Flow Structures in a Downer Reactor - Wirth, Karl-Ernst; Schiewe, Thilo (Preprints 9th International Conference on Fluidization, 1998)
UnivIS-Import:2015-04-16:Pub.1998.tech.ITC.mechve.flowst
Keywords: fluidization

Fluiddynamical Characterization of a Gas Jet in a Bubbling Fluidized Bed - Wirth, Karl-Ernst; Schober, Michael (Proceedings of the 11th International Conference on Fluidization, 2004)
UnivIS-Import:2015-04-16:Pub.2004.tech.ITC.mechve.fluidd_3

Fluiddynamics and Heat Transfer in a Continuously Operated Fluidized Bed System for High Temperature Treatment of Fine Particles - Wirth, Karl-Ernst; Heinlein, Markus (Proceedings Fluidization XI, 2004)
UnivIS-Import:2015-04-16:Pub.2004.tech.ITC.mechve.fluidd
Keywords: Fluid; dynamics; heat; transfer

Fluid Dynamics and Heat Transfer in Circulating Fluidized Beds - Wirth, Karl-Ernst (Preprints NIRE-Square, National Institute for Resources and Environment, 1997)
A circulating fluidized bed (CFB) is a special case of vertical gas/solid flows. The characteristic feature of these flows is that the gas flows in the opposite direction to gravity. Depending on the choice of particles, the gaseous medium and the adjusted superficial gas velocity, different types of gas/solid flow are obtained (Fig. 13.1). Because the accompanying flow structures influence the heat transfer, as shown in the following chapters, we begin with a detailed description of the fluid dynamics of CFBs.
UnivIS-Import:2015-04-16:Pub.1997.tech.ITC.mechve.fluidd
Keywords: fluidized; bed; circulating

Fluid Mechanics of Circulating Fluidized Beds with a Small Density Ratio of Solids to Fluid. - Wirth, Karl-Ernst; Gruber, Uwe (Preprints 5th International Conference on Circulating Fluidized Beds, 1996)
UnivIS-Import:2015-04-16:Pub.1996.tech.ITC.mechve.fluidm
Keywords: fluidized; bed

Fluid Mechanics of Pressurized Circulating Fluidized Beds - Wirth, Karl-Ernst (Preprints 7th Internat. Conference on Fluidization, 1992)
A fluid mechanical model of segregated vertical gas-solids flow has been developed. Mass and force balances were set up with the aid of this model and, finally, a dimensionless state and pressure drop diagram was calculated. In this diagram, the pressure gradient causedby the solids transport is plotted in dimensionless form versus the superficial gas velocity in the form of a par- ticle Froude number. Parameter is the ratio of the solids volumetric flow rate at minimum fluidization tothe gas volumetric flow rate. The state and pressure drop diagram is valid for a given gas-solids system, i.e. for a given Archimed es number and given inimum fluidizationporosity. The fluid mechanical behaviour of different types of circulating fluidized beds can be  explained with the aid of the state and pressure drop diagram for segregated vertical gas-solids flow. As an example, the operating behaviourof circulating fluidized bed with a syphon in the solids downcomer is discussed. Measurements of the circulating solids mass flow rates arecom- pared with calculation results
UnivIS-Import:2015-04-16:Pub.1992.tech.ITC.mechve.fluidm_73
Keywords: fluidization

Fluid Mechanics of the Downcomer in Circulating Fluidized Beds - Wirth, Karl-Ernst (Preprints Fluidization VIII, 1995)
A fluid mechanical model of segregated vertical gas-solids flow has been developed. Mass and force balances were set up with the aid of this model and, finally, a dimensionless state and pressure drop diagram was calculated. In this diagram, the pressure gradient caused by the solids transport is plotted in dimensionaless form versus the superficial gas velocity in the form of a particle Froude number. Parameter is the ratio of the solids volumetric flow rate at minimum fluidization to the gas volumetric flow rate. The state and pressure drop diagram is valid for a given gas-solids system, i.e. for a given Archimedes number and given minimum fluidization porosity. The fluid mechanical behaviour of different types of circulating fluidized beds can be explained with the aid of the state and pressure drop diagram for segregated vertical gas-solids flow. As an example, the operating behaviour of circulating fluidized bed with a syphon in the solids downcomer is discussed. Measurements of the circulating solids mass flow rates are compared with calculation results.
UnivIS-Import:2015-04-16:Pub.1995.tech.ITC.mechve.fluidm_91
Keywords: fluidization

Flüssig-Flüssig-Phasentrennung und Fällung zur Herstellung neuartiger Ausgangsmaterialien für das pulverbettbasierte Schmelzen von Polymeren - Schmidt, Jochen; Dechet, Maximilian (Proceedings of the 17th Rapid.Tech 3D Conference Erfurt, Germany, 22–23 June 2021, 2021)

Formation and Dissolution of Twin ZnO Nanostructures Promoted by Water and Control over Their Emitting Properties - Distaso, Monica; Mackovic, Mirza; Spiecker, Erdmann; Peukert, Wolfgang (Chemistry - A European Journal, 2014)
By using ZnO as a model system, the formation of twinned nanostructures has been investigated under microwave irradiation, exploiting experimental conditions ranging from purely solvothermal when N,N-dimethylformamide was used, to purely hydrothermal when water was the solvent. A progressive increase in size, elongation and roughness of the surface was observed with increasing water content in the solvent mixture. Particular attention was paid to the reactivity of the ZnO surfaces towards dissolution. Our results show that the formation of twinned nanorods is a dynamic process and that the coupling interphase itself is highly reactive. Consequently, the twinned rods undergo a number of complex dissolution processes that are responsible for the appearance of a wide distribution of defects either on the surface or inside the structure. Poly(N-vinyl pyrrolidone) influences the photoluminescent properties of the as-synthesised materials and allows control of the ratio of the intensity of the UV and visible emission.

Formation of drug-loaded nanoemulsions in stirred media mills - Schwendner, Julia; Konnerth, Christoph-Günther; Romeis, Stefan; Schmidt, Jochen; Peukert, Wolfgang (Advanced Powder Technology, 2019)
The feasibility of stirred media mills for the production of nanoemulsions loaded with active pharmaceutical ingredients (API)using plant oils as disperse phase and different types of the non-ionic emulsifier polysorbate is demonstrated. The influence of the emulsion formulation, namely oil type, surfactant and surfactant-to-oil-weight-ratio (SOR)on the product droplet size at constant stressing conditions is studied in detail. At similar stressing conditions and SOR, the type of the used plant oil and surfactant did not influence the product droplet size and the smallest achievable median droplet size was 20 nm. The API saturated oil phases and the pure oil phases exhibit similar viscosities, emulsification kinetics and final product droplet sizes, i.e. no influence of the API on the emulsification process could be identified. However, a strong dependency of the emulsion droplet size on the SOR has been observed. Moreover, very good long-term stabilities could be achieved for the obtained emulsions. A release test with fenofibrate-loaded peanut oil-polysorbate 80-water nanoemulsions showed remarkably fast drug distribution as compared to a formulation containing the same amount of the non-dissolved micronized drug.
CRIS-Team Scopus Importer:2019-06-04
Keywords: Active pharmaceutical ingredients; Formulation; In vitro release study; Nanoemulsion; Stirred media mill

Formation of Highly Ordered Alloy Nanoparticles Based on Precursor-Filled Latex Spheres - Vogel, Nicolas; et al. (Chemistry of Materials, 2012)
An experimental approach is presented, allowing the preparation of substrate supported, hexagonally arranged metallic alloy nanoparticles with narrow size distributions, well-defined interparticle distances, and controlled chemical composition. The method is based on miniemulsion polymerization and isotropic plasma etching. Polystyrene (PS) and poly(methyl methacrylate) (PMMA) colloids in the present study containing Fe- and Pt-precursor complexes in a predefined ratio are deposited onto hydrophilic Si/SiO2 substrates by dip-coating, forming a highly ordered monolayer. Contrary to colloidal lithography, here, precursor-filled polystyrene colloids serve as carriers for the alloy forming elements. After reactive ion etching and annealing, hexagonally ordered arrays of crystalline FePt nanoparticles are formed exhibiting the desired 1:1 Fe-Pt ratio, as revealed by detailed analysis after each preparation step. Formation of stoichiometric binary alloy FePt nanoparticles is confirmed by determining magnetic hysteresis loops, as well as applying aberration-corrected high-resolution transmission electron microscopy.
Keywords: miniemulsion; colloid monolayer; FePt; nanoparticles; colloidal lithography

Formation of Mefenamic Acid Nanocrystals with Improved Dissolution Characteristics - Konnerth, Christoph-Günther; Braig, Veronika; Schmidt, Jochen; Lee, Geoffrey; Peukert, Wolfgang; Ito, Atsutoshi (Chemie Ingenieur Technik, 2017)
An industrially feasible formulation approach combining media milling and spray-drying was applied to improve dissolu- tion characteristics of the poorly soluble drug mefenamic acid (MA). The approach was studied for two MA polymorphs at different stressing and pH conditions. It was found that final MA product particle sizes are rather determined by the solid-liquid equilibrium than by mechanical fracture. Obtained drug particles are only composed of the most stable poly- morph. Direct compressed tablets containing MA nanocrystals exhibit a significant improvement of in vitro dissolution kinetics as compared to tablets with micronized drug particles.
UnivIS-Import:2017-12-18:Pub.2017.nat.dchph.lphte.format
Keywords: Dissolution rate enhancement; Media milling; Nanocrystal; Polmorphism; Poorly water-soluble drug; Spray drying

Formation of nanoemulsions by stirred media milling - Schmidt, Jochen; Romeis, Stefan; Konnerth, Christoph-Günther; Damm, Cornelia; Peukert, Wolfgang (Proceedings 7th World Congress on Particle Technology, WCPT 2014, 2015)
Emulsions are widely used in the pharmaceutical and food industry. In recent years an increasing use of emulsion-based delivery systems for bioactive substances involving small particle sizes is notable. Apart from spontaneous formation of microemulsions, in general energy has to be introduced into the system, i.e. The formation process of nanoemulsions (thermodynamically metastable systems) is not spontaneous and the droplet-breakup process needs application of external energy input. Within this account we show that highly stable nanoemulsions can be produced by an alternative and scalable process applying stirred media milling. Alkane (hexadecane, dodecane)-Tween85-water-systems have been used as model emulsion systems to demonstrate the feasibility of the approach. The influence of fundamental process parameters such as emulsion formulation (c.f. oil mass fraction and oil-to-emulsifier mass ratio), stressing conditions (grinding bead size and stirrer tip speed), process time and especially temperature on the emulsion droplet size and size distribution has been studied in detail. Low oil-to-emulsifier ratios are most appropriate with respect to obtaining small mean droplet sizes and narrow droplet size distributions. It is shown that the smallest mean droplet sizes (at constant oil-to-emulsifier ratio) are obtained at the lowest oil mass concentrations. Product emulsions of Sauter diameters x below 25 nm have been obtained in the hexadecane-Tween85-water system using ZrO grinding beads of 100 μm and 400 μm in diameter, respectively. Interestingly, working at high stress intensities is not appropriate: higher stress intensities lead to a more intense mixing that increases the coalescence rate. Remarkably, lowering the process temperature below the solidification temperature of the oil phase, i.e. 'grinding' of the solid oil, is advantageous as compared to emulsification of the liquid oil: Coalescence and ripening can be significantly reduced. Smallest product droplets with x < 10 nm are obtained in the hexadecane-Tween85-water system after a short processing time of clearly below 1 hour. The feasibility of the process proposed to produce nanoemulsions using oil phases loaded with the hydrophobic organic compounds pyrene and trans-stilbene is demonstrate
Keywords: formulation; nanoemulsion; oil-in-water emulsion; stirred media mill

Formation of nanoemulsions in stirred media mills - Schmidt, Jochen; Damm, Cornelia; Romeis, Stefan; Peukert, Wolfgang (Chemical Engineering Science, 2013)
Alkane-Tween85-water-systems have been used as model emulsion systems to demonstrate the feasibility of emulsification in stirred media mills. The influence of fundamental process parameters, i.e. emulsion formulation (oil mass fraction and oil-to-emulsifier mass ratio), stress conditions (grinding bead size and stirrer tip speed), process time and especially temperature on the emulsion droplet size and size distribution has been studied for this approach. By lowering the process temperature below the solidification temperature of the oil phase, coalescence and ripening can be significantly reduced. Smallest product droplets with x<10nm thus are obtained even for nominal oil mass fractions up to 20wt% in the hexadecane-Tween85-water system. The feasibility of the process proposed to produce nanoscale emulsions using oil phases loaded with compounds such as pigments and other fillers is demonstrated. © 2013 Elsevier Ltd.
Keywords: Formulation; Nanoemulsion; Oil-in-water emulsion; Stirred media mill; Surfactant; Tween85

Formation of spherical micron-sized polyamide particles for additive manufacturing via liquid-liquid phase separation - Dechet, Maximilian; Kloos, Stephanie; Peukert, Wolfgang; Schmidt, Jochen (AIP Conference Proceedings, 2019)
Selective laser sintering (SLS) is an additive manufacturing (AM) process that yields excellent part qualities with good mechanical properties. The SLS process employs micron-sized polymer particles, which are selectively fused by a laser. While there seem to be hardly any boundaries regarding design, there are quite some restrictions concerning the variety of commercially available SLS materials. With a market share of roughly 90%, polyamide 12 (PA12) is currently the most widely used polymer material for SLS. In order to increase the understanding of the precipitation based manufacturing process for polyamide powders, production of polyamide 11 powders via precipitation in ethanol was investigated. The polymer particles need to be optimized regarding size, shape, flowability and packing characteristics. In this contribution particle manufacturing via liquid-liquid phase separation is discussed. Bulk polymer material of polyamide 11 is directly converted to spherical micron sized particles in a single unit operation. The produced particles are characterized regarding their size and morphology. Furthermore, also structural characteristics, crystallinity and flowability are analyzed and the product properties are correlated with process parameters. We discuss the potential of this process for the production of novel, easy-to-handle polymer particle systems for SLS.
CRIS-Team Scopus Importer:2019-10-22
Keywords: Additive manufacturing; Polymer powder; Precipitation; Selective laser sintering

Formulation of carbon black-ionomer dispersions for thin film formation in fuel cells - Hoffmann, Eva-Maria; Zhang, Su; Thoma, Martin; Damm, Cornelia; Peukert, Wolfgang (Particuology, 2019)
The performance of proton exchange membrane fuel cells (PEMFC) is strongly determined by the structure and composition of the electrode layer. The interactions between the ionomer, carbon black particles, and solvent affect the suspension properties and thus the layer morphology. We analyze the effect of the ionomer-to-carbon (I/C) weight ratio for two different types of carbon black on the suspension and layer characteristics. Highly branched carbon blacks with a high surface area tend to form less cracked layers. As less branched carbons can pack together more closely, a smaller pore size results in a larger capillary pressure during drying and thus more cracks. The added ionomer adsorbs on the carbon particles and improves the colloidal stability of the carbon black particles. The carbon black aggregates are thus smaller, resulting in closer packing and thinner layers. Moreover, the addition of the ionomer increases the critical coating thickness (CCT) of the layers because drying stresses are dissipated by the deformation of the ionomer, preventing crack formation. An optimum I/C weight ratio is identified for optimal layer formation and minimized crack formation.
CRIS-Team Scopus Importer:2019-05-02
Keywords: Carbon black; Cracking; Layer formation; Perfluorosulfonic acid (PFSA) ionomer; Porosity

