Polarized light transmission in distorted 2-dimensional slab colloidal plasmonic-photonic crystals - Peukert, Wolfgang; Romanov, Sergey; Belotitskii, Vladimir; Korovin, Alexander; Lobazh, V (7th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics Metamaterials 2013, 2013)
Polarization rotation was induced in 2-dimensional plasmonic-photonic crystal by uniformly distorting the shape of silver semishells. Physical mechanism of this phenomenon was analyzed using co-and cross-polarized transmission spectra. © 2013 IEEE.
Keywords: polarization; plasmon; crystal; transmission; photonic

Polarized Raman scattering and SEM combined full characterization of self-assembled nematic thin films - Srikantharajah, Rubitha; Gerstner, Karin; Romeis, Stefan; Peukert, Wolfgang (Nanoscale, 2016)
Elongated particles are predestined for a fast transfer of optical and electronical signals in a preferred direction, which is mandatory for a quick response in optoelectronic devices. The performance of the material is based on the quality of defect less alignment of the particles. On this account we present an easy non-invasive methodology for characterization of both surface and bulk order. The characterization of bulk order is performed by orientation dependent variation of the polarized Raman scattering signal on large areas by mapping. Scanning electron microscopy and image analysis on the surface complete the characterization. New insights in dip coated nematic structures clearly show the interplay of evaporation induced and shear-induced self-assembly and reveal a comprehensive mechanistic picture for nanorod assembly: the shear force dominated regime orients the particle in direction of withdrawal. At low withdrawal velocity, however, shear forces and evaporation counteract to produce a three-layered film where the top and bottom layers are oriented perpendicular to each other. The middle layer gives a clear evidence for a reorientation by convective flow.

Polyamide 11 nanocomposite feedstocks for powder bed fusion via liquid-liquid phase separation and crystallization - Tischer, Florentin; Cholewa, Simon; Düsenberg, Björn; Drummer, Dietmar; Peukert, Wolfgang; Schmidt, Jochen (Powder Technology, 2023)
Within this contribution, the incorporation of nanoparticles (SiO2, Al2O3, TiO2) into the matrix of precipitated polyamide particles during thermally induced phase separation (TIPS) is demonstrated. The obtained polymer composite powders are tailored for their application in powder bed fusion (PBF). The flexible process allows to tune and adapt the powder properties to meet specific challenges like narrow particle size distribution, spherical particles, high additive contents and good distribution of the additive within the powder. Thermogravimetric analysis and electron microscopy prove the incorporation of the nano-sized additive into the matrix of the polymer. The influence of the additive material during polymer precipitation on the particle size distribution and shape of the powders is discussed. Thermal properties of the composite powders were assessed by dynamic and isothermal DSC for subsequent Avrami analysis. The observed acceleration of the crystallization kinetics could be attributed to the nucleating effect of the additive. All powders showed an easy-flowing (flow index ffC > 4) behavior. This allowed the deposition of homogeneous powder layers during PBF experiments also at high temperatures. The processability of the composite powders in the PBF process was demonstrated by single layer experiments.
CRIS-Team Scopus Importer:2023-04-28
Keywords: Liquid-liquid phase separation; Nanocomposite; Polyamides; Polymer precipitation; Powder bed fusion; Tailoring bulk properties; Thermal analysis

Polymer-based separator for all-solid-state batteries produced by additive manufacturing - Wudy, Katrin; Sapishchuk, Svitlana; Hofmann, Joseph; Schmidt, Jochen; Konwitschny, Fabian; Töpper, Hans Christoph; Daub, Ruediger (Journal of Applied Polymer Science, 2023)
The high demand for an efficient energy supply for various applications facilitates the development of innovative storage technologies like all-solid-state batteries in addition to novel production technologies. Compared to the conventional manufacturing process, additive manufacturing (AM) is a promising technology used for the rapid and cost-effective production of battery components containing separators. However, AM technologies like laser-based powder bed fusion of polymers (PBF-LB/P) have been neglected so far. The present research aims to fill this research gap and outline a novel approach for processing polymers like polyethylene oxide (PEO) and polyvinylidene fluoride (PVDF) into separators using PBF-LB/P. Optimal process parameters for manufacturing PVDF and PEO with PBF-LB/P to generate homogeneous and dense layers represent the key findings of this paper and provide a deeper process understanding. The first proof of concept for producing separator layers by PBF-LB/P in a scalable process is demonstrated as a result.
CRIS-Team Scopus Importer:2023-02-17
Keywords: additive manufacturing; all-solid-state battery; laser-based powder bed fusion of plastics; PVDF powder; separator

Polymeric stabilization of fused corundum during nanogrinding in stirred media mills - Eisermann, Claudia; Mallembakam, Madhusudhan Rao; Damm, Cornelia; Peukert, Wolfgang; Breitung-Faes, Sandra; Kwade, Arno (Powder Technology, 2012)
This paper deals with the steric stabilization of fused corundum during milling in ethanol and water. Different molecular weights of DAPRAL, a block copolymer with lyophilic and lyophobic side chains, were used to stabilize the feed material particles during wet grinding. Preliminary studies of the adsorbed amounts of the polymer in different solvents were determined by TGA and by rheology measurements in order to select sufficient amount of polymer to stabilize the suspension. The median particle size of sterically stabilized milled alumina particles was obtained via Dynamic Light Scattering, Ultrasonic Extinction, BET and SEM. In this investigation primary median particle sizes of 60 nm were obtained in ethanol by applying the steric stabilization mechanism. The mechanochemical characterization was carried out on the milled alumina particles and a phase transformation from alumina to aluminum hydroxide in water was observed, irrespective of stabilization mechanisms. However, no phase transformation was observed in ethanol. (C) 2011 Elsevier B.V. All rights reserved.
Keywords: Steric stabilization; Corundum dispersion; DLVO theory; Wet grinding; Adsorption mechanism; Mechanochemical effects

Poly-N-isopropylacrylamide Nanogels and Microgels at Fluid Interfaces - Rey, Marcel; Fernandez-Rodriguez, Miguel Angel; Karg, Matthias; Isa, Lucio; Vogel, Nicolas (Accounts of Chemical Research, 2020)
ConspectusThe confinement of colloidal particles at liquid interfaces offers many opportunities for materials design. Adsorption is driven by a reduction of the total free energy as the contact area between the two liquids is partially replaced by the particle. From an application point of view, particle-stabilized interfaces form emulsions and foams with superior stability. Liquid interfaces also effectively confine colloidal particles in two dimensions and therefore provide ideal model systems to fundamentally study particle interactions, dynamics, and self-assembly. With progress in the synthesis of nanomaterials, more and more complex and functional particles are available for such studies.In this Account, we focus on poly(N-isopropylacrylamide) nanogels and microgels. These are cross-linked polymeric particles that swell and soften by uptaking large amounts of water. The incorporated water can be partially expelled, causing a volume phase transition into a collapsed state when the temperature is increased above approximately 32 °C.Soft microgels adsorbed to liquid interfaces significantly deform under the influence of interfacial tension and assume cross sections exceeding their bulk dimensions. In particular, a pronounced corona forms around the microgel core, consisting of dangling chains at the microgel periphery. These polymer chains expand at the interface and strongly affect the interparticle interactions. The particle deformability therefore leads to a significantly more complex interfacial phase behavior that provides a rich playground to explore structure formation processes.We first discuss the characteristic "fried-egg" or core-corona morphology of individual microgels adsorbed to a liquid interface and comment on the dependence of this interfacial morphology on their physicochemical properties. We introduce different theoretical models to describe their interfacial morphology. In a second part, we introduce how ensembles of microgels interact and self-assemble at liquid interfaces. The core-corona morphology and the possibility to force these elements into overlap upon compression results in a complex phase behavior with a phase transition between microgels with extended and collapsed coronae. We discuss the influence of the internal particle architecture, also including core-shell microgels with rigid cores, on the phase behavior. Finally, we present new routes for the realization of more complex structures, resulting from multiple deposition protocols and from engineering the interaction potential of the individual particles.
CRIS-Team Scopus Importer:2020-02-04

Polyurethane/silver-nanocomposites with enhanced silver ion release using multifunctional invertible polyesters - Peukert, Wolfgang; Damm, Cornelia; Triebel, Christian; Vasylyev, Serhiy; Stara, Hana; Özpinar, Celal; Münstedt, Helmut; Hausmann, Sebastian (Journal of Materials Chemistry, 2011)
Nano-silver composites with a thermoplastic polyurethane as the matrix were prepared by two different routes. Using the so-called in situ preparation, silver nanoparticles were obtained by a thermal reduction of silver acetate during melt mixing. In addition, a more sophisticated ex situ preparation method was developed. Here, the silver nanoparticles are synthesized in an invertible polyester resulting in much smaller particle sizes. The particles obtained are surrounded by the polyester cage, which stabilizes them with respect to agglomeration. Hence, an incorporation of those particles into a polymer melt with common techniques like extrusion leads to an even distribution. This is due to the fact that the invertible polyester and the polymer matrix are entirely miscible which was proven with DSC measurements. The silver ion release of the composites prepared was measured with anodic stripping voltammetry. At a constant weight percentage of silver in the polymer, the composite with the ex situ silver nanoparticles exhibits a silver ion release which is about two orders of magnitude higher than the release from the composite with the in situ silver nanoparticles. This observation is explained by the higher specific surface area of the smaller particles and a higher coefficient of diffusion for silver ions. A concentration of only 0.07 wt% silver nanoparticles, prepared with the ex situ method, exhibits a high enough release of silver ions to achieve antimicrobial properties. © 2011 The Royal Society of Chemistry.
Keywords: nanoparticle; polymer; thermal; reduction; ex-situ

Population balance equation for collisional breakage: A new numerical solution scheme and its convergence - Kushwah, Prakrati; Das, Arijit; Saha, Jitraj; Bück, Andreas (Communications in Nonlinear Science and Numerical Simulation, 2023)
A new numerical method for the solution of population balance equation modeling nonlinear collisional breakage is presented. The new scheme is obtained by modifying the birth term of discretized equation. Allocation of new born particles to their neighboring cells plays a vital role towards the efficiency of proposed model. A detailed investigation on mathematical properties of the scheme, e.g., consistency and stability, is presented for different mesh types. It shown that the new scheme is moment-consistent and has first order convergence rate. A new finite volume scheme for collisional breakage is also presented to validate the efficiency of new scheme over several physics embedded test problems.
CRIS-Team Scopus Importer:2023-04-07
Keywords: Collisional breakage; Consistency; Error analysis; Lipschitz stability; Sectional methods

Population balance modeling of formation and breakage of nanoparticle agglomerates in a spouted bed - Bhoi, Stutee; Kolan, Subash Reddy; Bück, Andreas; Tsotsas, Evangelos (Powder Technology, 2024)
A population balance framework for fluidization of Al2O3 nano-agglomerates in a ProCell-type spouted bed considering agglomeration and breakage phenomena is developed. An equipartition of kinetic energy (EKE kernel) is used to model the agglomeration phenomena. For breakage, two different fragment distribution functions are considered, the Dirac delta function and a function with confined uniform binary breakage. The fractal dimension property is incorporated in both the agglomeration and breakage models. The model parameters are extracted from batch fluidization experiments conducted by varying the air pressure of the top nozzle. The developed model shows a good agreement with experimental observation in regard of the temporal change in the area and volume-weighted average size of nano-agglomerates and of their final size distribution. The developed population balance model is simulated to study the influence of model parameters on the evolution of average size and coefficient of variation of the nano-agglomerates.
CRIS-Team Scopus Importer:2024-01-12
Keywords: Agglomeration; Breakage; Nano-agglomerates; Population balance model

Population balance modeling of InP quantum dots: Experimentally enabled global optimization to identify unknown material parameters - Wang, Zhuang; Traore, Nabi; Schikarski, Tobias; Stiegler, Lisa; Drobek, Dominik; Apeleo Zubiri, Benjamin; Spiecker, Erdmann; Walter, Johannes; Peukert, Wolfgang; Pflug, Lukas; Segets, Doris (Chemical Engineering Science, 2023)
Despite great progress in the synthetic chemistry of InP QDs, a predictive model to describe their temporal formation is still missing. In this work, we introduce a population balance model incorporating liquid phase reactions, homogeneous nucleation and reaction-limited growth of InP supported with the highly reproducible and reliable experimental data acquired from an automated robotic synthesis platform. A comparison between experimental kinetic data (different initial concentrations and temperatures) and simulations was made. The proposed model describes the temporal evolution of solid concentration, particle diameter and particle size distribution very well. The quantitative agreement between experiments and simulations was only achieved by global optimization to identify unknown and hardly measurable material parameters and kinetic constants such as surface energy, growth rate constants or activation energies. We see this model rendering the first step towards the development of more refined models that enable rigorous optimization and control of the production process for III-V semiconductors.
CRIS-Team Scopus Importer:2023-08-11
Keywords: Automated synthesis; InP; Population balance equation; Simulation

Positron emission particle tracking in fluidized beds with secondary gas injection - Hensler, Timo; Tupy, Martin; Strer, Timo; Pöschel, Thorsten; Wirth, Karl-Ernst (Powder Technology, 2015)
We apply positron emission particle tracking (PEPT) to a gas-solid fluidized bed with injection of a secondary gas through a centrally arranged nozzle and present a method to compute stationary fluid-dynamic characteristics of the system from the trajectories of a test particle. In order to evaluate this non-invasive method we compare the field of density obtained by PEPT with the density obtained by a traditional, well-established and approved, yet invasive, measurement technique to find good agreement. Besides the penetration depth of the jet region and the opening angle of the jet which are inferred from the density field, we use PEPT to measure quantities whose measurement using traditional methods is rather sophisticated, including the residence time of particles in the jet region and the suspended phase, the coefficients of axial and radial dispersion and the material flux across the jet boundaries. We conclude that PEPT is a reliable and at the same time versatile technique to measure stationary fluid-dynamic properties of dynamical particle systems at spatial resolution only limited by the duration of the measurement.
Keywords: Dispersion coefficient; Fluidized bed; Measurement technology; Positron emission particle tracking; Residence time; Secondary gas injection

Prallzerkleinerung in Fließbettgegenstrahlmühlen: Vom Einzelkorn zur Mühle - Romeis, Stefan; Köninger, Benedikt; Strobel, Alexander; Wirth, Karl-Ernst; Peukert, Wolfgang (Chemie Ingenieur Technik, 2016)
Keywords: zerkleinerung; prallmühle; partikel

Precipitation of In(OH)3 and InOOH nanocrystals for the use in nanoelectronics: Phase transition behavior and oriented aggregation - Klaumünzer, Martin; Mackovic, Mirza; Ferstl, Pascal; Voigt, Michael; Spiecker, Erdmann; Meyer, Bernd; Peukert, Wolfgang (Nanotechnology 2013: Advanced Materials, CNTs, Particles, Films and Composites - 2013 NSTI Nanotechnology Conference and Expo, NSTI-Nanotech 2013, 2013)
With respect to diverse applications in the wide field of nanoelectronics we characterize a specific phase transition behaviour and oriented aggregation (OA) during wet chemical synthesis of In(OH) nanocrystals as a wide band gap- and precursor material for InO. Contiguous to the cubic In(OH) phase, also orthorhombic InOOH is formed in a precipitation route with indium acetate as the In3+ source. Nano- and microcuboids are observed that consist exclusively of In(OH). The InOOH phase stays semi-crystalline even for long reaction times. On the basis of DFT calculations we find that for small crystallites the InOOH phase is more stable than the In(OH) phase, leading to a size-dependent transition from the InOOH phase to In(OH) above a critical crystallite size.
Keywords: Indium oxohydroxide; Nanocrystals; Oriented aggregation indium hydroxide; Precipitation

Precipitation of nanoparticles: A coupled LIF / PIV, DNS and PBE approach for prediction of the particle size distribution (PSD) - Peukert, Wolfgang; Gradl, Johannes; Schwertfirm, Florian; Schwarzer, Hans-Christoph; Manhart, Michael (2005)
Continuous precipitation is a promising process to generate nanoparticles with tailored properties. One challenge is to predict the PSD by considering all fluid dynamical, physiochemical and thermodynamical process parameters. A CFD-based approach using DNS in combination with Lagrangian Particle Tracking is applied coupled with micromixing and population balance models. The simulated flow field is validated by optical measurement methods (PIV and LIF). Whereas the mean particle size in dependence of the Re-number (over 6 orders of magnitude) can be predicted by a 1D approach, prediction of the complete PSD needs information from the fully resolved 3D fluid flow field.
Keywords: precipitation; continuous; mixing; prediction; simulation

Precipitation of nanoparticles in a T-mixer: Coupling the particle population dynamics with hydrodynamics through direct numerical simulation - Peukert, Wolfgang; Gradl, Johannes; Schwarzer, Hans-Christoph; Schwertfirm, Florian; Manhart, Michael (Chemical Engineering and Processing, 2006)
Mixing is a key parameter to tailor the particle size distribution (PSD) in nanoparticle precipitation. In this study we present two model approaches to simulate the impact of mixing on the PSD, using barium sulfate as exemplary material. In the first model, we combine a Lagrangian micromixing model with the population balance equation. This approach was found successful in predicting the influence of mixing on mean particle sizes but fails to predict the shape and width of the PSD. This is attributed to the neglect of spatial and temporal fluctuations in that model. Therefore, an improved CFD-based approach using direct numerical simulation (DNS) in combination with Lagrangian particle tracking strategy is applied. We found that the full DNS-approach, coupled to the population balance and a derived micromixing model, is capable of predicting the full PSD in nanoparticle precipitation. © 2006 Elsevier B.V. All rights reserved.
Keywords: Direct numeric simulation; Micromixing; Nanoparticle precipitation; Population balance; Supersaturation

Precision fermentation as a route to modify β-lactoglobulin structure through substitution of specific cysteine residues - Brune, Sarah E.; Hoppenreijs, Loes J.G.; Kuehl, Toni; Lautenbach, Vanessa; Walter, Johannes; Peukert, Wolfgang; Schwarz, Karin; Imhof, Diana; Boom, Remko M.; Krull, Rainer; Keppler, Julia K.; Biedendieck, Rebekka (International Dairy Journal, 2023)
Precision fermentation is a promising route to develop recombinant proteins with improved functionality. Protein functionality is highly influenced by protein structure, which can be significantly affected by conformational restraints induced by cysteines. Here, we study the impact of individual cysteines on β-lactoglobulin structure, by stepwise substituting them with alanine. Structural characterisation was performed from secondary to quaternary level. The findings demonstrated that the free Cys121 played no role in the folding and dimerisation of BLG. The β-barrel usually includes one disulphide bond (Cys106–Cys119), which was found to be crucial for its formation. The usually exposed disulphide bond (Cys66–Cys160) played no major role in folding of the β-barrel, but mainly modulated its accessibility and mediated dimerisation. Thereby, cysteine mutations can be used as a tool to modify protein structures. These different structures can now be used to further understand the impact on protein behaviour and their functionalit
Keywords: Amino acids; Recombinant proteins; Sulfur compounds; Cysteine residues; Different structure; Dimerizations; Disulphide bonds; Foldings; Lactoglobulin; Protein functionalities; Proteins structures; Structural characterization; Fermentation

Predicition of Pressure Drop with Pneumatic Conveying of Solids in Horizontal Pipelines - Wirth, Karl-Ernst; Molerus, Otto (Powder Technology, 1983)
Current relationships for determination of the pressure drop with pneumatic conveying of solids in pipes are not of general validity. The theoretical considerations underlying these relationships do not take into account the influence of the rotatory motion of the particles. On the other hand, extremely high rotatory speeds of the particles due to wall collision are observed. Therefore a new concept is presented which takes into account the rotatory motion of the particles. A further aim was to represent the data in the form of nondimensional groups which allow meaningful, physical interpretation of the results obtained. A state diagram for the prediction of pressure drop with pneumatic conveying in the form of sliding particles strands is described. Calculation of power loss per particle and of the force and the moment acting on a particle leads to a nondimensional representation of pressure drop in which a normalized pressure drop is combined with a particle Froude number and a Froude number which contains the particle fall velocity and the pipe diameter. This combination of nondimensional groups defines fully suspended flow. The normalized pressure drop is defined in such a way that it represents the nondimensional slip of the particles, too. Comparison with pressure drop measurements for pneumatic transport in horizontal pipes which included changes in particle size, particles density and pipe diameter confirms the physical significance of the parameters used with regard to the prediction of pressure drop and of particles slip velocity. A simple procedure for the prediction of pressure drop in the full range of steady-state pneumatic conveying is proposed.
UnivIS-Import:2015-03-05:Pub.1983.tech.ITC.mechve.predic_70

Prediction of adsorption equilibria from physical properties of the pure components - Peukert, Wolfgang; Jung, Holger (Reprints of the 20th European Symposium on Applied Thermodynamics (ESAT 2003), 2003)
The prediction of adsorption energies equilibria is often based on mixed terms influenced by both the adsorptive and the adsorbent. Our aim is to predict adsorption equilibria by using physical properties of the pure components. Based on the concept of equivalent surface properties we introduce models using one or two mean parameters (Hamaker constant, mean partial charge) as well as a model which takes partial charge distributions into account. Density functional theory (DFT) calculations can be used to describe well defined and regular surfaces. However, the structure and topology of heterogeneous surfaces are generally unknown. Thus the combination of DFT-calculations with a continuum solvation model and experimental data allows the prediction of the adsorption equilibrium at infinite dilution. For activated carbon in the gas phase and in water the Henry’s law coefficients obtained by this method cover a range of 7 orders of magnitude. In order to gain a better understanding of the role of heterogeneities, DFT-calculations of model surfaces like functionalized coronenes or fullerenes were performed. A good qualitative agreement with the experimentally determined results was observed.
UnivIS-Import:2015-04-16:Pub.2003.tech.ITC.mechve.predic
Keywords: adsorption; equilibrium; property

Prediction of adsorption equilibria from physical properties of the pure components - Schürer, Gudrun; Peukert, Wolfgang (Adsorption-Journal of the International Adsorption Society, 2005)
The prediction of adsorption energies equilibria is often based on mixed terms influenced by both the adsorptive and the adsorbent. Our aim is to predict adsorption equilibria by using physical properties of the pure components. Based on the concept of equivalent surface properties we introduce models using one or two mean parameters (Hamaker constant, mean partial charge) as well as a model which takes partial charge distributions into account. Density functional theory (DFT) calculations can be used to describe well defined and regular surfaces. However, the structure and topology of heterogeneous surfaces are generally unknown. Thus the combination of DFT-calculations with a continuum solvation model and experimental data allows the prediction of the adsorption equilibrium at infinite dilution. For activated carbon in the gas phase and in water the Henry’s law coefficients obtained by this method cover a range of 7 orders of magnitude. In order to gain a better understanding of the role of heterogeneities, DFT-calculations of model surfaces like functionalized coronenes or fullerenes were performed. A good qualitative agreement with the experimentally determined results was observe
Keywords: Activated carbon; COSMO-RS; Adsorption equilibria prediction; Henry's law coefficient

Prediction of aggregation kinetics based on surface properties of nanoparticles - Peukert, Wolfgang; Schwarzer, Hans-Christoph (Chemical Engineering Science, 2005)
Aggregation of nanoscaled particles is a challenge to be met when controlling or tailoring particle size distributions (PSDs) in many areas including precipitation, dip-coating and milling. Control of aggregation can be achieved for sparingly soluble salts through stabilization by electrostatic repulsive particle-particle interaction. The presented work shows a combined experimental/numerical approach to quantitatively determine the stability using barium sulfate as the model substance. The experimental data is obtained by measuring the temporal evolution of the PSD. A detailed aggregation model is presented based on the population balance equation including the influence of particle-particle interactions via the so-called stability ratio W. Values for this ratio are determined by a parameter estimation strategy from the experimental data and then successfully correlated via the surface charge density to the adsorption of potential-determining ions (H+- and Ba2+-ions in the investigated system). The model is validated and its ability to capture the influence of ionic strength and particle size is tested successfully. Many insights are gained and favorable feed concentrations for the production of nanoparticles through precipitation identified. Thus the presented multi-scale approach relating the aggregation behavior to surface properties is not only well-suited for finding optimal stability but also to determine surface properties of nanoparticles. © 2004 Elsevier Ltd. All rights reserved.
UnivIS-Import:2015-03-09:Pub.2005.tech.ITC.mechve.predic
Keywords: Aggregation; Barium sulfate; Ion adsorption; Nanoparticle precipitation; Stabilization; Surface charge density

Prediction of Heat Transfer in Circulating Fluidized Beds - Wirth, Karl-Ernst (Preprints 4th Internat. Conference on Circulating Fluidized Beds, 1993)
UnivIS-Import:2015-04-16:Pub.1993.tech.ITC.mechve.predic_36

Prediction of particle size and layer-thickness distributions in a continuous horizontal fluidized-bed coating process - Bachmann, P.; Chen, K.; Bück, Andreas; Tsotsas, E. (Particuology, 2020)
To predict the particle size and layer-thickness distributions (LTDs) in a continuously operated horizontal fluidized-bed granulation process, two alternative models were considered. A one-dimensional two-zone model was proposed, which describes with population-balance equations the particle growth in a spraying zone that is separated from the drying zone. The residence-time distribution (RTD) was calculated from a literature correlation and was coupled with a population-balance model via a tank-in-series model with reflux. A two-dimensional, one-zone population-balance model, which was based directly on the RTD and the feed particle-size distribution (PSD) was also used. Granulation experiments were conducted and analyzed microscopically and with a camera optical device to determine the sample PSDs. LTDs over the particle population were derived from the PSDs and were analyzed directly by micro-computer-tomography. To compare the simulated data with the experimentally determined distributions, the PSDs were converted to LTDs. The good agreement shows that both methods are suitable to determine the PSD from an RTD of an arbitrary granulation process in a horizontal fluidized bed. Improvement appears necessary with regards to the LTD spread.
CRIS-Team Scopus Importer:2020-04-14
Keywords: Coating; Continuous process; Fluidized bed; Layer-thickness distribution; Particle-size distribution; Residence-time distribution

Prediction of Pressure Drop in Horizontal Segregated Pneumatic Conveying with Particle Strands Sliding along Bottom of the Pipe - Wirth, Karl-Ernst; Molerus, Otto (German Chemical Engineering, 1981)
Pneumatic conveying in the form of strands of particles sliding along the bottom of the pipe is favorable in respect of protecting the material and shows a low energy consumption. This state of pneumatic conveying occurs near the non-steady states of plug flow and conveying in the form of dunes. Therefore, the knowledge of pressure drop is important for a reliable operation. Force and mass balances result in a relationship between dimensionless groups for calculating the pressure drop in strand-type pneumatic conveying. A steady state diagram for pneumatic conveying was developed on the basis of stability considerations.
UnivIS-Import:2015-03-05:Pub.1981.tech.ITC.mechve.predic_17
Keywords: pneumatic; conveying; powder

Prediction of pressure drop in the steady-state section of a downer reactor - Wirth, Karl-Ernst; Lehner, Peter (Fluidization X : proceedings of the Tenth Engineering Foundation Conference on Fluidization, Beijing, People Republic of China, May 20 - 25, 2001, 2001)
UnivIS-Import:2015-04-16:Pub.2001.tech.ITC.mechve.predic
Keywords: fluidization; bed

Prediction of Pressure Drop with Pneumatic Conveying of Solids in Horizontal Pipes - Wirth, Karl-Ernst; Molerus, Otto (Preprints "Pneumatech I", 1982)
Current relationships for determination of the pressure drop with pneumatic conveying of solids in pipes are not of general validity. The theoretical considerations underlying these relationships do not take into account the influence of the rotatory motion of the particles. On the other hand, extremely high rotatory speeds of the particles due to wall collision are observed. Therefore a new concept is presented which takes into account the rotatory motion of the particles. A further aim was to represent the data in the form of nondimensional groups which allow meaningful, physical interpretation of the results obtained. A state diagram for the prediction of pressure drop with pneumatic conveying in the form of sliding particles strands is described. Calculation of power loss per particle and of the force and the moment acting on a particle leads to a nondimensional representation of pressure drop in which a normalized pressure drop is combined with a particle Froude number and a Froude number which contains the particle fall velocity and the pipe diameter. This combination of nondimensional groups defines fully suspended flow. The normalized pressure drop is defined in such a way that it represents the nondimensional slip of the particles, too. Comparison with pressure drop measurements for pneumatic transport in horizontal pipes which included changes in particle size, particles density and pipe diameter confirms the physical significance of the parameters used with regard to the prediction of pressure drop and of particles slip velocity. A simple procedure for the prediction of pressure drop in the full range of steady-state pneumatic conveying is proposed.
UnivIS-Import:2015-04-16:Pub.1982.tech.ITC.mechve.predic_71
Keywords: pressure; pneumatic; conveying

