and backward diffraction efficiencies, backed by analytical correlation to the observed orders. Supported with electromagnetic modeling, the SPP and LSPR excitations are experimentally characterized under reflectance and transmittance measurements, along with a demonstration of their sensing capabilities. The LSPR supported flexible sensor provides superiority in terms of sensitivity, which is investigated under mechanical deformations to exhibit consistency of the resonant wavelength. Such consistency is strategically unraveled via "finite element method" based approaches, thus providing a new paradigm of cost-efficient, large-scaled flexible sensors.
CRIS-Team WoS Importer:2021-05-28

Extension of the Deep UV-Capabilities in Multiwavelength Spectrometry in Analytical Ultracentrifugation: The Role of Oil Deposits - Walter, Johannes; Segets, Doris; Peukert, Wolfgang (Particle & Particle Systems Characterization, 2016)
The optical performance of an analytical ultracentrifuge equipped with a fiber-coupled detector is investigated with special emphasis on the influence of oil leakage on the long-term deep ultraviolet stability. Two strategies for enhanced optical performance are presented. The first includes regeneration of fiber transmittance under atmospheric conditions, whereas the second utilizes an optimized vacuum system consisting of a turbomolecular pump.
EAM Import::2019-03-14

Fabrication, charge carrier transport, and application of printable nanocomposites based on indium tin oxide nanoparticles and conducting polymer 3,4-ethylenedioxythiophene/polystyrene sulfonic acid - Maksimenko, Ilja; Kilian, Daniel; Mehringer, Christian; Voigt, Michael; Peukert, Wolfgang; Wellmann, Peter (Journal of Applied Physics, 2011)
Printable transparent hybrid composites consisting of indium tin oxide (In2O3:Sn; ITO) nanoparticles and conducting polymer 3,4-polyethylenedioxythiophene (PEDOT) as matrix material were developed. The basic idea is to fill up the pores of the highly porous nanoparticulate ITO network to improve the interparticle contact and hence the conductivity of printed ITO thin films. Ready-to-use and stable aqueous dispersions were fabricated starting from ITO nanoparticles and aqueous formulation of conducting PEDOT and polystyrene sulfonic acid (PSS). This report presents and discusses key factors to obtain stable ITO-PEDOT dispersions with different mixing ratios and their application for printable devices as transparent electrode material. It was found that the f-potential value is crucial for preparation of stable dispersions. Electrical and optical properties of the hybrid ITO-PEDOT coatings were analyzed. Temperature dependent resistivity measurements reveal that conduction occurs by fluctuation induced tunneling. Transparent and conducting nanocomposite layers with a conductivity as high as 132 X1cm1 were fabricated by a low-temperature (T¼130 C) and entirely vacuum-free process. An all-printed electroluminescent lamp on a flexible substrate was realized as a demonstrator showing the applicability of such coatings for voltage-driven optoelectronic devices.<br

Fabrication of gold-nanoshell/polycaprolactonecomposite films with high electrical conductivity - Naseri, Shiva; Diba, Mani; Golkar, Saeedeh; Boccaccini, Aldo R.; Klupp Taylor, Robin (Materials Letters, 2014)
Gold nanoshells on 1.1 μm diameter silica cores were produced via a seeded growth approach and their quality evaluated using optical measurements. The particles were combined with polycaprolactone to produce a flexible biocompatible composite film with high conductivity (1.51 S cm-1) and relatively low effective gold loading (16.86 wt%) in comparison with other reports in the literature. The morphology of the composite was shown to comprise nanoshell-filled pores percolating a polymer-rich matrix. The obtained films have potential for biomedical applications such as in patches for cardiac tissue engineering, combining biocompatibility, flexibility and electrical conductivity. © 2014 Elsevier B.V.
Keywords: Conductivity; Metal nanoshells; Nanocomposite; Plasmon resonance; Polycaprolactone