Formulation of Nanostructured Heteroaggregates by Fluidization Technologies - Men, Jialin; Kolan, Subash Reddy; Massomi, Ali; Hoffmann, Torsten; Schmidt, Jochen; Tsotsas, Evangelos; Bück, Andreas (Chemie Ingenieur Technik, 2022)
Nanostructured heteroaggregates provide improved or new functionalities over homoaggregates due to the formation of heterocontacts. For a high number of heterocontacts, intense mixing of the primary particles and their reaggregation is required. This work presents results using the principle of fluidization for formulation of nanostructured heteroaggregates. Intraaggregate mixing of constituents is evaluated by SEM-EDX. The feasibility of two technologies, spouted bed and opposed jet fluidized bed, is demonstrated, also showing the variety of structures that can be achieved by the technologies.
CRIS-Team Scopus Importer:2022-11-04
Keywords: Aggregation; Fluidization; Heterocontact; Mixing; Nanoparticle

Fortschritte beim Erzeugen, Formulieren und Handhaben feinster Feststoffe; Product Design mit maßgeschneiderten Grenzflächen - Peukert, Wolfgang (Produktgestaltung und Grenzflächen, 2002)
UnivIS-Import:2015-04-16:Pub.2002.tech.ITC.mechve.fortsc
Keywords: Grenzflächen; product; design

Fractal analysis of aggregates: Correlation between the 2D and 3D box-counting fractal dimension and power law fractal dimension - Wang, Rui; Singh, Abhinandan Kumar; Kolan, Subash Reddy; Tsotsas, Evangelos (Chaos Solitons & Fractals, 2022)
Keywords: 3D fractal dimension; 2D fractal dimension; Box-counting; Aggregation; Power-law

Free Energy Landscape of Colloidal Clusters in Spherical Confinement - Wang, Junwei; Mbah Chrameh, Fru; Przybilla, Thomas; Englisch, Silvan; Spiecker, Erdmann; Engel, Michael; Vogel, Nicolas (Acs Nano, 2019)
The structure of finite self-assembling systems depends sensitively on the number of constituent building blocks. Recently, it was demonstrated that hard sphere-like colloidal particles show a magic number effect when confined in emulsion droplets. Geometric con-struction rules permit a few dozen magic numbers that correspond to a discrete series of completely filled concentric icosahedral shells. Here, we investigate the free energy landscape of these colloidal clusters as a function of the number of their constituent building blocks for system sizes up to several thousand particles. We find that minima in the free energy landscape, arising from the presence of filled, concentric shells, are significantly broadened, compared to their atomic analogues. Colloidal clusters in spherical confinement can flexibly accommodate excess particles by ordering icosahedrally in the cluster center while changing the structure near the cluster surface. In between these magic number regions, the building blocks cannot arrange into filled shells. Instead, we observe that defects accumulate in a single wedge and therefore only affect a few tetrahedral grains of the cluster. We predict the existence of this wedge by simulation and confirm its presence in experiment using electron tomography. The introduction of the wedge minimizes the free energy penalty by confining defects to small regions within the cluster. In addition, the remaining ordered tetrahedral grains can relax internal strain by breaking icosahedral symmetry. Our findings demonstrate how multiple defect mechanisms collude to form the complex free energy landscape of colloidal cluster
Keywords: self-assembly; hard spheres; supraparticles; emulsions; magic numbers; icosahedral symmetry; defects

From evaporation-induced self-assembly to shear-induced alignment - Srikantharajah, Rubitha; Schindler, Torben; Landwehr, Inga; Romeis, Stefan; Unruh, Tobias; Peukert, Wolfgang (Nanoscale, 2016)
The functionality of compact nanostructured thin films depends critically on the degree of order and hence on the underlying ordering mechanisms during film formation. For dip coating of rigid nanorods the counteracting mechanisms, evaporation-induced self-assembly (EISA) and shear-induced alignment (SIA) have recently been identified as competing ordering mechanisms. Here, we show how to achieve highly ordered and homogeneous thin films by controlling EISA and SIA in dip coating. Therefore we identify the influences of the process parameters including temperature, initial volume fraction and nanorod aspect ratio on evaporation-induced convective flow and externally applied shear forces and evaluate the resulting films. The impact of evaporation and shear can be distinguished by analysing film thickness, surface order and bulk order by careful in situ SAXS, Raman and SEM-based image analysis. For the first time we derive processing guidelines for the controlled application of EISA and SIA towards highly ordered thin nematic films.

From in situ characterization to process control of quantum dot systems - Peukert, Wolfgang; Segets, Doris; Haderlein, Michael; Pflug, Lukas; Leugering, Günter; Gröschel, Michael (7th World Congress on Particle Technology, WCPT 2014, 2015)
Keywords: in situ; characterization; process design; optical properties; quantum dots

From Meso to Macro: Controlling Hierarchical Porosity in Supraparticle Powders - Sultan, Umair; Götz, Alexander; Schlumberger, Carola; Drobek, Dominik; Bleyer, Gudrun; Walter, Teresa; Loewer, Erik; Peuker, Urs Alexander; Thommes, Matthias; Spiecker, Erdmann; Apeleo Zubiri, Benjamin; Inayat, Alexandra; et al. (Small, 2023)
A drying droplet containing colloidal particles can consolidate into a spherical assembly called a supraparticle. Such supraparticles are inherently porous due to the spaces between the constituent primary particles. Here, the emergent, hierarchical porosity in spray-dried supraparticles is tailored via three distinct strategies acting at different length scales. First, mesopores (<10 nm) are introduced via the primary particles. Second, the interstitial pores are tuned from the meso- (35 nm) to the macro scale (250 nm) by controlling the primary particle size. Third, defined macropores (>100 nm) are introduced via templating polymer particles, which can be selectively removed by calcination. Combining all three strategies creates hierarchical supraparticles with fully tailored pore size distributions. Moreover, another level of the hierarchy is added by fabricating supra-supraparticles, using the supraparticles themselves as building blocks, which provide additional pores with micrometer dimensions. The interconnectivity of the pore networks within all supraparticle types is investigated via detailed textural and tomographic analysis. This work provides a versatile toolbox for designing porous materials with precisely tunable, hierarchical porosity from the meso- (3 nm) to the macroscale (≈10 µm) that can be utilized for applications in catalysis, chromatography, or adsorption.
CRIS-Team Scopus Importer:2023-04-07
Keywords: adsorption; hierarchy; porous materials; self-assembly; supraparticles; tomography

From molecules to materials: The cluster of excellence "engineering of Advanced Materials" at Friedrich-Alexander University of Erlangen-Nuremberg - Peukert, Wolfgang; Wasserscheid, Peter; Hirsch, Andreas (Advanced Materials, 2011)
Engineering of Advanced Materials - Hierarchical Structure Formation for Functional Devices (EAM) focus on the development of advanced materials with properties customized on the nano and mesoscale. The EAM network comprises scientists from different departments including Applied Mathematics, Chemical Engineering, Chemistry, Computer Science, Electrical Engineering, Materials Science, and Mechanical Engineering and Physics. The development of EAM has been encouraged by the acquisition of world-class scientific instruments. These include an FEI Titan 80-300 transmission electron microscope enhancing an aberration corrector to enable the high resolution imaging of nanomaterials in unprecedented clarity. The instrument also includes a full suite of state of the art spectroscopic and tomographic techniques. EAM is also focusing on hybrid electronic systems which exploit the advantages of both organic and inorganic materials.

From single particle impact behaviour to modelling of impact mills - Vogel, Lutz; Peukert, Wolfgang (Chemical Engineering Science, 2005)
An approach to quantify the impact grinding performance of different materials is presented. Based on a dimensional analysis and on fracture mechanical considerations two material parameters, fMat. and Wm,min, are derived from theoretical considerations. fMat. characterises the resistance of particulate material against fracture in impact comminution. Wm,min gives the mass specific energy which a particle can absorb without fracture. Using this approach various materials in a wide size range, e.g. different polymers, crystalline substances, glass and limestone, can be characterised quantitatively. The derived material parameters are applied to the systematic and multi-scale modelling of grinding in impact mills. A population balance model is presented and the results of the simulation for two different impact mills are shown. The developed model allows for a clear separation of the influence of material properties, mill specific features and operating conditions, thus enabling a deeper understanding of the impact grinding process. © 2005 Elsevier Ltd. All rights reserved.
UnivIS-Import:2015-03-09:Pub.2005.tech.ITC.mechve.fromsi
Keywords: Comminution; Grinding; Impact mills; Material characterisation; Population balance model; Simulation

From soft to hard: The generation of functional and complex colloidal monolayers for nanolithography - Vogel, Nicolas; et al. (Soft Matter, 2012)

From Sticky to Slippery: Self-Functionalizing Lubricants for in Situ Fabrication of Liquid-Infused Surfaces - Chiera, Salvatore; Koch, Vanessa; Bleyer, Gudrun; Walter, Teresa; Bittner, Carina; Bachmann, Julien; Vogel, Nicolas (ACS Applied Materials and Interfaces, 2022)
Liquid-infused surfaces offer a versatile approach to create self-cleaning coatings. In such coatings, a thin film of a fluid lubricant homogeneously coats the substrate and thus prevents direct contact with a second, contaminating liquid. For stable repellency, the interfacial energies need to be controlled to ensure that the lubricant is not replaced by the contaminating liquid. Here, we introduce the concept of self-functionalizing lubricants. Functional molecular species that chemically match the lubricant but possess selective anchor groups are dissolved in the lubricant and self-adhere to the surface, forming the required surface chemistry in situ from within the applied lubricant layer. To add flexibility to the self-functionalizing concept, the substrate is first primed with a thin polydopamine base layer, which can be deposited to nearly any substrate material from aqueous solutions and retains reactivity toward electron-donating groups such as amines. The temporal progression of the in situ functionalization is investigated by ellipsometry and quartz crystal microbalance and correlated to macroscopic changes in contact angle and contact angle hysteresis. The flexibility of the approach is underlined by creating repellent coatings with various substrate/lubricant combinations. The prepared liquid-infused surfaces significantly reduce cement adhesion and provide easy-to-clean systems under real-world conditions on shoe soles.
CRIS-Team Scopus Importer:2022-04-22
Keywords: coatings; liquid-infused surfaces; polydopamine; self-cleaning; surface functionalization

From trash to treasure in additive manufacturing: Recycling of polymer powders by acid catalyzed hydrolysis - Hesse, Nicolas; Jaksch, Andreas; Kaschta, Joachim; Groh, Dominik; Drummer, Dietmar; Peukert, Wolfgang; Schmidt, Jochen (Additive Manufacturing, 2023)
A persistent problem in laser powder bed fusion (PBF) additive manufacturing (AM) of polymers is the accumulation of used feedstock material that cannot be reprocessed due to alterations in the physical and chemical structure upon ageing at elevated temperatures. The chemical ageing of polyamide 12, the most frequently used feedstock in PBF of polymers, occurs due to solid-state post-condensation during the AM process and can be reversed by appropriate processing. This paper investigates the application of acid-catalyzed hydrolytic reconditioning to restore virgin powder properties from used and annealed feedstock material, highlighting a pathway to more sustainability in AM. The proposed method is optimized towards PBF-printing relevant properties and mechanical characteristics of parts build with the recycled feedstock material, which are benchmarked against conventional powder refreshing strategies.
CRIS-Team Scopus Importer:2023-05-26
Keywords: Hydrolysis; Polyamide 12; Polymer ageing; Polymer recycling; Powder bed fusion; Powder characterization

From visions to products in industrial crystallization - Peukert, Wolfgang; Eble, A (SCOPUS, 2005)
The current industrial trends related to crystallization are characterized by strong needs for cost reduction for production of commodities followed by globalization and a general shift towards high added-value products. New products with higher added-value are developed which are characterized not only by their state of crystallinity but also by their size, structure, surface properties in order to allow integration of these products in highly integrated products. The need for very specific properties of crystalline particles is a main driving force of nanotechnology. Predictive models including mixing, reaction, and nucleation will help to understand crystallization and to better take control on the underlying mechanisms.
Keywords: Industrial crystallization; Crystallization; VDI

Functional Interfaces in Pure and Blended Oxide Nanoparticle Networks: Recombination versus Separation of Photogenerated Charges - Siedl, Nicolas; Elser, Michael J.; Bernardi, Johannes; Diwald, Oliver (Journal of Physical Chemistry C, 2009)
Solvent-mediated particle aggregation was employed to produce nanoparticle networks containing a high abundance of functional interfaces. Using electron paramagnetic resonance spectroscopy (EPR), we experimentally observed that the intentional attachment of vapor-grown ZrO_2 nanocrystals to TiO_2 particle surfaces yields networks of intermixed nanoparticles with substantially improved charge separation properties. The superior performance holds also in comparison to homogeneous ZrO_2 and TiO_2 nanoparticle networks that exhibit a higher charge recombination loss in comparison to powders of unconnected nanocrystals.
EAM Import::2019-03-14

Functionalization of polymer particles for additive manufacturing processes by plasma treatment in a fluidized bed reactor - Sachs, Marius; Schmidt, Jochen; Peukert, Wolfgang; Wirth, Karl-Ernst (8th International Conference for Conveying and Handling of Particulate Solids, CHoPS 2015, 2015)
Recently additive manufacturing processes such as laser beam melting (LBM) of polymers have gained more importance for industrial applications [1]. Tailor-made modification of polymers is essential in order to make these processes more efficient and to cover the industrial demands. The so far used polymer materials show weak performance regarding the mechanical stability of processed parts. To overcome this limitation, a new route to functionalize the surface of commercially available polymer particles (PA12) using an atmospheric plasma jet in combination with a fluidized bed reactor (FBR) has been investigated. Consequently, an improvement of adhesion and wettability [2] of the polymer surface without restraining the bulk properties of the powder is achieved. The atmospheric plasma jet process can provide reactive species at moderate temperatures which are suitable for polymer material. The functionalization of the polymer powders improves the quality of the devices build in a LBM-proces
Keywords: additive; manufacturing; polymer; tailor-made; functionalization; stability