Prediction of thermodynamic properties from pure compound information: Characterization of fullerenes - Peukert, Wolfgang; Schürer, Gudrun (Applied Surface Science, 2005)
Fullerenes are widely studied not only in material, but also in life science due to their special properties. Their surface properties determine their interaction with the environment and influence adsorption as well as biodistribution. In this work, the surfaces of a series of fullerenes and polyhydroxylated C-fullerenes were investigated using density functional theory (DFT)/conductor-like screening model (COSMO)-calculations. The dependence of the screening charge density from the curvature of a carbon hexagon and its effect on the adsorption behavior was studied. The estimation of thermodynamic properties of multiply functionalized C-molecules gives promising qualitative results using only properties of the pure compounds. © 2005 Elsevier B.V. All rights reserved.
Keywords: Adsorption; DFT; Fullerenes; Functionalization

Predictive simulation of nanoparticle precipitation based on the population balance equation - Peukert, Wolfgang; Schwarzer, Hans-Christoph; Schwertfirm, Florian; Manhart, Michael; Schmid, Hans-Joachim (Chemical Engineering Science, 2006)
Nanoparticle precipitation is an interesting process to generate particles with tailored properties. In this study we investigate the impact of various process steps such as solid formation, mixing and agglomeration on the resulting particle size distribution (PSD) as representative property using barium sulfate as exemplary material. Besides the experimental investigation, process simulations were carried out by solving the full 1D population balance equation coupled to a model describing the micromixing kinetics based on a finite-element Galerkin h-p-method. This combination of population balance and micromixing model was applied successfully to predict the influence of mixing on mean sizes (good quantitative agreement between experimental data and simulation results are obtained) and gain insights into nanoparticle precipitation: The interfacial energy was identified to be a critical parameter in predicting the particle size, poor mixing results in larger particles and the impact of agglomeration was found to increase with supersaturation due to larger particle numbers. Shear-induced agglomeration was found to be controllable through the residence time in turbulent regions and the intensity of turbulence, necessary for intense mixing but undesired due to agglomeration. By this approach, however, the distribution width is underestimated which is attributed to the large spectrum of mixing histories of fluid elements on their way through the mixer. Therefore, an improved computational fluid dynamics-based approach using direct numerical simulation with a Lagrangian particle tracking strategy is applied in combination with the coupled population balance-micromixing approach. We found that the full DNS-approach, coupled to the population balance and micromixing model is capable of predicting not only the mean sizes but the full PSD in nanoparticle precipitation. © 2005 Elsevier Ltd. All rights reserved.
Keywords: Computational fluid dynamics; Direct numerical simulation; Micromixing; Nanoparticle; Population balance; Precipitation

Predictive simulation of nanoparticles-precipitation in a T-mixer by coupling direct numerical simulation with population balance equations - Peukert, Wolfgang; Gradl, Johannes; et al. (2006 AIChE Spring National Meeting - 5th World Congress on Particle Technology, 2006)
Mixing and consequently fluid dynamics are key parameters to tailor the particle size distribution (PSD) in nanoparticle precipitation. The influence of the operating conditions on the flow and concentration field of the applied mixer is investigated experimentally by PIV and LIF. In this study we present two model approaches to simulate the impact of mixing on the PSD, using barium sulfate as exemplary material, In the first model, a Lagrangian micromixing model is combined with the population balance equation. This approach was found successful in predicting the influence of mixing on mean particle sizes but fails to predict the shape and width of the PSD. This is attributed to the neglect of spatial and temporal fluctuations in that model. Therefore, an improved CFD-based approach using Direct Numerical Simulation (DNS) in combination with Lagrangian Particle Tracking strategy is applied. We found that the DNS-approach including macro and micro mixing, coupled to the population balance is capable of predicting the full PSD in nanoparticle precipitation. Additionally to the resulting PSD this approach delivers 3D-information on all running subprocesses in the mixer, i.e. supersaturation built-up or nucleation, which are visualized for different process variables.
Keywords: Direct numerical simulation; Lagrangian particle tracking; LIF; Mixing; PIV; Population balance equations; Precipitation; Supersaturation

Preparation and Surface Functionalization of a Tunable Porous System Featuring Stacked Spheres in Cylindrical Pores - Ruiz Madronero, Christhy; Terlinden, Markus; Engelhardt, Matthias; Magnabosco, Giulia; Papastavrou, Georg; Vogel, Nicolas; Thommes, Matthias; Bachmann, Julien (Advanced Materials Interfaces, 2023)
A geometrically tunable nanoporous system featuring enhanced active surface area by stacking of spheres in cylindrical pores is fabricated. Highly ordered arrays of straight, constricted pores are obtained by anodization of metallic aluminum. Polystyrene (PS) spheres are assembled inside the pores by flowing their suspension through the porous membrane, whereas the construction serves as a filter. After surface functionalization with a noble metal catalyst, these model electrocatalysis systems exhibit functional properties (capacitance in electrochemical impedance spectroscopy) that mirror their geometric parameters. A systematic investigation of the system's geometry as it depends on the surface chemistry of the pores, on the one hand, and the physical parameters of the infiltration procedure, on the other hand, shows that mechanical stacking prevails over surface chemical interactions to determine the stacking density. The highest values of surface area are obtained when PS spheres are put in contact with HfO2 followed by ZnO according to adsorption measurements. Surface derivatization with organic layers does not improve stacking any further. However, choosing the proper concentration of PS spheres and flow rate are crucial for obtaining densely packed sphere assemblies without clogging of the pore entrance.
CRIS-Team Scopus Importer:2023-08-25
Keywords: anodic aluminum oxide; assembly; impedance spectroscopy; nanostructured electrodes; surface area

Preparation, formulation and deposition of mica flake supported cobalt oxide for nanostructured lithium ion battery anodes - Helmer, Alexandra; Rink, Anna; Esper, Julian Duane; Wu, Yanlin; Bachmann, Julien; Klupp Taylor, Robin (Advanced Powder Technology, 2019)
Abstract We describe the fabrication and morphological and electrochemical characterisation of lithium ion battery anodes whereby the active material is supported on flake-like microparticles. Using various physical analytical techniques we verify that nanostructured cobalt (II, III) oxide can be directly grown onto commercial titanium dioxide-coated mica flakes by a liquid phase oxidation route. We then investigate the formulation and deposition of this material along with carbon black in order to form electrodes. Here we consider two binder/solvent systems, one widely used based on polyvinylidene fluoride in N-methy-2-pyrrolidone, and one more recently identified based on sodium alginate in water. We show that the latter system is preferable for the formation of anodes using the cobalt oxide coated flake-like particles as it leads to a more homogeneous distribution of active and conductive material in the electrode. Using cyclic voltammetry and electrochemical impedance spectroscopy we show that this feature improves the access to active material and facilitates efficient charge transfer in the electrode while maintaining electrode integrity. Moreover, an electrode based on the alginate binder exhibited a high reversible specific capacity of 650 mAh/g along with 84.8% capacity retention after 70 cycles. Overall our study indicates the promise of including shape anisotropic particles such as microflakes in battery electrodes.<br
Keywords: Particle coating; Formulation; Deposition; Battery electrode; Electrochemistry

Pressure induced local phase transformation in nanocrystalline tetragonal zirconia microparticles - Schwenger, Jan; Romeis, Stefan; Herre, Patrick; Yokosawa, Tadahiro; Finsel, Maik; Leib, Elisabeth W.; Weller, Horst; Vossmeyer, Tobias; Spiecker, Erdmann; Peukert, Wolfgang (Scripta Materialia, 2019)
Keywords: Focused ion beam (FIB); Martensitic phase transformation; Compression testing; Electron diffraction; Zirconia microparticles

Preventing mussel adhesion using lubricant-infused materials - Amini, Shahrouz; Kolle, Stefan; Petrone, Luigi; Ahanotu, Onyemaechi; Sunny, Steffi; Sutanto, Clarinda N.; Hoon, Shawn; Cohen, Lucas; Weaver, James C.; Aizenberg, Joanna; Vogel, Nicolas; Miserez, Ali (Science, 2017)
Mussels are opportunistic macrofouling organisms that can attach to most immersed solid surfaces, leading to serious economic and ecological consequences for the maritime and aquaculture industries. We demonstrate that lubricant-infused coatings exhibit very low preferential mussel attachment and ultralow adhesive strengths under both controlled laboratory conditions and in marine field studies. Detailed investigations across multiple length scales-from the molecular-scale characterization of deposited adhesive proteins to nanoscale contact mechanics to macroscale live observations-suggest that lubricant infusion considerably reduces fouling by deceiving the mechanosensing ability of mussels, deterring secretion of adhesive threads, and decreasing the molecular work of adhesion. Our study demonstrates that lubricant infusion represents an effective strategy to mitigate marine biofouling and provides insights into the physical mechanisms underlying adhesion prevention.

Probing colloidal interfaces by angle-resolved second harmonic light scattering - Schürer, Benedikt; Wunderlich, Sarina; Sauerbeck, Christian; Peschel, Ulf; Peukert, Wolfgang (Physical Review B, 2010)
We report angle-resolved second harmonic light scattering from bare colloidal particles in water. A nonlinear Mie model is used to quantitatively analyze the nonresonant second harmonic (SH) scattering profiles and to determine the elements of the local second-order surface susceptibility. The SH signal is attributed to oriented and electrically polarized water molecules at the charged particle interface. The results show how angle-resolved SH light scattering can be applied to probe not only resonant excited dye molecules but also nonresonant molecules such as water at the interface of colloidal particles.

Probing guided modes in a monolayer colloidal crystal on a flat metal film - Romanov, Sergei G.; Vogel, Nicolas; Bley, Karina; Landfester, Katharina; Weiss, Clemens K.; Orlov, Sergej; Korovin, Alexander V.; Chuiko, Gennady P.; Regensburger, Alois; Romanova, Alexandra; Kriesch, Arian; Peschel, Ulf (Physical Review B, 2012)
Two-dimensional slab hybrid metal-dielectric photonic crystals, which are prepared by assembling polymer colloidal spheres into closely packed monolayers of hexagonal symmetry on a gold-coated glass substrate, show an improved confinement of light compared with a colloidal monolayer on a glass substrate. We demonstrated that the optical response of such hybrid crystals consists of diffractively coupled waveguiding modes, Fabry–Perot resonances, and Mie resonances. Correspondingly, two major mechanisms, namely, band transport and hopping of localized excitations, participate in the in-plane light transport in such hybrid crystals.

Probing particle heteroaggregation using analytical centrifugation - Rey, Marcel; Uttinger, Maximilian; Peukert, Wolfgang; Walter, Johannes; Vogel, Nicolas (Soft Matter, 2020)
The controlled aggregation of colloidal particles is not only a widespread natural phenomenon but also serves as a tool to design complex building blocks with tailored shape and functionalities. However, the quantitative characterization of such heteroaggregation processes remains challenging. Here, we demonstrate the use of analytical centrifugation to characterize the heteroaggregation of silica particles and soft microgels bearing similar surface charges. We investigate the attachment as well as the stability of the formed heteroaggregates as a function of particle to microgel surface ratio, microgel size and the influence of temperature. The attachment of microgels onto the colloidal particles induces a change in the sedimentation coefficient, which is used to quantitatively identify the number of attached microgels. We corroborate the shift in sedimentation coefficient by computer simulations of the frictional properties of heteroaggregates via a modified Brownian dynamic algorithm. The comparison between theoretical investigations and experiments suggest that the microgels deform and flatten upon attachment. <

Probing sedimentation non-ideality of particulate systems using analytical centrifugation - Uttinger, Maximilian; Jung, Wieland David Krischan; Dao, Thi Quynh Nhi; Canziani, Herbert; Lübbert, Christian; Vogel, Nicolas; Peukert, Wolfgang; Harting, Jens; Walter, Johannes (Soft Matter, 2021)
Analytical centrifugation is a versatile technique for the quantitative characterization of colloidal systems including colloidal stability. The recent developments in data acquisition and evaluation allow the accurate determination of particle size, shape anisotropy and particle density. High precision analytical centrifugation is in particular suited for the study of particle interactions and concentration-dependent sedimentation coefficients. We present a holistic approach for the quantitative determination of sedimentation non-ideality via analytical centrifugation for polydisperse, plain and amino-functionalized silica particles spanning over one order of magnitude in particle size between 100 nm and 1200 nm. These systems typically behave as neutral hard spheres as predicted by auxiliary lattice Boltzmann simulations. The extent of electrostatic interactions and their impact on sedimentation non-ideality can be quantified by the repulsion range, which is the ratio of the Debye length and the average interparticle distance. Experimental access to the repulsion range is provided through conductivity measurements. With the experimental repulsion range at hand, we estimate the effect of polydispersity on concentration-dependent sedimentation properties through a combination of lattice Boltzmann and Brownian dynamics simulations. Finally, we determine the concentration-dependent sedimentation properties of charge-stabilized, fluorescently-labeled silica particles with a nominal particle size of 30 nm and reduced interparticle distance, hence an elevated repulsion range. Overall, our results demonstrate how the influence of hard-sphere type and electrostatic interactions can be quantified when probing sedimentation non-ideality of particulate systems using analytical centrifugation even for systems exhibiting moderate sample heterogeneity and complex interactions.<br

Process control strategies for the gas phase synthesis of silicon nanoparticles - Gröschel, Michael; Koermer, Richard; Walther, Maximilian; Leugering, Günter; Peukert, Wolfgang (Chemical Engineering Science, 2012)
In this contribution the identification of new reaction conditions for the production of nearly monodisperse silicon nanoparticles via the pyrolysis of monosilane in a hot wall reactor is considered. For this purpose a full finite volume model has been combined with a state-of-the-art trust-region optimisation algorithm for process control. Verified against experimental data, specific process conditions are determined accomplishing a versatile range of prescribed product properties. The main achievement of the optimisation is the possibility to control the different mechanisms in the particle formation process by mainly adjusting the temperature profile. Due to a successful separation of the nucleation and growth process, significantly narrower particle size distributions are obtained. Moreover, the presented optimisation framework establishes rate constants based on measured data.

Process engineering of nanoparticles below 20 nm—a fundamental discussion of characterization, particle formation, stability and post processing - Peukert, Wolfgang; Segets, Doris (Springer International Publishing, 2015)
In the following chapter fundamental aspects that have to be considered during the processing of small nanoparticles will be addressed. We investigated quantum confined manganese doped ZnS, ZnO, PbS and PbSe semiconductor nanoparticles, so-called quantum dots (QDs) and silver noble metal nanorods. All materials were chosen due to their technical relevance for future applications in the emerging fields of solar cells, sensors and diagnostics as well as due to the possibility of their in situ characterization by UV/Vis absorbance spectroscopy. After a brief introduction to the specific prospects and challenges of these materials we will focus on the important processing issues that need to be solved for producing these particles at high quality on a larger scale: (i) the modelling of particle formation including nucleation, growth and ripening based on a mechanistic understanding and on experimentally derived data on solubility and surface energies, (ii) the stabilization of nanoparticles not only against agglomeration but also against shape changes and (iii) classification. The latter is realized by size selective precipitation which allows surprisingly sharp separations (κ= 0.75) of particles with only a few nm in diameter. Although the extremely small particle sizes (feed PSD between 1.5 and 3 nm), classification results were successfully analyzed by well-known concepts from particle technology. Our results are seen to be an essential contribution to colloidal processing. They enable a future optimization of process parameters by a knowledge-based design strategy that can be applied within continuous as well as automatized batch reactor concepts.
Keywords: Classification; Colloidal stability; Nanoparticle handling; Optical properties; Oriented attachment; Ostwald ripening; Particle formation mechanism; Quantum dots; Shape transformation

Process modeling of in situ-adsorption of a bacterial lipase - Peukert, Wolfgang; Militzer, Michael; Wenzig, Edda (Biotechnology and Bioengineering, 2005)
In situ adsorption, known as an in situ-product removal (ISPR) technique for low molecular mass bioproducts, was in this study applied to a bacterial exoenzyme proving that this method is also suitable for the separation of macromolecules like proteins. For this, adsorbent particles were added to growing cultures of Staphylococcus carnosus rec., therefore both production and adsorption occurred simultaneously in shaking flasks, stirred tank, or airlift bioreactor as the chosen types of fermenters. The exoenzyme lipase adsorbed rapidly and, after separating cells and adsorbents, desorbed in a packed bed column. Up to 85% of the produced lipase were recovered, fractions of these had been concentrated up to the factor 20 and purified up to a factor of 40 by the procedure. By using the airlift bioreactor an enhancement of biomass production was observed, but the necessity of the addition of an anti-foam reagent resulted in higher product losses in adsorption as well as in desorption. Production and adsorption kinetics have been modeled and applied to in situ-adsorption. The model was used to perform a parameter study in which the influence of biological and physical parameters as well as process parameters on discontinuous and continuous in situ-adsorption was investigate
Keywords: adsorption; bacterial; enzyme; kinetic; product

Process Routes towards Novel Polybutylene Terephthalate – Polycarbonate Blend Powders for Selective Laser Sintering - Schmidt, Jochen; Dechet, Maximilian; Gomez Bonilla, Juan Sebastian; Bück, Andreas; Peukert, Wolfgang (Proceedings of the 30th Annual International Solid Freeform Fabrication Symposium 2019, 2019)

Product engineering of nanoscaled materials - Peukert, Wolfgang; Voronov, Andriy (Particulate Systems in Nano- and Biotechnologies, 2008)

Production and analysis of electrically conductive polymer – Carbon-black composites for powder based Additive Manufacturing - Düsenberg, Björn; Tischer, Florentin; Seidel, Anne Marie; Kopp, Sebastian-Paul; Schmidt, Jochen; Roth, Stephan; Peukert, Wolfgang; Bück, Andreas (Procedia CIRP, 2022)
In laser powder bed fusion, micro-particles are selectively fused by a laser to produce parts, layer-by-layer. While this process offers a high freedom of design, the variety of commercially available materials, especially composites are limited. Conductive polymers blends, are very interesting for many applications, especially as sensors with freely definable shape. First, the amount of carbon-black needed to make the composite electrically conductive has to be determined; this limit is called percolation threshold (PT). The PT depends on many properties, such as particle size and shape of both polymer and carbon-black and will be determined experimentally. In this work, polypropylene is dry mixed with different types of micron sized carbon blacks. The PT and the conductivity is determined by means of impedance spectroscopy. Finally, layers are printed to evaluate the processability of the new composite.<br
Keywords: polypropylene; carbon black; percolation threshold

Production of Al/Cu-Particles and their potential for processing by Laser Beam Melting (LBM) - Sachs, Marius; Hentschel, Oliver; Schmidt, Jochen; Karg, Michael; Schmidt, Michael; Wirth, Karl-Ernst (Physics Procedia, 2014)
To investigate the potential of Laser Beam Melting (LBM) in powder bed process for wrought aluminium-copper alloys, tailor-made particles with a varying amount of copper on the particle surface are produced by decomposition of copper acetate (CuOAc). Decomposition of CuOAc and coating of the Al-particles are performed in a fluidized bed reactor (FBR) with nitrogen as carrier gas. Since heat and mass transfer in an FBR are regarded as ideal, no concentration gradients are observable which is preferable for gas-phase deposition processes. The amount of deposited Cu on the Al-particles has been investigated using different methods.Hereby also the growth mechanism has been investigated. The influence of the copper deposition on absorptivity is determined using integration spheres.
Keywords: Laser Beam Melting; additive manufacturing; aluminium alloy; powder modification; fluidized bed reactor; integrating sphere

Production of dispersions with small particle size from commercial indium tin oxide powder for the deposition of highly conductive and transparent films - Mahajeri, Mahdi; Schneider, Andreas; Baum, Marcus; Rechtenwald, T.; Voigt, Michael; Schmidt, Michael; Peukert, Wolfgang (Thin Solid Films, 2012)
Indium tin oxide (ITO) nanoparticle films for applications in printable electronics were prepared by dip-coating. The dispersion conditions (bead size, stabilizer concentration) strongly affect the particle size of the ITO suspensions and consequently determine the surface morphology of the ITO films. Deposition from ethanolic ITO suspensions with an extremely small particle size of 17 nm to 21 nm led to the formation of extremely smooth and spike-free ITO films with a typical root mean square surface roughness of 4.5 nm +/- 0.2 nm and a high optical transparency above 95%. The effect of annealing with forming gas and CO2 laser treatment on the electrical properties of the ITO films was investigated. Annealing with forming gas and CO2 laser treatment led to a temporary increase in the electrical conductivity of the ITO films by up to a factor of 10 and 6, respectively. Specific conductivities of up to 196 S cm(-1) were obtained for our ITO nanoparticle films under optimized conditions. (C) 2012 Elsevier B.V. All rights reserved.
Keywords: Indium tin oxide; Nanoparticles; Suspension; Conductivity; Laser treatment; Forming gas treatment

Production of filled hydrogels by mechanochemically induced polymerization - Damm, Cornelia; Mallembakam, Madhusudhan Rao; Voronov, Andriy; Peukert, Wolfgang (Journal of Applied Polymer Science, 2011)
Silica nanoparticles functionalized with polyvinylpyrrolidone (PVP) were obtained by the grinding/mechanical activation of quartz or nonfunctionalized silica nanoparticles in a stirred media mill in the presence of 1-vinyl-2-pyrrolidone, as proven by Fourier transform infrared spectroscopy. The polymer layer thickness formed on the silica nanoparticles after 8 h of mechanical activation in the absence of polymerization initiators amounted to about 10 nm, as derived from shear rheology. The silica nanoparticles functionalized with the hydrophilic PVP by mechanochemical polymerization reaction were used as fillers for hydrogels based on poly(hydroxyethyl methacrylate) (polyHEMA). The water absorption, release properties, and mechanical properties of the polyHEMA-silica composites were measured as functions of the filler content and particle size of the filler. PolyHEMA samples containing 20 wt % of the functionalized silica particles exhibited a higher maximum water absorption than the unfilled polymer; this showed that the hydrophilic interface between the filler and the matrix improved the water absorption. The release of methylene blue from the polyHEMA-silica composites was governed by diffusion and was almost unaffected by the silica particles. The values for the storage modulus and loss modulus of the polyHEMA-silica composites increased with growing filler content. For constant filler content, the storage modulus increased with decreasing particle diameter of the filler; this showed that the reinforcing effect increased with the interface between the filler particles and the matrix polymer. © 2010 Wiley Periodicals, Inc.
Keywords: composites; hydrophilic polymers; silicas; swelling

Production of Micron-Sized particles by melt emulsification - Fanselow, Stephanie; Schmidt, Jochen; Wirth, Karl-Ernst; Peukert, Wolfgang (8th International Conference for Conveying and Handling of Particulate Solids, CHoPS 2015, 2015)
Melt emulsification permits the production of spherical particles and is well-known for pharmaceutical applications and in the food industries. To increase the spectrum of applications the feasibility of the process for polymers is presented. In this study the influence of process parameters such as rotor-stator speed, temperature and dispersed phase viscosity on the particle size distribution of paraffin and polyethylene (PE) wax will be discussed. A major challenge is the stabilization of the droplet interface, thus, a new method for the selection of an efficient emulsifier using a high-pressure/high-temperature cell will be presented. Finally, results for higher viscous technical polymers, such as polypropylene (PP) will be presented. PP is a promising candidate for advanced powders to be used in additive manufacturing processes like laser beam melting (LBM) of polymers, i.e. melt emulsification might be a suitable approach to produce new and optimized LBM powder
Keywords: Laser beams; Particle size; Particle size analysis; Polymers; Polypropylenes; Powders; Additive manufacturing process; Dispersed phase; Food industries; Influence of process parameters; Laser beam melting; Micron-sized particles; Pharmaceutical applications; Spherical particle; Emulsification

Production of micron-sized polymer particles for additive manufacturing by melt emulsification - Peukert, Wolfgang; Fanselow, Stephanie; Schmidt, Jochen; Wirth, Karl-Ernst (Proceedings of PPS-31, 2016)
Melt emulsification is an advanced top-down approach that permits to produce spherical particles and thus widens the availability of polymer feed materials for additive manufacturing. In the process the polymer is molten in a continuous phase and droplet breakup is realized in a rotor-stator-device. The stabilization of the newly formed surfaces is quite challenging. Therefore, a new method to identify an appropriate emulsifier by measuring the interfacial tension between the polymer and continuous phase using a high pressure / high temperature cell is presented. The obtained powders are characterized by scanning electron microscopy (SEM) and by a Zimmermann tensile strength tester to determine the powder flowability. The processability of the polymer powders for additive manufacturing is investigated and demonstrated by building single layers by laser beam melting.
Keywords: additive manufacturing; melt emulsification; polymers

Production of PBT/PC multi-material particles via a combination of co-grinding and spray-agglomeration for powder bed fusion - Riedel, Florentin; Düsenberg, Björn; Schmidt, Jochen; Bück, Andreas; Peukert, Wolfgang (Procedia CIRP, 2020)
Polybutylene terephthalate (PBT) – polycarbonate (PC) multi-materials with a PBT mass content of 25% to 75% were produced for the powder bed fusion process by the means of co-grinding and spray agglomeration. The influence of the PC content and the process parameters on the thermal properties of the obtained powders are discussed in detail. Compared to pure PBT powder, the PBT/PC multi-materials crystallize at lower temperatures, which improves the handling during the additive manufacturing proces
Keywords: multi-material particles; polycarbonate; polybutylene terephthalate; comminution; spray agglomeration

Production of PBT/PC particle systems by wet grinding - Schmidt, Jochen; Romeis, Stefan; Peukert, Wolfgang (32nd International Conference of the Polymer Processing Society, PPS 2016, 2017)
Keywords: polycarbonate; polybutylene terephthalate; wet comminution; stirred media mill

Production of polyamide 11 microparticles for Additive Manufacturing by liquid-liquid phase separation and precipitation - Dechet, Maximilian; Goblirsch, Anja; Romeis, Stefan; Zhao, Meng; Lanyi, Franz; Kaschta, Joachim; Schubert, Dirk W.; Drummer, Dietmar; Peukert, Wolfgang; Schmidt, Jochen (Chemical Engineering Science, 2019)
Within this contribution liquid-liquid phase separation (LLPS) and precipitation from ethanol was studied as an approach to produce polyamide 11 (PA11) powders for selective laser sintering (SLS). To this end, the cloud point and solution temperature curve of the PAll-ethanol system was determined experimentally via turbidity measurements. The proper range of system composition and temperature for particle formation was deduced. The dependence of particle characteristics on process parameters (polymer concentration, stirring conditions and temperature regime) during LLPS and precipitation was assessed and the products were characterized with respect to their size and morphology. Furthermore, structural, rheological and thermal characteristics were analyzed and correlated with process parameters. Molecular weight distributions were determined. After removal of fines and dry coating with hydrophobic fumed silica, an optimized PA11 powder with mean particle size of 91 mu m showing good flowability for SLS was obtained. SLS processability of this optimized PA11 powder was demonstrated by building multilayered test specimens in a laser sintering machine. With this contribution, we present a comprehensive workflow for the process development, product characterization and product application of a SLS powder manufactured via precipitation. (C) 2018 Elsevier Ltd. All rights reserved.
CRIS-Team WoS Importer:2019-02-21

Production of polybutylene terephtalate glass composite powders and characterization for processing in selective laser sintering - Schmidt, Jochen; Gomez Bonilla, Juan Sebastian; Sachs, Marius; Lanzl, Lydia; Wudy, Katrin; Wirth, Karl-Ernst; Drummer, Dietmar; Peukert, Wolfgang (26th Annual International Solid Freeform Fabrication Symposium – An Additive Manufacturing Conference, 2016)

Production of polymer particles below 5 μm by wet grinding - Schmidt, Jochen; Plata Acevedo, Miguel Angel; Tröger, Sulay; Peukert, Wolfgang (Powder Technology, 2012)
Polymeric microparticles that may be used in rapid prototyping processes typically are produced by either polymerization processes or cryogenic grinding in impact mills at liquid nitrogen temperature (− 196 °C) or by dry grinding at solid carbon dioxide temperature (− 78 °C). Within this account an alternative approach for the production of polymer particles is presented. It is shown that wet grinding of polymers in a stirred media mill and organic solvents (ethanol, hexane) at reduced temperatures down to − 80 °C is a suitable method to produce polymer particles of mean diameter smaller than 5 μm with narrow particle size distribution. Results are presented for wet grinding of polystyrene (PS) and polyetheretherketone (PEEK). The influence of the mechanical properties of the polymers under consideration and the influence of the process parameters, namely stress energy, process time and especially temperature and solvent viscosity are addressed. Remarkably, we found in case of PEEK that the mean diameter is one order of magnitude smaller than the zone of plastic deformation estimated from fracture toughness and yield stres
Keywords: Wet grinding; Micro-grinding; Stirred media mill; Polymer; Polystyrene; PEEK