Fabrication of Micro-Nano Roughened Surface with Superhydrophobic Character on an Aluminum Alloy Surface by a Facile Chemical Etching Process - Attar, Mohammad Reza; Khajavani, Ehsan; Hosseinpour, Saman; Davoodi, Ali (Bulletin of Materials Science, 2019)
In the present study, we have fabricated a superhydrophobic surface on aluminum alloy 2024 through a simple immersion chemical etching method in hydrochloric acid followed by a functionalization step in stearic acid solution. The impact of etching time on water contact angle was investigated and a contact angle of 167° was reached on the superhydrophobic surface which was etched for four minutes. Morphology of the surface was evaluated by scanning electron microscopy and the surface chemical analysis was performed by energy dispersive X-ray spectroscopy and Raman spectroscopy. We show that the fabricated superhydrophobic samples can repel other liquids than water. We also demonstrate the self-cleaning properties of the fabricated samples using graphite particles. Ultimately, we assessed the corrosion resistance properties of the fabricated surfaces using potentiodynamic polarization method. Superhydrophobic surface exhibited increased corrosion potential and polarization resistance along with reduced corrosion current, all of which are indicative of a significant improvement in corrosion performance of the superhydrophobic surface in comparison with typical aluminum 2024. The cheap and facile superhydrophobic surface fabrication method presented in this study can be applied to large scale samples with no need for electricity or expensive raw materials
Keywords: Superhydrophobic; Aluminum Alloy 2024; Self-Cleaning; Corrosion

Fabrication of nanoparticulate inks for applications in printable electronics - Reindl, Armin; Aldabergenova, Saule; Altin, Ergün; Frank, Gerhard; Peukert, Wolfgang (4, 2007)
Semiconducting nanoparticles were dispersed systematically in organic solvents using a variety of methods. In the case of silicon particles prepared by gas phase synthesis a high specific energy input is necessary to obtain intrinsically stable suspensions. Therefore Si nanoparticles were dispersed for 24 hours in 1-butanol using a stirred media mill. Via this process intrinsically stable suspensions of Si nanoparticles were produced. The evolution of morphology, particle size and structure was investigated by dynamic light scattering, X-ray diffraction, Raman spectroscopy, and high resolution transmission electron microscopy as a function of dispersing time. The microstructural development with varying crystallite size and crystalline volume fraction was analyzed by Raman spectroscopy and directly confirmed by transmission electron microscopy measurements. The surface chemistry of the Si nanoparticles was analyzed by diffuse reflectance infrared Fourier transform spectroscop
Keywords: Raman spectroscopy; HRTEM; Stirred media mill; Silicon nanoparticles; XRD

Facile colloidal coating of polystyrene nanospheres with tunable gold dendritic patches - Bao, Huixin; Bihr, Timo; Smith, Ana-Suncana; Klupp Taylor, Robin (Nanoscale, 2014)
Patchy particles comprise regions of differing material or chemical functionality on otherwise isotropic cores. To meet the great potential of these anisotropic structures in a wide range of application fields, completely new approaches are sought for the scalable and tunable production of patchy particles, particularly those with nanoscale dimensions. In this paper the synthesis of patchy particles via a simple colloidal route is investigated. Using surfactant-free cationic polystyrene nanospheres as core particles, gold patches are produced through the in situ reduction of chloroauric acid with ascorbic acid. The fact that such nanostructured metal patches can be heterogeneously nucleated on polymer nanospheres is related to the electrostatic interaction between core and metal precursor. Furthermore, the lateral expansion of the gold patches over the polystyrene surface is facilitated by an excess of ascorbic acid. The morphology of the patches is highly dendritic and process-induced variations in the structure are related to gold surface mobility using Monte Carlo simulations based on the diffusion limited aggregation principle. Considering the pH dependent behaviour of ascorbic acid it is possible to predict the moiety which most likely adsorbs to the polymer surface and promotes gold surface diffusion. This enables the judicious adjustment of the pH to also obtain non-dendritic patches. On account of the plasmonic behaviour of gold, the patchy particles have morphology-dependent optical properties. The systematic development of the synthetic approach described here is expected to lay a foundation for the development of functional materials based on the self- or directed-assembly of nanoscale building blocks with anisotropic interactions and properties. © the Partner Organisations 2014.
Keywords: patchy; particle; functionality; anisotropic; morphology; Monte-Carlo; simulation; surface