Functionalization of polymer powders for SLS-processes using an atmospheric plasma jet in a fluidized bed reactor - Sachs, Marius; Schmitt, Adeliene; Schmidt, Jochen; Peukert, Wolfgang; Wirth, Karl-Ernst (AIP Conference Proceedings 1664, 2015)
Recently additive manufacturing processes such as selective laser sintering (SLS) of polymers have gained more importance for industrial applications [1]. Tailor-made modification of polymers is essential in order to make these processesmore efficient and to cover the industrial demands. The so far used polymer materials show weak performance regarding the mechanical stability of processed parts. To overcome this limitation, a new route to functionalize the surface of commerciallyavailable polymer particles (PA12; PE-HD; PP) using an atmospheric plasma jet in combination with a fluidized bed reactor has been investigated. Consequently, an improvement of adhesion and wettability [2] of the polymer surface without restraining the bulk properties of the powder is achieved. The atmospheric plasma jet process can provide reactive species at moderate temperatures which are suitable for polymer material. The functionalization of the polymer powders improves the quality of the devices build in a SLS-proces
Keywords: Atmospheric Plasma Jet; Polymer Functionalization; Fluidized Bed Reactor; SLS-Process

Functionalization of polymers using an atmospheric plasma jet in a fluidized bed reactor and its impact on selective laser melting processes - Sachs, Marius; Schmitt, Adeliene; Schmidt, Jochen; Peukert, Wolfgang; Wirth, Karl-Ernst (11th International Conference on Fluidized Bed Technology, CFB 2014, 2014)
In order to improve thermoplastic particles (e.g. Polyamide, Polypropylene and Polyethylene) for Selective Laser Melting (SLM) processes a new approach for functionalization of temperature-sensitive polymer powders at large scales is investigated. This is achieved by combining an atmospheric pressure plasma jet and a fluidized bed reactor. Using pressurized air as plasma gas, radicals including OH* are generated. The functionalization leads to an increase of surface energy of the treated polymer powder without changing the bulk properties. Application of the functionalized polymers in a SLM process to build single layers leads to an improvement of the melted layer
Keywords: Atmospheric pressure plasma jet; Polymer functionalization; Fluidized bed reactor

Functionalization of polymers using an atmospheric plasma jet in a fluidized bed reactor and the impact on SLM-Processes - Sachs, Marius; Schmitt, Adeliene; Schmidt, Jochen; Peukert, Wolfgang; Wirth, Karl-Ernst (29th International Conference of the Polymer Processing Society, 2014)
In order to improve thermoplastics (e. g. Polyamide, Polypropylene and Polyethylene) for Selective Laser Beam Melting (SLM) processes a new approach to functionalize temperature sensitive polymer powders in a large scale is investigated. This is achieved by combining an atmospheric pressure plasma jet and a fluidized bed reactor. Using pressurized air as the plasma gas, radicals like OH* are created. The functionalization leads to an increase of the hydrophilicity of the treated polymer powder without changing the bulk properties. Using the polymers in a SLM process to build single layers of melted material leads to an improvement of the melted layers.
Keywords: fluidized bed reactor; atmospheric pressure plasma jet; polymer functionalization

Functionalization of steel surfaces with organic acids: Influence on wetting and corrosion behavior - Alonso Frank, Micael; Meltzer, Christian; Braunschweig, Björn; Peukert, Wolfgang; Boccaccini, Aldo R.; Virtanen, Sannakaisa (Applied Surface Science, 2017)
Self-assembled monolayers (SAMs) have been used to tailor surface properties of different metal surfaces. Typically SAMs can be bound to surface hydroxyls of a thin oxide layer that forms on the surface of a less noble metal and dominates its properties. The effects of SAMs with different anchoring groups and chain lengths regarding wettability, corrosion resistance and homogeneity of the layer were studied in detail. Alkyl carbonic and phosphonic acids were selected to create a hydrophobic layer on the surface of stainless steel ASIS 316L and on carbon steel N80. SAMs were formed by dip-coating of the samples in an organic acid ethanolic solution. Sum frequency generation (SFG) analysis together with contact angle and electrochemical measurements were carried out to explore correlations between tailored wettability, corrosion resistance, and layer homogeneity on one side, and the chain length, anchor group, concentration and immersion time on the other side. The homogeneity of the layers as well as the resulting surface hydrophobicity increased with an increase of the immersion time, the contact angle reached a maximum (ca. 120°) for an immersion time of approximately 2 days.
Keywords: Carbon steel N80; Hydrophobicity; Myristic acid; Octadecylphosphonic acid (ODPA); Stainless steel 316 L; Stearic acid; Sum frequency generation; Surface functionalization

Gallium-rich Pd-Ga phases as supported liquid metal catalysts - Taccardi, Nicola; Grabau, Mathias; Debuschewitz, Jonas; Distaso, Monica; Brandl, Marco; Hock, Rainer; Maier, Florian; Papp, Christian; Erhard, Jannis; Neiß, Christian; Peukert, Wolfgang; Görling, Andreas; et al. (Nature chemistry, 2017)
A strategy to develop improved catalysts is to create systems that merge the advantages of heterogeneous and molecular catalysis. One such system involves supported liquid-phase catalysts, which feature a molecularly defined, catalytically active liquid film/droplet layer adsorbed on a porous solid support. In the past decade, this concept has also been extended to supported ionic liquid-phase catalysts. Here we develop this idea further and describe supported catalytically active liquid metal solutions (SCALMS). We report a liquid mixture of gallium and palladium deposited on porous glass that forms an active catalyst for alkane dehydrogenation that is resistant to coke formation and is thus highly stable. X-ray diffraction and X-ray photoelectron spectroscopy, supported by theoretical calculations, confirm the liquid state of the catalytic phase under the reaction conditions. Unlike traditional heterogeneous catalysts, the supported liquid metal reported here is highly dynamic and catalysis does not proceed at the surface of the metal nanoparticles, but presumably at homogeneously distributed metal atoms at the surface of a liquid metallic phas

Ga-Pt supported catalytically active liquid metal solutions (SCALMS) prepared by ultrasonication - influence of synthesis conditions on n-heptane dehydrogenation performance - Oshin, Sebastian; Al-Shaibani, Asem; Taccardi, Nicola; Sultan, Umair; Inayat, Alexandra; Vogel, Nicolas; Haumann, Marco; Wasserscheid, Peter (Catalysis: Science and Technology, 2023)
Supported catalytically active liquid metal solution (SCALMS) materials represent a recently developed class of heterogeneous catalysts, where the catalytic reaction takes place at the highly dynamic interface of supported liquid alloys. Ga nuggets were dispersed into nano-droplets in propan-2-ol using ultrasonication followed by the addition of Pt in a galvanic displacement reaction - either directly into the Ga/propan-2-ol dispersion (in situ) or consecutively onto the supported Ga droplets (ex situ). The in situ galvanic displacement reaction between Ga and Pt was studied in three different reaction media, namely propan-2-ol, water, and 20 vol% water containing propan-2-ol. TEM investigations reveal that the Ga-Pt reaction in propan-2-ol resulted in the formation of Pt aggregates on top of Ga nano-droplets. In the water/propan-2-ol mixture, the desired incorporation of Pt into the Ga matrix was achieved. The ex situ prepared Ga-Pt SCALMS were tested in n-heptane dehydrogenation. Ga-Pt SCALMS synthesized in pure alcoholic solution showed equal dehydrogenation and cracking activity. Ga-Pt SCALMS prepared in pure water, in contrast, showed mainly cracking activity due to oxidation of Ga droplets. The Ga-Pt SCALMS material prepared in water/propan-2-ol resulted in high activity, n-heptene selectivity of 63%, and only low cracking tendency. This can be attributed to the supported liquid Ga-Pt alloy where Pt atoms are present in the liquid Ga matrix at the highly dynamic catalytic interfac
Keywords: Binary alloys; Dehydrogenation; Drops; Heptane; Liquid metals; Platinum alloys; Substitution reactions; Cracking activity; Ex situ; Galvanic displacement reactions; matrix; Metal solutions; n-Heptanes; Nano-droplets; Performance; Synthesis conditions; Ultra-sonication; Catalysis

Gas phase synthesis of anisotropic silicon germanium hybrid nanoparticles - Mehringer, Christian; Wagner, Richard; Jakuttis, Thomas; Butz, Benjamin; Spiecker, Erdmann; Peukert, Wolfgang (Journal of Aerosol Science, 2014)
We demonstrate the capability of hot wall reactor gas phase synthesis to produce germanium (Ge) on silicon (Si) anisotropic particles. A two stage reactor setup is used to produce silicon nanoparticles (SiNPs) of 29.6 nm in diameter with a very narrow size distribution and to deposit Ge on them. The gaseous precursors are monosilane (SiH4) and monogermane (GeH4). In a SEM study Ge patch formation on the SiNPs due to Stranski–Krastanov growth is observed. The patch size as well as the number of patches per SiNP is dependent on the process temperature and the GeH4 partial pressure. By varying these parameters it is possible to synthesize Janus-like particles with only one e.g. facetted Ge patch per SiNP, as well as patchy particles carrying an average of four to eight patches. HRTEM analysis shows, that the Ge grows epitaxial and crystalline on the surface of the SiNPs. From geometric phase analysis (GPA) the termination of inserted (220) half planes corresponding to misfit dislocations can be deduced, indicating a largely relaxed lattice in the Ge patches. A continuous tilt of the (111) lattice planes in the Si core below a Ge patch indicates that elastic deformation also contributes to the strain relaxation.

Gas phase temperature measurements in a flame spray pyrolysis process by O2 pure rotational CARS - Peukert, Wolfgang; Seeger, Thomas; Engel, Sascha; Kögler, Andreas; Gao, Yi; Kilian, Daniel; Voigt, Michael; Leipertz, Alfred (Laser Applications to Chemical, Security and Environmental Analysis 2012, 2012)
For the production of oxide nanoparticles at a commercial scale, flame spray processes are frequently used. To preserve the original behavior of the sensitive flame spray pyrolysis process in situ, the gas phase temperatures were measured with pure rotational CARS. An O pure rotational CARS setup was applied due to the lack of N. The CARS technique benefit from a polarization filtering technique that is essential in particle and droplet environments for acquiring CARS spectra suitable for temperature fitting. The temperature results indicate the dissipation of energy by radiation in the presence of particles since the flame temperatures are decreasing with increasing particle concentrations. © 2012 OS
Keywords: flame; spray; pyrolysis; gas; phase; particle; nano; radiation

Gas phase temperature measurements in the liquid and particle regime of a flame spray pyrolysis process using O2-based pure rotational coherent anti-Stokes Raman scattering - Peukert, Wolfgang; Engel, Sascha; Kögler, Andreas; Gao, Yi; Kilian, Daniel; Voigt, Michael; Seeger, Thomas; Leipertz, Alfred (Applied Optics, 2012)
For the production of oxide nanoparticles at a commercial scale, flame spray processes are frequently used where mostly oxygen is fed to the flame if high combustion temperatures and thus small primary particle sizes are desired. To improve the understanding of these complex processes in situ, noninvasive optical measurement techniques were applied to characterize the extremely turbulent and unsteady combustion field at those positions where the particles are formed from precursor containing organic solvent droplets. This particle-forming regime was identified by laser-induced breakdown detection. The gas phase temperatures in the surrounding of droplets and particles were measured with O2 -based pure rotational coherent anti-Stokes Raman scattering (CARS). Pure rotational CARS measurements benefit from a polarization filtering technique that is essential in particle and droplet environments for acquiring CARS spectra suitable for temperature fitting. Due to different signal disturbing processes only the minority of the collected signals could be used for temperature evaluation. The selection of these suitable signals is one of the major problems to be solved for a reliable evaluation process. Applying these filtering and signal selection steps temperature measurements have successfully been conducted. Time-resolved, single-pulse measurements exhibit temperatures between near-room and combustion temperatures due to the strongly fluctuating and flickering behavior of the particle-generating flame. The mean flame temperatures determined from the single-pulse data are decreasing with increasing particle concentrations. They indicate the dissipation of large amounts of energy from the surrounding gas phase in the presence of particles.
Keywords: oxyide; nanoparticle; optical; noninvasive; droplet; combustion; raman; scattering

Gas/Solids Mixing-Behaviour in the Entrance Region of a Downer and its Effect on the Residence Time Distribution of the Gas - Wirth, Karl-Ernst; Brust, Holger (Proceedings Fluidization XI, 2004)
UnivIS-Import:2015-04-16:Pub.2004.tech.ITC.mechve.gassol
Keywords: fluidization; mixing

General concepts in nanoparticle technology and their possible implication on cultural science and philosophy - Peukert, Wolfgang (Powder Technology, 2005)
This paper consists of two parts. The first part describes generally applicable concepts in nanoparticle technology. A key objective in nanotechnology is to build functional structures from small building blocks, i.e. nanoparticles. Starting from the concept of product engineering we investigate the basic preconditions for tailoring functional structures and their properties. Formation of macroscopic structures is only possible through microscopic control of particulate interfaces, i.e. of particle interactions. Particle interactions result mainly from the molecular properties of the respective surfaces which are governed by quantum mechanics. However, in many cases particle interactions can be sufficiently described by classical force laws. The sum of all these forces plus external forces leads to the desired structure. The second part of this paper draws conclusions from these physical principles and dares to apply these to philosophy and cultural sciences. It seems that encounters between entities, in this case individuals, small groups, countries, for instance, leads to the development of social structures and in most general sense to culture. Changing the interactions between the entities will lead to different structures. The conclusion is straightforward but extremely complex in general: We as individuals are tailoring life and culture by our way of interacting. © 2005 Elsevier B.V. All rights reserved.
Keywords: Cultural sciences; Nanoparticles; Philosophy; Product engineering; Structure formation

Generally applicable breakage functions derived from single particle comminution data - Meier, Matthias; John, Edgar; Wieckhusen, Dierk; Wirth, Wolfgang; Peukert, Wolfgang (Powder Technology, 2009)
Nine different substances with widely varying properties have been impacted on a rigid target at different velocities. The obtained fragment size distributions have been analyzed in order to obtain a mathematical expression for the breakage functions. The breakage function was modeled as a bimodal logarithmic normal distribution. It was found that the parameters of these approximated breakage functions change with impact energy in the same way for all substances. It could be shown that the breakage function is both size and material dependent. The material dependency can be expressed via the dimensionless stressing parameter f* (Mat) . x . (W* (m.kin) - W* (m.min)), where f* (Mat) and x . W* (m.min) are breakage parameters that can be determined from single particle comminution experiments or estimated from other mechanical properties (namely the brittleness index of the material). No difference in the breakage functions was found for impacts under 60 degrees and 90 degrees. The results of this work allow the prediction of breakage functions for impacting particles. (C) 2009 Elsevier B.V. All rights reserved.
Keywords: Comminution; Grinding; Breakage function; Single particle experiments; Material properties

Generation of multi-material parts with alternating material layers by Simultaneous Laser Beam Melting of polymers - Laumer, Tobias; Stichel, Thomas; Fanselow, Stephanie; Koopmann, Jonas; Amend, Philipp; Schmidt, Michael (International Conference on Additive Technologies - ICAT 2014, 2014)
By using Additive Manufacturing technologies, like Laser Beam Melting (LBM) of polymers, parts can be realized within single days and necessary modifications can be quickly adapted. With increasing complexity, products are often made out of different polymer materials and the need for multi-material parts is an increasing industry requirement, which cannot be fulfilled by the single material parts realizable by LBM. Therefore, Simultaneous Laser Beam Melting (SLBM) as a new Additive Manufacturing technology offers the possibility to build parts consisting of different polymer materials. The realizable parts combine different material properties, like differing stiffness or chemical resistances, within a single part. Up to now, different materials are deposited next to each other on the building platform, thus the boundary surface between the different polymers is orientated perpendicular to the building direction. For this paper, the polymer powders are alternated in building direction. Thus, the boundary surface is orientated horizontally and is larger, both influencing the boundary surface and resulting part properties, which are analyzed by a high-resolution thermal imaging system and by cross sections.
Keywords: Additive Manufacturing; Simultaneous Laser Beam Melting; Multi-Material Parts

Germanium-silicon alloy and core-shell nanocrystals by gas phase synthesis - Mehringer, Christian; Kloner, Christian; Butz, Benjamin; Winter, Benjamin; Spiecker, Erdmann; Peukert, Wolfgang (Nanoscale, 2015)
In this work we present a novel route to synthesize well defined germanium-silicon alloy (GexSi1-x) and core-shell nanocrystals (NCs) employing monosilane (SiH4) and monogermane (GeH4) as precursors in a continuously operated two-stage hot-wall aerosol reactor setup. The first hot-wall reactor stage (HWR I) is used to produce silicon (Si) seed particles from SiH4 pyrolysis in Argon (Ar). The resulting seeding aerosol is fed into the second reactor stage (HWR II) and a mixture of SiH4 and GeH4 is added. The ratio of the precursors in the feed, their partial pressures, the synthesis temperature in HWR II and the overall pressure are varied depending on the desired morphology and composition. Alloy particle production is achieved in the heterogeneous surface reaction regime, meaning that germanium (Ge) and Si are deposited on the seed surface simultaneously. The NCs can be synthesized with any desired composition, whilst maintaining a mean diameter around 30 nm with a geometric standard deviation (GSD) around 1.25. The absorption behavior and the related fundamental optical band gap energy in dependence on the alloy composition are exemplarily presented. They prove the possibility to tailor NC properties for electronical and opto-electronical applications. In the homogeneous gas phase reaction regime facetted Ge-Si core-shell structures are accessible. The Ge deposition on the seeds precedes the Si deposition due to different gas phase reaction kinetics of the precursors. The Si layer grows epitaxially on the Ge core and is around 5 nm thick.