Production of spherical ester wax powders by melt emulsification for Additive Manufacturing - Tischer, Florentin; Düsenberg, Björn; Peukert, Wolfgang; Schmidt, Jochen (Procedia CIRP, 2022)
Powder bed fusion of polymers with laser beam (PBF-LB/P) involves selectively melting plastic micro particles with a laser and building up the parts layer by layer, which offers great freedom of design. However, the choice of commercially available thermoplast feedstock powders is limited (90% polyamides). In order to extend the range of materials, this contribution presents the production of highly spherical micro particles by melt emulsification followed by spray agglomeration for ester wax. The effect of process parameters during emulsification (energy input, surfactant to polymer ratio) on the particle size distribution is demonstrated in detail for the ester wax system. In order to generate and tune particle sizes to a range suitable for PBF, melt emulsified ester wax dispersions are spray agglomerated. Agglomerated ester wax powders were used for the PBF process to manufacture tensile strength specimens type 5A.
CRIS-Team Scopus Importer:2022-11-25
Keywords: Additive manufacturing; ester wax; Polycaprolactone; Melt emulsification; Polymers; Spray agglomeration

Production of Spherical Micron-Sized Polymer Particles for Additive Manufacturing by Liquid Phase Processes - Dechet, Maximilian; Kloos, Stephanie; Peukert, Wolfgang; Schmidt, Jochen (Proceedings of the Europe/Africa Conference Dresden 2017 Polymer Processing Society PPS, 2019)
CRIS-Team WoS Importer:2019-05-03

Production of spherical semi-crystalline polycarbonate microparticles for Additive Manufacturing by liquid-liquid phase separation - Kloos, Stephanie; Dechet, Maximilian; Peukert, Wolfgang; Schmidt, Jochen (Powder Technology, 2018)
Keywords: Polycarbonate (PC); Polymer microspheres; Additive Manufacturing (AM); Semi-crystalline thermoplast; Thermally induced phase separation (TIPS)

Production of spherical wax and polyolefin microparticles by melt emulsification for additive manufacturing - Fanselow, Stephanie; Emamjomeh, S. Ehsan; Wirth, Karl-Ernst; Schmidt, Jochen; Peukert, Wolfgang (Chemical Engineering Science, 2016)
Keywords: Melt emulsification; Polymer microspheres; Waxes; Polyethylene (PE); Polypropylene (PP); Additive manufacturing

Production of sub-micron particles by wet comminution in stirred media mills - Peukert, Wolfgang; Stenger, Frank; Mende, Stefan; Schwedes, Jörg (Journal of Materials Science, 2004)
A joined research project between the Technical University of Braunschweig and the Technical University of München investigates the possibilities for the production of stable product suspensions in a particle size range smaller than 100 nm. In this paper results for comminution of fused corundum showing the influence of the electrostatic stabilization at different pH-values on the grinding progress and the grinding media wear are presented. Furthermore, by means of experimental results the influence of the grinding media diameter and the stirrer tip speed is discussed. © 2004 Kluwer Academic Publishers.
Keywords: stabilization; comminution; electrostatic; grinding

Production of well dispersible single walled carbon nanotubes via a "floating catalyst"-method - Toni, Franziska; Xing, Haichen; Walter, Johannes; Strauß, Volker; Nacken, Thomas; Damm, Cornelia; Wirth, Karl-Ernst; Guldi, Dirk Michael; Peukert, Wolfgang (Chemical Engineering Science, 2015)
In this paper, we present a unique process chain for the production of single-walled carbon nanotubes (SWCNT) and document the relationship between the process parameters in gas phase production, the dispersibility of SWCNTs in aqueous solutions of sodium cholate and their properties. SWCNTs were prepared by a "floating catalyst" method using a solution of ferrocene in ethanol as precursor. Production rates in the range from 5 to 20. mg/h were achieved by using an optimized riser reactor design, which enables reduction of undesired wall-sticking of the catalyst particles and SWCNTs. Products featuring iron catalyst contents less than 30. wt% were obtained for low precursor concentrations in combination with short residence time in the reactor. Transmission electron microscopy (TEM) and statistical Raman analyses of the products reveal that the SWCNTs exhibit a diameter distribution ranging from 0.5 to 2.0. nm. Processing conditions, including precursor concentration, residence time, etc. were found to have only a slight impact on the mean geometric SWCNT diameter. Sonication based post-processing of the as-prepared SWCNTs in aqueous solutions of sodium cholate leads to an effective individualization of SWCNTs as proven by atomic force microscopy (AFM), 3D fluorescence spectroscopy, and by multi-wavelength analytical ultracentrifugation (AUC). Overall, the dispersibility of the non-purified SWCNTs in a 2. wt% aqueous solution of sodium cholate increases as the ferrocene partial pressure is decreased and, in turn, the catalyst concentration is reduced in the gas phase. Statistical Raman spectroscopy performed with the SWCNTs reveals that more than 75% of the produced carbon species are SWCNTs and that about 2/3 are semiconducting.
Keywords: Analytical ultracentrifugation and Raman spectroscopy; CNTs; Dispersion; Floating catalyst

Produktionsintegrierter Umweltschutz in Kohle-Kraftwerken - Wirth, Karl-Ernst (Handbuch des Umweltschutzes und der Umweltschutztechnik, 1996)
Umweltschutz im Bereich der Kohlekraftwerke läßt sich auf die folgenden Forderungen fokussieren: Schonung der Ressourcen, Minderung der Stoffströme Verringerung der Emissionen. Schonung der Ressourcen meint, daß mit möglichst geringem Primärenergieeinsatz ein Maximum an veredelter Energie in Form von z.B. elektrischem Strom produziert wird. Ein verringerter Kohleverbrauch bei gleicher Produktionshöhe an z.B. elektrischem Strom bewirkt eine Verlängerung des Zeitraumes in dem dieser Primärenergieträger zur Verfügung steht. Ressourcenschonung zielt also im wesentlichen auf eine Streckung des Zeitraumes, in dem die endlichen Kohlevorräte für einen Einsatz in Kraftwerken zur Verfügung stehen. Die Forderung nach Ressourcenschonung kann als Vorsorgemaßnahme für die zukünftigen Generationen angesehen werden. Produktionsintegrierter Umweltschutz in Kohlekraftwerken</i
UnivIS-Import:2015-04-20:Pub.1996.tech.ITC.mechve.produk

Progress in Multidimensional Particle Characterization - Frank, Uwe; Uttinger, Maximilian; Wawra, Simon; Lübbert, Christian; Peukert, Wolfgang (KONA Powder and Particle Journal, 2021)
The properties of particle ensembles are defined by a complex multidimensional parameter space, namely particle size, shape, surface, structure, composition and their distributions. Macroscopic product properties are a direct result of these disperse particle properties. Therefore, the comprehensive multidimensional characterization of particle ensembles is a key task in any product design. However, the determination of complex property distributions is major challenge. We provide a broad overview of the current tools for multidimensional particle characterization. First, the mathematical handling of multidimensional (nD) property distribution is outlined as a necessary framework for the correct handling of nD particle size distributions (PSDs). Then, well-established techniques as well as recent developments with the potential to extract nD property distributions are reviewed. Exsitu imaging techniques like electron tomography or Raman spectroscopy with AFM co-localization, for instance, provide a resolution on the level of single particles but are limited in terms of sample statistics. A particular focus lies therefore on methods in the gas and the liquid phase, which provide multidimensional particle properties either directly or by a combination of one-dimensional technique

Progress in the understanding of bulk solids attrition in dilute phase pneumatic conveying - Peukert, Wolfgang; Frye, Lars (Powder Technology, 2004)
To investigate attrition processes in pneumatic conveying, it is distinguished between process parameters, determining the stress conditions (SC) the particles are subjected to during conveying (process function), and material properties, being responsible for the individual reaction of different materials to these stress conditions (material function). For dilute phase conveying, the process function was determined for a pipe bend preceded by a straight pipe by employing computational fluid dynamics (CFD). The influence of the main parameters as obtained by dimensional analysis, namely, Stokes parameter, Froude number, Reynolds number and the ratio of bend radius to pipe diameter, was investigated and discussed. The results showed that the impact conditions were different from what is commonly expected. The impact angles in a pipe bend (r /D=5; D=80 mm) were determined to lie between 5° and 35°. Consequently, the tangential impact velocity components are considerably higher than the normal ones. The experiments carried out to determine the material function revealed that the dominating attrition mechanisms differ between polypropylene (PP) particles on one hand and polymethylmethacrylates (PMMA) and polystyrenes (PS) on the other. By applying dynamic mechanical analysis (DMA), the glass transition temperature of the polymers was identified to be a key factor in the determination of the prevailing attrition mechanism. Based on these findings, a qualitative three-level model of the attrition process, involving stress mode, material-specific attrition mechanisms and basic (microscopic) attrition mechanisms, was developed. © 2004 Published by Elsevier B.V.
Keywords: Attrition mechanisms; Dynamic mechanical analysis (DMA); Material function; Pneumatic conveying; Polymers; Process function

Protein adsorption at the air-water interface studied by surface vibrational spectroscopy - Rumpel, Armin; Engelhardt, Kathrin; Braunschweig, Björn; Peukert, Wolfgang (Engineering Sciences and Fundamentals - Core Programming Topic at the 2011 AIChE Annual Meeting, 2011)

Protein adsorption at the electrified air-water interface: Effects on foam stability - Engelhardt, Kathrin; Peukert, Wolfgang; Braunschweig, Björn (Engineering Sciences and Fundamentals 2013 - Core Programming Area at the 2013 AIChE Annual Meeting: Global Challenges for Engineering a Sustainable Future, 2013)

Protein adsorption at the electrified air-water interface: Implications on foam stability - Braunschweig, Björn; Engelhardt, Kathrin; Rumpel, Armin; Walter, Johannes; Peukert, Wolfgang (2012)

Protein adsorption at the electrified air-water interface: Implications on foam stability - Engelhardt, Kathrin; Rumpel, Armin; Walter, Johannes; Dombrowski, Jannika; Kulozik, Ulrich; Braunschweig, Björn; Peukert, Wolfgang (Langmuir, 2012)
The surface chemistry of ions, water molecules, and proteins as well as their ability to form stable networks in foams can influence and control macroscopic properties such as taste and texture of dairy products considerably. Despite the significant relevance of protein adsorption at liquid interfaces, a molecular level understanding on the arrangement of proteins at interfaces and their interactions has been elusive. Therefore, we have addressed the adsorption of the model protein bovine serum albumin (BSA) at the air-water interface with vibrational sum-frequency generation (SFG) and ellipsometry. SFG provides specific information on the composition and average orientation of molecules at interfaces, while complementary information on the thickness of the adsorbed layer can be obtained with ellipsometry. Adsorption of charged BSA proteins at the water surface leads to an electrified interface, pH dependent charging, and electric field-induced polar ordering of interfacial H 2O and BSA. Varying the bulk pH of protein solutions changes the intensities of the protein related vibrational bands substantially, while dramatic changes in vibrational bands of interfacial H 2O are simultaneously observed. These observations have allowed us to determine the isoelectric point of BSA directly at the electrolyte-air interface for the first time. BSA covered air-water interfaces with a pH near the isoelectric point form an amorphous network of possibly agglomerated BSA proteins. Finally, we provide a direct correlation of the molecular structure of BSA interfaces with foam stability and new information on the link between microscopic properties of BSA at water surfaces and macroscopic properties such as the stability of protein foams. © 2012 American Chemical Society.
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PTV experiments and DEM simulations of the coefficient of restitution for irregular particles impacting on horizontal substrates - Jiang, Zhaochen; Du, Jiajie; Rieck, Christian; Bück, Andreas; Tsotsas, Evangelos (Powder Technology, 2020)
For systems of particles with irregular shapes, the collisions between particles and between particles and walls are highly complex and strongly related to the contact geometry. In this work, the collision behavior between irregular maltodextrin particles (with a characteristic size of approximately 100 μm) and horizontal substrates was experimentally measured by an improved particle tracking velocimetry (PTV), which simultaneously reconstructed the trajectories of many particles during the process of free fall and rebound. In addition, the measurement data were compared with DEM simulations using the multi-sphere model and the superquadric model, regarding the distributions of total and normal coefficients of restitution and corresponding relationships with the rotational speed after collision and the absolute difference of incidence angle and rebound angle. Compared to the superquadric model, the multi-sphere model well predicts the macroscopic particle-wall collision behaviors of irregular non-convex particles.
CRIS-Team Scopus Importer:2019-11-29
Keywords: Coefficient of restitution; Irregular non-convex particle; Multi-sphere; Non-spherical DEM; PTV; Superquadric

PTV measurement and DEM simulation of the particle motion in a flighted rotating drum - Zhang, Lanyue; Jiang, Zhaochen; Weigler, Fabian; Herz, Fabian; Mellmann, Jochen; Tsotsas, Evangelos (Powder Technology, 2020)
To investigate the particle motion in the flighted rotating drum (FRD), a laboratory drum with four rectangular flights is horizontally arranged and filled with plastic particles in this work. The FRD is operated by varying the drum rotating speed (10, 20, and 30 rpm) and filling degree (10, 15, and 20%). The particle tracking velocimetry (PTV) method and DEM simulation (with LIGGGHTS software) are applied to analyze the particle movements. The results have shown that, as the drum rotating speed is increased, the holdup ratio and cascading rate of an individual flight increase. The drum rotating speed also affects the particle ratios in three phases and the falling time distribution of the dilute phase. Moreover, the average velocities and granular temperatures of the particle system in FRD increase as the drum rotating speed increases and the filling degree decreases. Good agreements are observed between the PTV measurements and DEM simulations.
CRIS-Team Scopus Importer:2020-01-21
Keywords: DEM; Flighted rotating drum; Granular temperature; Particle motion; Particle velocity; PTV

Pulsed direct flame deposition and thermal annealing of transparent amorphous indium zinc oxide films as active layers in field effect transistors - Kilian, Daniel; Polster, Sebastian; Vogeler, Isabell; Frey, Lothar; Jank, Michael; Peukert, Wolfgang (ACS Applied Materials and Interfaces, 2014)
Indium-zinc oxide (IZO) films were deposited via flame spray pyrolysis (FSP) by pulsewise shooting a Si/SiO2 substrate directly into the combustion area of the flame. Based on UV-vis measurements of thin-films deposited on glass substrates, the optimal deposition parameters with respect to low haze values and film thicknesses of around 100 nm were determined. Thermal annealing of the deposited films at temperatures between 300 and 700 °C was carried out and staggered bottom gate thin-film transistors (TFT) were fabricated. The thin films were investigated by scanning electron microscopy, atomic force microscopy, X-ray diffraction, Fourier transformed infrared spectroscopy, and room-temperature photoluminescence measurements. The outcome of these investigations lead to two major requirements in order to implement a working TFT: (i) organic residues from the deposition process need to be removed and (ii) the net free charge carrier concentration has to be minimized by controlling the trap states in the semiconductor. The optimal annealing temperature was 300 °C as both requirements are fulfilled best in this case. This leads to field effect transistors with a low hysteresis, a saturation mobility of μSat = 0.1 cm2/(V s), a threshold voltage of Vth = -18.9 V, and an Ion/Ioff ratio on the order of 107. Depending on thermal treatment, the defect density changes significantly strongly influencing the transfer characteristics of the device. © 2014 American Chemical Society.
UnivIS-Import:2015-03-09:Pub.2014.tech.IE.LEB.pulsed
Keywords: amorphous metal oxides; direct deposition; field-effect transistor; flame spray pyrolysis; indium-zinc oxide; thermal annealing

Pulverschüttungsanalyse für das selektive Laser-Sintern mittels Computertomographie - Zhao, Meng; Greiner, Sandra; Wudy, Katrin; Schmidt, Jochen; Peukert, Wolfgang; Drummer, Dietmar (Proceedings of the 15th Rapid.Tech Conference, 2018)

Pulvertechnologie: Im Verdampfen mitgerissen - Wirth, Karl-Ernst (Pneumologie, 2000)
Hoher Druck hindert auch sehr heiße Flüssigkeiten am Verdampfen - der Siedepunkt ist überschritten, doch die energiegeladenen Teilchen sind eingesperrt und können sich nicht ablösen. Entkommen sie plötzlich dem Druck, so reißt der Flüssigkeitsfilm auf und zerstäubt zu feinsten Tröpfchen, bevor der Gaszustand erreicht wird. In einem Projekt von Prof. Dr. Karl-Ernst Wirth am Lehrstuhl für Mechanische Verfahrenstechnik der Universität Erlangen-Nürnberg wird dieser Umstand ausgenutzt, um Pulver aus sehr feinkörnigen Partikeln gleichmäßig zu verteilen: durch Verdüsung von überhitzten Suspensionen, von Mischungen aus Flüssigkeiten und Feststoffteilchen. Die Deutsche Forschungsgemeinschaft hat dazu für zwei Jahre eine Sachbeihilfe gewährt.
UnivIS-Import:2015-03-09:Pub.2000.tech.ITC.mechve.pulver
Keywords: Medizin; technik; tropfen; pulver

Purification and structural elucidation of carbon dots by column chromatography - Hinterberger, Vanessa; Damm, Cornelia; Haines, Philipp; Guldi, Dirk Michael; Peukert, Wolfgang (Nanoscale, 2019)
Carbon dots (CDs) are an astonishing class of fluorescent materials with many applications in bioimaging, drug delivery, photovoltaics and photocatalysis due to their outstanding luminescence properties and low toxicity. However, the internal CD structure of bottom-up synthesized CDs is still the subject of considerable debate. Unambiguous analysis of the internal CD composition is hampered by the fact that reaction products usually contain mixtures of several CD fractions as well as molecular intermediate and side products. Therefore, purification and careful separation of the various CD fractions is vital for structural analysis and isolation of pure CDs possessing optimized optical properties. In this study, CD solutions were synthesized from citric acid and cysteine via a one-pot hydrothermal synthesis. A simple column chromatography unit was used to systematically study the influence of the molar precursor ratios and synthesis conditions (temperature, reaction time) on the CD solution composition. By investigating the structural and optical properties of the chromatographically separated fractions, three different fluorescent species could be identified. Freely floating molecular fluorophores left the column first, followed by highly fluorescent CDs with fluorophores bound to the carbon core, finally followed by low-fluorescent carbon particles without fluorophores. We demonstrate that the CD solution composition and the internal structure of the individual fluorescent components can be clarified via chromatographic separation. This information can be further applied to isolate pure CDs with optimized optical properties.
CRIS-Team Scopus Importer:2019-05-09

Quality over quantity: How different dispersion qualities of minute amounts of nano-additives affect material properties in powder bed fusion of polyamide 12 - Sommereyns, Alexander; Gann, Stan; Schmidt, Jochen; Chehreh, Abootorab Baqerzadeh; Luddecke, Arne; Walther, Frank; Goekce, Bilal; Barcikowski, Stephan; Schmidt, Michael (Materials, 2021)
The great interest, within the fields of research and industry, in enhancing the range and functionality of polymer powders for laser powder bed fusion (LB-PBF-P) increases the need for material modifications. To exploit the full potential of the additivation method of feedstock powders with nanoparticles, the influence of nanoparticles on the LB-PBF process and the material behavior must be understood. In this study, the impact of the quantity and dispersion quality of carbon nanoparticles deposited on polyamide 12 particles is investigated using tensile and cubic specimens manufactured under the same process conditions. The nano-additives are added through dry coating and colloidal deposition. The specimens are analyzed by tensile testing, differential scanning calorimetry, polarized light and electron microscopy, X-ray diffraction, infrared spectroscopy, and micro-computed tomography. The results show that minute amounts (0.005 vol%) of highly dispersed carbon nanoparticles shift the mechanical properties to higher ductility at the expense of tensile strength. Despite changes in crystallinity due to nano-additives, the crystalline phases of polyamide 12 are retained. Layer bonding and part densities strongly depend on the quantity and dispersion quality of the nanoparticles. Nanoparticle loadings for CO2 laser-operated PBF show only minor changes in material properties, while the potential is greater at lower laser wavelengths.
CRIS-Team Scopus Importer:2021-10-01
Keywords: Additively manufactured parts; Dispersion; Laser powder bed fusion; LB-PBF; Mechanical properties; Nanocomposites; Nanoparticles; Polyamide 12

Quantification of grinding relevant material properties - Peukert, Wolfgang; Vogel, Lutz (World Congress Particle Technology 4, 2002)
UnivIS-Import:2015-04-16:Pub.2002.tech.ITC.mechve.quanti
Keywords: grinding; material; property

Quantifying Surface Properties of Silica Particles by Combining Hansen Parameters and Reichardt's Dye Indicator Data - Stauch, Claudia; Süß, Sebastian; Luxenhofer, Robert; Binks, Bernard P.; Segets, Doris; Mandel, Karl (Particle & Particle Systems Characterization, 2018)
To obtain quantitative understanding of the effects of a chemisorbed organic modification on the surface of particles, the use of Reichardt's dye (RD) and Hansen solubility parameter (HSP) is discussed, whereby the S should be understood in terms of “similarity” rather than solubility as dispersibility is in focus. Silica nanoparticles modified to different extents with a medium chain silane including completely hydrophilic and hydrophobic particles are chosen. During spray-drying such particles form fully redispersible micro-raspberry superstructures. After qualitative estimations of the particles' polarity based on measuring both immersion time and ability of modified particles to stabilize oil–water emulsions, surface properties are quantified by HSP and RD. With increasing hydrophobicity, i.e., increasing amount of silane at the surface, all three contributions to HSP change. At the same time, RD analysis reveals that the normalized solvent polarity parameter decreases progressively. HSP and RD analysis are in good agreement, giving strong confidence on each method applied individually. This work demonstrates that after noticeable attempts for combined solubility parameters in case of molecules, carbon allotropes, and gelators, such studies can be extended toward functional (nano)particles and that a full picture of particle surface properties is possible via the combination of different, quantitative techniques.
CRIS-Team Scopus Importer:2020-04-02
Keywords: analytical centrifugation; colloidal stability; interface characterization; silica particles; surface coating

Quantitative evaluation of delamination of graphite by wet media milling - Damm, Cornelia; Nacken, Thomas; Peukert, Wolfgang (Carbon, 2015)
Surfactant-free Few-Layer-Graphene (FLG) suspensions were prepared by wet media delamination of unmodified isostatic graphite in organic solvents using a shaking plate for fast screening of favorable process parameters and a stirred media mill as a delamination tool. The achieved FLG-concentration was determined by a combination of UV/Vis and Raman spectroscopy. A study of wet delamination for different solvents reveals an analogue behavior as for ultrasound-assisted delaminated samples. In N-methylpyrrolidone as dispersing medium the influence of delamination process parameters on FLG concentration was studied and an optimal set of parameters was found. A comparison between various delamination methods shows that delamination by enhanced shear leads to largest flake structures. The highest value for the FLG production rate (produced mass/time) is obtained in a stirred media mill. The formation of FLG was also proved by measuring the flake thickness by atomic force microscopy (AFM). The FLG percentage derived from AFM agrees well with the results determined by statistical Raman spectroscopic analyses.

Quantitative evaluation of electrophoretic deposition kinetics of graphene oxide - Diba, Mani; Garcia-Gallastegui, Ainara; Klupp Taylor, Robin; Pishbin, Fatemeh; Ryan, Mary P.; Shaffer, Milo S. P.; Boccaccini, Aldo R. (Carbon, 2014)
The electrophoretic deposition (EPD) technique is an attractive approach for development of graphene and graphene oxide (GO) films for a variety of applications. However, in order to establish the influence of the EPD parameters on the properties of the deposited films, a deeper investigation of the fundamental GO-EPD kinetics is required. Previous studies have reported a simultaneous anodic reduction of GO flakes during EPD, complicating the kinetics and process control. Therefore, in this study, low voltages were used to prevent significant GO reduction during EPD, as confirmed by XPS and FTIR. Accordingly, the GO-EPD kinetics was established as a function of deposition time and voltage, accompanied by microscopic characterization of the deposited films. The experimental results show that the deposition follows a linear growth law, in good agreement with the predictions of Hamaker's law. Comparisons of optical absorbance and profilometry provide estimates of (reduced) GO deposition rate, extinction coefficient, and density. © 2013 Elsevier Ltd. All rights reserved.

Quantitative Evaluation of Fullerene Separation by Liquid Chromatography - Süß, Sebastian; Michaud, Vanessa; Amsharov, Konstantin; Akhmetov, Vladimir; Kaspereit, Malte; Damm, Cornelia; Peukert, Wolfgang (Journal of Physical Chemistry C, 2019)
Although a huge number of facile synthesis methods for nanoparticles (NPs) do exist, the products usually exhibit a distribution in particle size and shape. Thus, a separation step needs to be applied to adjust the particle properties according to the needs of the later application. Chromatography is a potentially scalable separation method which is well-established for separating molecules and promising for classifying NPs by size. Herein, we lay the foundations of particle chromatography by studying the separation of a C-60/C-70 fullerene mixture as well-defined particle probes using a pyrene-functionalized silica stationary phase. C-60 fullerenes are perfect model particles as they are spherical, roughly 1 nm in diameter, interacting via van der Waals interactions only. First, we extract the Henry coefficients for C-60 and C-70 fullerenes from the elution behavior of the fullerene mixture. Using a particle-wall as well as particle-particle model for the van der Waals interaction potential, we determine the Hamaker constant of the stationary phase material from the measured Henry coefficients. Moreover, we investigate the concentration-dependent diffusion and mass transport in the column by quantitative evaluation of the flow rate dependent elution behavior of the fullerenes. Our study shows the huge potential of chromatography for the separation of nanoparticles and demonstrates the strength of physical-chemical concepts for the quantitative analysis and the prediction of nanoparticle classification.
CRIS-Team WoS Importer:2019-07-30

Quantitative evaluation of nanoparticle classification by size-exclusion chromatography - Süß, Sebastian; Metzger, Christoph; Damm, Cornelia; Segets, Doris; Peukert, Wolfgang (Powder Technology, 2018)
Although few attempts for classification of nanoparticles (NPs) in labscale do exist, the transfer to industrial applications is still challenging. One promising separation method, which is already established for biological molecules, is chromatography. Herein, we study the classification of differently sized gold NPs (AuNPs) by size-exclusion chromatography (SEC). First, we investigated the interactions of AuNPs with potential stationary phases in order to identify a suitable material for the chromatographic process where irreversible NP adhesion is excluded. Then, we demonstrate the high reproducibility of our SEC experiments by multiple sample injections that lead to constant peak areas. In particular, we show the size-dependent elution behavior of AuNP mixtures resulting in bimodal elution peaks, where size separation was confirmed by inline measured UV/Vis spectra. Finally, NP classification results by using a fraction collector are characterized by retention time, mass balances and size-dependent separation efficiencies. The adjustment of the particle size distributions (PSDs) is demonstrated by changing the switching time of the fraction collector. Our study evidences the high potential of SEC for preparative and continuous separation of NPs.
Keywords: (Gold) particles; Separation efficiency; Chromatography; Separation

Quantitative evaluation of size selective precipitation of Mn-doped ZnS quantum dots by size distributions calculated from UV/Vis absorbance spectra - Segets, Doris; Komada, So; Butz, Benjamin; Spiecker, Erdmann; Mori, Yasushige; Peukert, Wolfgang (Journal of Nanoparticle Research, 2013)
We demonstrate the quantitative evaluation of the sharp classification of manganese-doped zinc sulfide (ZnS:Mn) quantum dots by size selective precipitation. The particles were characterized by the direct conversion of absorbance spectra to particle size distributions (PSDs) and high-resolution transmission electron micrographs (HRTEM). Gradual addition of a poor solvent (2-propanol) to the aqueous colloid led to the flocculation of larger particles. Though the starting suspension after synthesis had an already narrow PSD between 1.5 and 3.2 nm, different particle size fractions were subsequently isolated by the careful adjustment of the good solvent/poor solvent ratio. Moreover, due to the fact that for the analysis of the classification results the size distributions were available, an in-depth understanding of the quality of the distinct classification steps could be achieved. From the PSDs of the feed, as well as the coarse and the fine fractions with their corresponding yields determined after each classification step, an optimum after the first addition of poor solvent was identified with a maximal separation sharpness κ as high as 0.75. Only by the quantitative evaluation of classification results leading to an in-depth understanding of the relevant driving forces, a future transfer of this lab scale post-processing to larger quantities will be possible.