Facile route to morphologically tailored silver patches on colloidal particles - Klupp Taylor, Robin; Bao, Huixin; Vasylyev, Serhiy; Peukert, Wolfgang; Tian, Chenting (Langmuir, 2010)
Here we demonstrate, for the first time, the heterogeneous nucleation and growth of silver patches on submicrometer silica spheres. While patches can be grown directly onto native silica particles, it is shown that a higher patch yield can be obtained by first treating the silica with a mixture of an alkanolamine and silver nitrate. Variation of the pretreatment and subsequent coating reactions allowed the patch yield, number, size, thickness, and shape to be adjusted. The patchy particles were shown to possess plasmon modes extending from the visible into the near-IR region, making these structures highly interesting for both their asymmetric morphological and functional properties.
Keywords: tailored; particle; colloid; heterogeneous; nucleation

Facile synthesis and post-processing of eco-friendly, highly conductive copper zinc tin sulphide nanoparticles - Ahmad, Rameez; Distaso, Monica; Azimi, Seyed Hamed; Brabec, Christoph; Peukert, Wolfgang (Journal of Nanoparticle Research, 2013)
Cu2ZnSnS4 (CZTS) nanoparticles have shown promising properties to be used as an energy harvesting material. They are usually synthesised under inert atmosphere or vacuum, whereas the subsequent step of film formation is carried out under an atmosphere of sulphur and/or Sn in order to avoid the decomposition of CZTS nanoparticles into binary and ternary species as well as the formation of the corresponding oxides. In the present paper we show that both the synthesis of CZTS nanoparticles and the film formation from the corresponding suspension can be considerably simplified. Namely, the synthesis can be carried out without controlling the atmosphere, whereas during the film annealing a nitrogen atmosphere is sufficient to avoid the depletion of the CZTS kesterite phase. Furthermore, an integrated approach including in-depth Raman analysis is developed in order to deal with the challenges associated with the characterization of CZTS nanoparticles in comparison to bulk systems. The formation of competitive compounds during the synthesis such as binary and ternary sulphides as well as metal oxides nanoparticles is discussed in detail. Finally, the as-produced films have ten times higher conductivity than the state of the art.
Keywords: By-products; Defects; Kesterite; Raman spectroscopy; Stannite CZTS nanoparticles; Thermodynamic study

Facile Synthesis of Gallium (III)-Chitosan Complexes as Antibacterial Biomaterial - Akhtar, Muhammad Asim; Hadzhieva, Zoya; Ilyas, Kanwal; Ali, Muhammad Saad; Peukert, Wolfgang; Boccaccini, Aldo R. (Pharmaceutics, 2021)
Even though antibiotic treatment remains one of the most common tools to handle bacterial infections, the excessive antibiotic concentration at the target site may lead to undesired effects. Aiming at the fabrication of antibiotic-free biomaterials for antibacterial applications, in this work, we propose the synthesis of gallium (III)-chitosan (Ga (III)-CS) complexes with six different gallium concentrations via an in situ precipitation method. Fourier Transform infrared spectroscopy indicated the chelation of chitosan with Ga (III) by peak shifts and changes in the relative absorbance of key spectral bands, while energy-dispersive X-ray spectroscopy indicated the homogenous distribution of the metal ions within the polymer matrix. Additionally, similar to CS, all Ga (III)-CS complexes showed hydrophobic behavior during static contact-angle measurements. The antibacterial property of the complexes against both Gram-negative and Gram-positive bacteria was positively correlated with the Ga (III) concentration. Moreover, cell studies confirmed the nontoxic behavior of the complexes against the human osteosarcoma cell line (MG-63 cells) and mouse embryonic fibroblasts cell line (MEFs). Based on the results of this study, new antibiotic-free antibacterial biomaterials based on Ga (III)-CS can be developed, expanding the scope of CS applications in the biomedical field.