Grafting porphyrins (face-to-edge/orthogonal versus face-to-face/parallel) to ZnO en route toward dye-sensitized solar cells - Werner, Fabian; Gnichwitz, Jan-Frederik; Marczak, Renata; Palomares, Emilio; Peukert, Wolfgang; Hirsch, Andreas; Guldi, Dirk Michael (Journal of Physical Chemistry B, 2010)
Novel types of binding motives have been investigated within the context of sensitizing ZnO-based dyesensitized solar cells with metalloporphyrins. In particular, a complementary class of metalloporphyrin has been synthesized to probe the impact of a face-to-edge/orthogonal versus face-to-face/parallel orientation of the metalloporphyrin with respect to ZnO and has been compared to TiO-based dye-sensitized solar cells. Our studies provide a deep and detailed understanding of the individual electron-transfer processes at the ZnO/metalloporphyrin interface, that is, electron injection, recombination, and dye regeneration, by means of steady-state and time-resolved techniques. Interestingly, we found that for our novel ZnO/metalloporphyrin systems, the injection efficiencies are close to unity, despite their long, nonconjugated anchoring group length. © 2010 American Chemical Society.

Grain Structure Evolution of Al–Cu Alloys in Powder Bed Fusion with Laser Beam for Excellent Mechanical Properties - Rasch, Michael; Heberle, Johannes; Dechet, Maximilian; Bartels, Dominic; Gotterbarm, Martin; Klein, Lukas; Gorunov, Andrey; Schmidt, Jochen; Körner, Carolin; Peukert, Wolfgang; Schmidt, Michael (Materials, 2019)
Powder Bed Fusion with Laser Beam of Metals (PBF-LB/M) is one of the fastest growing technology branches. More and more metallic alloys are being qualified, but processing of aluminum wrought alloys without cracks and defects is still challenging. It has already been shown that small parts with low residual porosity can be produced. However, suering from microscopic hot cracks, the fracture behavior has been rather brittle. In this paper dierent combinations of temperature gradients and solidification rates are used to achieve specific solidification conditions in order to influence the resulting microstructure, as well as internal stresses. By this approach it could be shown that EN AW-2024, an aluminum-copper wrought alloy, is processable via PBF-LB/M fully dense and crack-free with outstanding material properties, exceeding those reported for commonly manufactured EN AW-2024 after T4 heat treatment.<br
Keywords: Powder Bed Fusion with Laser Beam; aluminum-copper wrought alloy; solidification conditions; hot cracking sensitivity; grain structure evolution

Gram-Scale Continuous Flow Synthesis of Silver-on-Silica Patchy Nanoparticles with Widely Tunable Resonances for Plasmonics Applications - Völkl, Andreas; Toutouly, Jannick; Drobek, Dominik; Apeleo Zubiri, Benjamin; Spiecker, Erdmann; Klupp Taylor, Robin (ACS Applied Nano Materials, 2023)
Extensive research has been conducted on colloids that incorporate nanostructured noble metals, motivated in particular by their highly tunable optical properties. However, the lack of approaches that offer reproducibility, tunability and scalable production is limiting their exploitation in many application areas. Here we present an innovative process for the controlled formation of silver patches on silica nanospheres using gold nanocrystal seeds. The synthesis of the seeds and their attachment in very small numbers to the silica spheres is achieved without employing any surfactants, stabilizers or linker molecules. Using advanced transmission electron microscopy techniques, we show that electroless deposition of nanostructured silver occurs at the introduced seeds and leads to a central protrusion from the metal patches not observed in earlier, seed-free work. We demonstrate both seeding and growth processes can be achieved in millimixer flow reactors. With this simple and scalable approach we provide compelling evidence for the use of seeds in producing targeted morphology and function. Specifically, patch size and optical properties can be tailored in a predictive manner by adjusting the density of seeds on the silica nanospheres as well as reagent concentrations during growth. As a result, our process can be used to obtain colloidal dispersions with localized surface plasmon resonance peaks anywhere in the range 400 nm to nearly 1300 nm. We confirm the scalability of our method by operating the growth process for around 70 minutes. Apart from changes in the first few minutes, the product properties remained rather stable and over a gram of high quality silver patch coated silica could be recovered. Our approach opens up exciting new avenues for plasmonics applications which typically require large amounts of nanoparticles with specifically designed optical properties. These include color and IR pigments, photocatalysts, and as light management components in optoelectronic devices like photovoltaic cells.<br
Keywords: Patchy particles; continuous flow synthesis; continuous flow; static T-mixer; seeded growth; gold nanoparticles; silver patches; interface engineering; localized surface plasmon resonance; scale-up

Graphene production with stirred media mills - Knieke, Catharina; Berger, Angela; Peukert, Wolfgang (2010 MRS Spring Meeting, 2010)
Since the discovery of stable graphene sheets by Novoselov und Geim in 2004 the one atom thick carbon material has been attracted great interest because of its outstanding physical, mechanical and chemical properties. Although there had been intensive research to find new ways in the preparation of single-layer graphene sheets in the last few years, especially the large-scale production of graphene still remains challenging. In this paper we present a new approach, which allows the high-yield production of graphene sheets in a simple stirred media milling process. Under mild milling conditions single- and multilayer graphene sheets have been successfully produced from commercial graphite powder in a liquid medium. During the delamination procedure, the graphite particles were stressed between the milling beads. Shear and compressive normal forces can lead under mild milling conditions, i.e. low stress energies, to a continuous mechanical peeling of graphene sheets from the graphite surface. By means of Atomic Force Microscopy a high yield of single- and multilayer graphene sheets was detected. A concentration of exfoliated sheets of 2 wt% starting from a 5 wt% suspension of coarse graphite particles could be determined after a milling time of only 3 h. This concentration is much higher than those, which were reached by most of the known chemical methods. Since stirred media milling can be realized as large-scale process, a high-yield and low-cost production of graphene flakes becomes possible at ambient temperatur
Keywords: C; carbon; scanning probe microscopy (SPM); fracture

Green and Scalable Fractionation of Gold Nanoclusters by Anion Exchange Chromatography: Proof of Principle and Scale-Up - Gromotka, Lukas; Lübbert, Christian; Traore, Nabi; Peukert, Wolfgang (ACS Applied Nano Materials, 2023)
The chromatographic separation of atomically precise glutathione-stabilized gold nanocluster (AuNC) mixtures is demonstrated for purely aqueous anion exchange chromatography (AEX) and compared to the results of hydrophilic interaction liquid chromatography (HILIC), which requires mixtures of water and acetonitrile. For isocratic HILIC separations, the influence of the mobile phase composition with respect to ionic strength and acetonitrile content is investigated. Individual AuNCs are identified by their optical properties directly from chromatograms and by comprehensive electrospray ionization differential mobility mass spectrometry. Separations by AEX are performed in aqueous mobile phases and are thus considered as a green and sustainable technique for the efficient fractionation of AuNCs. Henry coefficients are determined, which describe the retention behavior of single AuNCs and thus form the basis for modeling, optimization, and scale-up of the separation. The separation by AEX is optimized by linear salt gradient experiments. The scalability of the separation is demonstrated by increasing the AuNC feed concentration up to 64 g/L. Moreover, we quantify the amounts of individual AuNCs by inductively coupled plasma-optical emission spectroscopy after separation and close the mass balance demonstrating the reversible adsorption from the stationary phase. Our AEX approach is superior to HILIC since it offers a higher resolution, provides access to larger clusters, is readily scalable, and is purely water-based. AEX is considered as a sustainable, scalable, and widely applicable technique for the isolation of all types of water-soluble single cluster species. Therefore, we anticipate applications for instance for highly specialized nanocatalysts, sensors, or in medicine.
CRIS-Team Scopus Importer:2023-05-12
Keywords: anion exchange; chromatography; gold nanocluster; hydrophilic; interactions; scalable; separation; sustainable

"Green'' Particle Technology? - Peukert, Wolfgang; Bück, Andreas (2022)
In this essay, we discuss the evolution of particle technology in the context of climate change. We begin with a brief outline of the history of particle technology. In addition to the fascination of fine particle systems, it will become clear that particles have also been associated with negative consequences of human activities since the industrial revolution and still are. Some examples of how dispersive systems contribute to solving current challenges are discussed. Finally, we identify white fields and open questions in particle engineering in the context of climate change hoping that this will stimulate further research.
Keywords: Particles; Particle technology; Sustainability

Green room temperature synthesis of silver-gold alloy nanoparticles - Traore, Nabi; Uttinger, Maximilian; Cardenas Lopez, Paola; Drobek, Dominik; Gromotka, Lukas; Schmidt, Jochen; Walter, Johannes; Apeleo Zubiri, Benjamin; Spiecker, Erdmann; Peukert, Wolfgang (Nanoscale Advances, 2023)
Metallic alloy nanoparticles (NPs) exhibit interesting optical, electrical and catalytic properties, dependent on their size, shape and composition. In particular, silver-gold alloy NPs are widely applied as model systems to better understand the syntheses and formation (kinetics) of alloy NPs, as the two elements are fully miscible. Our study targets product design via environmentally friendly synthesis conditions. We use dextran as the reducing and stabilizing agent for the synthesis of homogeneous silver-gold alloy NPs at room temperature. Our approach is a one-pot, low temperature, reaction-controlled, green and scalable synthesis route of well-controlled composition and narrow particle size distribution. The composition over a broad range of molar gold contents is confirmed by scanning transmission electron microscopy-energy-dispersive X-ray spectroscopy (STEM-EDX) measurements and auxiliary inductively coupled plasma-optical emission spectroscopy measurements (ICP-OES). The distributions of the resulting particles in size and composition are obtained from multi-wavelength analytical ultracentrifugation using the optical back coupling method and further confirmed by high-pressure liquid chromatography. Finally, we provide insight into the reaction kinetics during the synthesis, discuss the reaction mechanism and demonstrate possibilities for scale-up by a factor of more than 250 by increasing the reactor volume and NP concentration.
Keywords: particle-size distribution; ray computed-tomography; bimetallic nanoalloys; dielectric function; formation mechanism; contrast agent; Au; Ag; sedimentation; dependence

Grenzflächen charakterisieren - Peukert, Wolfgang; Martinez Tomalino, Lars-Owe (Nachrichten aus der Chemie, 2008)
Nichtlineare optische Spektroskopie ist die erste Methode, mit der sich die Oberflächeneigenschaften von Partikeln in technischen Systemen direkt untersuchen lassen.
Keywords: Grenzflächen; Spektroskopie; Partikel; Vakuum; nano

Grey facet-controlled anatase nanosheets for photocatalytic H2 evolution without co-catalyst - Qin, Shanshan; Kim, Hyesung; Denisov, Nikita; Fehn, Dominik; Schmidt, Jochen; Meyer, Karsten; Schmuki, Patrik (JPhys Energy, 2020)
Recently, black and grey titania in various morphologies have been intensively investigated for their high performance in photocatalytic H2 generation. Here we use titania nanosheets with a large percentage of (001) facets and hydrogenate them to activate suitable Ti3+-Ov defects for co-catalyst free H2 generation. Key to a highly active nanosheet-catalyst is the prevention of serious deformation and sintering during the thermal hydrogenation. In this work, we present a systematic investigation of different thermally treated nanosheets characterized by SEM, HR-TEM, TEM-EDX, XRD, EPR, XPS, and photocatalytic H2 evolution performance. We describe how to achieve robust grey nanosheets with an intact two-dimensional shape that can endure hydrogenation at the required high temperatures. Due to a defined faceting, these optimized "grey" nanosheets can produce photocatalytic H2 at a higher rate than previously reported best performing grey nanoparticles – this in spite of having a lower BET than the reduced nanoparticles.<br

Grinding in an air classifier mill - Part I: Characterisation of the one-phase flow - Toneva, Petya Ivanova; Epple, Philipp; Breuer, Michael; Peukert, Wolfgang; Wirth, Karl-Ernst (Powder Technology, 2011)
In this and the related second paper [1], we present an in-depth study of the two-phase flow and the stressing conditions of particles in an air classifier hammer mill. This type of mill belongs to the mostly used mills at all. In order to develop a predictive grinding model not only the material's reaction to the applied stress but also the stressing conditions within the mill, e.g. impact velocity, incidence angle, number of stress events, have to be known. The latter are strongly affected by the interactions between the fluid and the solid phase within the mill. Systematic flow investigations in the vicinity of the impact elements and in the region of the internal classifier have been performed by Particle Image Velocimetry (PIV) and by numerical predictions of the fluid flow in the complete mill using a commercial CFD solver. Different pin geometries have been studied at various peripheral velocities of the grinding disk and the classifier. The classifier velocity does not influence the velocity profiles near the impact elements in the main flow direction and vice versa, the flow in the grinding zone has little influence on the classification. The velocity profile in front of the impact element, where the comminution process takes place, is constant with time and preserves a characteristic form independent of the operational conditions. © 2011 Elsevier B.V.
UnivIS-Import:2015-03-09:Pub.2011.tech.ITC.stmmec.grindi
Keywords: CFD; Comminution; Grinding; Impact mills; Multiphase flow; PIV