Quantitative investigation of the fragmentation process and defect density evolution of oxo-functionalized graphene due to ultrasonication and milling - Halbig, Christian Eberhard; Nacken, Thomas; Walter, Johannes; Damm, Cornelia; Eigler, Siegfried; Peukert, Wolfgang (Carbon, 2016)
In the view of technical and medical applications we examined the effect of ultrasonication and ball milling of oxo-functionalized graphene bearing an almost intact carbon lattice (oxo-G) with respect to the lateral flake size reduction and defect formation in the carbon lattice for the first time. The energy input was screened for both methods and quantitative changes in lateral flake size distribution were characterized in solution by analytical ultracentrifugation (AUC) supported by atomic force microscopy (AFM). For the first time, we applied statistical Raman spectroscopy to reliably evaluate the formation of lattice defects with processing time. Surprisingly, the density of lattice defects remains unaffected with energy inputs below a limiting threshold. Furthermore, for both processing techniques, the size reduction scales with the energy input according to a power law function, which is well known for emulsification and mechanical comminution processes. With the results of this study it is possible to precisely predetermine the lateral size of flakes of oxo-G upon sonication or milling processing, preserving the carbon lattice. Understanding this controlled formation of oxo-G flakes enables target oriented technical, medical and electronic applications with tailored properties.
EAM Import::2019-03-13

Quantitative modeling of precipitation processes - Schikarski, Tobias; Avila, Marc; Trzenschiok, Holger; Güldenpfennig, Andreas; Peukert, Wolfgang (Chemical Engineering Journal, 2022)
Precipitation from the liquid phase is a powerful and common unit operation for the continuous, highly reproducible production of nanoparticles. However, a general, predictive and quantitative modeling framework is still missing due to the inherent multiscale nature of the precipitation process and the complex interplay between the relevant sub-processes. We apply direct numerical simulation of the fluid flow coupled with a population balance framework to investigate the precipitation of stabilized ibuprofen nanoparticles in a T-mixer. Our findings suggest that the Damkohler number (the ratio between the mixing time and solid formation time) determines the precipitation outcome. We demonstrate how the primarily unknown solid formation kinetics can be estimated in the simulations with the guidance of experimental input at a single process condition. We subsequently vary the Damkohler number by changing the inflow rates (global mixing time) and the initial ibuprofen concentration. In doing so, excellent agreement between numerical simulations and experiments in the full particle size distribution at different process conditions (from laminar to turbulent flow and different initial ibuprofen concentrations) is obtained using the beforehand estimated solid formation kinetics. Our model opens avenues for the predictive simulation of particle-formation dynamics and is a stepping stone for the tailored, scalable production of nanoparticles.
CRIS-Team WoS Importer:2022-06-17

Quantitative Optical and Structural Comparison of 3D and (2+1)D Colloidal Photonic Crystals - Römling, Lukas; Bleyer, Gudrun; Görlitzer, Eric; Onishchukov, Georgy; Vogel, Nicolas (Langmuir, 2023)
Colloidal crystals are excellent model systems to study self-assembly and structural coloration because their periodicities coincide with the wavelength range of visible light. Different assembly methods inherently introduce characteristic defects and irregularities, even with nearly monodisperse colloidal particles. Here, we investigate how these imperfections influence the structural coloration by comparing two techniques to obtain colloidal crystals. 3D colloidal crystals produced by convective assembly are well-ordered and periodically arranged but show microscopic cracks. (2+1)D colloidal crystals fabricated by stacking individual monolayers show a decreased hexagonal order and limited crystal registration between single monolayers in the z-direction. We investigate the optical properties of both systems by comparing identical numbers of layers using correlative microspectroscopy. These measurements show that the less ordered (2+1)D colloidal crystals exhibit higher reflected light intensities. Macroscopic reflection integrating all angles shows that the reflected light intensity levels out with an increasing number of layers, whereas incoherent scattering increases. Although both types of colloidal crystal show similar angle-dependent color shifts in specular reflection, the less-ordered structure of the (2+1)D colloidal crystal scatters light within a larger angular range under diffusive illumination. Our results suggest that structural coloration is surprisingly robust toward local defects and irregularities.
CRIS-Team Scopus Importer:2023-04-14

Radial and Axial Profiles of Solids Concentration in a High-loaded Riser Reactor - Wirth, Karl-Ernst; Graßler, Thomas (Circulating Fluidized Bed Technology VI, 1999)
To characterize flow patterns in a high-loaded riser reactor a cold running plant with an inner diameter of 0.19 m and 15 m height has been built up. Experiments have been carried out with glass beads (mean diameter dp = 60 μm) at superficial gas velocities UG from 2 to 8 m/s which leads to solids mass fluxes Gs from 30 to 600 kg/m2s). Local information about the solids concentration distribution are obtained by an x-ray computed tomography system consisting of a 60 keV x-ray source and an x-ray linear detector with 1024 sensitive elements. Radial solids concentration profiles show the typical core-annulus structure of a riser. Results from x-ray CT have been area weighted and compared to an average solids concentration calculated from static pressure profiles. Both methods show good coincidence except at the exit of the riser where acceleration effects influence the pressure profiles. Radial and axial profiles of solids concentration distribution are compared for three different operating conditions. The typical core-annulus structure of the radial solids concentration distribution is more distinct at higher mass fluxes whereas the axial solids concentration profile is getting more equal. From axial pressure profiles the interstitial gas velocity has been calculated and was found to be almost constant over the whole height of the riser. Die Verf. beschreiben Versuchsergebnisse der gemessenen örtlichen Feststoffkonzentrationen und der statische Druckprofile in einem kalt betriebenen Steigrohr bei drei verschiedenen Versuchsbedingungen. Der Reaktor besaß einen Dmr. von 19 cm und eine Höhe von 15 m, als Feststoff wurden Glasperlen mit 0,6 cm Dmr. verwendet und die Gasgeschwindigkeit wurde von 2 bis 8 m/s variiert. Die Messungen erfolgten sowohl mit Röntgenstrahlung, die mit einem Computertomograph aufgezeichnet wurde, als auch über die Berechnung mittlerer Feststoffkonzentrationen aus den aufgenommen statischen Druckprofilen und zeigten gute Übereinstimmung.
UnivIS-Import:2015-04-20:Pub.1999.tech.ITC.mechve.radial_93
Keywords: riser; high-load; profile; x-ray analyzer; circulating fluidized bed; solid flow; riser reactor; gas flow; velocity field; Versuch; Reaktor; Steigrohr; Konzentration; Gas; Feststoff

Radial Growth in 2D Revisited: The Effect of Finite Density, Binding Affinity, Reaction Rates, and Diffusion - Bihr, Timo; Sadafi, Fabrizio-Zagros; Smith, Ana-Suncana; Klupp Taylor, Robin; Seifert, Udo (Advanced Materials Interfaces, 2017)
Dendrite growth of metal patches on colloidal particles shows a variety of structures depending on the preparation conditions. The morphology of these patches suggests a cross-over from a reaction to a diffusion limited growth, implicating diffusion on the particle surface. Interestingly, the morphological and optical characteristics of the patches continuously change between two limiting behaviors. To understand this growth process, extensive simulations are performed, studying the fractal dimension and the dynamics of growth of a patch on a particle of a finite size, as a function of the initial density and the binding affinity of diffusing tracers. Several important growth regimes are characterized that enable to optimize the pathway for the synthesis of optically active, patchy particles.
Keywords: LIMITED AGGREGATION; CELL-ADHESION; FRACTAL AGGREGATION; COLLOIDAL SYNTHESIS; NANOSPHERES; DIMENSIONS; SIMULATION; NUCLEATION; PARTICLES; STABILITY

Radial Profiles of local solids distribution in a high-loaded Riser-Reactor measured with x-ray computed Tomography - Wirth, Karl-Ernst; et al. (Proceedings of the ASME Heat Transfer Division, 1998)
Since years high-loaded riser-reactors have been used successfully for different commercial applications, e.g. for fluid catalytic cracking. The fundamental study of hydrodynamics of such reactors will help to improve the design and operating conditions of existing plants and may lead to higher conversion rates and selectivity. The solids concentration distribution of a riser with an inner diameter of 0.19 m and 15 m height is investigated with x-ray computed tomography with a minimum spatial resolution of 0.2 mm and 0.4 mm thickness. A number of experiments have been carried out with narrowly size distributed glass beads between 50 and 70 μm at superficial gas velocities from 2 to 7 m/s. Even at higher circulation rates obtained radial solids concentration profiles still show a typical core-annulus structure, which gets more uniform at higher elevations.
UnivIS-Import:2015-04-16:Pub.1998.tech.ITC.mechve.radial_19
Keywords: riser; fluidized; bed

Radiation induced corrosion of copper for spent nuclear fuel storage - Hosseinpour, Saman (Radiation Physics and Chemistry, 2013)

Radiation Induced Corrosion of Copper in Anoxic Aqueous Solution - Hosseinpour, Saman; et al. (Electrochemical and Solid State Letters, 2012)

Rapid Characterization and Parameter Space Exploration of Perovskites Using an Automated Routine - Reinhardt, Elisabeth; Salaheldin, Ahmed M.; Distaso, Monica; Segets, Doris; Peukert, Wolfgang (ACS Combinatorial Science, 2020)
Hybrid, e.g., organic inorganic, perovskites from the type methylammonium lead iodide CH3NH3PbI3 are promising solar cell materials. However, due to the large parameter space spanned by the manifold combinations of divalent metals with organic cations and anions, an efficient approach is needed to rapidly test and categorize new promising materials. Herein, we developed a high throughput approach for the automated synthesis of perovskite layers with different precursor ratios at varying annealing temperatures. The layers were analyzed by optical absorption and photo-luminescence (PL) spectroscopy as well as X-ray diffraction (XRD) and evaluated using two different procedures. The first one is a stepwise exclusion of nonperforming reactant ratios and synthesis conditions by using both spectroscopic techniques, followed by a final validation of the procedure by XRD. In the second procedure, only PL results were consulted in combination with high throughput screening using design of experiments (DoE) to reduce the total number of experiments needed and compared to the manual cascade approach. Noteworthy, by simple PL screening, it was possible to identify the best ratio of perovskite to byproducts and annealing temperature. Thus, only with PL, more detailed results as with the manual protocol were reached, while at the same time the effort for characterization was significantly reduced (by 60% of the experimental time). In conclusion, our approach opens a way toward fast and efficient identification of new promising materials under different reaction and process conditions.
CRIS-Team WoS Importer:2020-01-31

Rapid fabrication and interface structure of highly faceted epitaxial Ni-Au solid solution nanoparticles on sapphire - Herre, Patrick; Will, Johannes; Dierner, Martin; Wang, Dong; Yokosawa, Tadahiro; Zech, Tobias; Wu, Mingjian; Przybilla, Thomas; Romeis, Stefan; Unruh, Tobias; Peukert, Wolfgang; Spiecker, Erdmann (Acta Materialia, 2021)
Supersaturated Ni-Au solid solution particles were synthesized by rapid solid-state dewetting of bilayer thin films deposited onto c-plane sapphire single-crystals. Rapid thermal annealing above the miscibility gap of the Ni-Au system followed by quenching to room temperature resulted in textured and faceted submicron-sized particles as a function of alloying content in the range of 0–28 at% Au. Morphologically, the observed kinetic crystal shapes are confined by close-packed planes; in addition, high-index facets are identified as a function of alloying content by TEM cross-sectioning and equilibrium crystal shape simulations. All samples exhibit a distinct 〈111〉 out-of-plane as well as in-plane texture along densely packed directions. Lattice parameters extracted from independent orthogonal X-ray and electron diffraction techniques prove the formation of a solid solution without tetragonal distortion imposed by the sapphire substrate. At the particle-substrate interface of highly alloyed particles segregation of Au atoms as well as dislocations in stand-off position are found. These observations are in-line with a semi-coherent interface, where Au segregation is triggered by the reduction of the overall strain energy due to: (i) a lower shear modulus on the particle side of the interface, (ii) the shifting of misfit dislocations in stand-off position further away from the stiffer substrate and (iii) a reduction of intrinsic misfit dislocation strain energy on the tensile side. In addition, the mechanical properties of pure and alloyed particles were characterized by in situ compression experiments in the SEM. Typical force-displacement data of defect-free single-crystals were obtained, reaching the theoretical strength of Ni for particles smaller than 400 nm. Alloying changes the mechanical response from an intermittent and discrete plastic flow behavior into a homogeneous deformation regime at large compressive strain.
CRIS-Team Scopus Importer:2021-10-22
Keywords: Solid-state dewetting; Orientation relationship; Interface segregation; Scanning electron microscopy; Compression test

Reactor system for the study of high-temperature short-time sintering of nanoparticles - Peukert, Wolfgang; Kirchhof, Martin; Schmid, Hans-Joachim (Review of Scientific Instruments, 2004)
A high-temperature short residence time flow reactor system has been realized for the investigation of the gas phase sintering kinetics of nanoparticles separated from all other synthesis mechanisms, e.g.. chemical reaction, nucleation, coagulation and condensation. Major components are a hot-wall tubular reactor for the production of unsintered aggregates consisting of spherical primary particles in the size range 10-80 nm and a sintering reactor for the investigation of the sintering kinetics at well-defined temperature and residence time history. Therefore, rapid heating and quenching of the particles at the beginning and at the end of the reaction zone, respectively, is maintained. Main parameters in the sintering reactor are: temperatures up to 1873 K and residence times in the range 8-1000 ms. The reactor conditions are characterized by temperature profile measurements with a newly constructed suction thermocouple probe and by computational fluid dynamics simulations of the residence time distributions. Exemplary results of the sintering of silica nanoparticles obtained by transmission electron microscopy analysis are presented. © 2004 American Institute of Physics.
Keywords: high-temperature; sintering; kinetic; aggregates; nanoparticle; quenching; thermocouple

Real-Time Monitoring of the Nucleation and Growth of ZnO Nanoparticles Using an Optical Hyper-Rayleigh Scattering Method - Segets, Doris; Martinez Tomalino, Lars-Owe; Gradl, Johannes; Peukert, Wolfgang (Journal of Physical Chemistry C, 2009)
Incoherent nonlinear hyper-Rayleigh scattering (HRS) has been applied to monitor the different stages in the synthesis of sub-10 nm ZnO nanoparticles. During time-resolved investigation of the ripening process, we measured an increase in the particle hyperpolarizability, βZnO, with increasing particle size. Millisecond time resolution measurements revealed regions of prevalent nucleation, growth, and ripening. Using the size-dependent hyperpolarizabilities, a new general approach is introduced for the quantitative determination of nucleation, growth, and ripening rates via in situ HRS measurements. The derived solubility also allowed the determination of reasonable values of the ZnO surface energy.

Recycled Cobalt from Spent Li-ion Batteries as a Superhydrophobic Coating for Corrosion Protection of Plain Carbon Steel - Rafsanjani-Abbasi, Ali; Rahimi, Ehsan; Shalchian, Hossein; Vahdati-Khaki, Jalil; Babakhani, Abolfazl; Hosseinpour, Saman; Davoodi, Ali (Materials, 2018)
A new recycling and film formation scheme is developed for spent Li-ion batteries, which involves the combination of ascorbic-assisted sulfuric leaching and electrodeposition to fabricate a corrosion resistance superhydrophobic coating. The idea behind the simultaneous use of sulfuric and ascorbic is to benefit from the double effect of ascorbic acid, as a leaching reducing agent and as morphological modifier during electrodeposition. Quantum chemical calculations based on the density functional theory are performed to explain the cobalt-ascorbate complexation during the electrocristalization. The optimum parameters for the leaching step are directly utilized in the preparation of an electrolyte for the electrodeposition process, to fabricate a superhydrophobic film with a contact angle of >150° on plain carbon steel. The potentiodynamic polarization measurments in 3.5 wt % NaCl showed that boric-pulsed electrodeposited cobalt film has 20-times lower corrosion current density and higher corrosion potential than those on the non-coated substrate.
Keywords: Li-ion battery; recycling; superhydrophobic coating; electrodeposition

Relation of Nanostructure and Recombination Dynamics in a Low-Temperature Solution-Processed CuInS2 Nanocrystalline Solar Cell - Azimi, Seyed Hamed; Heumüller, Thomas; Gerl, Andreas; Matt, Gebhard; Kubis, Peter; Distaso, Monica; Ahmad, Rameez; Akdas, Tugce; Richter, Moses; Peukert, Wolfgang; Brabec, Christoph (Advanced Energy Materials, 2013)
The understanding and control of nanostructures with regard to transport and recombination mechanisms is of key importance in the optimization of the power conversion efficiency (PCE) of solar cells based on inorganic nanocrystals. Here, the transport properties of solution-processed solar cells are investigated using photo-CELIV (photogenerated charge carrier extraction by linearly increasing voltage) and transient photovoltage techniques; the solar cells are prepared by an in-situ formation of CuInS2 nanocrystals (CIS NCs) at the low temperature of 270 °C. Structural and morphological analyses reveal the presence of a metastable CuIn5S8 phase and a disordered morphology in the CuInS2 nanocrytalline films consisting of polycrystalline grains at the nanoscale range. Consistent with the disordered morphology of the CIS NC thin films, the CIS NC devices are characterized by a low carrier mobility. The carrier density dynamic indicates that the recombination kinetics in these devices follows the dispersive bimolecular recombination model and does not fully behave in a diffusion-controlled manner, as expected by Langevin-type recombination. The mobility–lifetime product of the charge carriers properly explains the performance of the thin (200 nm) CIS NC solar cell with a high fill-factor of 64% and a PCE of over 3.5\
Keywords: nanostructures; power; conversion; nanocrystal

Relationship between Rheological Properties of Concentrated Colloidal Suspensions and the Structure of Dip-drawn Coatings Zusammenhang zwischen rheologischen Eigenschaften konzentrierter kolloidaler Suspensionen und der Struktur tauchgezogener Schichten - Günther, Lydia; Peukert, Wolfgang (Chemie Ingenieur Technik, 2003)

Retention mechanisms of 1.7 nm ZnS quantum dots and sub-20 nm Au nanoparticles in ultrafiltration membranes - Lee, Handol; Segets, Doris; Süß, Sebastian; Peukert, Wolfgang; Chen, Sheng-Chieh; Pui, David Y. H. (Journal of Membrane Science, 2018)
Keywords: Ultrafiltration; Rejection; Membrane categorization; Colloids; Diffusion deposition

Reusable Localized Surface Plasmon Sensors Based on Ultrastable Nanostructures - Vogel, Nicolas; et al. (Small, 2010)
Nanoparticle arrays created by nanosphere lithography are widely used in sensing applications since their localized surface plasmon resonances are extremely sensitive to changes in the local dielectric environment. A major drawback for any biologically oriented sensing application of conventionally produced particle arrays is the lack of stability of the nanoparticles in aqueous media and buffer solutions. Here, a robust and reusable nanoscale sensing platform based on localized surface plasmon resonances of gold nanoparticles embedded in a silicon dioxide matrix is presented. The architecture exhibits extremely high stability in aqueous environments and can be regenerated several times by simple mechanical cleaning of the surface. The platforms surface is ultraflat by design, thus making it an ideal substrate for any bio-oriented sensing application.
Keywords: embedded nanoparticles; hybrid materials; localized surface plasmon resonance; nanosphere lithography; sensors

Review: Second harmonic generation spectroscopy as a method for in Situ and online characterization of particle surface properties - Peukert, Wolfgang; Schneider, Lars (Particle & Particle Systems Characterization, 2007)
Non-linear optical spectroscopy is a recently established technique used in the investigation of the properties of colloidal interfaces. Since it is an optical method it is non-invasive, can be applied in situ, and can provide real time resolution. Until recently, only a few papers concerning this method have been published, but these all show the great potential and the large field of applications of the technique. This paper gives an overview of the fundamentals of the technique and its possible applications. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA.
Keywords: Adsorption; Non-linear optical spectroscopy; Online-measurement; Particle surface characterization; Surface charge

Robust feedback control of continuously operated convective dryers for particulate materials - Seidel, C.; Neugebauer, C.; Durr, R.; Bück, Andreas (IDS'2018: 21ST INTERNATIONAL DRYING SYMPOSIUM, 2018)
Convective drying is a common process for the treatment of particulate solids also operated in continuous mode. Continuous operation is characterised by operation in steady-state with constant product throughput and constant product quality. Due to external influences, i. e. seasonal or local variations in the properties of the initial wet material, deviations in the product quality can result, for example over- or under-drying, or on-set of unwanted reaction. In this contribution a new feedback control concept is developed that is robust with respect to variations and uncertainties in the drying kinetics of the material and can reject and attenuate process disturbance
CRIS-Team WoS Importer:2019-08-16
Keywords: Process control; drying kinetics; robustness; fluidized bed; yeast

Robust feedback control of convective drying of particulate solids - Bück, Andreas; Seidel, Carsten; Duerr, Robert; Neugebauer, Christoph (Journal of Process Control, 2018)
This work considers robust control of continuous convective drying of particulate solids where the major process uncertainty lies in the kinetics of the second (falling-rate) drying period. Using the concept of normalised drying curve, for arbitrary shape of the curve, the steady state particle moisture content is derived. Applying appropriate uncertainty models, a robust feedback controller is designed to guarantee desired product moisture. Advantages of this approach are discussed in comparison to convential PI and LQ-optimal control. The approach is exemplified for the case of fluidised bed drying of baker's yeast particles. Results show very good performance with respect to parametric uncertainty and disturbance rejection even at non-nominal steady-state
Keywords: Convective drying; H∞ control; Process control; Robust control; LQR; Particles; Yeast

Robust multi-variable control of continuous yeast drying - Seidel, Carsten; Dürr, Robert; Bück, Andreas (Journal of Process Control, 2022)
This work considers robust moisture content and activity control in a continuous convective drying for particulate bio-materials. The major process uncertainty is in the kinetics of the second (falling-rate) drying period. Robust feedback controllers in the multi-variable and de-central case are designed to guarantee desired product specifications. The advantages of the robust controllers are discussed in comparison with a conventional PI controller. The case study presented is the drying of baker's yeast in a fluidized bed dryer. The results show constant performances concerning the uncertainty of the drying kinetics and disturbance rejection at different operating points.
CRIS-Team Scopus Importer:2022-05-13
Keywords: Convective drying; H; Multi-variable control; Particles; Process control; Robust control; Yeast

Robust Optimization in Nanoparticle Technology: A Proof of Principle by Quantum Dot Growth in a Residence Time Reactor - Dienstbier, Jana; Aigner, Kevin-Martin; Rolfes, Jan; Peukert, Wolfgang; Segets, Doris; Pflug, Lukas; Liers, Frauke (Computers & Chemical Engineering, 2021)
Knowledge-based determination of the best-possible experimental setups for nanoparticle design is highly challenging. Additionally, such processes are accompanied by noticeable uncertainties. Therefore, protection against these uncertainties is needed. Robust optimization helps determining such best possible processes. The latter guarantees quality requirements regardless of how the uncertainties, e.g. with regard to variations in raw materials, heat and mass transport characteristics, material properties and (growth) rates, manifest within predefined ranges. To approach this huge task, in this paper we exemplarily model a particle synthesis process with seeded growth by population balance equations and study different growth kinetics. We determine the mean residence time maximizing the product mass subject to a guaranteed yield. Additionally, we hedge against uncertain growth rates and derive an algorithmically tractable reformulation for the robustified problem. We evaluate our approach for seeded growth synthesis of zinc oxide quantum dots and demonstrate computationally that a guaranteed yield is met for all growth rates within previously defined regions. The protection against uncertainties only reduces the maximum amount of product that can be obtained by a negligible margin.<br
Keywords: particle design; robust optimization; process optimization; reformulation

Role of Citrate and NaBr at the Surface of Colloidal Gold Nanoparticles during Functionalization - Dinkel, Rebecca; Jakobi, Jurij; Ziefuß, Anna Rosa; Barcikowski, Stephan; Braunschweig, Björn; Peukert, Wolfgang (Journal of Physical Chemistry C, 2018)
A molecular understanding of the ligand shell and the functionalization process is essential for the development of surface-functionalized gold nanoparticles (AuNPs). Obviously, the initial ligand shell from the synthesis plays a crucial role in this process. Here, in situ second-harmonic scattering is applied to study the adsorption of a 3-mercapto-1-propanesulfonate (MPS) at the surface of laser-ablated NaBr- and citrate-stabilized AuNPs with sizes of 5 nm. This systematic comparison is possible due to the fact that laser ablation in micromolar saline water gives access to narrowly distributed colloidal AuNPs without organic stabilizers. The Gibbs free energy of adsorption was determined to be of similar order for both AuNP batches (ca. −40 kJ/mol). The surface concentration of MPS, however, differed strongly and was more than 30% higher for NaBr-stabilized AuNP than for citrate-stabilized AuNP. Compared to planar Au substrates, the surface concentration of MPS on NaBr-AuNP suggests formation of a complete monolayer of MPS and demonstrates the fast functionalization of ligand-free AuNP up to monolayer coverage. On citrate-AuNP, however, an MPS coverage of only two-thirds of a monolayer is observed, which indicates that citrate partially resists functionalization and is mostly exchanged at low-coordinated Au surface sites. High surface coverage, however, is often closely linked to functionality, for example, when avidity effects are exploited during conjugate–receptor interaction
Keywords: Thiols; Metal nanoparticles; Adsorption; Gold; Nanoparticles

Role of Flagella in Adhesion of Escherichia coli to Abiotic Surfaces - Friedlander, Ronn S.; Vogel, Nicolas; Aizenberg, Joanna (Langmuir, 2015)
Understanding the interfacial activity of bacteria is of critical importance due to the huge economic and public health implications associated with surface fouling and biofilm formation. The complexity of the process and difficulties of predicting microbial adhesion to novel materials demand study of the properties of specific bacterial surface features and their potential contribution to surface attachment. Here, we examine flagella, cell appendages primarily studied for their cell motility function, to elucidate their potential role in the surface adhesion of Escherichia coli-a model organism and potential pathogen. We use self-assembled monolayers (SAMs) of thiol-bearing molecules on gold films to generate surfaces of varying hydrophobicity, and measure adhesion of purified flagella using quartz crystal microbalance. We show that flagella adhere more extensively and bind more tightly to hydrophobic SAMs than to hydrophilic ones, and we propose a two-step vs a single-step adhesion mechanism that accounts for the observed dissipation and frequency changes for the two types of surfaces, respectively. Subsequently, study of the adhesion of wild-type and flagella knockout cells confirms that flagella improve adhesion to hydrophobic substrates, whereas cells lacking flagella do not show preferred affinity to hydrophobic substrates. Together, these properties bring about an interesting ability of cells with flagella to stabilize emulsions of aqueous culture and dodecane, not observed for cells lacking flagella. This work contributes to our overall understanding of nonspecific bacterial adhesion and confirms that flagella, beyond motility, may play an important role in surface adhesion.