Facile synthesis of monodisperse maghemite and ferrite nanocrystals from metal powder and octanoic acid - Kifah, Salih; Mamone, Patricia; Doerr, Gunder; Bauer, Thomas; Brodyanski, Alexander; Wagner, Christine; Kopnarski, Michael; Klupp Taylor, Robin; Demeshko, Serhiy; Meyer, Franc; Schünemann, Volker; Ernst, Stefan; et al. (Chemistry of Materials, 2013)
Extremely small, monodisperse, and spheric maghemite (γ-Fe O, 2-3 nm) and manganese (4-7 nm), cobalt (3-5 nm), and zinc ferrite (5-7 nm) nanocrystals are directly accessible on a large scale starting from inexpensive metal powders and octanoic acid by thermolysis in a high-boiling solvent. Bigger particle size is obtainable by prolonged reaction time according to the Ostwald ripening principle. The superparamagnetic nanocrystals and their assembly have been characterized by transmission electron microscopy, powder X-ray diffraction, Mössbauer spectroscopy, magnetic measurements, and energy-dispersive X-ray spectroscopy. © 2013 American Chemical Societ
Keywords: ferrites; maghemite; Mössbauer spectroscopy; nanoparticles; octanoic acid; TEM

Facilitated Lattice Oxygen Depletion in Consolidated TiO2 Nanocrystal Ensembles: A Quantitative Spectroscopic O2 Adsorption Study - Elser, Michael J.; Diwald, Oliver (Journal of Physical Chemistry C, 2012)
On TiO2 nanocrystal powders, pressure-induced consolidation and subsequent annealing generates mesopores inside the pellet and leads to the depletion of specific surface area. This loss corresponds to the introduction of particle–particle interfaces and grain boundaries. In previous work, they were found to be susceptible to facilitated lattice oxygen depletion as compared to free particle surfaces during vacuum annealing. For the first time, we determined the adsorption of molecular oxygen on these consolidated and nonstoichiometric nanocrystal samples. As a function of repeated cycles of vacuum annealing and O2 exposure, the amount of paramagnetic and diamagnetic surface oxygen species was determined using mass spectroscopy in combination with FT-IR, electron paramagnetic resonance (EPR), and UV–vis–NIR diffuse reflectance.
EAM Import::2019-03-14

Fast and Slow Ligand Exchange at the Surface of Colloidal Gold Nanoparticles - Dinkel, Rebecca; Braunschweig, Björn; Peukert, Wolfgang (Journal of Physical Chemistry C, 2016)
Applications of gold nanoparticles often demand that the particle's ligand shell is modified after particle formation. Obviously, there is a great need for a molecular understanding of this process which is often not accessible in situ. Here, we have applied second-harmonic light scattering (SHS) to investigate the ligand exchange at the surface of colloidal gold nanoparticles in situ and in real time. We demonstrate that the ligand exchange at the surface of citrate-covered Au nanoparticles with 3-mercapto-1-propanesulfonate (MPS) must be described by a fast (<100 s) and a slow reaction process (<23 min), which can be attributed to MPS adsorption on low- and high-coordinated Au surface sites. Using a modified Langmuir isotherm, the average Gibbs free energy of adsorption extgreekDG (-46 kJ/mol) and the surface coverage extgreekG ( 3.5 extgreekmmol/m2) for MPS on Au nanoparticles were determined. The latter was found to be much smaller compared to planar gold surfaces which points to coadsorption of MPS with citrate on high-coordinated sites, i.e., Au terraces. On more reactive low-coordinated Au sites, i.e., edge sites, citrate is easily replaced by MPS. In fact, we find that a substantial portion (49%) of the surface-adsorbed MPS is present on these low-coordinated sites.
EAM Import::2019-03-14