Grinding in an air classifier mill - Part II: Characterisation of the two-phase flow - Toneva, Petya Ivanova; Wirth, Karl-Ernst; Peukert, Wolfgang (Powder Technology, 2011)
Based on the insights about the air flow within the air classifier mill presented in the first part of the paper [1] the particle laden flow in the vicinity of the grinding pins and through the impeller wheel classifier is studied. The particle motion in the size range between 29 and 573 μm is investigated using Particle Image Velocimetry (PIV). The mathematical model for the fluid flow is extended to a fully coupled two-phase flow numerical calculation. The particle motion in the grinding zone is not influenced by the peripheral velocity of the impeller wheel classifier. The grinding disk velocity doesn't affect the particle behaviour at the classification region. The impact velocity at the grinding pins is independent from the particle size. The average impact velocity normal to the pin wall amounts for the cylindrical pin geometry to 68% and for the prismatic pin geometry to 80% of the peripheral grinding disk velocity. The particles entering the classifier region move with the air velocity in radial direction while their transport in sucking direction slows down in comparison to the air motion. Because of the flow separation between the classifier blades the majority of the particles undergo impacts at the blades and consequently undesired stochastic particle motion of the rebounding particles occurs. © 2011 Elsevier B.V.
Keywords: Air classifier mill; Classification; Grinding; Multiphase flow; Particle Motion

Growth of gold nanoshells on colloidal silica characterized by in situ second-harmonic generation - Sauerbeck, Christian; Schürer, Benedikt; Haderlein, Michael; Braunschweig, Björn; Peukert, Wolfgang; Klupp Taylor, Robin (Engineering Sciences and Fundamentals 2013 - Core Programming Area at the 2013 AIChE Annual Meeting: Global Challenges for Engineering a Sustainable Future, 2013)
Metal nanoparticles and metal composite nanoparticles can have unique optical properties due to localized surface plasmon resonances and are therefore of particular interest in various applications. The resonance frequency of such particles is a function of their composition and their geometry. Gold nanoshells are comprised of a dielectric core and a thin gold shell. The optical properties of such particles can be readily tuned over a wide range by changing the ratio of the core diameter to the shell thickness. In order to impart better control over the optical properties of gold nanoshells a detailed understanding of the shell formation is of great importance. For that purpose it is necessary to monitor changes in surface composition and morphology in situ and in real time. However, most experimental methods lack the desired surface sensitivity or cannot be applied in situ under the required experimental conditions. For that reason we have applied second-harmonic generation (SHG) spectroscopy as a powerful surface sensitive technique which shows great potential to probe surfaces of nanoparticles under relevant experimental conditions1-3. In our contribution, we present results from synchronized SHG and UV/Vis/NIR spectroscopies that were obtained on-line during the seeded growth of gold shells on silica core particles. UV/Vis/NIR spectroscopy allows the monitoring of the coverage of gold and to estimate whether the shells are closed or not, while SHG shows a remarkable sensitivity to changes in the surface morphology which has not been accessible by other in situmethods so far. Notably, at intermediate conditions where a still incomplete shell exists on the core particle during shell growth, we observe first a steep increase in the second-harmonic intensity that is followed by a subsequent rapid decrease in SHG intensity. As the SHG signal is a function of the fundamental electric field to the fourth power, we propose that the observed maximum in the temporal evolution of the SHG intensity is caused by a local field enhancement due to crevices that are being formed in between individual gold islands. As shell growth proceeds, the surface coverage of these crevices decreases and closed shells are formed which results in a substantially decreased SHG signal. This hypothesis is corroborated by additional angle-resolved SHG experiments and ex-situ electron microscopy of gold shells with different gold coverages and surface morphologie
Keywords: nanoparticle; composite; plasmon; resonance; second-harmonic; core; shell

Grundlagenuntersuchung zu einem neuen Verfahren zur Handhabung feinster Partikeln und Herstellung dünner Schichten am Beispiel der Pulverlackierung mit Flüssigstickstoff - Wirth, Karl-Ernst; Molerus, Otto; Nagel, Johannes (Jahrbuch 1998, 1998)
UnivIS-Import:2015-04-20:Pub.1998.tech.ITC.mechve.grundl_76
Keywords: particle; synthesis; powder; film

Grundprinzipien der Produktgestaltung - Peukert, Wolfgang (Chemie Ingenieur Technik, 2016)
Unit operations und Produktdesign sind die beiden wichtigsten Säulen der Verfahrenstechnik. Unter Produktdesign wird die Bildung, Formulierung und Charakterisierung von komplex zusammengesetzten Produkten verstanden. Die jeweiligen Anwendungen definieren dabei die geforderten Produkteigenschaften sowohl in den klassischen Feldern der chemischen Industrie als auch in neuen Feldern wie der druckbaren Elektronik, der Energie- und Umwelttechnik, den Lebenswissenschaften, der pharmazeutischen Technologie und der Nanotechnologie. Im Beitrag werden Grundprinzipien des Produktdesigns vorgeschlagen, die auf eine Vielzahl von Produkten einschließlich fester, flüssiger oder gasförmiger Partikelsysteme anwendbar sind. Ergebnisse aus dem Erlanger Exzellenzcluster "Engineering of Ad- vanced Materials" zeigen, dass die enge Zusammenarbeit zwischen Verfahrenstechnik, Materialwissenschaft und den Naturwissenschaften fruchtbare neue Optionen für die beteiligten Fachbereiche eröffnet. Rigorose mathematische Optimierung auf der Basis prädiktiver Modelle für Produkte und Prozesse katalysieren dabei neue Möglichkeiten zum Design partikelbasierter Produkte in Zukunftsbereichen wie etwa der Elektronik, Photonik oder dem 3D-Druck
Keywords: Partikel; System; Eigenschaften; Produkt

Guidelines for the production of nanoscaled particles and products - Peukert, Wolfgang; Schwarzer, Hans-Christoph; Leugering, Günter (Produktgestaltung in der Partikeltechnologie, 2002)
UnivIS-Import:2015-04-20:Pub.2002.tech.ITC.mechve.guidel
Keywords: nano; particle; product

GVC-Dezember-Tagung: Grenzflächen in der feststoffverfahrenstechnik - Peukert, Wolfgang (Chemie Ingenieur Technik, 2003)

Heat and mass transfer modelling of continuous Wurster spray granulation with external product classification - Mueller, D.; Bück, Andreas; Tsotsas, E. (IDS'2018: 21ST INTERNATIONAL DRYING SYMPOSIUM, 2018)
CRIS-Team WoS Importer:2019-08-16

Heat transfer enhancement of conventional aluminum heat sinks with an innovative, cost-effective, and simple chemical roughening method - Attar, Mohammad Reza; Mohammadi, Majid; Taheri, Amin; Hosseinpour, Saman; Pasandideh-fard, Mohammad; Haddad Sabzevar, Mohsen; Davoodi, Ali (Journal of Thermal Science and Engineering Applications, 2020)
Increased temperature of electronic devices during their performance results in the decline of their performance and reduces their lifetime due to the increased thermal damage, a problem which is very substantial in miniaturized electronic components. Here, we present an innovative, cost-efficient, simple, and environmentally benign chemical method for creating micro/nano roughened structure on the conventional aluminum heat sinks to increase their cooling capability. The surface structures of the roughened heat sinks were examined using scanning electron microscopy and atomic force microscopy. The performance of conventional and micro/nano roughened aluminum heat sinks was analyzed for thermal management of a printed circuit board (PCB) producing heat fluxes equivalent to those of a Core i7-1068NG7 processor. At forced air convection condition and under heat fluxes of 8000, 10,000 and 12,000 W/m2, the temperature of PCBs cooled with roughened heat sinks were found to be lower than those cooled with the conventional heat sinks by impressive values of 9.2 ◦C, 11.0 ◦C, and 12.8 ◦C, respectively. The thermal resistance of the novel heat sink decreased by 38.01%, 39.14%, and 39.96%, respectively, compared to that of the conventional heat sink. In free convection, employing the roughened heat sink improved the PCB cooling effectiveness by roughly 14% at heat fluxes of 8000 W/m2 at cutoff temperature. The proposed simple method in this study opens up the possibility of reducing the size (or mass) of aluminum heat sinks or employing a heat sink of a certain size for the thermal management of a system with higher heat flux.<br
Keywords: Cooling efficiency; Chemical roughening; Heat sink; Thermal management; Thermal resistance

Heat Transfer in a Co-Current Downflow Circulating Fluidized Bed. - Wirth, Karl-Ernst; Lehner, Peter (Circulating Fluidized Bed Technology VI, 1999)
UnivIS-Import:2015-04-20:Pub.1999.tech.ITC.mechve.heattr_89
Keywords: heat; transfer; fluidized; bed

Heat Transfer in Circulating Fluidized Beds - Wirth, Karl-Ernst (Chemical Engineering Science, 1995)
The wall-to-suspension heat transfer in circulating fluidized beds depends on the fluid mechanics immediately near the wall and on the thermal properties of the gas used. Experimental investigations of circulating fluidized beds of low dimensionless pressure gradients with different solid particles like bronze, glass and polystyrene at ambient temperatures show no influence of the conductivity and the heat capacity of the solids on the heat transfer coefficient. Consequently the heat transfer coefficient in form of the dimensionless Nusselt number can be described in dependence of dimensionless numbers which characterize the gas-solid flow near the wall. These numbers are the Archimedes number and the pressure-drop number. The last number relates the cross-sectional average solids concentration to the solids concentration at minimum fluidization condition. With the aid of the model of the segregated vertical gas-solid flow the flow pattern in the wall region can be calculated and consequently the wall heat transfer which depends only on heat conduction in the gas and on the convective heat transfer by the gas. With elevated suspension temperatures radiation contributes additionally to the heat transfer. When the solids concentration is low the effect of the radiation on the heat transfer is high. Increasing solids concentration results in a decrease of the radiation. With high solids concentration the wall will be shielded by the cold solids clusters moving down the wall from the radiation of the hot particles in the core region. A simple correlation is presented for calculating the heat transfer in circulating fluidized beds. © 1995.
UnivIS-Import:2015-03-05:Pub.1995.tech.ITC.mechve.heattr_36

Heat Transfer in Fluidized Beds - Wirth, Karl-Ernst; Molerus, Otto (Chapman & Hall, 1997)
UnivIS-Import:2015-04-02:Pub.1997.tech.ITC.mechve.heattr
Keywords: heat; transfer; fluidized; bed

Heat Transfer in Pressurized Fluidized Beds - Wirth, Karl-Ernst (Preprints 14th International Conference on Fluidized Bed Combustion, 1997)
UnivIS-Import:2015-04-16:Pub.1997.tech.ITC.mechve.heattr_86

Herausforderungen für die Lehre am Beispiel der mechanischen Verfahrenstechnik - Peukert, Wolfgang; Schmid, Hans-Joachim (Chemie Ingenieur Technik, 2003)
Rasche technologische Entwicklungen haben für Chemieingenieure bzw. Verfahrenstechniker neue Beschäftigungsmöglichkeiten eröffnet, wodurch sich zusätzliche Anforderungen an die Ausbildung ergeben. Der vorliegende Beitrag beschreibt die Lösungsansätze im Fachgebiet der Partikeltechnik: Es findet eine noch stärkere Betonung der Grundlagen statt, wobei Beispiele aus klassischen und neuen Anwendungen exemplarisch vertieft werden. Kernpunkt des Curriculums sind die Produkteigenschaften. Besonderes Gewicht wird außerdem auf die Betrachtung ganzer Prozesse gelegt. Die Vorlesungen sind in drei Ebenen strukturiert: Grundlagen, Grundoperationen und Prozesse/Anwendungen. Methodisch wird ein zweifacher Ansatz verfolgt: Die Lehre der grundlegenden Fakten wird ergänzt durch eine aktive Teilnahme der Studenten, insbesondere bei der Erarbeitung von Beispielen und in Labor- bzw. Rechnerpraktika. Durch eine ganzheitliche Sicht der Universitätsausbildung sollen auch „soft skills“ gefördert werden.
UnivIS-Import:2015-03-09:Pub.2003.tech.ITC.mechve.heraus
Keywords: teaching; particle; technology

Herstellung und Charakterisierung von Pulvern für das selektive Laserstrahlschmelzen von Kunststoffen aus Flüssigphasenprozessen am Beispiel von PA11 - Dechet, Maximilian; Zhao, Meng; Drummer, Dietmar; Peukert, Wolfgang; Schmidt, Jochen (6. Industriekolloquium des Sonderforschungsbereichs 814 - Additive Fertigung, 2018)
Keywords: 3D-Druck • Additive Fertigung • Sonderforschungsbereich 814

Herstellung und Funktionalisierung neuartiger Pulverwerkstoffe für die additive Fertigung - Schmidt, Jochen; Sachs, Marius; Fanselow, Stephanie; Wirth, Karl-Ernst; Peukert, Wolfgang (Chemie Ingenieur Technik, 2016)

Herstellung von Polyolefinstrahlschmelzmaterialien mittels Schmelzeemulgieren zum Einsatz in der additiven Fertigung - Schmidt, Jochen; Fanselow, Stephanie; Wirth, Karl-Ernst; Peukert, Wolfgang; Hiller, Saskia; Laumer, Tobias; Schmidt, Michael (Neue Entwicklungen in der Additiven Fertigung, 2015)
Im Rahmen dieses Beitrags wird das Schmelzeemulgieren als Verfahren zur Herstel-lung von Polymermikropartikeln vorgestellt. In diesem Prozess wird zunächst ein Polymergranulat in einer kontinuierlichen Phase in Gegenwart geeigneter Additive in einem Rührbehälter aufgeschmolzen, die Rohemulsion in einer Rotor-Stator-Einheit feinemulgiert und anschließend zu einer Suspension abgekühlt. Der Einfluss von Prozessparametern und Systemzusam-mensetzung auf das Emulgierergebnis wird diskutiert und die Anwendbarkeit des Verfahrens für polymere Mikropartikeln anhand von Polypropylen (PP) und Polyethylen (PE-HD) dargestellt. Die erhaltenen Suspensionen werden zur Überführung in Pulverform sprühgetrocknet und die Fließeigenschaften des Pulvers analysiert. Durch trockenes Beschichten mit pyrogener Kieselsäure kann die Fließfähigkeit der erhaltenen Partikeln weiter verbessert werden. Das Verfahren bietet somit einen neuen Zugang zur Herstellung neuer Ausgangsmaterialien für die Additive Fertigung.<br