Role of Prenucleation Building Units in Determining Metal-Organic Framework MIL-53(Al) Morphology - Embrechts, Heidemarie; Kriesten, Martin; Ermer, Matthias; Peukert, Wolfgang; Hartmann, Martin; Distaso, Monica (Crystal Growth and Design, 2020)
While it is well-known that the particle size of solvothermally synthesized metal-organic frameworks (MOFs) can be controlled by tuning the solvent composition, which affects the solubility of the linker and metal salt educts, the exact relationship between linker solubility, initial chemical coordination steps occurring in solution, and the resulting MOFs' particle size has not yet been investigated. Here, we have studied the solvothermal synthesis of MIL-53(Al) in DMF and water/DMF mixtures with in situ Raman spectroscopy, which reveals the formation of intermediate prenucleation building unit (PNBU) species that consist of one linker molecule and one metal atom and self-assemble in solution to form MIL-53(Al). The concentration of PNBUs in solution prior to particle precipitation is dependent on the synthesis solvent ratio used and influences the MIL-53 particle size. Synthesis in pure DMF results in a high concentration of PNBUs in solution prior to MOF supersaturation and precipitation. This results in a large burst of MOF nucleation and the formation of nanosized MIL-53(Al) particles. Adding water to the DMF solution leads to reduced PNBU accumulation in solution prior to MOF precipitation due to the reduced linker solubility. The reduced accumulation of PNBUs prior to particle precipitation causes reduced nucleation and favors particle growth. The MIL-53(Al) particle size, in contrast, is independent of the MOF phase growth rate, which is highly dependent on the synthesis temperature.
CRIS-Team WoS Importer:2020-06-26

Role of shear and extensional stress on the degradation of proteins during downstream processing - Simon, Sonja; Weber, Carsten; Peukert, Wolfgang (2010 AIChE Annual Meeting, 10AIChE, 2010)
In most applications of biotechnology and downstream processing proteins are stressed in various flow configurations by shear and extensional stress. In this work we present stress experiments of several proteins under well-defined flow conditions. In combination with insitu analytics flow-induced aggregation phenomena and conformational changes can be successfully monitored. In addition to shear and elongation, the contribution of adsorption phenomena to interfaces is investigate
Keywords: Prefil; Syringe; Protein Aggregate; Adsorption phenomena; Aggregation phenomena; Conformational change; Downstream-processing; Extensional stress; Flow condition; Flow configurations; In-situ; Adsorption; Proteins

Roughly Spherical: Tailored PMMA-SiO2 Composite Supraparticles with Optimized Powder Flowability for Additive Manufacturing - Canziani, Herbert; Bever, Frederik; Sommereyns, Alexander; Schmidt, Michael; Vogel, Nicolas (ACS Applied Materials and Interfaces, 2021)
Particulate materials with well-engineered properties are of key importance for many aspects in our daily life. Polymer powders with high flowability, for example, play a crucial role in the emerging field of powder-based additive manufacturing processes. However, the polymer- and composite material selection for these technologies is still limited. Here, we demonstrate the design of spherical polymethyl methacrylate (PMMA) and PMMA-SiO2 composite supraparticle powders with excellent powder flowability and tailored composition for powder-based additive manufacturing. Our process assembles these powders from the bottom up and affords a precise control over surface roughness and internal morphology via the choice of colloidal primary particles. We establish process-structure-property relationships connecting external spray-drying parameters and primary particle sizes with the resulting supraparticle roughness and, subsequently, with the macroscopic powder flowability and powder bed density. In a second step, we demonstrate the control of composition and internal morphology of PMMA-SiO2 composite supraparticles based on different mass mixings and diameter ratios of the two primary particle dispersions. Finally, we successfully apply the prepared supraparticle powders in powder bed additive manufacturing. The optimized flowability of the composite powders allows the production of two-layered square specimens with fusion between the individual layers and a uniform and tunable distribution of nanoscale SiO2 additives without requiring the addition of any flowing aids.
Keywords: PMMA; additive manufacturing; composite powder; nanoscale; spray drying; supraparticles

Rounding of irregular polymer particles in a downer reactor - Sachs, Marius; Schmidt, Jochen; Toni, Franziska; Blümel, Christina; Winzer, Bettina; Peukert, Wolfgang; Wirth, Karl-Ernst (Procedia Engineering 102, 2015)
In the past additive manufacturing processes relying on beam-based methods such as selective laser sintering (SLS) of polymers were almost exclusively applied for the generation of prototypes. In recent years, however, these methods are increasingly applied in the serial production of e.g. special parts to be used in the automotive industry. With this increased relevance in industrial applications, the demands on the powder material increased as well [1]. The so far used polymer materials show weak performance regarding the mechanical stability of processed parts. In consequence, there is a need for fine powders of different polymers showing good powder flowability and high bulk density. Currently, the commercial availability of polymer powders for SLS is very limited and the production processes are still not reliable enough due to poor powder characteristics. Within this contribution a process for the production of spherical polymer micro particles showing good powder flowability is presented [2]. It has been recently shown [3] for different materials that commercially available polymer granules can be ground down to the micron size range by a wet grinding process. Due to the grinding process the produced micron-sized particles are in a chiseled state, which leads to a bad flowability of the powder material. To overcome this problem the single particles are melted in a heated downer reactor and spherical particles are obtained by using the effect of the surface tension [3]. The rounding of ground PS microparticles was performed in a downer reactor with a length of 1,600 mm and a diameter of 25 mm. The reactor temperature was set 100 °C above the melting temperature of the treated material. The laminar flow regime in the downer reactor allows a well-defined residence time of particles and the surrounding gas [4]. The design of the downer reactor allows transferring the polymer particles in the molten state whilst avoiding contact between the single particles and between molten particles and the reactor wall. The mechanism of the rounding process in dependence of particle size, interfacial tension and melt viscosity will be shown within a sintering model [6]. The influence of residence time and overall solids density in the downer reactor on the particle shape and on the flowability of the bulk material is shown. Estimates from the sintering model allow for a reliable reactor design.<br
Keywords: additive manufacturing; particle rounding; downer reactor; polymers

Scalable classification of nanoparticles: A proof of principle for process design - Menter, Christina; Segets, Doris (Advanced Powder Technology, 2019)
Nanoparticles like quantum confined ZnS semiconductor nanocrystals, exhibit unique structure-property relationships. Narrow particle size distributions (PSDs) become one of the most important factors to tailor product performance. Size selective precipitation has already been proven to be an effective post processing strategy for ZnS nanoparticles. It is based on the titration of a poor liquid into a stable dispersion, which leads to the preferred flocculation of larger particles. Afterwards, these flocks must be separated from the continuous phase. While on lab scale the formed flocks can be easily separated by centrifugation from the fine fraction, for larger scale production using continuous processes, new concepts are urgently needed. Herein we developed a filtration process for flock removal that allows the handling of larger quantities. For process design, we first investigated the flock properties in order to know how stable the generated flocks are and how the flock properties can be controlled. Then, we replaced the classical flock separation by centrifugation through separation by surface filtration under the constraint that the underlying separation efficiency was not affected. By the future use of properly controlled, alternating filtration modules, our work opens the door for establishing an urgently needed, scalable post-processing for sub-10 nm nanoparticles.
CRIS-Team Scopus Importer:2019-09-24
Keywords: Flock analysis; Nanoparticle technology; Pressure filtration; Separation; Size selective agglomeration

Scalable production of glass flakes via compression in the liquid phase - Esper, Julian Duane; Liu, Lingfeng; Willnauer, Johannes; Strobel, Alexander; Schwenger, Jan; Romeis, Stefan; Peukert, Wolfgang (Advanced Powder Technology, 2020)
A comprehensive study on controlled shape formation with high yield of three commercially relevant SiO2-based amorphous glasses in a stirred media mill is presented. Stressing under well-controlled conditions leads to micron-sized amorphous glass flakes with high aspect ratios. This unique result is quite contrary to the fundamental observation that comminution processes generally result in irregular shaped particles. The influences of glass composition, processing time, stirrer tip speed and grinding media size on the obtained products have been investigated. The size and shape of the obtained glass flakes have been characterized by scanning electron microscopy and atomic force microscopy. The glass flakes exhibit thicknesses as low as 155 nm while the lateral dimensions are well within the micrometer range. Our study shows that particle size reduction occurs within the first hour of grinding. Afterwards plastic deformation of the fragments, which can be accompanied by densification of the glass network, leads to the formation and further thinning of the glass flakes. To demonstrate the quality and applicability of the glass flakes interference pigments were realized by a TiO2 coating via an aqueous titration process. The presented approach offers a simple, convenient and fully scalable top-down method to produce flake-like particles from various silica glasses. The obtained flakes are suitable substrates for further modifications and applications and the process can be transferred to other materials and glasses with tailor-made chemical composition
Keywords: Stirred media mill; Comminution; Liquid phase compression; Particle processing; Glass flakes; Pigments

Scalable production of graphene sheets by mechanical delamination - Knieke, Catharina; Berger, Angela; Voigt, Michael; Klupp Taylor, Robin; Röhrl, Jonas; Peukert, Wolfgang (Carbon, 2010)
Mono- and multilayer graphene sheets have been successfully produced from commercial graphite powder in a wet grinding process under mild milling conditions. The shear forces in the milling chamber lead to a continuous delamination of ultrathin graphene flakes which are dispersed in a liquid medium. To avoid agglomeration of the exfoliated flakes the anionic surfactant sodium dodecyl sulfate was used. By adjusting the process parameters in a way to overcome the weak interlayer forces between the sheets without breaking them leads to the fabrication of thin flakes with high aspect ratios. The presented scalable process allows a high-yield and low-cost production of free-standing graphene sheets for various application
Keywords: monolayer; graphene; graphite; wet; grinding; interlayer; forces; flake; scaleable; sheet

Scale-Bridging 3D-Analysis of Colloidal Clusters Using 360° Electron Tomography and X-Ray Nano-CT - Englisch, Silvan; Wirth, Janis; Przybilla, Thomas; Apeleo Zubiri, Benjamin; Wang, Junwei; Vogel, Nicolas; Spiecker, Erdmann (Cambridge University Press, 2019)

Scale-Bridging 3D-Analysis of Colloidal Clusters Using 360° Electron Tomography and X-Ray Nano-CT - Englisch, Silvan; Wirth, Janis; Przybilla, Thomas; Apeleo Zubiri, Benjamin; Wang, Junwei; Vogel, Nicolas; Spiecker, Erdmann (Microscopy and Microanalysis, 2019)

Second Harmonic Generation from metallic and dielectric spherical nanoparticles - Peukert, Wolfgang; Wunderlich, Sarina; Zhuromskyy, Oleksandr; Schürer, Benedikt; Haderlein, Michael; Sauerbeck, Christian; Peschel, Ulf (2012 Conference on Lasers and Electro-Optics (CLEO), 2012)
Due to symmetry-breaking at an interface, Second Harmonic Generation (SHG) is an extremely surface sensitive process. Therefore it is a widely used tool to study surfaces. Applied to colloidal nanoparticles it offers efficient means to monitor growth and molecular adsorption processes in real time and in situ. This makes SHG a preferred method to study the formation of core-shell plasmonic nanoparticles, which recently became quite popular because of their strong and tunable plasmonic resonances.
Keywords: Symmetry; spherical; nanoparticle; second; harmonic; generation; plasmon; Optical; surface; wave; Harmonic analysis; Plasmons; Frequency conversion; Dielectrics

Second Harmonic Light Scattering from Spherical Polyelectrolyte Brushes - Peukert, Wolfgang; Schürer, Benedikt; Hoffmann, Martin; Wunderlich, Sarina; Peschel, Ulf; Harnau, Ludger; Ballauf, Matthias (Journal of Physical Chemistry C, 2011)
Optical second harmonic generation (SHG) was applied to study the shell layer of spherical polyelectrolyte brushes (SPB) as a function of ionic strength. The particles consist of a polystyrene core from which linear chains of a quenched polyelectrolyte are grafted. Compared to all systems studied by SHG previously, the shell layer in this study has a remarkable thickness of ca. 100 nm. Angle-resolved second harmonic (SH) scattering profiles were recorded and compared to simulations with different model geometries using a nonlinear Mie scattering model. The analysis reveals that the second harmonic signal is not generated by the polyelectrolyte molecules, but rather by oriented and polarized water molecules at the inner (polystyrene / polyelectrolyte) and at the outer (polyelectrolyte / solvent) interface of the polyelectrolyte shell. The results demonstrate that angle-resolved SH light scattering provides direct access to the structure of water and the screening of charges at the inner and outer interface of the polyelectrolyte shell. Correspondingly, this work sets the experimental and theoretical basis for the study of the extended interfacial layer of electrosterically stabilized particles by SH light scattering.
Keywords: optical; second; harmonic; generation; particle; polyelectrolyte

Selection function in breakage processes: PBM and Monte Carlo modeling - Das, Ashok; Bück, Andreas; Kumar, Jitendra (Advanced Powder Technology, 2020)
Breakage, i.e., formation of smaller fragments from larger initial particles, is an important phenomenon – wanted or unwanted – in many particulate processes. In this work, the volume and time dependent selection function for pure breakage process is modeled based on the population balance modeling approach. It is found that the selection function is directly correlated with the stressing frequency, probability of successful events, and some integral properties of the number density function. A discrete population balance equation is applied to compute the total number of particles and particle size distribution numerically. Moreover, an event-driven constant number Monte Carlo simulation algorithm is presented, and the simulation results are used as an alternative to experimental results. The volume dependency of the selection function is incorporated successfully in the Monte Carlo simulation while selecting particles for stressing event. Some important properties of any particulate process, such as the total number of particles and the size distribution of particles are validated successfully using the Monte Carlo results. This offers new insights into the estimation and interpretation of breakage kinetics.
CRIS-Team Scopus Importer:2020-02-14
Keywords: Breakage; Monte Carlo simulation; Population balance equation; Selection function; Stressing frequency

Selective and caspase-independent cytotoxicity of bioactive glasses towards giant cell tumor of bone derived neoplastic stromal cells but not to bone marrow derived stromal cells. - Westhauser, Fabian; Arango Ospina, Marcela; Losch, Sarina; Wilkesmann, Sebastian; Lehner, Burkhard; Ali, Muhammad Saad; Peukert, Wolfgang; Boccaccini, Aldo R.; Fellenberg, Jörg (Biomaterials, 2021)
Semi-malignant giant cell tumors of bone (GCTB) are associated with large osteolytic defects and significant bone destructions. Surgical resection remains the standard therapy that is, however, associated with very high recurrence rates. Bioactive glasses (BGs) that are osteogenic but under certain conditions also cytotoxic might be suitable to achieve biological reconstruction with simultaneous reduction of tumor recurrence in GCTB. In this study, a concentration and time dependent cytotoxic effect of five different BG compositions towards neoplastic GCTB cells was identified while bone marrow derived mesenchymal stromal cells were mostly unaffected. Time course and extent of the cytotoxic effect were dependent on the BG composition and were not associated with caspases activation, indicating that apoptotic mechanisms are not involved. Rather, detection of BG-induced disruption of the cell membranes and a rapid drop of intracellular HMG1 (High Mobility Group Box 1 protein) levels suggest a necrotic cell death. Notably, the cytotoxic effects were dependent on a direct contact of cells and BGs and could not be observed using indirect cultivation settings. Our data suggest that BGs might represent promising materials for the treatment of GCTB in order to reduce tumor recurrence with simultaneous enhancement of bone regeneration.
Keywords: Apoptosis; Bioactive glass; Caspases; Cytotoxicity; Giant cell tumor of bone; Mesenchymal stromal cells; Necrosis

Selektives Laserstrahlschmelzen von Kunststoffen: Lokale Bauteileigenschaften in Abhängigkeit unterschiedlicher Alterungszustände des Ausgangspulvers - Jaksch, Andreas; Hesse, Nicolas; Drummer, Dietmar; Schmidt, Jochen (6. Industriekolloquium des SFB 814,, 2018)

Selektives Laserstrahlschmelzen von Polyamid 12 - Einfluss von Fließhilfsmitteln auf Verarbeitbarkeit und Bauteileigenschaften - Jaksch, Andreas; Hesse, Nicolas; Schmidt, Jochen; Drummer, Dietmar (Proceedings of the 17th Rapid.Tech Conference, 2021)

Self-alignment of zinc oxide nanorods into a 3D-smectic phase - Schäfer, Stefan; Srikantharajah, Rubitha; Klaumünzer, Martin; Lobaz, Volodymyr; Voigt, Michael; Peukert, Wolfgang (Thin Solid Films, 2014)
We focus on thin films from ZnO nanorod dispersions in order to generate a high lateral order and a dense space filling structure applicable e. g. in printed optoelectronic devices. Highly stable dispersions with a solid content of up to 60 wt.% in ethanol were prepared using trioxadecanoic acid as stabilizer. With the dispersions we prepared thin films on substrates with a 3D-smectic phase in lateral dimension of cm2 and thicknesses from below 100 nm up to 1 μm. We show how the concentration of the initial solid content is influencing the formation of domains in our films and discuss the self-assembly process into ordered structures.

Self-Assembled Au Nanoparticle Monolayers on Silicon in Two- and Three-Dimensions for Surface-Enhanced Raman Scattering Sensing - Bartschmid, Theresa; Farhadi, Amin; Musso, Maurizio E.; Görlitzer, Eric; Vogel, Nicolas; Bourret, Gilles R. (ACS Applied Nano Materials, 2022)
Gold nanoparticle/silicon composites are canonical substrates for sensing applications because of their geometry-dependent physicochemical properties and high sensing activity via surface-enhanced Raman spectroscopy (SERS). The self-assembly of gold nanoparticles (AuNPs) synthesized via wet-chemistry on functionalized flat silicon (Si) and vertically aligned Si nanowire (VA-SiNW) arrays is a simple and cost-effective approach to prepare such substrates. Herein, we report on the critical parameters that influence nanoparticle coverage, aggregation, and assembly sites in two- and three-dimensions to prepare substrates with homogeneous optical properties and SERS activity. We show that the degree of AuNP aggregation on flat Si depends on the silane used for the Si functionalization, while the AuNP coverage can be adjusted by the incubation time in the AuNP solution, both of which directly affect the substrate properties. In particular, we report the reproducible synthesis of nearly touching AuNP chain monolayers where the AuNPs are separated by nanoscale gaps, likely to be formed due to the capillary forces generated during the drying process. Such substrates, when used for SERS sensing, produce a uniform and large enhancement of the Raman signal due to the high density of hot spots that they provide. We also report the controlled self-assembly of AuNPs on VA-SiNW arrays, which can provide even higher Raman signal enhancement. The directed assembly of the AuNPs in specific regions of the SiNWs with a control over NP density and monolayer morphology (i.e., isolated vs nearly touching NPs) is demonstrated, together with its influence on the resulting SERS activity.
CRIS-Team Scopus Importer:2022-09-09
Keywords: Au nanoparticles; metal-assisted chemical etching; plasmonics; self-assembly; SERS; silicon nanowires

Self-Assembled Laser-Activated Plasmonic Substrates for High-Throughput, High-Efficiency Intracellular Delivery - Madrid, Marinna; Saklayen, Nabiha; Huber, Marinus; Vogel, Nicolas; Mazur, Eric (SPRINGER, 101 PHILIP DRIVE, NORWELL, MA 02061 USA, 2017)

Self-assembled monolayers as corrosion inhibitors; indoor, marine and biologically relevant exposure - Hosseinpour, Saman; Leygraf, Christofer; Gretic, Zana Hajdari; Mioc, Ekatarina Kristan; Curkovic, Helena Otmacic; Bochmann, Sebastian; Bachmann, Julien; Waegner, Victoria; Virtanen, Sannakaisa; Peukert, Wolfgang (Joint European Corrosion Congress 2017, EUROCORR 2017 and 20th International Corrosion Congress and Process Safety Congress 2017, 2017)

Self-assembled monolayers as inhibitors for the atmospheric corrosion of copper induced by formic acid: A comparison between hexanethiol and hexaneselenol - Hosseinpour, Saman; et al. (Journal of The Electrochemical Society, 2014)

Self-Assembled Monolayers Get Their Final Finish via a Quasi-Langmuir-Blodgett Transfer - Meltzer, Christian; Dietrich, Hanno; Zahn, Dirk; Peukert, Wolfgang; Braunschweig, Björn (Langmuir, 2015)
The growth of self-assembled monolayers (SAMs) of octadecylphosphonic acid (ODPA) molecules on α-Al2O3(0001) and subsequent dewetting of the SAMs were studied with a combination of in situ sum-frequency generation (SFG) and molecular dynamics (MD) simulations. Although SAM growth after deposition times >8 h reduces to nearly negligible values, the resultant ODPA SAMs in solution are still not in a well-ordered state with the alkyl chains in all-trans configurations. In fact, in situ SFG spectroscopy revealed a comparatively high concentration of gauche defects of the SAM in the ODPA 2-propanol solution even after a growth time of 16 h. Here, results of the MD simulations strongly suggest that defects can be caused by ODPA molecules which are not attached to the substrate but are incorporated into the SAM layer with the polar headgroup oriented into the 2-propanol solvent. This inverted adsorption geometry of additional ODPA molecules blocks adsorption sites and thus stabilizes the SAM without improving ordering to an extent that all molecules are in the all-trans configuration. While persistent in solution, the observed defects can be healed out when the SAMs are transferred from the solvent to a gas phase. During this process, a quasi-Langmuir-Blodgett transfer of molecules takes place which drives the SAM into a higher conformational state and significantly improves its quality.

Self-tuning control of continuous fluidized bed drying of baker's yeast pellets - Duerr, Robert; Seidel, Carsten; Neugebauer, Christoph; Bück, Andreas (Drying Technology, 2019)
Uncertainty in the kinetics of the second drying period represents the major challenge in continuous drying of particulate solids which can be overcome by adaptive feedback control. In this contribution, self-tuning control comprising online-state estimation and adaptive PI-control is considered to guarantee desired product moisture. Advantages of the approach over conventional PI-control are discussed. The performance is shown for fluidized bed drying of baker's yeast. It is shown that the self-tuning approach is superior to nonadaptive approaches in case of parametric uncertainty even at non-nominal steady-states.
CRIS-Team WoS Importer:2019-10-08
Keywords: adaptive control; Yeast; fluidized bed drying; self-tuning control

Semi‐Crystalline Polyetherimide Microparticles via Liquid‐Liquid Phase Separation and Precipitation - Unger, Laura; Dechet, Maximilian; Fischer, Sybille; Schmidt, Jochen; Bück, Andreas (Macromolecular Materials and Engineering, 2022)
A novel approach for production of polyetherimide (PEI) microparticles by liquid–liquid phase separation (LLPS) and precipitation is demonstrated and the effect of the used solvents acetophenone and dimethyl phthalate on the obtained powders is outlined. Interestingly, the method allows one to produce semi-crystalline particles, while PEI is known to be hard to crystallize and typically obtained in amorphous form. To get a deeper understanding of the phase behavior of the polymer-solvent systems, cloud point curves in dependence on system composition are determined. The obtained particles are thoroughly characterized. They are highly semi-crystalline, as proven by DSC and X-ray diffraction and are an ideal novel feedstock for powder bed fusion of polymers with laser beam (PBF-LB/P). Polymorphism and, thus, thermal characteristics like the melting point, can be tuned by the used solvent. After heating the precipitated powder samples above their melting temperature and subsequent cooling fully amorphous polymer is obtained, which is assessed to be advantageous with respect to mechanical properties (toughness) of the PBF-LB/P-produced component from this novel feedstock.
CRIS-Team WoS Importer:2022-01-21

Separation of nanoparticles: Filtration and scavenging from waste incineration plants - Förster, Henning; Thajudeen, Thaseem; Funk, Christine; Peukert, Wolfgang (Waste Management, 2016)
Increased amounts of nanoparticles are applied in products of everyday life and despite material recycling efforts, at the end of their life cycle they are fed into waste incineration plants. This raises the question on the fate of nanoparticles during incineration. In terms of environmental impact the key question is how well airborne nanoparticles are removed by separation processes on their way to the bag house filters and by the existing filtration process based on pulse-jet cleanable fibrous filter media. Therefore, we investigate the scavenging and the filtration of metal nanoparticles under typical conditions in waste incineration plants. The scavenging process is investigated by a population balance model while the nanoparticle filtration experiments are realized in a filter test rig. The results show that depending on the particle sizes, in some cases nearly 80% of the nanoparticles are scavenged by fly ash particles before they reach the bag house filter. For the filtration step dust cakes with a pressure drop of 500 Pa or higher are found to be very effective in preventing nanoparticles from penetrating through the filter. Thus, regeneration of the filter must be undertaken with care in order to guarantee highly efficient collection of particles even in the lower nanometre size regime.
Keywords: Filtration efficiency; Nanoparticle scavenging; Population balance modelling; Ultrafine particle emission; Waste incineration

Separation of the influences of material and machine in impact comminuton – Modelling with with population balances - Peukert, Wolfgang; Vogel, Lutz (Developments in Mineral Processing, 2002)
UnivIS-Import:2015-03-09:Pub.2002.tech.ITC.mechve.separa
Keywords: separation; modeling; simulation

Settling of Fractal Aggregates in Viscous Media - Binder, Christian (Friedrich-Alexander-Universität Erlangen-Nürnberg, 2012)
Particles dispersed in liquids are of interest in a broad range of industrial applications: as pigments, fillers, thickeners, emulsions, etc. In these applications, problems occur mostly in handling suspensions which contain irregular aggregates. This is due to an unknown behavior during their transport. Especially if the aggregated structures are highly complex, common models fail to describe the hydrodynamic behavior. In this thesis, the hydrodynamic behavior of particles and aggregates in viscous suspensions was examined numerically, allowing for the determination of the orientation and drag force on fractal aggregates. Hereby, the numerical method of Accelerated Stokesian Dynamics (ASD) accounting for hydrodynamics was extended to include the free movement of aggregates. These aggregates were built of monosized spheres acting together as a rigid body (eASD). The developed method was validated by comparison with literature data for simple doublets, with experiments for regular aggregates and with the Lattice Boltzmann method for fractal aggregates. Furthermore, it was applied to investigate the hydrodynamic behavior of fractal aggregates in terms of aggregate settling. The fractal aggregates were generated by a Monte Carlo method using diffusion limited cluster-cluster aggregation. Static simulations were performed in order to determine drag forces on particle assemblies in suspended state. It was shown that, especially for viscous media, the drag force is dominated by the individual structure of the aggregates which can be described by geometric parameters. Dynamic simulations were performed for the investigation of the hydrodynamic behavior of such freely moving aggregates. Based on these simulations, a fast orientation prediction algorithm was developed. Using the predicted aggregate orientation, a simple correlation for the drag force dependency on the aggregate structure and orientation was found. The behavior due to the hydrodynamic interaction between two settling aggregates formed of three linearly arranged particles was described in dependence of the angle of inclination, the relative positions and the corresponding settling velocities. The limit was determined, where the faster settling aggregate starts to change its settling path in dependence on the initial offset of the aggregates center of mass projected into settling direction. It was demonstrated that the collision efficiency is much smaller for aggregates in motion than the collision efficiency calculated with one aggregate being held fixed. Finally, the possible collision of these anisotropic aggregates during settling was investigated. As a result, a collision map was given for the case of two settling aggregates formed each of three aligned particle

Shape-anisotropic cobalt-germanium-borate glass flakes as novel Li-ion battery anodes - Esper, Julian Duane; Zhuo, Ying; Barr, Maissa; Yokosawa, Tadahiro; Spiecker, Erdmann; de Ligny, Dominique; Bachmann, Julien; Peukert, Wolfgang; Romeis, Stefan (Powder Technology, 2020)
Novel CoO-Li2O-B2O3 and CoO-GeO2-Li2O-B2O3 flake-like glass particles for battery applications are produced by an innovative technique: Glasses from melt quenching are processed into micron-sized glass flakes in a stirred media mill. Processing under well-controlled conditions yields flake-like particles with high aspect ratios which are suitable for anodes in Lithium-ion batteries. Electrochemical characterization by cyclic voltammetry, electrochemical impedance spectroscopy, galvanostatic charge/discharge cycles and rate capability measurements indicates that the flakes show superior electrochemical properties compared to the bulk glass counterparts with a stable specific capacity of 620 mAh g−1 after 100 cycles. The majority of charge is stored by Li+ ion diffusion inside the material and impedance spectroscopy shows enhanced lithium ion diffusion capabilities of the flakes. The proposed fabrication process is performed under ambient conditions and is simple, cost-efficient, fully scalable and can be easily transferred to other glass compositions with electrochemically active metal oxide
Keywords: Anode; Particle design; Glasses; Shape-anisotropy; Lithium-ion battery

Shape Transformation Mechanism of Silver Nanorods in Aqueous Solution - Damm, Cornelia; Segets, Doris; Yang, Guang; Vieweg, Benito; Spiecker, Erdmann; Peukert, Wolfgang (Small, 2011)
The spontaneous shape transformation of silver nanorods with an initial length of several hundred nanometers towards spherical particle shapes in aqueous solution is investigated by means of scanning electron microscopy, UV–vis absorption spectroscopy, anodic stripping voltammetry, and high-resolution transmission electron microscopy (HRTEM). The consolidation of the results reveals an increase in the particle number density with time. Moreover, HRTEM image analysis along the cross section of the rods evidences the presence of fivefold twinning defects which extend along the whole rod length. According to the analytical model of Monk et al. this kind of rod structure is only thermodynamically stable if the rod length is below a critical value at a given diameter. The rods investigated in the present work do not fulfill the stability criterion as they exceed the critical length. Thus, the rods decay into smaller “nanobuns” and defective as well as defect-free spheres. A mechanism based on findings from the literature, HRTEM image analysis of former rods, transition states, and the final particle structures is proposed. The defects along the surface are seen as starting points for the dissolution of material, which is reintegrated into the solid phase by homogeneous as well as heterogeneous nucleation and growth.

Shedding light on the effective fluorophore structure of high fluorescence quantum yield carbon nanodots - Wang, Wenshuo; Wang, Bingzhe; Embrechts, Heidemarie; Damm, Cornelia; Cadranel, Alejandro; Strauß, Volker; Distaso, Monica; Hinterberger, Vanessa; Guldi, Dirk Michael; Peukert, Wolfgang (RSC Advances, 2017)
Carbon nanodots (CD) have great potential for imaging and sensing applications, due to their unique luminescence properties in combination with their low toxicity. Although CDs are currently the subject of intensive research activity, the exact structure of their effective fluorophore species has to be clarified because it can depend on the starting materials and reaction conditions. Most importantly, the limited photostability of some CDs presents an impediment to the much-needed breakthroughs required in the field. In this work, the photobleaching of CDs synthesized hydrothermally from citric acid and urea undervarious conditions is studied in detail. By visualizing changes in the absorption and fluorescence properties of CDs over time upon exposure to UV-light by means of in situ spectroscopic probes, we demonstrate a trade-off between high initial quantum yield and photostability. We found that the CDs consist of low-molecular weight fluorophores bound to extgreekp-conjugated domains (carbon core). In the case of CDs synthesized at higher reaction temperatures and/or for longer reaction times, lower initial quantum yields and higher photostability originate from partial conversion of the low-molecular weight fluorophores to extgreekp-conjugated domains during synthesis. Thus, the remaining surface bound fluorophores are bound to larger extgreekp-conjugated domains, which, in turn, enable dissipation of absorbed UV-energy and protection against photochemical damage. Reference experiments were performed with citrazinic acid – a pyridone-based structure – using ultrafast time-resolved spectroscopy, steady-state spectroscopy, and theoretical DFT simulations. We conclude that pyridone-like structures are most likely responsible for both the high quantum yields and the photobleaching of CDs.