Fast Gas-Adsorption Kinetics in Supraparticle-Based MOF Packings with Hierarchical Porosity - Fujiwara, Atsushi; Wang, Junwei; Hiraide, Shotaro; Götz, Alexander; Miyahara, Minoru T.; Hartmann, Martin; Apeleo Zubiri, Benjamin; Spiecker, Erdmann; Vogel, Nicolas; Watanabe, Satoshi (Advanced Materials, 2023)
Metal–organic frameworks (MOFs) are microporous adsorbents for high-throughput gas separation. Such materials exhibit distinct adsorption characteristics owing to the flexibility of the crystal framework in a nanoparticle, which can be different from its bulk crystal. However, for practical applications, such particles need to be compacted into macroscopic pellets, creating mass-transport limitations. In this work, this problem is addressed by forming materials with structural hierarchy, using a supraparticle-based approach. Spherical supraparticles composed of nanosized MOF particles are fabricated by emulsion templating and they are used as the structural component forming a macroscopic material. Zeolitic imidazolate framework-8 (ZIF-8) particles are used as a model system and the gas-adsorption kinetics of the hierarchical material are compared with conventional pellets without structural hierarchy. It is demonstrated that a pellet packed with supraparticles exhibits a 30 times faster adsorption rate compared to an unstructured ZIF-8 powder pellet. These results underline the importance of controlling structural hierarchy to maximize the performance of existing materials. In the hierarchical MOFs, large macropores between the supraparticles, smaller macropores between individual ZIF-8 primary particles, and micropores inherent to the ZIF-8 framework collude to combine large surface area, defined adsorption sites, and efficient mass transport to enhance performance.
CRIS-Team Scopus Importer:2023-10-06
Keywords: adsorption kinetics; hierarchical porosity; metal–organic frameworks; self-assembly; supraparticles

Femtosecond spectroscopic study of carminic acid-DNA interactions - Gabel, Loredana-Bianca; Kryschi, Carola; Rusu, Catalin Florin; et al. (Chemical Physics, 2006)
Photo-excited carminic acid and carminic acid-DNA complexes in a buffer solution at pH 7 have been examined using a variety of spectroscopy techniques, that are in particular, the femtosecond resolved fluorescence upconversion and transient absorption spectroscopy. The observation of dual fluorescence emission, one peaks at 470 nm and the other at 570 nm, indicates to an excited-state (S) intramolecular proton transfer (ESIPT). A detailed analysis of the transient absorption measurements of an aqueous carminic-acid solution at pH 7 yielded four lifetimes for the excited-state (S): 8, 15, 33 and 46 ps. On the other hand, only two lifetimes, 34 and 47 ps, were observed by fluorescence upconversion spectroscopy because of the detection limitation to the long wavelength edge of the carminic-acid spectrum. The four S lifetimes were ascribed to the coexistence of respectively two tautomer (normal and tautomer) forms of carminic acid, in the non-dissociated state (CAH) and in the deprotonated state (CA). The fluorescence upconversion measurements of carminic acid-DNA complexes exhibited a prolongation of the fluorescence lifetimes. This effect was accepted as evidence for the formation of intercalation complexes between the carminic acid and the DNA. The intercalative binding of the carminic acid to DNA was confirmed by the fluorescence titration experiments resulting to a binding constant of 2 × 10 M that is typical for anthracycline-DNA complexes. © 2006 Elsevier B.V. All rights reserved.