Heterogeneous nucleation and surface conformal growth of silver nanocoatings on colloidal silica in a continuous flow static T-mixer - Meincke, Thomas; Bao, Huixin; Pflug, Lukas; Stingl, Michael; Klupp Taylor, Robin (Chemical Engineering Journal, 2017)
Dielectric-metal core-shell particles with morphologically tunable optical properties are highly promising candidates for applications ranging from theranostics, energy harvesting and storage to pigments and sensors. Most structures of interest have, until now, been produced in small volume wet chemical batch approaches which are difficult to scale. In extension to the growing interest in continuous flow process for the scalable synthesis of single phase nanomaterials, here we describe the formation of two-phase core-shell particles. Specifically, the coating of silver onto colloidal silica particles using a static T-mixer approach is presented. The coating is achieved in a single reaction step in which careful control of educt concentration and process conditions leads to nucleation and surface conformal growth of silver. Through two generations of reactor, good coating yield and process reproducibility are demonstrated. In particular, the ability to control the characteristic time of mixing, as verified by the Villermaux-Dushmann reaction, was shown to be crucial in narrowing the range of morphologies obtained in the product particles. Moreover we could tune, through process parameters, the degree of coating of the core particles, leading to patchy particles, Janus particles and even complete nanoshells. Since silver nanostructures have a strong structure-dependent plasmon resonance, we could verify the coating morphologies via optical spectroscopy and electrodynamic simulations. Optical measurements were also used in order to optimize, via trial and error, the continuous flow process parameters to produce a high coating yield. This opens up future potential for feedback-driven optimization of particle coating. Finally, we demonstrate that the silver coatings can be morphologically stabilized, opening up the possibility of effective formulation for applications.
Keywords: Continuous flow nanoparticle synthesis; Diffusion limited growth; Metal nanoshell; Microreactor; Patchy particle; Plasmon resonance

Hexane selenol dissociation on Cu: The protective role of oxide and water - Goethelid, M.; Hosseinpour, Saman; Ahmadi, S.; Leygraf, C.; Johnson, C. M. (Applied Surface Science, 2017)

Hierarchical Design of Metal Micro/Nanohole Array Films Optimizes Transparency and Haze Factor - Bley, Karina; Semmler, Johannes; Rey, Marcel; Zhao, Chunjing; Martic, Nemanja; Klupp Taylor, Robin; Stingl, Michael; Vogel, Nicolas (Advanced Functional Materials, 2018)
Keywords: Colloidal lithography; Haze factor; Hierarchy; Nanophotonics; Transparent electrodes

Hierarchical structural control of visual properties in self-assembled photonic-plasmonic pigments - Vogel, Nicolas; et al. (Optics Express, 2014)

High-density risers as reactor system for benzene synthesis by non-oxidative dehydroaromatization of methane - fluid-dynamic investigations - Hensler, Timo; Zhang, Yingxue; Mleczko, Leslaw; Assmann, Jens; Bellinghausen, Rainer; Schwieger, Wilhelm; Wirth, Karl-Ernst (11th International Conference on Fluidized Bed Technology, CFB 2014, 2014)
As a precursor for synthesis of dyes, polymers, fuel additives and various solvents benzene has become an indispensable base chemical in a large field of industrial processes. To date the industrial benzene demand is covered in large part by benzene which is extracted from crude oil. However, scarcity of oil resources accompanied by increasing prices for oil derived chemicals necessitates the development of alternative processes to satisfy the market's benzene demand. The presented work deals with the development of a reactor model for benzene synthesis by non-oxidative dehydroaromatization of methane. Based on model calculations a riser reactor operated at high solids concentrations has been found to allow for most efficient operation. Together with the model experimental data are presented in order to evaluate the fluid-dynamic feasibility of the suggested flow condition within a pilot plant scale circulating fluidized bed. Experimental data show that stable operation can be achieved at cross-section averaged solids concentrations up to 30 vol.%.

Highly accurate and numerical tractable coupling of nanoparticle nucleation, growth and fluid flow - Bänsch, Eberhard; Pflug, Lukas; Schikarski, Tobias (Chemical Engineering Research & Design, 2023)
Supersaturation as the thermodynamic driving force of particulate precipitation couples the mixing of solute compounds with the solid formation consisting of nucleation and molecular growth. Because the process spans many orders of magnitude in space and time, gathering spatio-temporal information by experiments is hardly achievable. Numerical simulation of the nonlinear, non-local balance equations for mass, momentum and dispersed phase provide detailed solution information in space and time. We here introduce a novel, highly accurate and very efficient numerical formulation of the population balance equations for the dispersed phase coupled to the concentration and velocity field. We reformulate the problem in terms of a fixed-point equation solving the population balance equation along Lagrangian paths with the recently developed exact Method of Moments (eMoM, Pflug et al., 2020) coupled to the concentration field (Eulerian frame). The analytical reformulation provides the information about the full particle size distribution while the computational effort remains in the order of classical moment methods and is much less than numerical schemes approximating the full particle size distribution such as finite volume methods. Furthermore, we explore the difference between an Euler-Euler and Euler-Lagrange coupling considering moderate to large P é clet numbers for the solutes and particles. It turns out that the mean particle size as a solution of the population balance is much more sensitive to the numerical discretization of the advection term than the approximation of the number density function. Based on this finding, we eventually explore the impact of particle diffusion on the solid formation process and give guidelines, when particle diffusion should be taken into account.
CRIS-Team Scopus Importer:2023-03-24
Keywords: Computational fluid dynamics; Euler-Euler and Euler-Lagrange coupling; Fixed-Point-Reformulation; Moment methods; Nanoparticle diffusion; Nucleation and size-dependent growth; Population balance equations

Highly magnetizable superparamagnetic colloidal aggregates with narrowed size distribution from ferrofluid emulsion - Lobaz, Volodymyr; Klupp Taylor, Robin; Peukert, Wolfgang (Journal of Colloid and Interface Science, 2012)
The formation of spherical superparamagnetic colloidal aggregates of magnetite nanoparticles by emulsification of a ferrofluid and subsequent solvent evaporation has been systematically studied. The colloidal aggregates occur as a dense sphere with magnetite nanoparticles randomly packed and preserved particle-particle separation due to chemisorbed oleic acid. The voids between nanoparticles are filled with solvent and free oleic acid. The latter was found to influence the formation of colloidal aggregates and their surface properties. The choice of surfactant, whether low molecular weight or polymeric, was shown to lead to the colloidal aggregates having tailored interfacial behavior. Magnetization measurements at ambient temperature revealed that the magnetite colloidal aggregates preserve the superparamagnetic properties of the starting nanoparticle units and show high saturation magnetization values up to 57. emu/g. The size distribution of magnetite nanoparticle colloidal aggregates produced by such an approach was found to be a function of emulsion droplet breakup - coalescence and stabilization kinetics and therefore is influenced by the emulsification process conditions and concentrations of the emulsion compounds. © 2012 Elsevier In
Keywords: Colloidal aggregate; Emulsion; Magnetite nanoparticle; Superparamagnetic particle

Highly Ordered Monolayers of μm-Sized Polystyrene Spheres Studied by Grazing-Incidence Small-Angle X-ray Scattering, Simulations, and Geometrical Calculations - Maiti, Santanu; Senavirathna, L. N.; Minguez Bacho, Ignacio; Menath, Johannes; Gruber, W.; Vogel, Nicolas; Bachmann, Julien; Unruh, Tobias (Langmuir, 2024)
Unraveling the two-dimensional (2D) structural ordering of colloidal particles assembled at a flat surface is essential for understanding and optimizing their physical properties. So far, grazing-incidence small-angle X-ray scattering (GISAXS) has been widely used to determine crystallographic information on 2D self-assembled structures of nanosize objects. However, solving the structure of 2D lattices consisting of micrometer (μm)-sized objects still remains a challenge using scattering methods. Here, a model 2D SCALMS (supported catalytically active liquid metal solution) template is fabricated from μm-sized polystyrene (PS) spheres that form a monolayer on top of the flat solid support. GISAXS patterns of the sample were collected for rotation angles around its surface normal in steps of 3°. For every rotation angle, different Bragg-type interference maxima along the out-of-plane (qz) direction were observed. On the basis of simulations of GISXAS patterns of single domains of ordered particle arrangements using the distorted wave Born approximation (DWBA) and validation against a simple geometrical scattering model, the interference maxima could nicely be interpreted to originate from a monolayer of the μm-sized spherical particles which are arranged in domains of hexagonal 2D paracrystalline order. This novel GISAXS evaluation technique serves as a proof of principle for determining the μm-size periodicity of 2D crystalline domains and demonstrates its potential to spatially resolve the relative orientations of such domains with respect to a reference direction.
CRIS-Team Scopus Importer:2024-02-09

High-performance direct conversion X-ray detectors based on sintered hybrid lead triiodide perovskite wafers - Shrestha, Shreetu; Fischer, Rene; Matt, Gebhard; Feldner, Patrick; Michel, Thilo; Osvet, Andres; Levchuk, Ievgen; Merle, Benoit; Golkar, Saeedeh; Chen, Haiwei; Tedde, Sandro F.; Schmidt, Oliver; et al. (Nature Photonics, 2017)
Lead halide perovskite semiconductors are in general known to have an inherently high X-ray absorption cross-section and a significantly higher carrier mobility than any other low-temperature solution-processed semiconductor. So far, the processing of several-hundred-micrometres-thick high-quality crystalline perovskite films over a large area has been unresolved for efficient X-ray detection. In this Article, we present a mechanical sintering process to fabricate polycrystalline methyl ammonium lead triiodide perovskite (MAPbI(3)) wafers with millimetre thickness and well-defined crystallinity. Benchmarking of the MAPbI(3) wafers against state-of-the-art CdTe detectors reveals competitive conversion efficiencies of 2,527 mu C Gy(air)(-1) cm(-2) under 70 kV(p) X-ray exposure. The high ambipolar mobility-lifetime product of 2 x 10(-4) cm(2) V-1 is suggested to be responsible for this exceptionally high sensitivity. Our findings inform a new generation of highly efficient and low-cost X-ray detectors based on perovskite wafer

Horizontal secondary gas injection in fluidized beds: Solid concentration and velocity in multiphase jets - Köninger, Benedikt; Hensler, Timo; Schug, Sebastian; Arlt, Wolfgang; Wirth, Karl-Ernst (Powder Technology, 2017)

How Colloidal Lithography Limits the Optical Quality of Plasmonic Nanohole Arrays - Görlitzer, Eric; Zhan, Meichen; Choi, Sukyung; Vogel, Nicolas (Langmuir, 2023)
Colloidal lithography utilizes self-assembled particle monolayers as lithographic masks to fabricate arrays of nanostructures by combination of directed evaporation and etching steps. This process provides complex nanostructures over macroscopic areas in a simple, convenient, and parallel fashion without requiring clean-room infrastructure and specialized equipment. The appeal of the method comes at the price of imperfections impairing the optical quality, especially for arrayed nanostructures relying on well-ordered lattices. Imperfections are often generically mentioned to rationalize the discrepancy between experimental and simulated resonances. Yet, little attention is given to detailed structure-property relationships connecting typical defects directly with the optical properties. Here, we use a correlative approach to connect nano- and microscopic defects occurring from the colloidal lithography process with the resulting local optical properties. We use nanohole arrays as a common plasmonic structure known to be sensitive to lattice imperfections. Correlative optical and electron microscopies reveal the individual role of packing order, organic impurities, and solid polymer bridges. Our findings show that simple cleaning processes with solvents and oxygen plasma already improve the optical quality but also highlight how well-controlled self-assembly processes are required for predictable optical properties of such nanostructures.
CRIS-Team Scopus Importer:2023-04-14

How to avoid interfering electrochemical reactions in ESI-MS analysis - Lübbert, Christian; Peukert, Wolfgang (Journal of Mass Spectrometry, 2019)
The presence of electrochemical reactions occurring in an electrospray processes at the point where the current enters the liquid is discussed since the early 1990's. This current transfer to the liquid results in oxidation or reduction of either electrolyte species in the liquid sprayed or of the electrode material in contact with the liquid. As a result, new chemical species are generated. These products of the electrochemical reaction might be detected as altered species in mass spectra; they might be volatile and not recognized at all or accumulate on the electrode surface and cause cross contamination later on. In other cases, it might happen that the products of the electrochemical reactions are the only detectable species formed from an otherwise nondetectable analyte. An electrospray setup in which electrochemical reactions do not interfere with the analyte under investigation excludes the electrochemical reaction as source of sample contamination and sample altering and may serve as reference setup for experiments focused on the electrochemical reaction itself. We present a simple and inexpensive current coupling approach and specify operation conditions for which any impact of the electrochemical reaction on the sample under investigation is inherently excluded. On the basis of a practical example, we show the impact of the electrochemical reaction on sample composition and demonstrate the benefit of using the proposed current coupling method. Because of the obvious benefit of this method and its simple realization, it has the potential to be employed as standard feeding approach, especially for electrosprays operated at small flow rates.
CRIS-Team Scopus Importer:2019-05-02
Keywords: corrosion; electrochemistry; electrospray; nanospray; negative ion mode

How to Estimate Material Parameters for Multiphase, Multicomponent Precipitation Modeling - Güldenpfennig, Andreas; Pflug, Lukas; Peukert, Wolfgang (Crystal Growth and Design, 2019)
The simultaneous precipitation of multiple solid phases inside a T-mixer was investigated both numerically and experimentally based on the model system BaSO 4 and BaCO 3 . With a population balance equation model including mixing, hydrochemistry, and solid formation kinetics, the global solid phase composition was calculated and compared to experimental results. We show that physical material parameters can be extracted from the simulations by matching calculated curves to measured data. In particular, the surface energies and solubility products of the solids, which are both crucial parameters to describe nucleation and often not known accurately enough, are discussed. The estimated parameters are in the same size range as literature values, and simulations are compared to experiments for variable anion concentration ratios, pH, and solid concentrations. The good agreement between the data for several different process conditions proves both the general validity of our multiphase model and the effectiveness of the presented method.
CRIS-Team Scopus Importer:2019-05-14

How water flips at charged titanium dioxide: An SFG-study on the water–TiO2 interface - Schlegel, Simon J.; Hosseinpour, Saman; Gebhard, Maximilian; Devi, Anjana; Bonn, Mischa; Backus, Ellen H.G. (Physical Chemistry Chemical Physics, 2019)
Photocatalytic splitting of water into hydrogen and oxygen by utilizing sunlight and a photocatalyst is a promising way of generating clean energy. Here, we report a molecular-level study on heavy water (D 2 O) interacting with TiO 2 as a model photocatalyst. We employed the surface specific technique Sum-Frequency-Generation (SFG) spectroscopy to determine the nature of the hydrogen bonding environment and the orientation of interfacial water molecules using their OD-stretch vibrations as reporters. By examining solutions with various pD-values, we observe an intensity-minimum at around pD 5, corresponding to the balance of protonation and deprotonation of TiO 2 (point of zero charge). The majority of water molecules' deuterium atoms point away from the interface when the pD is below 5, and point towards the surface when the pD is higher than 5, with strong hydrogen bonds towards the surface.
CRIS-Team Scopus Importer:2019-05-09