Shedding light on the growth of gold nanoshells - Sauerbeck, Christian; Haderlein, Michael; Schürer, Benedikt; Braunschweig, Björn; Peukert, Wolfgang; Klupp Taylor, Robin (ACS nano, 2014)
Nanostructured particles containing noble metals can have highly tunable localized surface plasmon resonances and are therefore of particular interest for numerous applications. Nanoshells comprising a dielectric core and gold or silver shell are a widely researched systems because of the strong dependence of their optical properties on the ratio of core diameter to shell thickness. Although seeded-growth procedures have been developed to produce these particles, the many reported studies show significant variation in the nanoshell morphologies and hence optical properties. In order to establish processes that reproducibly synthesize nanoshells with high optical quality, it is necessary to develop techniques that monitor changes at the core particle surface during shell growth. For that purpose, we have carried out in situ nonlinear second-harmonic scattering (SHS) and linear vis-NIR extinction spectroscopy simultaneously during the seeded growth of gold nanoshells on silica core particles. Our SHS measurements show a striking variation in the nonlinear optical properties of the growing gold nanoshells. In comparison with linear optical measurements and with scanning electron microscopy (SEM) images made of gold nanoshells produced with varying shell completenesses, the SHS signal was observed to reach a peak intensity at a stage prior to shell closure. We attribute this high sensitivity of the SHS signal to the incomplete nanoshell surface morphology to the generation and subsequent degeneration of regions of electric field enhancement at gaps between isolated gold islands, which grow and coalesce. This conclusion is corroborated by finite-difference time-domain simulations of incomplete nanoshells. We suggest that the in situ analytical approach demonstrated here offers significant promise for future activities regarding the in-process optimization of the morphology and optical properties of metal nanoshells and other nanostructured plasmonic particles. © 2014 American Chemical Society.
Keywords: electric field enhancement; in situ vis-NIR spectroscopy; nanostructured particles; plasmonic particles; second-harmonic generation

Silica-titania hybrids for structurally robust inverse opals with controllable refractive index - Phillips, Katherine R.; Shirman, Tanya; Aizenberg, Michael; England, Grant T.; Vogel, Nicolas; Aizenberg, Joanna (Journal of Materials Chemistry C, 2020)
Templated from sacrificial colloidal assemblies, inverse opals are comprised of an interconnected periodic network of pores, forming a photonic crystal. They are used in a variety of applications, most of which, especially those in optics and photocatalysis, require a high degree of control over the long-range order, composition and refractive index. It has been shown that hybrid materials combining different components can yield materials with properties that are superior to the individual components. Here, we describe the assembly of hybrid titania/silica inverse opals using sol-gel chemistry, resulting in a mixed oxide with well-dispersed titanium and silicon. Titania has a high refractive index (2.4-2.9), but cracks typically form in the inverse opal structure; conversely, silica can produce highly ordered crack-free inverse opals, but it has a lower refractive index (similar to 1.4). By adjusting the ratio of titania and silica, the refractive index can be tailored while minimizing the crack density and maintaining structural order, allowing for control over the optical properties of this hybrid nanoporous material.
CRIS-Team WoS Importer:2020-01-31

Silver-assisted colloidal synthesis of gold patchy particles with tunable patchiness - Bao, Huixin; Butz, Benjamin; Zhou, Zhou; Spiecker, Erdmann; Hartmann, Martin; Klupp Taylor, Robin (Langmuir, 2012)
Patchy particles possessing heterogeneous surface composition show great promise as self-organizing building blocks for new classes of hierarchical functional structures. A major hurdle is the scalable synthesis of stable patches on nanosized core particles with arbitrarily defined patch number and coverage. So far, few methods have been reported which could be expected to meet these challenges. Recently we described the heterogeneous nucleation and growth of silver patches on silica nanospheres via a template free colloidal route. The patches produced, although tunable in size and number and showing interesting plasmon resonant properties, were rather unstable and degraded rapidly during attempts to process them further. In the present work, therefore, we set out to explore if related approaches can be employed to produce patchy particles involving gold, which is known to be more stable. The differences between typical patch precursors Ag+ and [AuClx (OH)4-x]- and their respective interactions with amorphous silica make this a significant challenge. We show that preformed small silver patches in addition to the presence of a reducing agent are necessary for the formation of gold patches conformal to the silica nanosphere surface. Systematic study of the process parameters and their influence on the patchiness as well as in-depth analytical TEM investigation of the patch composition reveal that patches spread over the silica surface via a cycle of galvanic dissolution and redeposition of silver. The resulting gold patchy particles remain stable during subsequent storage or washing and display tunable plasmon resonances within the visible and near-IR spectrum.
EAM Import::2019-03-13

Silver-Assisted Colloidal Synthesis of Stable, Plasmon Resonant Gold Patches on Silica Nanospheres - Bao, Huixin; Butz, Benjamin; Zhou, Zhou; Spiecker, Erdmann; Hartmann, Martin; Klupp Taylor, Robin (Langmuir, 2012)
Patchy particles possessing heterogeneous surface composition show great promise as self-organizing building blocks for new classes of hierarchical functional structures. A major hurdle is the scalable synthesis of stable patches on nanosized core particles with arbitrarily defined patch number and coverage. So far, few methods have been reported which could be expected to meet these challenges. Recently, we described the heterogeneous nucleation and growth of silver patches on silica nanospheres via a template free colloidal route. The patches produced, although tunable in size and number and showing interesting plasmon resonant properties, were rather unstable and degraded rapidly during attempts to process them further. In the present work, therefore, we set out to explore if related approaches can be employed to produce patchy particles involving gold, which is known to be more stable. The differences between typical patch precursors Ag+ and [AuClx(OH)(4-x)](-) and their respective interactions with amorphous silica make this a significant challenge. We show that preformed small silver patches in addition to the presence of a reducing agent are necessary for the formation of gold patches conformal to the silica nanosphere surface. Systematic study of the process parameters and their influence on the patchy particle morphology as well as in-depth analytical transmission electron microscopy investigation of the patch composition reveal that patches spread over the silica surface via a cycle of galvanic dissolution and redeposition of silver. The resulting gold patchy particles remain stable during subsequent storage or washing and display tunable plasmon resonances within the visible and near-IR spectrum.
Keywords: colloid; plasmon; resonant; nanospheres; silica; self; organizing; heterogeneous; nucleation

Simple and Reliable Method for Studying the Adsorption Behavior of Aquivion lonomers on Carbon Black Surfaces - Damm, Cornelia; Thoma, Martin; Hoffmann, Eva-Maria; Sattes, Maria-Melanie; Segets, Doris; Peukert, Wolfgang; Lin, Wei (Langmuir, 2018)
A better understanding of the interactions of carbon black and perfluorinated sulfonic acid (PFSA) ionomer helps to improve the effectiveness of polymer electrolyte membrane fuel cells. We present a simple and fast method for quantitative PFSA ionomer analysis based on suspension density measurements. After validation of the reliability of our method by thermogravimetric analysis and isothermal titration calorimetry (ITC), we investigate the adsorption equilibrium of short-side-chain PFSA ionomers of different equivalent weights (EW) and polarities on carbon black. The measured adsorption isotherms exhibit a plateau in the ionomer surface concentration for ionomer equilibrium concentrations <= 2 g/L. In this concentration range, the adsorption isotherms are described by the Langmuir model, whereby the surface concentrations in the plateau region are between 0.041 and 0.070 g/g. The plateau value of the ionomer surface concentration increases with EW and therefore with decreasing number of side chains with terminal sulfonic acid group per ionomer molecule, while the amount of adsorbed sulfonic acid groups remains constant for all investigated ionomers, resulting in similar zeta-potentials and sedimentation stability of the suspensions. The free energies of adsorption Delta G calculated from the association constants of the adsorption isotherms agree well with Delta G values obtained by isothermal titration calorimetry (ITC) and thus validate the adsorption isotherm measurement method. From the values of adsorption enthalpy Delta H ((-7.3 +/- 0.8) kJ/mol) and entropy Delta S (ca. 100 J/(mol K)), which were extracted from ITC, we conclude that the ionomer adsorption on carbon black is a spontaneous physisorption process.
Keywords: nano; carbon; allotrope; black

Simulating grinding in impact mills - Separation of mill and material function - Peukert, Wolfgang; Vogel, Lutz; Sommer, Marc; Schäfer, Micheal; Grünwald, J (World Congress Particle Technology 4, 2002)
UnivIS-Import:2015-04-16:Pub.2002.tech.ITC.mechve.simula

Simulation and Verification of Defect-Dominated Permeation Mechanisms in Multiple Structures of Inorganic and Polymeric Barrier Layers - Hanika, Markus; Langowski, Horst-Christian; Peukert, Wolfgang (Proceedings of the Society of Vacuum Coaters 46th Annual Technical Conference, 2003)
In flexible barrier materials, the required barrier properties are obtained via combinations of polymeric and inorganic layers. In standard configurations like common laminates, the barrier effect is achieved by the combined action of the inorganic layer together with the substrate and an additional polymeric top layer, whereas the inorganic layer alone would be no barrier at all. For higher barrier requirements, more complex systems are tailored, consisting of a sequence of polymeric layers (organic or inorganic-organic hybrid materials) and inorganic barrier layers. Their final functionality is given by the bulk permeability properties of the polymeric layers and their thickness and by the microscopic and macroscopic properties of the inorganic layers. In this paper, the defect structures of the inorganic layers - as assessed via different analytical methods - are used as basis for numerical simulations, for which always a defect dominated permeation mechanism was taken. The complexity of the layer structures is increased stepwise, from the known configurations of one inorganic layer on top of a substrate and one inorganic layer embedded between two different polymers up to a description of one polymeric layer of varying thickness between two inorganic layers and its extension to repeated sequences of this structure. The results demonstrate the importance of the inherent barrier properties of the polymeric interlayers as a scaling factor for the performance of multi layer stacks.<br
Keywords: Permeation barrier coatings; Polymer base coats; Pinholes/porosity; Polymer substrates; moisture permeation; oxygen permeation

Simulation of Moving Nano-Particles with the Lattice Boltzmann Method in 3D - Iglberger, Klaus; Thürey, Nils; Rüde, Ulrich; Peukert, Wolfgang; Schmid, Hans-Joachim (18th Symposium Simulationstechnique ASIM 2005 Proceedings, 2005)
We will present our simulation to predict the behavior of moving nano-particles in a flow using the Lattice Boltzmann method. Targeted applications for this simulation are the pre- diction of particle movement in shear flows for large agglomerates and possible break ups or structural changes within the particles. The focus for the implementation is a stable and correct simulation even for high Reynolds numbers. Therefore, the Lattice Boltzmann Method is extended by complex geometries for an improved particle boundary treatment (4) and the method of momentum exchange for the force interaction between the fluid and the particle (1). The Lattice Boltzmann sim- ulation system is coupled to a rigid-body physics engine to build a two-system simulation (3). We will show results of simulations with static particles, which show consistent drag forces in comparison with the analytical results (2). The influence of the domain and particle radius were investigated. Further results for moving particles agree with real world measurements and, where possible, with the analytical results. Furthermore, an outlook to future work will be given, which will focus on performance improvements by grid refinement and parallelization for large scale simulations. Larger sim- ulations will also oer the possibility to include multi body interactions with agglomerations and potentials.
UnivIS-Import:2015-04-16:Pub.2005.tech.IMMD.lsinfs.simula_87
Keywords: nanoparticle; agglomerate; simulation; lattice; boltzmann

Simulation of structure and mobility of aggregates formed by simultaneous coagulation, sintering and surface growth - Peukert, Wolfgang; Schmid, Hans-Joachim; Al Zaitone, Belal (Journal of Aerosol Science, 2009)
In this work, a new model for the simulation of nanostructured aggregates by simultaneous coagulation, sintering and surface growth is presented. Coagulation is treated as cluster-cluster agglomeration along the line connecting the center of mass of both agglomerates and is implemented using a Monte Carlo algorithm. Sintering is modeled as successive overlapping of spheres which cause reduction in the surface area based on a rate law for surface reduction. Surface growth is modeled as an increase in primary particle diameter, e.g. as a result of surface reactions. The evolved aggregates are analyzed by calculating their fractal dimension, radius of gyration, mobility diameter and mobility shape factor. It is found that the aggregates structure tends to be more compact when introducing the surface growth in shorter time comparing to the coagulation-sintering step only. Fractal dimension and the mobility shape factor of the resulting aggregates are correlated to an effective dimensionless time that combines the characteristic times of these three fundamental mechanisms. It is shown that the mobility diameter in the free molecular regime is not proportional to the radius of gyration. A power law relation that correlates the aggregates projected area and the equivalent number of primary particles is found to be in a very good agreement with estimates published in literature. © 2009 Elsevier Ltd. All rights reserved.
Keywords: Agglomeration; Fractal dimension; Mobility diameter; Nanostructure; Particle formation; Simulation; Sintering

Simulation of the hydrodynamic behaviour of aggregated particles - Peukert, Wolfgang; Binder, Christian; Thürey, Nils; Schmid, Hans-Joachim; Rüde, Ulrich (2006 AIChE Spring National Meeting - 5th World Congress on Particle Technology, 2006)
The drag force on aggregates and partially sintered agglomerates is assessed using different techniques. In the free molecular regime - most relevant for nanoscaled particles in air at ambient or lower pressures - it has been shown that the projected area is very well representing the drag force of aggregates. In the continuum regime however, the projected area is not suitable to get a unique correlation with the drag force. This has been shown by applying two different techniques, namely the Lattice-Boltzmann Method (LBM) and Accelerated Stokesian Dynamics (ASD) to study the drag of agglomerates. Both methods have been compared in terms of accuracy and computational effort. It is shown that they give comparable results if all numerical parameters are controlled carefully. LBM requires a much higher computational effort, however, in contrast to ASD it is able to simulate partially sintered agglomerates as well. The results show that even a very small amount of sintering leads to a significant reduction in the drag force. The variation in drag force for single aggregates at different orientations or for the orientation averaged drag force of different aggregates of the same size is examined and discussed in both regimes.
Keywords: Aggregate structure; Nanoparticles; Physical properties; Simulation

Simulation of the Hydrodynamic Drag of Aggregated Particles - Binder, Christian; Feichtinger, Christian; Schmid, Hans-Joachim; Thürey, Nils; Peukert, Wolfgang; Rüde, Ulrich (Journal of Colloid and Interface Science, 2006)
The drag force on aggregates and partially sintered agglomerates is assessed using the lattice Boltzmann method (LBM) and accelerated Stokesian dynamics (ASD). Both methods have been compared in terms of accuracy and computational effort. It is shown that they give comparable results if all numerical parameters are controlled carefully. LBM requires a much higher computational effort, however, in contrast to ASD it is able to simulate partially sintered agglomerates as well. The results show that even a very small amount of sintering leads to a significant reduction in the drag force. The analysis of the drag force on agglomerates as well as on aggregates shows that there is no simple geometric quantity which is uniquely related to the drag force. Moreover, there is a significant variation in drag force for single aggregates at different orientations or for the orientation averaged drag force of different aggregates of the same size. This is explained by the structural effects which may lead to a variation in the drag force up to ± 20 %. © 2006.
UnivIS-Import:2015-03-09:Pub.2006.tech.IMMD.lsinfs.simula_1
Keywords: Agglomerates; Aggregates; Drag force; Fractal clusters; Lattice Boltzmann method; Simulation; Stokesian dynamics

Simultaneous 3D observation of different kinetic subprocesses for precipitation in a T-mixer - Gradl, Johannes; Peukert, Wolfgang (Chemical Engineering Science, 2009)
A coupled direct numerical simulation (DNS)—population balance equation (PBE)–DLVO approach is presented to calculate the product properties of particles originating from precipitation in a T-mixer. A special focus is given to the coupling of different subprocesses such as mixing, nucleation, growth, stabilization and aggregation for a rapid precipitation process. Based on the predictive computation of the resulting particle size distributions (PSD) full 3D-field information of all transient parameters are accessible, e.g., supersaturations, nucleation rates, particle sizes and stabilities. By interpolating the kinetic data, relevant subprocesses can be visualized and studied separately in the mixer. The resulting PSDs are predicted for different conditions where aggregation can be neglected. For unstable conditions aggregation and transient stabilization effects are determined by the DLVO theory. The size of the particles, their surface potential and the ionic strength of the solution vary extensively during the solid formation process. The dynamic evolution of the particle stability leads to a better description of the PSD based on the DNS–PBE–DLVO approach for unstable conditions and allows to develop strategies how to better stabilize particles. This approach is verified for barium sulphate precipitation but can be transferred to any other ionic system for which the relevant material specific data are known.

Simultaneous Analysis of Hydrodynamic and Optical Properties Using Analytical Ultracentrifugation Equipped with Multiwavelength Detection - Peukert, Wolfgang; Walter, Johannes; Lin, Wei; Segets, Doris; Sherwood, Peter; Stafford, Walter (Analytical Chemistry, 2015)
Analytical ultracentrifugation (AUC) has proven to be a powerful tool for the study of particle size distributions, particle shapes, and interactions with high accuracy and unrevealed resolution. In this work we show how the analysis of sedimentation velocity data from the AUC equipped with a multiwavelength detector (MWL) can be used to gain an even deeper understanding of colloidal and macromolecular mixtures. New data evaluation routines have been integrated in the software SEDANAL to allow for the handling of MWL data. This opens up a variety of new possibilities because spectroscopic information becomes available for individual components in mixtures at the same time using MWL-AUC. For systems of known optical properties information on the hydrodynamic properties of the individual components in a mixture becomes accessible. For the first time, the determination of individual extinction spectra of components in mixtures is demonstrated via MWL evaluation of sedimentation velocity data. In our paper we first provide the informational background for the data analysis and expose the accessible parameters of our methodology. We further demonstrate the data evaluation by means of simulated data. Finally, we give two examples which are highly relevant in the field of nanotechnology using colored silica and gold nanoparticles of different size and extinction properties.
Keywords: analytical; ultracentrifugation; sedimentation; colloid; macromolecular; simulation

Simultaneous analysis of the dispersed liquid and the bulk gas phase of water sprays using Raman spectroscopy - Schuster, Julian; Siegler, Philipp; Günther, Astrid; Wirth, Karl-Ernst; Bräuer, Andreas (Applied Spectroscopy, 2016)

Simultaneous Identification of Spectral Properties and Sizes of Multiple Particles in Solution with Subnanometer Resolution - Peukert, Wolfgang; Karabudak, Engin; Brookes, Emre; Lesnyak, Vladimir; Gaponik, Nikolai; Eychmüller, Alexander; Walter, Johannes; Segets, Doris; Wohlleben, Wendel; Demeler, Borries; Cölfen, Helmut (Angewandte Chemie-International Edition, 2016)
We report an unsurpassed solution characterization technique based on analytical ultracentrifugation, which demonstrates exceptional potential for resolving particle sizes in solution with sub-nm resolution. We achieve this improvement in resolution by simultaneously measuring UV/Vis spectra while hydrodynamically separating individual components in the mixture. By equipping an analytical ultracentrifuge with a novel multi-wavelength detector, we are adding a new spectral discovery dimension to traditional hydrodynamic characterization, and amplify the information obtained by orders of magnitude. We demonstrate the power of this technique by characterizing unpurified CdTe nanoparticle samples, avoiding tedious and often impossible purification and fractionation of nanoparticles into apparently monodisperse fractions. With this approach, we have for the first time identified the pure spectral properties and band-gap positions of discrete species present in the CdTe mixture.
Keywords: analytical methods; colloids; nanoparticles

Simultaneous in situ Raman monitoring of the solid and gas phases during the formation and growth of carbon nanotubes inside a cold wall CCVD reactor - Reinhold Lopez, Karla; Bräuer, Andreas; Romann, Bettina; Popovska-Leipertz, Nadejda; Leipertz, Alfred (Carbon, 2014)

Simultaneous Nanolocal Polymer and In Situ Readout Unit Placement in Mesoporous Separation Layers - Stanzel, Mathias; Zhao, Lucy; Mohammadi Eslami, Reza; Pardehkhorram, Raheleh; Kunz, Ulrike; Vogel, Nicolas; Andrieu-Brunsen, Annette (Analytical Chemistry, 2021)
Bioinspired solid-state nanopores and nanochannels have attracted interest in the last two decades, as they are envisioned to advance future sensing, energy conversion, and separation concepts. Although much effort has been made regarding functionalization of these materials, multifunctionality and accurate positioning of functionalities with nanoscale precision still remain challenging. However, this precision is necessary to meet transport performance and complexity of natural pores in living systems, which are often based on nonequilibrium states and compartmentalization. In this work, a nanolocal functionalization and simultaneous localized sensing strategy inside a filtering mesoporous film using precisely placed plasmonic metal nanoparticles inside mesoporous films with pore accessibility control is demonstrated. A single layer of gold nanoparticles is incorporated into mesoporous thin films with precise spatial control along the nanoscale layer thickness. The local surface plasmon resonance is applied to induce a photopolymerization leading to a nanoscopic polymer shell around the particles and thus nanolocal polymer placement inside the mesoporous material. As near-field modes are sensitive to the dielectric properties of their surrounding, the in situ sensing capability is demonstrated using UV-vis spectroscopy. It is demonstrated that the sensing sensitivity only slightly decreases upon functionalization. The presented nanolocal placement of responsive functional polymers into nanopores offers a simultaneous filtering and nanoscopic readout function. Such a nanoscale local control is envisioned to have a strong impact onto the development of new transport and sensor concepts, especially as the system can be developed into higher complexity using different metal nanoparticles and additional design of mesoporous film filtering properties.

Single-Molecule Pycnometry and Shape Analysis of Ions in the Gas Phase - Lübbert, Christian; Supper, Malvina; Kaspereit, Malte; Walter, Johannes; Peukert, Wolfgang (Analytical Chemistry, 2023)
The analysis of ions and clusters by mobility-classified mass spectrometry provides information on the mobility of analytes in the drift gas and the analyte mass. Mass equivalent and mobility equivalent diameters of globular analytes, such as ions, poly(ethylene glycol) (PEG), and ionic liquid nanodroplets, can be correlated with good accuracy by the Stokes-Millikan mobility model. A prerequisite to such an analysis is, however, the assumption of a globular analyte shape, which then allows determination of material density for globular ions. We show that the analyte density can be evaluated with high precision, independent of any assumptions on the analyte shape, by careful analysis of analyte-PEG-cluster ions following the concept of classical pycnometry. In particular, the analyte is entrapped in a globular PEG-analyte droplet. Based on the now independently derived mobility diameter and volume equivalent diameter, it is possible to attribute two parameters, size and shape, to the analyte molecule. We demonstrate the approach for lysozyme, cyano-cobalamin (vitamin B12), and glucose, which cover two orders of magnitude in analyte mass (180···14 300 Da). The derived densities for these analytes are highly accurate, i.e., they deviate less than 1% from literature values. Our method can be applied to newly synthesized molecules, supramolecular assemblies, isolated biomolecules, and molecular clusters, where only minor amounts of materials are available. The obtained shape parameters of lysozyme and cyano-cobalamin agree well with the expected molecular shapes. Data evaluation relies only on locations of the species in the mass-mobility plane and is in principle independent of any mobility theory. Our approach is thus robust with respect to experimental uncertainties and produces identical results irrespective of the type of mobility classification and drift ga
Keywords: Enzymes; Ionic liquids; Mass spectrometry; Molecules; Polyethylene glycols; Synthesis (chemical); Analytes; Classifieds; Drift gas; Gas-phases; Liquid nanodroplets; Mobility equivalent diameter; Poly(ethylene glycol)(PEG); Pycnometry; Shape-analysis; Single molecule; Ions

Single-step aerosol synthesis of oxygen-deficient blue titania - Domaschke, Maximilian; Strunz, Lea; Peukert, Wolfgang (Chemical Engineering Science, 2019)
We present a novel approach for the single-step, continuous aerosol synthesis of blue, oxygen-deficient titania in a hot-wall reactor operated under reducing conditions by adding hydrogen. The precursor titanium(IV) tetraisopropoxide is evaporated in a bubbler and consecutively carried into the reactor by a nitrogen stream where it undergoes thermal decomposition. According to X-ray diffraction analysis, several reduced titania states, among them the Magneli phases Ti4O7 and Ti5O9, are formed via the intermediates anatase and rutile. By slight modifications in the reactor setup both nanoparticles in the size range from 20 to 50 nm with high surface area and well-defined spherical submicron particles of 100 to 160 nm diameter can be produced. In particular, crystallographically phase-pure Ti4O7 is formed at high reactor temperatures. The presented synthesis process is scalable and poses an attractive alternative for the multi-step synthesis of oxygen deficient titania nanoparticles that is currently done via batch-wise annealing. Such nanoparticles are attractive material in the field of photocatalysis. They can be used for both water splitting to produce hydrogen and the decomposition of organic pollutants. (C) 2019 Elsevier Ltd. All rights reserved.
CRIS-Team WoS Importer:2019-07-02

Singlet Fission for Photovoltaics with 130 % Injection Efficiency - Kunzmann, Andreas; Gruber, Marco; Casillas Pacheco, Ruben; Zirzlmeier, Johannes; Stanzel, Melanie; Peukert, Wolfgang; Tykwinski, Rik; Guldi, Dirk Michael (Angewandte Chemie International Edition, 2018)
A novel pentacene dimer (P2) and a structurally analogous monomer (P1) were synthesized for use in n-type dye-sensitized solar cells. In P2, the triplet excited states formed by the rapid, spin-allowed process singlet fission were expected to enable carrier multiplication in comparison to the slow, spin-forbidden intersystem crossing seen in P1. A meta-positioning of the two pentacenes and the carboxylate anchor were chosen in P2 to balance the intramolecular dynamics of singlet fission and electron injection. Electron injection from energetically low-lying triplet excited states of pentacene units necessitated the intrinsic and extrinsic lowering of the Fermi level of the semiconductor. Indium-zinc oxide in the presence of Li+ was found to be the optimum choice for the photoelectrodes. Efficient electron injection from the triplet excited states of P1 and P2 was found, with a carrier multiplication of nearly 130 %.
Keywords: pentacene sensitizers; singlet fission; dye-sensitized solar cells; transient absorption spectroscopy

Singulettspaltung für Photovoltaikanwendungen mit Injektionseffizienzen von bis zu 130 % - Kunzmann, Andreas; Gruber, Marco; Casillas, Ruben; Zirzlmeier, Johannes; Stanzel, Melanie; Peukert, Wolfgang; Tykwinski, Rik R.; Guldi, Dirk Michael (Angewandte Chemie, 2018)

Sintering kinetics and mechanism of vitreous nanoparticles - Kirchhof, Martin; Förster, Henning; Schmid, Hans-Joachim; Peukert, Wolfgang (Journal of Aerosol Science, 2012)
The sintering of vitreous nanoparticle doublets is investigated numerically by a volume of fluid method coupled to Hamaker summation and experimentally by a high-temperature sintering flow reactor as well as by doublet shape analysis in the transmission electron microscope. In particular, the characteristic differences between nanoparticulate and bulk sintering are studied. The sintering mechanism of vitreous nanoparticles is determined to be viscous flow with interparticle van der Waals interactions acting as additional driving force. The early stages of the nanoparticle sintering kinetics are inversely proportional to the square of the particle size, instead of an indirect proportionality to the first order of the particle size for the entire bulk process. The transition between nanoparticulate and bulk sintering is localised to primary particle diameters of approx. 200-300nm. © 2011 Elsevier Ltd.
Keywords: Nanoparticles; Silica; Sintering; Van Der Waals interactions; Viscous flow

SiO2–GeO2 Glass–Ceramic Flakes as an Anode Material for High-Performance Lithium-Ion Batteries - Esper, Julian Duane; Maußner, Felix; Romeis, Stefan; Zhuo, Ying; Barr, Maissa; Yokosawa, Tadahiro; Spiecker, Erdmann; Bachmann, Julien; Peukert, Wolfgang (Energy Technology, 2022)
The preparation of a flake-like glass–ceramic anode material comprised of SiO2 and GeO2 for Li-ion batteries (LIBs) is demonstrated. The precursor glass material is prepared via a traditional melt quenching technique. Flake-like glass particles are obtained by compression in the liquid phase via ball milling. A subsequent heat treatment induces crystallization of GexSiyO6 domains inside the vitreous SiO2–GeO2 matrix. This novel glass-ceramic material is applied as an anode material for LIBs and shows a stable reversible capacity of 520 mAh g−1 at 0.2 C combined with good capacity retention of 87% after 100 cycles. This cycling stability can be attributed to the synergistic effects of having nanocrystalline domains embedded in the glass matrix: The open glass network can withstand the volume change and stress caused by the lithium insertion during cycling, while the nanocrystals act as active sites for the electrochemical conversion and alloying reactions. The glass–ceramic anode material exhibits superior electrochemical properties compared to its pure glass counterparts.
CRIS-Team Scopus Importer:2022-06-10
Keywords: anodes; flake-like particles; glass ceramics; lithium-ion batteries; shape-anisotropy; thermal annealing