Femtosecond transient absorption spectroscopy of silanized silicon quantum dots - Kuntermann, Volker; Cimpean, Carla Ramona; Brehm, Georg; Sauer, Guido; Kryschi, Carola; Wiggers, Hartmut (Physical Review B, 2008)
Excitonic properties of colloidal silicon quantum dots (Si qdots) with mean sizes of 4 nm were examined using stationary and time-resolved optical spectroscopy. Chemically stable silicon oxide shells were prepared by controlled surface oxidation and silanization of HF-etched Si qdots. The ultrafast relaxation dynamics of photogenerated excitons in Si qdot colloids were studied on the picosecond time scale from 0.3 ps to 2.3 ns using femtosecond-resolved transient absorption spectroscopy. The time evolution of the transient absorption spectra of the Si qdots excited with a 150 fs pump pulse at 390 nm was observed to consist of decays of various absorption transitions of photoexcited electrons in the conduction band which overlap with both the photoluminescence and the photobleaching of the valence band population density. Gaussian deconvolution of the spectroscopic data allowed for disentangling various carrier relaxation processes involving electron-phonon and phonon-phonon scatterings or arising from surface-state trapping. The initial energy and momentum relaxation of hot carriers was observed to take place via scattering by optical phonons within 0.6 ps. Exciton capturing by surface states forming shallow traps in the amorphous Si Ox shell was found to occur with a time constant of 4 ps, whereas deeper traps presumably localized in the Si-Si Ox interface gave rise to exciton trapping processes with time constants of 110 and 180 ps. Electron transfer from initially populated, higher-lying surface states to the conduction band of Si qdots (>2 nm) was observed to take place within 400 or 700 fs. © 2008 The American Physical Society.
Keywords: absorption; quantum; dots; spectroscopy

Feststoffkonzentration und -geschwindigkeiten in wandnahen Bereichen zirkulierender Wirbelschichten - Wirth, Karl-Ernst; Molerus, Otto; Seiter, Michael (VGB Kraftswerkstechnik, 1991)
UnivIS-Import:2015-03-05:Pub.1991.tech.ITC.mechve.festst

Feststoffkonzentration und -geschwindigkeiten in wandnahen Bereichen zirkulierender Wirbelschichten - Wirth, Karl-Ernst; Molerus, Otto; Seiter, Michael (VGB-Konferenz "Wirbelschichtsysteme 1990", 1990)
UnivIS-Import:2015-04-16:Pub.1990.tech.ITC.mechve.festst_94
Keywords: wirbelschicht; fluidisation

FIMOR: An efficient simulation for ZnO quantum dot ripening applied to the optimization of nanoparticle synthesis - Haderlein, Michael; Segets, Doris; Gröschel, Michael; Pflug, Lukas; Leugering, Günter; Peukert, Wolfgang (Chemical Engineering Journal, 2015)
This work presents the application of a Fully Implicit Method for Ostwald Ripening (FIMOR) for simulating the ripening of ZnO quantum dots (QDs). Its stable numerics allow FIMOR to employ the full exponential term of the Gibbs–Thomson equation which significantly outperforms the common Taylor-approximation at typical QD sizes below 10 nm. The implementation is consistent with experimental data for temperatures between 10 and 50 °C and the computational effort is reduced by a factor of 100–1000 compared to previous approaches. This reduced the simulation time on a standard PC from several hours to a few minutes. In the second part, we demonstrate the high potential and accuracy of FIMOR by its application to several challenging studies. First, we compare numeric results obtained for ripening of ZnO QDs exposed to temperature ramps with experimental data. The deviation between simulation and experiment in the mean volume weighted particle size was as small as 5%. Second, a map for the process parameter space spanned by ripening time and temperature is created based on a large number (>50) of FIMOR runs. From this map appropriate process parameters to adjust a desired dispersity are easily deduced. Further data analysis reveals in agreement with literature findings that the particle size distribution converges towards a self-preserving stable shape. Equations describing the time dependent particle size distribution with high accuracy are presented. Finally, we realized the transfer from low volume batch experiments to continuous QD processing. We modeled the continuous ZnO synthesis in a fully automated microreaction plant and found an excellent agreement between the numeric prediction and the experimental results by considering the residence time distribution.

First combined electron paramagnetic resonance and FT-IR spectroscopic evidence for reversible O2 adsorption on In2O3-x nanoparticles - Siedl, Nicolas; Gügel, Philipp; Diwald, Oliver (Journal of Physical Chemistry C, 2013)
Adsorption-induced electronic property changes determine the performance of nanostructured transparent conductive oxides and sensor materials. For the study of O2 adsorption on electron rich In2O3-x nanoparticles we used transmission FT-IR spectroscopy in combination with electron paramagnetic resonance (EPR). The reversible emergence and annihilation of conduction band electrons is subject to O2 adsorption and was tracked at different oxygen pressures via IR active Drude absorptions. Corresponding results were related to EPR measurements that were performed under identical experimental conditions. For the first time we identified a weak adsorption complex between O2 and the surface of In2O 3-x nanoparticles in the temperature range between T = 90 K and T = 298 K. Complementing and supporting our FT-IR observations, this evidence opens the way to study sensing relevant adsorption processes at room temperature with spectroscop