Human laryngeal mucus from the vocal folds: Rheological characterization by particle tracking microrheology and oscillatory shear rheology - Peters, Gregor; Wendler, Olaf; Böhringer, David; Gostian, Antoniu Oreste; Müller, Susanna; Canziani, Herbert; Hesse, Nicolas; Semmler, Marion; Berry, David A.; Kniesburges, Stefan; Peukert, Wolfgang; Döllinger, Michael (Applied Sciences, 2021)
Mucus consistency affects voice physiology and is connected to voice disorders. Neverthe-less, the rheological characteristics of human laryngeal mucus from the vocal folds remain unknown. Knowledge about mucus viscoelasticity enables fabrication of artificial mucus with natural properties, more realistic ex-vivo experiments and promotes a better understanding and improved treatment of dysphonia with regard to mucus consistency. We studied human laryngeal mucus samples from the vocal folds with two complementary approaches: 19 samples were successfully applied to particle tracking microrheology (PTM) and five additional samples to oscillatory shear rheology (OSR). Mucus was collected by experienced laryngologists from patients together with demographic data. The analysis of the viscoelasticity revealed diversity among the investigated mucus samples according to their rigidity (absolute G’ and G”). Moreover some samples revealed throughout solid-like character (G’ > G”), whereas some underwent a change from solid-like to liquid-like (G’ < G”). This led to a subdivision into three groups. We assume that the reason for the differences is a variation in the hydration level of the mucus, which affects the mucin concentration and network formation factors of the mucin mesh. The demographic data could not be correlated to the differences, except for the smoking behavior. Mucus of predominant liquid-like character was associated with current smokers.
CRIS-Team Scopus Importer:2021-04-16
Keywords: Human laryngeal mucus; Oscillatory shear rheology; Particle tracking microrheology; Viscoelasticity; Vocal folds

Hybrid Metal-Dielectric Photonic Crystals with Enhanced Plasmonic-Photonic Interaction - Bahrami, M. Reza; Lobaz, Volodymyr; Peukert, Wolfgang; Korovin, Alexander V.; Peschel, Ulf; Romanov, Sergei G. (13th International Conference on Transparent Optical Networks (ICTON), 2011)
Control on the optical response of 2-dimensional colloidal photonic crystals was achieved by combining them with thin metal films. In such hybrids the light transport depends on the parameters of the sphere lattice and the topology of the metal film. This approach allows mixing Bloch modes and surface plasmon polariton modes in the total optical response of hybrid architectures. Stronger modification of the hybrid's optical properties was achieved in the case of tighter light confinement.
Keywords: hybrid photonic crystal; surface plasmon polariton; optical transmission

Hydrodynamic simulations of sedimenting dilute particle suspensions under repulsive DLVO interactions - Jung, David; Uttinger, Maximilian; Malgaretti, Paolo; Peukert, Wolfgang; Walter, Johannes; Harting, Jens (Soft Matter, 2022)
We present guidelines to estimate the effect of electrostatic repulsion in sedimenting dilute particle suspensions. Our results are based on combined Langevin dynamics and lattice Boltzmann simulations for a range of particle radii, Debye lengths and particle concentrations. They show a simple relationship between the slope K of the concentration-dependent sedimentation velocity and the range chi of the electrostatic repulsion normalized by the average particle-particle distance. When chi -> 0, the particles are too far away from each other to interact electrostatically and K = 6.55 as predicted by the theory of Batchelor. As chi increases, K likewise increases as if the particle radius increased in proportion to chi up to a maximum around chi = 0.4. Over the range chi = 0.4-1, K relaxes exponentially to a concentration-dependent constant consistent with known results for ordered particle distributions. Meanwhile the radial distribution function transitions from a disordered gas-like to a liquid-like form. Power law fits to the concentration-dependent sedimentation velocity similarly yield a simple master curve for the exponent as a function of chi, with a step-like transition from 1 to 1/3 centered around chi = 0.6.

Identification of material specific attrition mechanisms for polymers in dilute phase pneumatic conveying - Peukert, Wolfgang; Frye, Lars (Chemical Engineering and Processing, 2005)
In the approach presented, attrition of bulk solids in pneumatic conveying is regarded as a result of a process function (stress conditions) and a material function (influence of material properties). For dilute phase conveying the process function was determined by employing computational fluid dynamics (CFD). Opposed to what was expected initially, the numerical simulations indicate that sliding friction apparently is of importance in dilute phase conveying. This conclusion can be drawn from the low calculated impact angles in a pipe bend (rB/Dn = 5; Dn = 80 mm) which lie between 5 and 35°. Consequently, the tangential impact velocity components ranging from 33 to 44 m/s are considerably higher than the normal ones (5-25 m/s). These results were at first endorsed by observations made in experiments to determine the material function. The relative attrition behavior of four different polypropylenes (PP) under pure sliding friction conditions closely resembles that observed in attrition experiments carried out in a pipe bend of the above geometry, while differences are observed for normal impact conditions. But further experiments with polymethylmethacrylates (PMMA) and polystyrenes (PS) showed that here the attrition behavior encountered under normal impact conditions is similar to that observed in the pipe bend. With dynamic mechanical analysis (DMA) it was possible to show that PP on one hand and PMMA and PS on the other are attrited by different mechanisms and that the glass transition temperature of the polymers is a key factor in the determination of the prevailing attrition mechanism. © 2004 Elsevier B.V. All rights reserved.
UnivIS-Import:2015-03-09:Pub.2005.tech.ITC.mechve.identi
Keywords: Attrition; Dynamic mechanical analysis (dma); Material function; Pneumatic conveying; Polymers; Process function

Identifying the apparent and true grinding limit - Knieke, Catharina; Sommer, Marc; Peukert, Wolfgang (Powder Technology, 2009)
Comminution in stirred media mills enables the production of ultrafine particles down to the nanometer range. The grinding results are mainly determined by two contrary mechanisms: particle breakage and agglomeration of the so-created fragments. These competing phenomena often lead to a plateau in particle size above a certain energy input. The degree of agglomeration and therefore the final aggregate size can be controlled by the addition of stabilizers and by the applied shear forces. In this paper the agglomeration behavior of silica particles under different milling and stability conditions is presented. Furthermore the particle breakage behavior in the nanometer range as the other size-determining mechanism will be discussed. In long term grinding experiments with different materials the kinetics of particle breakage as well as the grinding limit as the minimal achievable particle size could be obtained. Graphical abstract In wet grinding processes most materials show after certain milling time no further grinding progress and a plateau in particle size is reached. One can distinguish between the apparent grinding limit, which is an agglomerate size strongly depending on the stability of the suspension, and the true grinding limit. This true grinding limit is determined by microstructural changes inside the particles and can be influenced by material and process parameters.

Impact comminution in jet mills - Strobel, Alexander; Köninger, Benedikt; Romeis, Stefan; Wirth, Karl Ernst; Peukert, Wolfgang (Dynamic Flowsheet Simulation of Solids Processes, 2020)
Modelling the comminution in jet mills with respect to the complex twophase flow and the dynamic process behaviour is still a challenging task. The processed solids pass through several stages in the mill: The comminution process in the lower part, the pneumatic transport towards the classifier in the middle section, and the classification step at the top. In this contribution, the grinding kinetics and process behaviour during quasi-batch and fed-batch operational mode for different holdups, classifier speeds, and particle sizes are examined in detail. A previously developed method using well-characterized aluminium particle probes to access the stressing conditions is adapted for application in the investigated jet mill: The relative particle impact velocity is linked to the geometric changes of the particles upon impact. A high number of impact events happen in the mill, while at the same time, the average particle velocity is comparatively low. Besides the stressing conditions, breakage probabilities for the used glass beads are determined by single particle impact experiments and described by the model of Vogel and Peukert. Solids concentration measurements and high-speed imaging reveal the formation of particle clusters at the classifier and its periphery. These clusters have a massive impact on the classification step itself: Fine particles are trapped inside the clusters and are not discharged. Based on an adaption of the breakage model, and using the mean relative particle impact velocity determined by the particle probes, a model for the product mass flow is introduced.
CRIS-Team Scopus Importer:2020-08-28

Impact fragmentation of metal nanoparticle agglomerates - Peukert, Wolfgang; Seipenbusch, Martin; Toneva, Petya Ivanova; Weber, Alfred P. (Particle & Particle Systems Characterization, 2007)
Deagglomeration experiments were performed with agglomerates of nanoparticles of Ni and Pt. The fragmentation was induced by high velocity impaction of the agglomerates in a single-stage low pressure impactor and the fragmentation patterns were evaluated by TEM analysis. Weibull statistics are employed for a quantitative description of the fragmentation behavior. This study shows that for well-defined interparticle contacts, the impact fragmentation technique combined with the evaluation according to Weibull statistics, allows the recovery of the expected size dependencies. For Pt and Ag, the adhesion force particle size dependency was dominated by van der Waals forces. In contrast, the adhesion force between Ni particles in the size range from 12-28 nm revealed a much stronger increase with particle size. This phenomenon may be attributed to permanent magnetic dipole moments which are also reflected in the chain-like shape of the agglomerates. For nanoparticle agglomerates with less well-defined contacts, such as those in industrial environments, the method provides a promising application to reveal the bond strength and cohesiveness of nanoparticle powders. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.
Keywords: Deagglomeration; Diffusional agglomeration; Nanoparticle agglomerates; Weibull statistics

Impact of DAA/water composition on PFSA ionomer conformation. - Hoffmann, Eva-Maria; Fischer, Daniela; Thoma, Martin; Damm, Cornelia; Lobaz, Volodymyr; Zhigunov, Alexander; Peukert, Wolfgang (Journal of Colloid and Interface Science, 2020)
Performance of a proton exchange membrane fuel cell (PEMFC) is significantly determined by the structure and composition of the electrode layer. Electrode layers are formed from inks consisting of platinum-doped carbon black particles, perfluorosulfonic acid (PFSA) ionomer and a dispersing solvent. Interaction between these materials mainly influences suspension stability, ionomer conformation and therewith layer morphology. We characterize the interplay between a short sidechain (SSC) PFSA ionomer (Aquivion® D79-25BS) and a solvent mixture (diacetone alcohol (DAA) and water with different weight ratios) by using Hansen solubility/dispersibility parameters (HSP) and by experimental tests. It was found that HSPs are well suitable to describe the ionomer/solvent interactions. In particular, the HSP difference in terms of the hydrogen bonds is responsible for the poor affinity between ionomer and solvent at low DAA concentrations. With increasing DAA content the affinity between ionomer and solvent increases as indicated by better matching HSPs. For an ionomer concentration of 4 wt%, Aquivion always forms molecular solutions for all DAA-in-water mixing ratios. Self-organization of the ionomer molecules changes from densely packed/collapsed molecules with highly deprotonated sulfonic acid side groups at low DAA concentrations to unfolded Aquivion molecules with a low dissociation degree of the sulfonic acid groups at high DAA concentrations.

Impact of formulation and operating parameters on particle size and grinding media wear in wet media milling of organic compounds – A case study for pyrene - Flach, F.; Konnerth, Christoph-Günther; Peppersack, C.; Schmidt, Jochen; Damm, Cornelia; Breitung-Faes, S.; Peukert, Wolfgang; Kwade, Arno (Advanced Powder Technology, 2016)
This study presents the influence of process and formulation parameters on fine grinding of the crystalline organic model compound pyrene. Submicron particles were produced by wet media milling in water. By applying an electrosteric stabilization and optimized process parameters, particle sizes below 100 nm were obtained. Additionally, the influence of formulation and process parameters on grinding media wear were investigated. The product formulation with an ionic surfactant and a nonionic polymer was identified as a significant parameter to reduce the grinding wear. Furthermore, the set of operating parameters as well as the choice of grinding media material were found as key parameters to reduce product contamination. Grinding media wear is proportional to the specific energy input and can be minimized by optimizing the stress energy of grinding medi
Keywords: Stirred media milling; Organic crystals; Stabilization; Grinding media wear; Formulation

Impact of oxygen plasma treatment on the device performance of zinc oxide nanoparticle based thin-film transistors - Halik, Marcus; Peukert, Wolfgang; Braunschweig, Björn; Klaumünzer, Martin; Hirschmann, Johannes; Faber, Hendrik (ACS Applied Materials and Interfaces, 2012)
Thin-films of zinc oxide nanoparticles were investigated by photoluminescence spectroscopy and a broad defect-related yellow-green emission was observed. Oxygen plasma treatment was applied in order to reduce the number of defects, and the emission intensity was quenched to 4% of the initial value. Thin-film transistors that incorporate the nanoparticles as active semiconducting layers show an improved device performance after oxygen plasma treatment. The maximum drain current and the charge carrier mobility increased more than 1 order of magnitude up to a nominal value of 23 cm2 V−1 s−1 and the threshold voltage was lowered.
Keywords: nanoparticles; Plasma treatment; thin-film transistors; zinc oxide

Impact of solvent properties on the precipitation of active pharmaceutical ingredients - Schikarski, Tobias; Trzenschiok, Holger; Avila, Marc; Peukert, Wolfgang (Powder Technology, 2023)
In antisolvent precipitation, water and an organic drug-containing solvent induces particle formation. For each water-solvent mixture, the fluid properties such as viscosity, density and diffusion coefficient but also the drug solubility depend nonlinearily on the fluid mixture compositions. Each property in itself has a strong impact on the solid formation, and thus on the outcome of the precipitation. The simulation framework recently developed by Schikarski et al. [1] allows investigating separately the impact of each fluid property on the precipitation. For a T-mixer and a novel 3-inlet-mixer, we first show that the viscosity and density variations largely determine the macroscopic mixing behavior and, thus, the build-up of supersaturation. The composition-dependent diffusion properties of the drug molecules largely govern the transport-controlled nucleation and particle growth at small scales. In a second step, we numerically predict the experimentally obtained full particle size distribution of the precipitated Ibuprofen nanoparticles using different water-solvent mixtures and different operating conditions. Our numerical results are in excellent agreement with our experimental measurements using ethanol, methanol and 2-propanol as solvents.
CRIS-Team Scopus Importer:2023-01-13
Keywords: Active pharmaceutical ingredients; Antisolvent precipitation; Binary mixtures; Computational fluid dynamics; Nucleation and growth of particles; Population balance equation; Water; ethanol; methanol; 2-propanol

Impact of stressing conditions and polymer-surfactant interactions on product characteristics of organic nanoparticles produced by media milling - Konnerth, Christoph-Günther; Flach, Frederik; Breitung-Faes, Sandra; Damm, Cornelia; Schmidt, Jochen; Kwade, Arno; Peukert, Wolfgang (Powder Technology, 2016)
Stirred media milling as a feasible method to produce organic nanoparticles was studied for the polycyclic aromatic hydrocarbon pyrene in aqueous environment using vinylpyrrolidone-vinyl acetate copolymer (KVA 64) and sodium dodecyl sulphate (SDS) as well as hydroxypropylcellulose (HPC-SSL) as stabilising agents during batch and continuous processing. The influence of stressing conditions described by means of stress energy, stress number as well as mass-specific energy input on product particle sizes is presented. Grinding kinetics observed for batch and continuous operation are comparable under similar stressing and formulation conditions. Furthermore, it was found that the use of small grinding media, i.e. stress conditions where low stress energies and high stress numbers apply, are advantageous with respect to fast kinetics and minimum energy consumption. Moreover, the relationship between product characteristics and formulation parameters, i.e. type and concentration of stabilising agents are thoroughly investigated. Complex formation of KVA 64 and SDS has been proven by means of tensiometry and fluorescence spectroscopy. It is demonstrated that solubilisation of pyrene occurs in the system and that product characteristics are not only determined by pure breakage events or colloidal stability issues but also by dissolution and ripening phenomena: Minimum product particle sizes at similar stressing conditions are observed under conditions where solubilisation and ripening are less pronounced, whereas larger product particles are observed in systems with high solubilisation capacities.
EAM Import::2019-03-13