Size and shape engineering of ZnO nanoparticles - Klupp Taylor, Robin; Voigt, Michael; Segets, Doris; Peukert, Wolfgang; Marczak, Renata (2008 AIChE Annual Meeting, 2008)
The investigation of ZnO nanoparticles is of great interest due to the wide range of potential applications for this material. Despite this, a thorough understanding of the optical, electronic and structural properties of ZnO nanoparticles with respect to their synthesis is still lacking. We tackled this problem by synthesizing ZnO nanoparticles with nanocrystal, nanorod and self-assembled aggregate form using ambient and hydrothermal wet chemical processes. Dynamic light scattering, absorption and emission spectroscopies, thermogravimetric analysis, X-ray powder diffraction, Fourier infrared spectroscopy as well as transmission and scanning electron microscopies were employed to characterize and compare the nanoparticles composition, their shape, size and crystallinity. By varying different parameters of the synthesis processes like precursors and their concentrations, solvent used, surfactant, temperature, and reaction time we were able to control the size and shape of the particles. In particular we noted the tendency of ZnO nanocrystals to self-assemble into dense structures which preserve the anisotropic crystal structure. Using surface-mediating polymers such as PVP, this self-organisation could be modified so as to produce nanostructures with a tunable porosity, with great potential for application.
Keywords: ZnO; nanoparticle; nanostructure; growth; crystal; self-assembly

Size-dependent nanoscale soldering of polystyrene colloidal crystals by supercritical fluids - Varghese, Jeena; Mohammadi, Reza; Pochylski, Mikolaj; Babacic, Visnja; Gapinski, Jacek; Vogel, Nicolas; Butt, Hans Juergen; Fytas, George; Graczykowski, Bartlomiej (Journal of Colloid and Interface Science, 2023)
Hypothesis: Polymer particles self-assembled into colloidal crystals have exciting applications in photonics, phononics, templates for nanolithography, and coatings. Cold soldering utilizing polymer plasticization by supercritical fluids enables a novel, low-cost, low-effort, chemical-free means for uniform mechanical strengthening of fragile polymer colloidal crystals at moderate temperatures. Here, we aim to elucidate the role of particle size and gas-specific response for the most efficient soldering, exploring the full potential of this method. Experiments: We investigate the elastic properties of polystyrene colloidal crystals made of nanoparticles with different diameters (143 to 830 nm) upon treatment with supercritical Ar and He at room temperature. By employing Brillouin light scattering, we quantify the effect of nanoparticle size on the strengthening of interparticle contacts, evaluating the permanent change in the effective elastic modulus upon cold soldering. Findings: The relative change in the effective elastic modulus reveals nonmonotonic dependence on the particle size with the most efficient soldering for mid-sized nanoparticles (about 610 nm diameter). We attribute this behavior to the crucial role of intrinsic fabrication impurities, which reduces the nanoparticles’ free surface exposed to plasticization by supercritical fluids. Supercritical Ar, a good solvent for polystyrene, enabled effective soldering of nanoparticles, whereas high-pressure He treatment is entirely reversible.
CRIS-Team Scopus Importer:2023-01-13
Keywords: Brillouin light scattering; Colloidal crystals; Mechanical and interfacial properties; Polystyrene nanoparticles; Supercritical fluids

Size effects in MgO cube dissolution - Baumann, Stefan O.; Schneider, Johannes; Sternig, Andreas; Thomele, Daniel; Stankic, Slavica; Berger, Thomas; Gronbeck, Henrik; Diwald, Oliver (Langmuir, 2015)
Stability parameters and dissolution behavior of engineered nanomaterials in aqueous systems are critical to assess their functionality and fate under environmental conditions. Using scanning electron microscopy, transmission electron microscopy, and X-ray diffraction, we investigated the stability of cubic MgO particles in water. MgO dissolution proceeding via water dissociation at the oxide surface, disintegration of Mg2+–O2– surface elements, and their subsequent solvation ultimately leads to precipitation of Mg(OH)2 nanosheets. At a pH ≥ 10, MgO nanocubes with a size distribution below 10 nm quantitatively dissolve within few minutes and convert into Mg(OH)2 nanosheets. This effect is different from MgO cubes originating from magnesium combustion in air. With a size distribution in the range 10 nm ≤ d ≤ 1000 nm they dissolve with a significantly smaller dissolution rate in water. On these particles water induced etching generates (110) faces which, above a certain face area, dissolve at a rate equal to that of (100) planes.1 The delayed solubility of microcrystalline MgO is attributed to surface hydroxide induced self-inhibition effects occurring at the (100) and (110) microplanes. The present work underlines the importance of morphology evolution and surface faceting of engineered nanomaterials particles during their dissolutio

Size effects in the elastic deformation behavior of metallic nanoparticles - Armstrong, Patrick; Peukert, Wolfgang (Journal of Nanoparticle Research, 2012)
In this work, the results of a series of molecular statics simulations to investigate the size dependence of the elastic properties of metallic nanoparticles are presented. The per-atom stiffness tensor was calculated from the derivative of the used embedded atom method potentials and, from it, lower order elastic parameters, such as the Young's modulus or the Poisson ratio. The Young's modulus decayed up to 30 % relative to the bulk values for 2.5 nm small particles, whereas the Poisson ratio showed an increase with decreasing particle size for most materials. Particles with a diameter of 30 nm approached the continuum values to around 1 %, marking the transition to continuum theory. The size-dependent Young's modulus and several other material properties can be described by a simple algebraic function of the number of atoms per particle. By plotting the radial distribution of the local Young's modulus within particles of different size, it is shown that only the outermost 2-3 atomic layers are responsible for the size-dependent change of elastic properties. Within these layers, the average atomic stiffness was found to decay linearly and independent of the particle siz
Keywords: Size effect; Elasticity; Molecular statics; Nanoparticles; Young's modulus

Size exclusion chromatography (SEC) - Peukert, Wolfgang; Kaspereit, Malte; Hofe, Thorsten; Gromotka, Lukas (Particle Separation Techniques, 2022)
Size exclusion chromatography (SEC) is a liquid phase chromatographic technique for separating molecules, proteins, macromolecules, and nanoparticles (below 100 nm) solely according to their hydrodynamic volume in solution. Classification depends on the size- and shape-dependent exclusion of components in the pores of the stationary phase material, that is, larger and less mobile components leave the column first. Ideally, the separation is purely driven by entropy, the absence of strong enthalpic interactions encompasses mild operating conditions. SEC is a standard method in polymer science and technology for the characterization of molecular weight distributions. SEC is also well established for preparative applications, for example, for the separation of proteins from aggregates in biotechnology. The size-dependent classification of nanoparticles is a promising new field of application.<br

Size specific energy (SSE) - Energy required to generate minus 75 micron material - Ballantyne, Grant; Peukert, Wolfgang; Powell, Malcolm (International Journal of Mineral Processing, 2015)
This paper explores the relationship between energy and the generation of minus 75 micron material. Rittinger's law of comminution states that the energy input is proportional to the generation of new surface area. An accurate and consistent measurement of surface area, applicable across multiple size ranges, is required to apply this practically. The amount of new - 75 μm material generated has previously been proposed as a proxy for surface area. This has been demonstrated to some extent on a range of different laboratory equipment, but not in a manner suited to equipment-independent ore characterisation. To this end the JK Rotary Breakage Tester (JKRBT) and Schönert breakage device have been used to measure the progressive production of fines from cumulative single impacts starting with 37.5 mm particles down to 250 μm. As per expectation, the generation of - 75 μm material was found to be proportional to the specific energy, but there was a secondary influence of size. A model was developed to describe the breakage and it was found that the standard t relationship could be used to effectively calculate the size specific energy. Measuring the intrinsic competence of an ore in this way can then be used to assess the energy efficiency of full-scale mills in relation to a lab scale test. It is envisaged that this relationship also has the potential to be used in the design of new comminution circuits. The methodology and the results from its application are presented for discussion and revie
Keywords: Benchmarking; Comminution; Efficiency; Energy

Smart Optical Composite Materials: Dispersions of Metal-Organic Framework@Superparamagnetic Microrods for Switchable Isotropic-Anisotropic Optical Properties - Mandel, Karl; Granath, Tim; Wehner, Tobias; Rey, Marcel; Stracke, Werner; Vogel, Nicolas; Sextl, Gerhard; Mueller-Buschbaum, Klaus (Acs Nano, 2017)
A smart optical composite material with dynamic isotropic and anisotropic optical properties by combination of luminescence and high reflectivity was developed. This combination enables switching between luminescence and angle-dependent reflectivity by changing the applied wavelength of light. The composite is formed as anisotropic core/shell particles by coating superparamagnetic iron oxide-silica microrods with a layer of the luminescent metal-organic framework (MOF) 3ınfty[Eu2(BDC)3]·2DMF·2H2O (BDC2- = 1,4-benzenedicarboxylate). The composite particles can be rotated by an external magnet. Their anisotropic shape causes changes in the reflectivity and diffraction of light depending on the orientation of the composite particle. These rotation-dependent optical properties are complemented by an isotropic luminescence resulting from the MOF shell. If illuminated by UV light, the particles exhibit isotropic luminescence while the same sample shows anisotropic optical properties when illuminated with visible light. In addition to direct switching, the optical properties can be tailored continuously between isotropic red emission and anisotropic reflection of light if the illuminating light is tuned through fractions of both UV and visible light. The integration and control of light emission modes within a homogeneous particle dispersion marks a smart optical material, addressing fundamental directions for research on switchable multifunctional materials. The material can function as an optic compass or could be used as an optic shutter that can be switched by a magnetic field, e.g., for an intensity control for waveguides in the visible range.
Keywords: anisotropy; composites; isotropy; magnetic actuation; metal organic frameworks; optical properties; smart materials; superparamagnetism; switching

Smart silver nanoparticles from nanoreactors made by invertible polyesters - Kohut, Ananiy; Voronov, Andriy; Peukert, Wolfgang (2, 2007)
We developed a simple way to prepare smart silver nanoparticles that are well dispersible in both polar and nonpolar media. The synthesis was performed using solutions of an invertible amphiphilic polyester made via a polycondensation reaction of sebacic acid and poly(ethylene glycol). Reduction, formation of silver nanoparticles, and their stabilization occur in the polyester micellar domains (nanoreactors) that are formed in the reaction medium. Comparison of XRD experimental data shows that microphase separation of polyester units resulting in subsequent large range ordering occurs by change of the polyester concentration. The shape and size of the domains depend on the polyester concentration and the ratio between the lipophilic and hydrophilic constituents in the macromolecule as well as on solvent (reaction medium) polarit
Keywords: Smart nanoparticles; Polymeric nanoreactors

Soft Particles at Liquid Interfaces: From Molecular Particle Architecture to Collective Phase Behavior. - Ciarella, Simone; Rey, Marcel; Harrer, Johannes; Holstein, Nicolas; Ickler, Maret; Löwen, Hartmut; Vogel, Nicolas; Janssen, Liesbeth M. C. (Langmuir, 2021)
-isopropylacrylamide) particle systems using phase-contrast atomic force microscopy and correlate the distinct interfacial morphology with their bulk molecular architecture. We subsequently introduce a new coarse-grained simulation method that uses augmented potentials to translate this interfacial morphology into the resulting phase behavior upon compression. The main novelty of this method is the possibility to efficiently encode multibody interactions, the effects of which are key to distinguishing between heterostructural (anisotropic collapse) and isostructural (isotropic collapse) phase transitions. Our approach allows us to qualitatively resolve existing discrepancies between experiments and simulations. Notably, we demonstrate the first in silico account of the two-dimensional isostructural transition, which is frequently found in experiments but elusive in simulations. In addition, we provide the first experimental demonstration of a heterostructural transition to a chain phase in a single-component system, which has been theoretically predicted decades ago. Overall, our multiscale framework provides a phenomenological bridge between physicochemical soft-particle characteristics at the molecular scale and nanoscale and the collective self-assembly phenomenology at the macroscale, serving as a stepping stone toward an ultimately more quantitative and predictive design approach.

Solar Light and Dopant-Induced Recombination Effects: Photoactive Nitrogen in TiO2 as a Case Study - D'Arienzo, Massimiliano; Siedl, Nicolas; Sternig, Andreas; Scotti, Roberto; Morazzoni, Franca; Bernardi, Johannes; Diwald, Oliver (Journal of Physical Chemistry C, 2010)
The spectral response of newly synthesized and doped TiO_2 nanostructures, which are designed for the operation under solar light, is key to their potential performance as photocatalyst materials. In the case of nitrogen-doped TiO_2 particles, the presence of the photoactive defect can be verified via characteristic spectroscopic fingerprints, such as (1) an optical absorption band above extgreekl > 400 nm, (2) paramagnetic defect states related to substitutional and interstitial nitrogen atoms, and (3) a photoluminescence emission feature that can be induced by band gap excitation. We report these spectroscopic fingerprints for hydrothermally derived and N-doped TiO_2 powder samples. On the basis of defined annealing procedures, we also found a way to eliminate the photoactive nitrogen defects and performed light-induced charge separation experiments on samples before and after dopant elimination in O_2 atmosphere. The concentrations of adsorbed O_2 - ions, which stand for scavenged photogenerated electrons, were determined by electron paramagnetic resonance (EPR) spectroscopy. On the basis of these data, we calculated the number of photons, which (a) were additionally utilized because of the beneficial effect of photoactive nitrogen and (b) were lost because of the dopant-induced recombination of UV light generated charge carriers. As a major result, we found for the doped materials that both effects actually compensate each other. With regard to the synthesis and characterization of doped TiO_2 systems, these findings underline the importance to include dopant-induced charge-carrier recombination effects in the evaluation of the photocatalyst's spectral response in order to reach a fair evaluation of its properties.
EAM Import::2019-03-13

Solid distribution in fluidized and fixed beds with horizontal high speed gas jets - Köninger, Benedikt; Koegl, Thilo; Hensler, Timo; Arlt, Wolfgang; Wirth, Karl-Ernst (Powder Technology, 2018)
High speed jet penetration in fluidized beds can be used for particle size control or comminution processes. Thus, particle breakage is determined by the kinetic energy of the solids and the frequency of particle-particle impacts inside the flow. Both aspects are influenced by the solid concentration inside the jets and at the boundary. For understanding the fundamental breakage mechanism, the determination of the solid distribution in those complex flows is an important contribution. In order to access the turbulent and delicate multiphase flow, a modern fast X-ray computed tomography unit was used in this work. To obtain quantitative solid concentrations, the measurement system was optimized by means of hardware filtering, exposure time and reconstruction algorithm. These methods allowed the investigation of influencing parameters like jet velocity, fluidization velocity or particle size on the solid distribution in a single jet. With the obtained experimental data, correlations for the axial and radial solid distribution were developed. In addition, the influence of multiple jet injection with a common focal point is presented.
Keywords: Horizontal secondary gas injection; Jet milling; X-ray computed tomography; Solid distribution; Visualization of flow pattern

Solids Concentration and Solids Velocity in the Wall Region of Circulating Fluidzed Beds - Wirth, Karl-Ernst; et al. (Preprints 11th Internat. Conference on Fluidized Bed Combustion, 1991)
In circulating fluidized beds, heat is transferred to the watersteam-system by wall heat exchangers. In order to understand both the heat transfer process and the erosion of the heat exchanger it is particularly interesting to know the solids concentration and the solids velocity near the wall of the circulating fluidized bed. Two systems for measuring these quantities were developed. The principle of the measurement of the solids concentration is based on the attenuation of a γ-beam passing the circulating fluidized beds. Shifting the radiation source and the detector across the cross-section of the circulating fluidized bed it was possible to measure the radial solids concentration profile. The experiments showed that the solids concentration in the wall region is about three times as large as that in the core region of the bed and that a small layer free of solids and about 1 mm thick exists immediate near the wall. This measuring system is applicable in industrial fluidized bed combusters, because no part of the systems is placed in the bed. The velocity was measured by using a phosphorescent material. A small part of this material was marked by a light flash and then traced with a video camera. We observed that all the material immediate near the wall is falling down and the velocity of this falling film is in the order of one to three meter per second.
UnivIS-Import:2015-04-16:Pub.1991.tech.ITC.mechve.solids
Keywords: fluidized; bed; combustion

Solid-Solid Interface Formation in TiO2 Nanoparticle Networks - Baumann, Stefan O.; Elser, Michael J.; Auer, Michael; Bernardi, Johannes; Huesing, Nicola; Diwald, Oliver (Langmuir, 2011)
Aiming at a comparison of microstructure and paramagnetic properties of mesoporous TiO_2 nanoparticle networks, we subjected entirely different TiO2-x precursor structures to vacuum annealing. The transformation of an amorphous TiO2-x gel—obtained by sol-gel processing of an ethylene glycol-modified titanium precursor—into a network of interconnected anatase nanocrystals was explored by means of X-ray diffraction, nitrogen sorption, and electron microscopy. Crystalline junctions between the particles emerge from temperature treatment. This process of particle network formation is different from that related to the vapor phase grown anatase nanocrystals where particle-particle interface formation is induced by contact with water. It was found that, after annealing up to 873 K and controlled sample purification in oxygen atmosphere, both types of samples exhibit high concentrations of particle-particle interfaces and comparable properties in terms of surface area, porosity, and microstructure. With electron paramagnetic resonance (EPR) we observed on nonstoichiometric TiO2-x networks an identical type of subsurface defect which is related to the presence of solid-solid interfaces.
EAM Import::2019-03-13

Solid state interdigitated Sb(2)S(3)based TiO(2)nanotube solar cells - Büttner, Pascal; Döhler, Dirk; Korenko, Sofia; Möhrlein, Sebastian; Bochmann, Sebastian; Vogel, Nicolas; Minguez Bacho, Ignacio; Bachmann, Julien (RSC Advances, 2020)
TiO(2)nanotubes generated by anodization of metallic titanium sputter-coated on indium tin oxide (ITO) substrates are used as a conductive scaffold for all solid-state Sb2S3-sensitized extremely thin absorber (ETA) solar cells. A blocking layer of TiO(2)placed between Ti and ITO in combination with optimized Ti deposition and anodization conditions enables the formation of crack-free layers of straight, cylindrical TiO(2)nanotubes of tunable length and diameter. ALD (atomic layer deposition) is subsequently used to coat this substrate conformally with a highly pure Sb(2)S(3)light absorber layer under an inert atmosphere. The high absorption coefficient of Sb(2)S(3)as compared to molecular dyes allows for the utilization of very short nanotubes, which facilitates the infiltration of the organic hole transport material and formation of a p-i-n heterojunction in an interdigitated and tunable geometry. We investigate the influence of nanotube length and of the absorber thickness to enhance the photocurrent value to twice that of planar reference structures.

Solid state interdigitated Sb(2)S(3)based TiO(2)nanotube solar cells - Büttner, Pascal; Döhler, Dirk; Korenko, Sofia; Moehrlein, Sebastian; Bochmann, Sebastian; Vogel, Nicolas; Minguez-Bacho, Ignacio; Bachmann, Julien (RSC Advances, 2020)
TiO(2)nanotubes generated by anodization of metallic titanium sputter-coated on indium tin oxide (ITO) substrates are used as a conductive scaffold for all solid-state Sb2S3-sensitized extremely thin absorber (ETA) solar cells. A blocking layer of TiO(2)placed between Ti and ITO in combination with optimized Ti deposition and anodization conditions enables the formation of crack-free layers of straight, cylindrical TiO(2)nanotubes of tunable length and diameter. ALD (atomic layer deposition) is subsequently used to coat this substrate conformally with a highly pure Sb(2)S(3)light absorber layer under an inert atmosphere. The high absorption coefficient of Sb(2)S(3)as compared to molecular dyes allows for the utilization of very short nanotubes, which facilitates the infiltration of the organic hole transport material and formation of a p-i-n heterojunction in an interdigitated and tunable geometry. We investigate the influence of nanotube length and of the absorber thickness to enhance the photocurrent value to twice that of planar reference structures.
CRIS-Team WoS Importer:2020-08-28

Solvent effects of zinc sulfide quantum dots classified by size selective precipitation - Mori, Y.; Yamamoto, K.; Segets, Doris; Peukert, Wolfgang; Tuchiya, K. (22nd International Congress of Chemical and Process Engineering (CHISA 2016) and 19th Conference on Process Integration, Modelling and Optimisation for Energy Saving and Pollution Reduction (PRES 2016), 2016)

Sonochemical processing and characterization of composite materials based on soy protein and alginate containing micron-sized bioactive glass particles - Silva Lourenco, Rauqel; Bulut, Buse; Roether, Judith; Kaschta, Joachim; Schubert, Dirk W.; Boccaccini, Aldo R. (Journal of Molecular Structure, 2014)
Novel composite hydrogels based on the combination of natural polymers; namely alginate and soy protein isolate, and bioactive glass (BC) particles (mean size: 2 pm) were developed. For this purpose a sono-chemical approach was used and homogeneous composite hydrogels, incorporating two concentrations of BC particles, were successfully obtained. Further physico-chemical characterization was performed in order to evaluate the influence of each component on hydrogel properties. The water uptake ability, weight loss, protein release, as well as FTIR, SEM and DMTA characterization were carried out. The bio-mineralization process in simulated body fluid (SBF) was followed over time and the results demonstrated that the composite materials have the ability to form a surface apatite layer after 7 days in SBF. The design of novel composite hydrogels based on soy protein, alginate and BC can be a suitable approach for bone regeneration applications. (C) 2014 Elsevier B.V. All rights reserved.
Keywords: Alginate; Soy isolate protein; Bioactive glass; Hydrogel; Tissue engineering

Spatially resolved flame zone classification of a flame spray nanoparticle synthesis process by combining different optical techniques - Kilian, Daniel; Engel, Sascha; Borsdorf, B.; Gao, Yi; Kögler, Andreas; Kobler, S.; Seeger, Thomas; Will, Stefan; Leipertz, Alfred; Peukert, Wolfgang (Journal of Aerosol Science, 2014)
Flame spray synthesis of silica nanoparticles is characterized by a set of complementary optical techniques. By means of laser-sheet based Mie scattering imaging, 2D-chemiluminescence imaging and coherent anti-Stokes Raman spectroscopy (CARS) local information on spatial droplet distribution, combustion zone, nucleation zone and temperature in the flame could be obtained. In addition, the outcomes from optical metrology are validated by thermophoretic sampling at different flame heights and the synthesized powders were analyzed by N2 gas sorption. By comparing these results the flame can be quantitatively classified into three distinct zones: (i) the droplet zone where precursor atomization and evaporation take place, (ii) the nucleation zone indicated by SiO*/Si* radicals as a preliminary species before SiO2 particle formation and (iii) the sintering zone characterized by the highest temperatures in flame. In addition the spatial spreading of the nucleation zone as a function of precursor concentration is investigated. Theoretical calculations and experimental results show an extended nucleation regime for the lowest precursor concentration compared to higher concentrations. Although this study is performed with hexamethyldisiloxane (HMDS) precursor to synthesize silica nanoparticles as a model system, dimensionless analysis shows that the results, concerning the spray formation, can be transferred to the synthesis of other materials as well.

Spatioselective Deposition of Passivating and Electrocatalytic Layers on Silicon Nanowire Arrays. - Wendisch, Fedja J.; Abazari, Mehri; Werner, Valerie; Barb, Horia; Rey, Marcel; Görlitzer, Eric; Vogel, Nicolas; Mahdavi, Hossein; Bourret, Gilles R. (ACS Applied Materials and Interfaces, 2020)
Metal–silicon nanowire array photoelectrodes provide a promising architecture for water-splitting because they can afford high catalyst loading and decouple charge separation from the light absorption process. To further improve and understand these hybrid nanowire photoelectrodes, control of the catalyst amount and location within the wire array is required. Such a level of control is currently synthetically challenging to achieve. Here, we report the synthesis of cm2-sized hybrid silicon nanowire arrays with electrocatalytically active Ni–Mo and Pt patches placed at defined vertical locations within the individual nanowires. Our method is based on a modified three-dimensional electrochemical axial lithography (3DEAL), which combines metal-assisted chemical etching (MACE) to produce Si nanowires with spatially defined SiO2 protection layers to selectively cover and uncover specific areas within the nanowire arrays. This spatioselective SiO2 passivation yields nanowire arrays with well-defined exposed Si surfaces, with feature sizes down to 100 nm in the axial direction. Subsequent electrodeposition directs the growth of the metal catalysts at the exposed silicon surfaces. As a proof of concept, we report photoelectrocatalytic activity of the deposited catalysts for the hydrogen evolution reaction on p-type Si nanowire photocathodes. This demonstrates the functionality of these hybrid metal/Si nanowire arrays patterned via 3DEAL, which paves the way for investigations of the influence of three-dimensional geometrical parameters on the conversion efficiency of nanostructured photoelectrodes interfaced with metal catalysts.
Keywords: Metals; Nanowires; Nanowire arrays; Catalysts; Deposition

Special Issue of Core-to-Core Young Researchers Meeting 2008 Preface - Peukert, Wolfgang; Higashitani, Ko; Marczak, Renata (Advanced Powder Technology, 2010)

Specific effects of Ca2+ ions and molecular structure of β-lactoglobulin interfacial layers that drive macroscopic foam stability - Braunschweig, Björn; Schulze-Zachau, Felix; Nagel, Eva; Engelhardt, Kathrin; Stoyanov, Stefan; Gochev, Georgi; Khristov, Khr.; Mileva, Elena; Exerowa, Dotchi; Miller, Reinhard; Peukert, Wolfgang (Soft Matter, 2016)
β-Lactoglobulin (BLG) adsorption layers at air–water interfaces were studied in situ with vibrational sum-frequency generation (SFG), tensiometry, surface dilatational rheology and ellipsometry as a function of bulk Ca2+ concentration. The relation between the interfacial molecular structure of adsorbed BLG and the interactions with the supporting electrolyte is additionally addressed on higher length scales along the foam hierarchy – from the ubiquitous air–water interface through thin foam films to macroscopic foam. For concentrations <1 mM, a strong decrease in SFG intensity from O–H stretching bands and a slight increase in layer thickness and surface pressure are observed. A further increase in Ca2+ concentrations above 1 mM causes an apparent change in the polarity of aromatic C–H stretching vibrations from interfacial BLG which we associate to a charge reversal at the interface. Foam film measurements show formation of common black films at Ca2+ concentrations above 1 mM due to considerable decrease of the stabilizing electrostatic disjoining pressure. These observations also correlate with a minimum in macroscopic foam stability. For concentrations >30 mM Ca2+, micrographs of foam films show clear signatures of aggregates which tend to increase the stability of foam films. Here, the interfacial layers have a higher surface dilatational elasticity. In fact, macroscopic foams formed from BLG dilutions with high Ca2+ concentrations where aggregates and interfacial layers with higher elasticity are found, showed the highest stability with much smaller bubble size

Specific Properties of Nanoparticles - Peukert, Wolfgang; Walter, Johannes (Powder Technology Handbook, Fourth Edition, 2019)

Spectra library: An assumption-free in situ method to access the kinetics of catechols binding to colloidal ZnO quantum dots - Lin, Wei; Haderlein, Michael; Walter, Johannes; Peukert, Wolfgang; Segets, Doris (Angewandte Chemie International Edition, 2016)
Assumption-free and in situ resolving of the kinetics of ligand binding to colloidal nanoparticles (NPs) with high time resolution is still a challenge in NP research. A unique concept of using spectra library and stopped-flow together with a "search best-match" Matlab algorithm to access the kinetics of ligand binding in colloidal systems is reported. Instead of deconvoluting superimposed spectra using assumptions, species absorbance contributions (ligand@ZnO NPs and ligand in solution) are obtained by offline experiments. Therefrom, a library of well-defined targets with known ligand distribution between particle surface and solution is created. Finally, the evolution of bound ligand is derived by comparing in situ spectra recorded by stopped-flow and the library spectra with the algorithm. Our concept is a widely applicable strategy for kinetic studies of ligand adsorption to colloidal NPs and a big step towards deep understanding of surface functionalization kinetics. Well-established libraries of target spectra that are derived by means of careful offline analysis and identification of equilibrium data within larger kinetic datasets can be used for any particle-ligand system. Kinetics of ligand binding to nanoparticles can be derived free of assumption, in situ, and with high time resolution.
Keywords: colloids; kinetics; ligand exchange; nanoparticles; surface analysis

Spectroscopy of Electrified Interfaces with Broadband Sum Frequency Generation: From Electrocatalysis to Protein Foams - Braunschweig, Björn; Mukherjee, Prabuddha; Kutz, Robert; Rumpel, Armin; Engelhardt, Kathrin; Peukert, Wolfgang; Dlott, Dana; Wieckowski, Andrzej (Vibrational Spectroscopy at Electrified Interfaces, 2013)
This chapter focuses on the application of vibrational sum frequency generation (SFG) spectroscopy to study the molecular structure of electrode‐electrolyte and electrified liquid‐gas interfaces. Vibrational SFG is inherently interface specific because a second‐order process such as SFG is not allowed in the bulk of materials with inversion symmetry. The development of direct ethanol fuel cells demands an in‐depth understanding of ethanol's electrooxidation reactions. With recent advances in the practical design of alkaline fuel cells, a thorough understanding of the ethanol electrooxidation mechanism in alkaline media is now more important than ever. The chapter provides novel insights into this mechanism by examining new data on surface‐adsorbed reaction intermediates at fuel cell relevant conditions. Foams are materials of particular importance since they have a broad range of applications such as metal foams for light‐weight structures, polymer foams for thermal insulation, as well as in textured food product
Keywords: Electrooxidation reactions; Ethanol fuel cells; Electrified interfaces; Electrocatalysis; Vibrational sum frequency generation (SFG); Protein foams; Spectroscopy

Spherical Polybutylene Terephtalate (PBT)-Polycarbonate (PC) Blend Particles by Mechanical Alloying and Thermal Rounding - Dechet, Maximilian; Gomez Bonilla, Juan Sebastian; Lanzl, Lydia; Drummer, Dietmar; Bück, Andreas; Schmidt, Jochen; Peukert, Wolfgang (Polymers, 2018)
In this study, the feasibility of co-grinding and the subsequent thermal rounding to produce spherical polymer blend particles for selective laser sintering (SLS) is demonstrated for polybutylene terephthalate (PBT) and polycarbonate (PC). The polymers are jointly comminuted in a planetary ball mill, and the obtained product particles are rounded in a heated downer reactor. The size distribution of PBT-PC composite particles is characterized with laser diffraction particle sizing, while the shape and morphology are investigated via scanning electron microscopy (SEM). A thorough investigation and characterization of the polymer intermixing in single particles is achieved via staining techniques and Raman microscopy. Furthermore, polarized light microscopy on thin film cuts enables the visualization of polymer mixing inside the particles. Trans-esterification between PBT and PC during the process steps is investigated via vibrational spectroscopy and differential scanning calorimetry (DSC). In this way, a new process route for the production of novel polymer blend particle systems for SLS is developed and carefully analyzed.
Keywords: polybutylene terephthalate (PBT); polycarbonate (PC); polymer blend particles; spheroidization; additive manufacturing; Raman microscopy; SEM staining; trans-esterification

SPIONs functionalized with small peptides for binding of lipopolysaccharide, a pathophysiologically relevant microbial product. - Karawacka, Weronika; Janko, Christina; Unterweger, Harald; Mühlberger, Marina; Lyer, Stefan; Taccardi, Nicola; Mokhir, Andriy; Jira, Wolfgang; Peukert, Wolfgang; Boccaccini, Aldo R.; Kolot, Mikhail; Strauss, Richard; et al. (Colloids and Surfaces B-Biointerfaces, 2018)
Systemic inflammation such as sepsis represents an acute life-threatening condition, to which often no timely remedy can be found. A promising strategy may be to functionalize magnetic nanoparticles with specific peptides, derived from the binding motives of agglutinating salivary proteins, that allow immobilization of pathogens. In this work, superparamagnetic iron oxide nanoparticles with stable polycondensed aminoalkylsilane layer were developed, to which the heterobifunctional linkers N-succinimidyl 3-(2-pyridyldithio)-propanoate (SDPD) and N-succinimidyl bromoacetate (SBA) were bound. These linkers were further chemoselectively reacted with the thiol group of singularly present cysteines of selected peptides. The resulting functional nanoparticles underwent a detailed physicochemical characterization. The biocompatibility of the primarily coated aminoalkylsilane particles was also investigated. To test the pathogen-binding efficacy of the particles, the lipopolysaccharide-immobilization capacity of the peptide-coated particles was compared with free peptides. Here, one particle-bound peptide species succeeded in capturing 90% of the toxin, whereas the degree of immobilization of the toxin with a system that varied in the sequence of the peptide dropped to 35%. With these promising results, we hope to develop extracorporeal magnetic clearance systems for removing pathogens from the human body in order to accelerate diagnosis and alleviate acute disease conditions such as sepsis.