First studies on the rheological behavior of suspensions in ionic liquids - Peukert, Wolfgang; Altin, Ergün; Gradl, Johannes (Chemical Engineering & Technology, 2006)
The suspension rheology of hematite in the ionic liquid Ecoeng ™.212 was studied in detail and compared to the pure ionic liquid. This is the first report on the rheological behavior of suspensions in ionic liquids, and it is postulated that colloidal stability and rheology must be considered to understand these results, and to overcome limitations on the production of nanosized particles in industrial applications. Concentrated suspensions of particles in the nanometer range show non-Newtonian flow behavior including shear thinning and shear thickening. These phenomena are mainly caused by particle-particle interactions in the suspension, and control of these interactions is critical. The influences of temperature and solid concentration on flow behavior were shown for the pure liquid and the suspensions. It is seen that the ionic liquid follows the Arrhenius equation for non-associating electrolytes. It is possible to shift all hematite suspension curves to a master curve according to the model of Gleiβle and Baloch. Furthermore, the flow behavior of the suspensions can be modeled with the well-known Herschel-Bulkley plot. A 10 wt % suspension of FeO follows Newtonian behavior over the entire range, similar to the pure ionic liquid. It is believed that the ionic liquid has an influence on the stability of the particles, leading to a decrease of attractive particle-particle forces. © 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
Keywords: Ionic liquids; Rheology; Suspensions

Flowability of plant based food powders: Almond, chestnut, chickpea, coconut, hazelnut and rice - Düsenberg, Björn; Schmidt, Jochen; Sensoy, Ikay; Bück, Andreas (Journal of Food Engineering, 2023)
This study presents bulk material characterization, especially powder flowability, of eight food powders from six different plants (almond, chestnut, chickpea, coconut, hazelnut and rice). The characterization of the bulk powders includes the particle size distributions, true densities, bulk and tapped densities, as well as the powder porosity and moisture content. The flowability is determined by means of Hausner ratio, Carr's index, flow function by an annular shear cell and dynamic angle of repose. The flowability characteristics are discussed in regard to the bulk powder properties and evaluated for their applicability as some methods could give misleading results for the flowabilit
Keywords: Grains and nuts; Bulk characterization; Powder properties; Powder flowability

Flow field characterization in a vertically oriented cold wall CCVD reactor by particle image velocimetry - Reinhold Lopez, Karla; Bräuer, Andreas; Schmitt, Adeliene; Popovska, Nadejda; Leipertz, Alfred (Chemical Engineering Journal, 2012)

Flowsheet simulation of integrated precipitation processes - Michaud, Mark; Haderlein, Michael; Segets, Doris; Peukert, Wolfgang (Dynamic Flowsheet Simulation of Solids Processes, 2020)
This work presents the fundamentals and exemplary applications of a generalized model for precipitation, aggregation and ripening processes including the formation of solid phases with two dimensions. The particle formation is governed by awidely applicable population balance approach. Solid formation processes are described via the numerically efficient Direct Quadrature Method of Moments (DQMOM), which can calculate the evolution of multiple solid phases simultaneously. The particle size distribution (PSD) is approximated by a summation of delta functions while the moment source term is approximated by a two-point quadrature. The moments to calculate the multivariate distributions are chosen carefully to represent the second order moments. Solid formation is based on themodel of Haderlein et al. (2017) and is extended by a multidimensional aggregation model. Now, the influences of mixing, complex hydrochemistry and particle formation dynamics including nucleation, growth and aggregation on multiphase precipitation processes are modelled and simulated along independent dimensions with high efficiency.
CRIS-Team Scopus Importer:2020-08-28