Spontaneous Growth of Magnesium Hydroxide Fibers at Ambient Conditions - Gheisi, Amirreza; Sternig, Andreas; Rangus, Mojca; Redhammer, Günther; Hartmann, Martin; Diwald, Oliver (Crystal Growth & Design, 2014)
Spontaneous transformation paths of nanomaterials point to guiding, principles for synthesis. We describe the room temperature transformation of MgO nanocubes into Mg-3(OH)(5)Cl center dot 4H(2)O nanofibers in air and investigated the underlying formation mechanism using electron microscopy, X-ray diffraction, and solid-state NMR spectroscopy. Upon contact with water vapor, the magnesium hydroxide needles were found to grow out of agglomerates of highly dispersed MgO nanocubes with preadsorbed SiCl4. Corresponding one-dimensional nanostructures do not form on low surface area materials. The presented growth approach is potentially extendable to other hydrolyzable metal oxides at ultrafine dispersion.

Spray agglomeration of polymer particles: Influence of spray parameters on shape factors - Düsenberg, Björn; Schmidt, Jochen; Singh, Abhinandan Kumar; Bück, Andreas (Powder Technology, 2023)
This work systematically investigates the influence of spray parameters on the shape factor descriptors and the fractal dimensions of polymer agglomerates produced by fluidised bed spray agglomeration. Polystyrene primary-particles with sizes <100 μm (Geldart C/A) are used to investigate the shape formation during the agglomeration process with regard to the spray-parameters, i.e., volume flows of the atomization gas and the binder liquid. As binding agent, a solution of polymethyl-methacrylate in acetone is used. Analysis of the agglomerates is carried out using scanning electron microscopy and laser diffraction. Development of agglomerate-size and the distributions of the shape factors circularity, roundness and compactness are monitored by image analysis and correlated with the spray parameters. The calculation of the fractal dimensions with regard to the Sauter mean diameter using the box counting method is performed and compared with the shape factors, resulting in two complementary methods to describe the shape of agglomerates.
CRIS-Team Scopus Importer:2023-04-07
Keywords: Fluidized bed; Fractal dimensions; Shape factor; Spray agglomeration

Spray-Dried Photonic Balls with a Disordered/Ordered Hybrid Structure for Shear-Stress Indication - Wenderoth, Sarah; Bleyer, Gudrun; Endres, Jakob; Prieschl, Johannes; Vogel, Nicolas; Wintzheimer, Susanne; Mandel, Karl (Small, 2022)
Optical microscale shear-stress indicator particles are of interest for the in situ recording of localized forces, e.g., during 3D printing or smart skins in robotic applications. Recently developed particle systems are based on optical responses enabled by integrated organic dyes. They thus suffer from potential chemical instability and cross-sensitivities toward humidity or temperature. These drawbacks can be circumvented using photonic balls as shear-stress indicator particles, which employ structural color as the element to record forces. Here, such photonic balls are prepared from silica and iron oxide nanoparticles via the scalable and fast spray-drying technique. Process parameters to create photonic balls with a disordered core and an ordered particle structure toward the exterior of the supraparticles are reported. This hybrid disordered–ordered structure is responsible for a color loss of the indicator particles during shear-stress application because of irreversible structural destruction. By adjusting the primary silica particle sizes, nearly all colors of the visible spectrum can be achieved and the sensitivity of the response to shear stress can be adjusted.
CRIS-Team Scopus Importer:2022-10-28
Keywords: disordered/ordered core–shell structures; hybrid materials; photonic balls; shear-stress indicators; supraparticles

Spray Printing of Porous Substrates from Nanosuspensions - Panduro Vela, David; Schlumberger, Carola; Thommes, Matthias; Bück, Andreas (Processes, 2023)
In this work, we present and characterise an experimental setup that allows the generation of porous packings from nanosuspensions. By defined positioning and drying of solid-containing droplets, large-scale porous structures can be generated. Examples of such structures are shown and characterised. Operational challenges are presented, and it is discussed how they can be overcome to allow the maximum degree of freedom in packing generation.
CRIS-Team Scopus Importer:2023-05-12
Keywords: drop-on-demand; drying; porosity; suspension; textural characterization

Stability and local environment of iron in vapor phase grown MgO nanocrystals - Niedermaier, Matthias; Dolcet, Paolo; Gheisi, Amirreza; Tippelt, Gerold; Lottermoser, Werner; Gross, Silvia; Bernardi, Johannes; Diwald, Oliver (Journal of Physical Chemistry C, 2017)
Metallocene injection into a metal combustion flame has been used for trapping transition metal ions inside MgO nanocrystals. Vacuum annealing changes the properties of resulting nonequilibrium solids toward thermodynamic equilibrium and provides means to control impurity localization and, as a result, the nanomaterials’ functional properties. By combining structure characterization (X-ray diffraction and transmission electron microscopy) with X-ray absorption spectroscopy and Mössbauer measurements, we tracked valence state and local chemical environment changes of Fe3+ ions inside vapor phase synthesized MgO nanocrystals. At a concentration of (1.5 ± 0.2) at. % Fe about (1400 ± 200) Fe3+ ions are effectively diluted within 12 nm sized nanocubes, where they form complexes between Fe3+ ions and Mg2+ vacancies. Increase of the iron concentration produces additional effects: enhanced ion diffusion and particle coarsening at elevated temperatures, clustering of Fe3+–Mg2+ vacancy complexes and, after annealing to T = 1173 K, the nucleation of a magnesioferrite phase that can be detected by X-ray diffraction for 4 at. % samples. At 3 at. % Fe, corresponding impurity ions induce surface energy changes that have a substantial impact on particle shape. With regard to the functional properties associated with transition metal ions in insulating MgO host lattices, the here presented insights underline that annealing-induced reorganization of oxide nanoparticles provides important parameters to control distribution and localization of impurity ion

Stability and Photoelectronic Properties of Layered Titanate Nanostructures - Riss, Alexander; Elser, Michael J.; Bernardi, Johannes; Diwald, Oliver (Journal of the American Chemical Society, 2009)
Layered titanate nanostructures offer promising photoelectronic properties that are subject to surface chemistry-induced morphology changes. For a systematic evaluation of the bulk and surface contributions to the photoactivity of these structures, we investigated their photoelectronic properties and in particular their dependence on the condition of the gas-solid interface. We comprehensively explored the stability of Na_2Ti_3O7 nanowires and scrolled up H_2Ti_3O7 nanotubes by means of transmission electron microscopy, Raman, and FT-IR spectroscopy and subjected both titanate sheet-based structures to controlled thermal activation treatment under high vacuum conditions. We found that throughout thermal annealing up to T = 870 K the structure and morphology of Na_2Ti_3O7 nanowires are retained. Consistent with the significant photoluminescence emission that is attributed to radiative exciton annihilation in the bulk, UV-induced charge separation is strongly suppressed in these structures. H_2Ti_3O7 nanotubes, however, undergo transformation into elongated anatase nanocrystals during annealing at temperatures T ≥ 670 K. Photoexcitation experiments in O_2 atmosphere reveal that these structures efficiently sustain the separation of photogenerated charges. Trends in the abundance of trapped holes and scavenged electrons were characterized quantitatively by tracking the concentration of paramagnetic O- and O_2- species with electron paramagnetic resonance spectroscopy EPR, respectively. An incisive analysis of these results in comparison to those obtained on airborne anatase nanocrystals underlines the critical role of surface composition and structure on charge separation and, in consequence, on the chemical utilization of photogenerated charge carriers.
EAM Import::2019-03-13

Stabilization mechanism of ZnO quantum dots - Peukert, Wolfgang; Marczak, Renata; Schäfer, Stefan; Segets, Doris (Nanotechnology 2010: Advanced Materials, CNTs, Particles, Films and Composites - 2010 NSTI Nanotechnology Conference and Expo, NSTI-Nanotech 2010, 2010)
The current work addresses the understanding of the stabilization of small ZnO quantum dots in ethanolic suspension. Thereby different degrees of purification were investigated. The results revealed that not only the well-known ζ-potential as a representative for the surface charge determines the colloidal stability but also the surface coverage of acetate groups bound to the particle surface. Those acetate groups act as molecular spacers between the nanoparticles and prevent agglomeration. Regarding DLVO-calculations using a core-shell model, not only the height of the maximum but also the depth of the primary minimum has to be considered to see if a colloidal suspension is stable or not.
Keywords: Core-shell model; Purification; Quantum dot; Stability; ZnO

Stabilization of carbon black particles with Cetyltrimethylammoniumbromide in aqueous media - Eisermann, Claudia; Damm, Cornelia; Winzer, Bettina; Peukert, Wolfgang (Powder Technology, 2014)
The stabilization mechanism of aqueous carbon black suspensions by Cetyltrimethylammoniumbromide (CTAB) is studied in this paper. The adsorption of the surfactant CTAB on the carbon black particles was investigated on dried samples by thermogravimetric analyses (TGA), nitrogen adsorption and attenuated total reflection Fourier transformation infrared spectroscopy (ATR-FTIR) as well as in suspension by zeta potential measurements and atomic force microscopy. The particles are stabilized by an adsorbed CTAB monolayer as can be concluded from the results of TGA and of AFM investigations using a liquid cell. Extended DLVO calculations including the steric contribution of CTAB reveal that carbon particles with an adsorbed monolayer of CTAB exhibit sufficient colloidal stability. This result is in qualitative agreement with the experimental results. © 2013 Elsevier B.V.
Keywords: Carbon black; CTAB adsorption; Dispersion; DLVO calculations; Electrosteric stabilization

State Diagrams of Gas/Solid Flow with Partial Phase Separation - Wirth, Karl-Ernst; Molerus, Otto (KONA Powder and Particle Journal, 1991)
Preferable operational conditions of gas/solid flows are often situated in the transitional regime between two well defined modes, typical examples being pneumatic transport in a horizontal pipe and circulating fluidized beds. The energetic optimum of horizontal pneumatic transport is situated in the transitional regime between strand flow and fully developed flow in which regimes with different physical factors (wall friction of sliding material or single particle wall impact, respectively) prevail. The circulating fluidized bed may be regarded as the transition from a bubbling fluidized bed to pneumatic transport vertically upwards. Experimental results indicate particle slip velocities which are quite a bit higher than predicted by single particle fall velocity, hence indicating strong phase separation in terms of clusters. In both situations, empirical correlations fail because they ignore the complicated structure of the system in question, i.e. being transitional. On the other hand, even very sophisticated modelling can fail, because it is mostly based on inherent a priori assumptions concerning the state of flow. As an alternative, comparably simple models of two phase flows in horizontal pipes and for circulating fluidized beds are presented. The models originate from very obvious visual observations and from considerations of momentum exchange between the two phases. The evaluation of the respective resulting sets of algebraic equations can be represented in terms of state diagrams for gas/solid flows with partial phase separatio
UnivIS-Import:2015-03-05:Pub.1991.tech.ITC.mechve.stated_78
Keywords: gas; solid; flow; fluidization

State Diagrams of Gas/Solids Flows with Partial Phase Separation - Wirth, Karl-Ernst; Molerus, Otto (Shell Conference on Particle Technology, 1990)
Preferable operational conditions of gas/solid flows are often situated in the transitional regime between two well defined modes, typical examples being pneumatic transport in a horizontal pipe and circulating fluidized beds. The energetic optimum of horizontal pneumatic transport is situated in the transitional regime between strand flow and fully developed flow in which regimes with different physical factors (wall friction of sliding material or single particle wall impact, respectively) prevail. The circulating fluidized bed may be regarded as the transition from a bubbling fluidized bed to pneumatic transport vertically upwards. Experimental results indicate particle slip velocities which are quite a bit higher than predicted by single particle fall velocity, hence indicating strong phase separation in terms of clusters. In both situations, empirical correlations fail because they ignore the complicated structure of the system in question, i.e. being transitional. On the other hand, even very sophisticated modelling can fail, because it is mostly based on inherent a priori assumptions concerning the state of flow. As an alternative, comparably simple models of two phase flows in horizontal pipes and for circulating fluidized beds are presented. The models originate from very obvious visual observations and from considerations of momentum exchange between the two phases. The evaluation of the respective resulting sets of algebraic equations can be represented in terms of state diagrams for gas/solid flows with partial phase separation.
UnivIS-Import:2015-04-16:Pub.1990.tech.ITC.mechve.stated
Keywords: phase; flow; particle

Steady-State-Diagram for Cirulating Fluidized Beds - Wirth, Karl-Ernst (Preprints "International Symposium in Coal Combustion", 1987)
This special issue contains a select 19 of 121 papers presented at the 8th International Symposium on Coal Combustion (ISCC-8), which was held at the Beijing Convention Center on 19−22 July 2015. The first ISCC was inaugurated at Tsinghua University, Beijing, China in 1987 under the consistent support of many distinguished scholars including Prof. Junkai Feng, Prof. Xuchang Xu, Prof. Douglas Smoot, Prof. Adel Sarofim, Prof. Klaus Hein, Prof. Ulrich Renz, Prof. Lothar Reh, Prof. Masayosh Sadakata, Prof. Keiji Makino, and Prof. Jianxiong Mao, etc. Since then, the ISCC has been proudly hosted by Tsinghua University for almost three decades, once every four years, as a non-profit platform to promote Research and Development in the field of science and technology of coal combustion, gasification, and the controls of pollutants and CO2 emissions. The most recent ISCC-8 attracted over 200 engineers and scientists from 14 countries including China, USA, Germany, Japan, UK, Canada, Russia, Australia, Korea, India, Sweden, Poland, Portugal, and Estonia. It was chaired by Prof. Guangxi Yue of Tsinghua University, along with the renewed international advisory committee consisting of 52 leading combustion scholars and experts from 14 countries. For the first time, the ISCC adopted the colloquium chair system to guarantee the quality of the conference papers. After two rounds of peer reviews, 196 technical papers including 5 keynotes, 121 oral presentations and 70 posters were selected, covering six main colloquium topics: <dl class="listitem" id="list_l0005"> – Basic Coal Quality & Combustion – Pulverized Coal Combustion – Fluidized Bed Combustion – Special for CO2 Issues-CCS – Emission Characteristics and Controls – Industrial Application & Coal Utilization. </dl> Among them, 19 papers were chosen for this special issue on FUEL, and other 99 technical papers of high quality were recommended and collected into the Proceedings of the 8th ISCC, to be published by Springer-Tsinghua University Press. The Symposium has once again obtained the vigorous support from the industry as well. International experts from the American Institute of Electrical Engineers, the All-Russian Thermal Engineering Institute and Japanese Coal Company were all present. Domestic experts from the top three power equipment manufacturers, i.e., Harbin Boiler Company Limited, DongFang Boiler Group Co., Ltd. and Shanghai Electric Group, also attended, as well as experts from domestic energy companies like Shenhua, Guodian, and Huaneng groups, thus well representing the global industrial application of clean coal technology. The symposium has strongly reinforced the collaboration and discussion between academic researchers and industry experts, which emphasizes the main theme of the ISCC of establishing an effective bridge between academia and industry. We, all Guest Editors, would like to owe our sincere thanks to FUEL principal editor Prof. John Patrick, and the editorial board of FUEL for giving us the opportunity to publish this special issue of the ISCC-8. We also acknowledge the local organizing committee of the ISCC-8 for organizing a successful symposium, providing passionate services and for recommending these excellent papers. Finally, we thank all the authors and the referees for their contributions in making this issue fruitful and successful.
UnivIS-Import:2015-04-16:Pub.1987.tech.ITC.mechve.steady_73
Keywords: combustion; coal; fluidized; bed

Steady State Diagrams for Circulating Fluidzed Beds - Wirth, Karl-Ernst (Preprints 3rd International Conference on Circulating Fluidized Beds, 1990)
Circulating fluidization is a growing new  technology in  many fields where good  fiuid-solid contact is required. Combustion. power generation, catalytic reactions, drying. waste  incineration and iron ore prereduction ate good examples of its application. New  material processing and other fine technology  area will be  as well included soon. The Third International Conference on Circulating Fluidized Beds (ICCFB- 3) was held at  Nagoya.  Japan. from October 15 to 18. 1990. organized by the Society of Chemical Engineers. Japan in  cooperation with the secretariat of ICCPB. In  this conference the attendants vould have the good balances between academic and  industrial subjects as well as between fundamentals and applications or developments. There were 113  papers from  twenty countries and approximately  133  participants from foreign counlries and 150 from  Japan. To establish common Understandings on the state of  arts in  the  CFB society and at  the same time to  encourage as many people to present their papers or opinions, plenary  lectures. combined oral 8 poster sessions, and workshops were assembled. The conference  language was English. All papers to  be presented at the conference  were handed to  all attendants in  a  form of bounded  loose leaves (preprints). The conference site Nagoya is a cozy city located at  the center of pacific  metropolitan belt of the Mainisland  of Japan. People in  the greater Nagoya  area have been proud of her production of  three SAMURAI heroes in  the age of  feudalistic civil war who after all unified  Japan and opened The Tokugara Era that  lasted for 268 years. Nagoya is surrounded by many  basic  and high-tech  industries  including  automobiles. aircrafts,  electronics, iron and steel,  petroleum  and  petrochemicals. ceramics. etc. Resort and picturesque areas including  Japan Alps mountains.  Kyoto.  Nara  and Ise-Shima are all very close from  Nagoya. within one and half hours travel (by train) or at most  three hours by  car via highways. Business trips to Tokyo and/or Osaka are again very simple if they vere made from Nagoya (two hours to Tokyo and one hour and half to Osaka by  Super Express Hikari)
UnivIS-Import:2015-04-16:Pub.1990.tech.ITC.mechve.steady
Keywords: circulating; fluidized; bed

Steering self-organisation through confinement - Araújo, Nuno A.M.; Janssen, Liesbeth M.C.; Barois, Thomas; Boffetta, Guido; Cohen, Itai; Corbetta, Alessandro; Dauchot, Olivier; Dijkstra, Marjolein; Durham, William M.; Dussutour, Audrey; Garnier, Simon; Gelderblom, Hanneke; et al. (Soft Matter, 2023)
Self-organisation is the spontaneous emergence of spatio-temporal structures and patterns from the interaction of smaller individual units. Examples are found across many scales in very different systems and scientific disciplines, from physics, materials science and robotics to biology, geophysics and astronomy. Recent research has highlighted how self-organisation can be both mediated and controlled by confinement. Confinement is an action over a system that limits its units’ translational and rotational degrees of freedom, thus also influencing the system's phase space probability density; it can function as either a catalyst or inhibitor of self-organisation. Confinement can then become a means to actively steer the emergence or suppression of collective phenomena in space and time. Here, to provide a common framework and perspective for future research, we examine the role of confinement in the self-organisation of soft-matter systems and identify overarching scientific challenges that need to be addressed to harness its full scientific and technological potential in soft matter and related fields. By drawing analogies with other disciplines, this framework will accelerate a common deeper understanding of self-organisation and trigger the development of innovative strategies to steer it using confinement, with impact on, e.g., the design of smarter materials, tissue engineering for biomedicine and in guiding active matter.
CRIS-Team Scopus Importer:2023-03-03

“Sticky” carbon coating enables high-area-capacity lithium storage of silicon-graphitic carbon hybrid - Chen, Zidong; Li, Lun; Zhang, Zheng; Li, Hao; Xie, Bo; Chen, Yungui; Davoodi, Ali; Hosseinpour, Saman; Liu, Wei (Carbon, 2021)
Pulverization and surface instability has been identified as the main impediments to the application of Si anodes in high-energy lithium-ion batteries (LIBs). In this study, a Si-graphitic carbon hybrid (SiG) is created via embedding Si nanoparticles in between expanding graphite interlayers, thus to be adopted as a model system to unravel structure-properties relations for LIBs applications. We explore the impact of artificial surface coating layers on the lithium cycling performance of SiG particles. In comparison with native SiG and carbon-coated SiG (CC-SiG), we find that the “sticky-carbon” coating, i.e., an epoxy-rich layer on top of the carbon coating, gave rise to superior cycle performance. In the “sticky carbon” coated SiG (SCC-SiG), the surface chemistry appears to have a pivotal role in both alleviating electrode disintegration and forming a favorable SEI rich in fluorine-polymers. These positive findings are examined in electrodes with mass loading ranging from 1.0 to 5.0 mg/cm2, achieving area capacities up to 5.0 mAh/cm2. A full cell adopting >6 mg/cm2 LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode and SCC-SiG delivers stable cycling performances. It is hence unraveled that the carbon coating layer with reactive surface groups on the top is an unrecognized key for various Si anodes.<br
Keywords: Si anode; surface moieties; solid electrolyte interface; high-area capacity; lithium storage

Stimuli-Responsive Behavior of PNiPAm Microgels under Interfacial Confinement - Harrer, Johannes; Rey, Marcel; Ciarella, Simone; Löwen, Hartmut; Janssen, Liesbeth M.C.; Vogel, Nicolas (Langmuir, 2019)
The volume phase transition of microgels is one of the most paradigmatic examples of stimuli-responsiveness, enabling a collapse from a highly swollen microgel state into a densely coiled state by an external stimulus. Although well characterized in bulk, it remains unclear how the phase transition is affected by the presence of a confining interface. Here, we demonstrate that the temperature-induced volume phase transition of poly(N-isopropylacrylamide) microgels, conventionally considered an intrinsic molecular property of the polymer, is in fact largely suppressed when the microgel is adsorbed to an air/liquid interface. We further observe a hysteresis in the core morphology and interfacial pressure between heating and cooling cycles. Our results, supported by molecular dynamics simulations, reveal that the dangling polymer chains of microgel particles, spread at the interface under the influence of surface tension, do not undergo any volume phase transition. The balance in free energy responsible for the volume phase transition is fundamentally altered by interfacial confinement. These results imply that important technological properties of such systems, including the temperature-induced destabilization of emulsions, do not occur via a decrease in the interfacial coverage of the microgels.
CRIS-Team Scopus Importer:2019-08-23

Stochastic model to simulate spray fluidized bed agglomeration: a morphological approach - Singh, Abhinandan Kumar; Tsotsas, Evangelos (Powder Technology, 2019)
Keywords: Fractal dimension; Monte Carlo method; Agglomeration; Fluidization; Morphological descriptors; Agglomerate porosity

Stochastic simulation of spray agglomeration process in a continuously operated horizontal fluidized bed by Monte Carlo method - Du, Jiajie; Chen, Kaicheng; Bück, Andreas; Tsotsas, Evangelos (13th International Conference on Fluidized Bed Technology, CFB 2021, 2021)

Stochastic simulation of spray fluidized bed agglomeration by modeling the morphology - Singh, Abhinandan Kumar; Tsotsas, Evangelos (13th International Conference on Fluidized Bed Technology, CFB 2021, 2021)

Stopfgrenze und Druckverlust bei der horizontalen pneumatischen Strähnenförderung in nichtkreisförmigen Rohrquerschnitten - Wirth, Karl-Ernst; Molerus, Otto (Chemie Ingenieur Technik, 1985)
Bei der Einphasenströmung ist die Verwendung kreisförmiger Förderrohre optimal. Die Ursache hierfür ist, dass bei diesen Rohrquerschnitten wegen der Rotationssymmetrie des Strömungsfeldes das Verhältnis von benetzem Umfang zu Rohrquerschnittsfläche und dmit der Druckverlust minimal ist. Die gleichen Überlegungen gelten auch für zweiphasige Gas/Feststoff-Rohrströmungen, solange der Feststoff homogen über den Rohrquerschnitt verteillt ist. Sobald allerdings eine Entmischung der Zweiphasenstromung vorliegt, d. h.,  daB ein Teil des durchgesetzten Feststoffmassenstromes als  Strahne am  Rohrboden  gleitet  und  der  restliche  Anteil  des Feststoffmassenstromes in Form der Flugforderung iiber die Strahne transportiert wird, ist nicht mehr das Verhaltnis von Rohrumfang zu Rohrquerschnittsflache fur den sich einstellenden Druckverlust von  Bedeutung.  In  diesem Fall muB vielmehr die Geometrie der Strahne Auswirkungen auf das Druckverlustverhalten und die minimale  Fordergeschwindigkeit  haben.  Im besonderen  stellt sich die Frage, ob durch  Verwendung eines nichtkreisformigen Rohrquerschnittes die Strahnengeometrie so beeinflufit werden kann, dab im Vergleich zum  Kreisrohr  eine  Reduzierung  der fur eine  sichere Forderung  notwendigen  minimalen  Gasleerrohrgeschwindigkeit (Stopfgrenze) erzielt wird. Ausgehend von der Berechnung des Zusatzdruckverlustes  bei horizontaler pneumatischer Strähnenförderung grobkörniger Feststoffe in einem Förderrohr mit Vollkreisquerschnitt wurden für unterschiedliche Rohrquerschnittsformen der Zusatzdruckverlust und die Stopfgrenze berechnet.
UnivIS-Import:2015-03-05:Pub.1985.tech.ITC.mechve.stopfg
Keywords: druckverlust; förderung; pulver; gas; Feststoff