Impact of the nanoparticle-protein corona on colloidal stability and protein structure - Peukert, Wolfgang; Gebauer, Julia; Malissek, Marcelina; Simon, Sonja; Knauer, Shirley; Maskos, Michael; Stauber, Roland; Treuel, Lennart (Langmuir, 2012)
In biological fluids, proteins may associate with nanoparticles (NPs), leading to the formation of a so-called "protein corona" largely defining the biological identity of the particle. Here, we present a novel approach to assess apparent binding affinities for the adsorption/desorption of proteins to silver NPs based on the impact of the corona formation on the agglomeration kinetics of the colloid. Affinities derived from circular dichroism measurements complement these results, simultaneously elucidating structural changes in the adsorbed protein. Employing human serum albumin as a model, apparent affinities in the nanomolar regime resulted from both approaches. Collectively, our findings now allow discrimination between the formation of protein mono- and multilayers on NP surfaces. © 2012 American Chemical Society.
Keywords: fluid; protein; nanoparticle; protein; corona; agglomeration; multilayer

Improved accuracy and convergence analysis of finite volume methods for particle fragmentation models - Saha, Jitraj; Bück, Andreas (Mathematical Methods in the Applied Sciences, 2020)
In this work, two new number- and volume-consistent finite volume methods for the numerical solution of binary and multifragmentation problems are introduced. The new number-consistency is achieved by introducing a single weight function. Several benchmark problems of different complexity are solved to assess the accuracy. Mathematical convergence analysis suggests that both of the new methods are numerically second order convergent with respect to the grid size on uniform and nonuniform meshes.
CRIS-Team Scopus Importer:2020-09-25
Keywords: conservative formulation; finite volume scheme; fragmentation equation; volume conservation; weight functions

Improvement of polymer properties for powder bed fusion by combining in situ PECVD nanoparticle synthesis and dry coating - Gomez Bonilla, Juan Sebastian; Düsenberg, Björn; Lanyi, Franz; Schmuki, Patrik; Schubert, Dirk W.; Schmidt, Jochen; Peukert, Wolfgang; Bück, Andreas (Plasma Processes and Polymers, 2021)
Polypropylene (PP) powders are coated with silica nanoparticles in a fluidized bed to improve the flow behavior of the powders and the processability in powder bed fusion. The nanoparticles are produced in situ via dusty plasma‐enhanced chemical vapor deposition (PECVD) in an atmospheric‐pressure Ar/O2 plasma jet fixed at the distributor plate of the fluidized bed. Hexamethyldisiloxane is used as a precursor of the nanoparticles. The influence of the oxygen concentration in the plasma gas and the number of treatment cycles on the chemical composition of the nanoparticles, the amount of nanoparticles deposited, and the flow properties of the coated PP powders is investigated. The chemical composition of the formed silica particles is determined by X‐ray photon spectroscopy and infrared spectroscopy. The results reveal that the composition of the nanoparticles is SiOxCy, that is, the portion of organic residues introduced by the precursor can be controlled by changing the oxygen concentration in the plasma gas. The mass of nanoparticles deposited on the polymer powder's surface, as determined by inductively coupled optical emission spectroscopy, shows a linear dependence of the number of cycles and the oxygen concentration in the plasma gas. A considerable improvement of the flow behavior of the PP powders is observed after PECVD treatment.<br
Keywords: nanocomposites; particle coating; plasma‐enhanced chemical vapor deposition; powder bed fusion; powder flowability

Improving the coloring of polypropylene materials for powder bed fusion by plasma surface functionalization - Gomez Bonilla, Juan Sebastian; Szymczak, Tim; Zhou, Xuemei; Schrüfer, Stefan; Dechet, Maximilian; Schmuki, Patrik; Schubert, Dirk W.; Schmidt, Jochen; Peukert, Wolfgang; Bück, Andreas (Additive Manufacturing, 2020)
Polypropylene (PP) powder is treated in a fluidized bed reactor with an atmospheric Ar/O2 plasma jet to investigate the influence of the plasma treatment on the coloring of the powders. The oxygen concentration in the plasma gas and duration of the treatment was varied. Contact angle and X-ray photoelectron spectroscopy measurements confirmed and quantified the formation of surface functionalities and their dependence on the process parameters. The plasma treatment contributes to a significant improvement of the dispersibility and coloring of PP. Powder bulk properties such as particle size distribution and flowability were not modified by the process. Effects of the plasma treatment on the material bulk properties are also negligible.
CRIS-Team Scopus Importer:2020-06-26
Keywords: Color strength; Dispersibility; Plasma surface functionalization; Powder bed fusion; Powder coloring; Wettability

Improving the properties of an Al matrix composite fabricated by laser powder bed fusion using graphene–TiO2 nanohybrid - Ghazanlou, Siavash Imanian; Ghazanlou, Siamak Imanian; Ghazanlou, Sroush Imanian; Hosseinpour, Saman; Liao, Yiliang; Javidani, Mousa (Journal of Alloys and Compounds, 2023)
The impact of graphene–TiO2 nanohybrid reinforcement on an aluminum matrix after the laser powder bed fusion process was investigated. The microstructure characteristics, mechanical properties, wear resistance, and corrosion behavior of the fabricated nanocomposite structures with different contents of the graphene–TiO2 nanohybrid were compared with those of the pure aluminum and aluminum matrix composite reinforced with separated graphene and nano-TiO2. X-ray diffraction, Raman and X-ray photoelectron spectroscopy, mechanical and tribological characterization, fractography, and corrosion assessments were performed to identify the role of the graphene–TiO2 nanohybrid in improving the properties of the Al matrix composite after reinforced laser powder bed fusion. In the presence of graphene–TiO2 nanohybrid in the Al matrix, Al4C3 formation could not be detected, which may be due to the existence of TiO2 nanoparticles on the surface of the graphene. Despite this result, the Al4C3 structure was identified in LPBF Al matrix composite containing separated graphene and nano-TiO2. The results indicated a synergistic effect between the graphene and TiO2 particles in the nanohybrid structure. In the unified nanohybrid structure, due to the raising surface roughness of graphene with the presence of TiO2 on its surface, strong interfacial bonding between the graphene–TiO2 nanohybrid and Al matrix is created. Thus, the graphene–TiO2 nanohybrid incorporated within the Al matrix can bridge between the subsurface cracks and reduces the cracks propagation in the matrix, thereby enhancing the mechanical properties, wear resistance, and corrosion behavior of the composite.
CRIS-Team Scopus Importer:2023-01-13
Keywords: Aluminum; Composite; Graphene–TiO; LPBF; Property enhancement

Increasing flowability and bulk density of PE-HD powders by a dry particle coating process and impact on LBM processes - Blümel, Christina; Sachs, Marius; Laumer, Tobias; Winzer, Bettina; Schmidt, Jochen; Schmidt, Michael; Peukert, Wolfgang; Wirth, Karl-Ernst (Rapid Prototyping Journal, 2015)
Purpose - The purpose of this paper is to demonstrate the processability of cohesive PE-HD particles in laser beam melting processes (LBM) of polymers. Furthermore, we present a characterization method for polymer particles, which can predict the quality of the powder deposition via LBM processes. Design/methodology/approach - This study focuses on the application of dry particle coating processes to increase flowability and bulk density of PE-HD particles. Both has been measured and afterwards validated via powder deposition of PE-HD particles in a LBM machine. Findings - For efficient coating in a dry particle coating process, the PE-HD particles and the attached nanoparticles need to show similar surface chemistry, i.e. both need to behave either hydrophobic or hydrophilic. It is demonstrated that dry particle coating is appropriate to enhance flowability and bulk density of PE-HD particles and hence considerably improves LBM processes and the resulting product quality. Originality/value - At present, in LBM processes mainly polyamide (PA), 12 particles are used, which are so far quite expensive in comparison to, for example, PE-HD particles. This work provides a unique and versatile method for nanoparticulate surface modification which may be applied to a wide variety of materials. After the coating, the particles are applicable for the LBM process. Our results provide a correlation between flowability and bulk density and the resulting product qualit
Keywords: Bulk density; Dry particle coating; Flowability; Hydrophilic; Hydrophobic; Polymers

Increasing flow rates in polydimethylsiloxane-based deterministic lateral displacement devices for sub-micrometer particle separation - Marhenke, Julius; Dirnecker, Tobias; Vogel, Nicolas; Rommel, Mathias (Microfluidics and Nanofluidics, 2022)
In this study, we show the design and manufacturing of microfluidic deterministic lateral displacement (DLD) devices for sub-micrometer particle separation. For that purpose, devices with pillar gaps of 4 µm and a periodicity of 50 were designed. After photolithographic manufacturing of SU-8 masters with different heights (15 and 30 µm) and vertical sidewalls for soft-lithographic replication with polydimethylsiloxane (PDMS) the influence of flow rate on the separation efficiency of 0.45 and 0.97 µm particles was investigated. The 15 µm devices were operated at 0.125 and 0.5 µl/min sample flow rate and the 30 µm devices at 0.5 and 2.0 µl/min, respectively. Excellent separation efficiencies were observed for both device heights at the lower sample flow rates, while separation efficiencies decreased at the respective higher sample flow rates. The decrease in separation efficiency was attributed to deformation of the soft PDMS pillars, which causes an increase in pillar gaps at the higher sample flow rates as shown by microscopy imaging. The advantage of the 30 µm devices over the 15 µm devices is clearly shown by the separation of 0.45 and 0.97 µm particles at 0.5 µl/min. Due to reduced hydrodynamic resistance in the 30 µm devices and thus less pillar deformation, the displacement efficiency of 0.97 µm particles was above 99% compared to 46–57% for the 15 µm devices. Our 30 µm devices demonstrated excellent separation at a tenfold higher sample flow rate with 0.5 µl/min compared to comparable PDMS-based devices operating in the same size regime.<br
Keywords: Deterministic lateral displacement (DLD); Polydimethylsiloxane (PDMS); Flow rate; Deformation

Indentation and Self-Healing Mechanisms of a Self-Assembled Monolayer-A Combined Experimental and Modeling Study - Meltzer, Christian; Paul, Jonas; Dietrich, Hanno; Jäger, Christof; Clark, Timothy; Zahn, Dirk; Braunschweig, Björn; Peukert, Wolfgang (Journal of the American Chemical Society, 2014)
A combination of in situ vibrational sum-frequency generation (SFG) spectroscopy and molecular-dynamics (MD) simulations has allowed us to study the effects of indentation of self-assembled octadecylphosphonic acid (ODPA) monolayers on α-Al2O3(0001). Stress-induced changes in the vibrational signatures of C-H stretching vibrations in SFG spectra and the results of MD simulations provide clear evidence for an increase in gauche-defect density in the monolayer as a response to indentation. A stress-dependent analysis indicates that the defect density reaches saturation at approximately 155 MPa. After stress is released, the MD simulations show an almost instantaneous healing of pressure-induced defects in good agreement with experimental results. The lateral extent of the contact areas was studied with colocalized SFG spectroscopy and compared to theoretical predictions for pressure gradients from Hertzian contact theory. SFG experiments reveal a gradual increase in gauche-defect density with pressure before saturation close to the contact center. Furthermore, our MD simulations show a spatial anisotropy of pressure-induced effects within ODPA domains: molecules tilted in the direction of the pressure gradient increase in tilt angle while those on the opposite side form gauche-defects.
Keywords: spectroscopy; monolayer; self-assembly

Individualization and Stabilization of Zinc Oxide Nanorods by Covalent Functionalization with Positively Charged Catechol Derivatives - Burger, Alexandra; Srikantharajah, Rubitha; Peukert, Wolfgang; Hirsch, Andreas (Chemistry - A European Journal, 2017)
We present the formation of individualized and stabilized zinc oxide (ZnO) nanorods by functionalization with positively charged catechol derivatives by means of ligand exchange reactions. The electrosteric stabilization of ZnO nanorods was studied using two catechol derivatives, introducing either three(1) or six(2) pH independent positive charges per molecule and sterically demanding groups onto the surface. ZnO nanorods providing initially acetate (Ac) or 2-[2-(2-methoxyethoxy)-ethoxy]acetic acid (TODA) ligands on their surface were used. The ligand exchange was performed by using mono and mixed functionalization approaches, utilizing either exclusively the positively charged catechols or mixtures of the latter with small commercially available catechol derivatives, namely 4-methylcatechol (Me-cat), 4-tert-butylcatechol (tBu-cat), and dopamine hydrochloride (Dop). Using a combination of various analytical methods such as zeta potential, dynamic light scattering (DLS), UV/Vis, and scanning electron microscopy (SEM) measurements we found that the initial surfactants on the nanorods surface, the number of positive charges per molecule, the steric demand, and the added amount of the catechol derivative strongly influence the colloidal behavior of the nanorods. Stable suspensions containing individualized ZnO nanorods were successfully formed upon functionalization of ZnO-TODA nanorods with 30monolayers (MLs) of the higher charged catechol (2), as well as using mixtures of 20/10 and 18/10MLs of 2/Dop.
Keywords: catechol; colloidal sabilization; ligand exchange; surface functionalization; ZnO nanorods

Inductive heating of fluidized beds: Mobile versus stationary heat exchange elements - Idakiev, Vesselin V.; Bueck, Andreas; Moerl, Lothar; Tsotsas, Evangelos (Drying Technology, 2019)
Fluidized beds play an important role in many industrial processes due to their very good heat and mass transfer. Usually heated convectively, inductive energy input is a promising alternative utilizing an electromagnetic field and an electrically conductive material [e.g. mobile iron hollow balls (IHB) or stationary iron tube (IT)]. In this research article, the heat exchange between moving IHB or stationary tube and the fluidizing medium or substrate is modeled. Very good correspondence is achieved between calculated and experimental results.
CRIS-Team WoS Importer:2019-05-17

Inductive heating of fluidized beds: Spray coating process - Idakiev, Vesselin V.; Steinke, Claudia; Sondej, Franziska; Bück, Andreas; Tsotsas, Evangelos; Mörl, Lothar (Powder Technology, 2018)
Spray fluidized bed coating is an established process for the treatment of solid particles. Commonly fluidized beds are heated convectively. Another method is inductive heating by electrically conductive particles. In this work spray coating with inductive heating is investigated. Coating experiments with convective or inductive heating and different process parameters (temperature, spraying rate, initial particle diameter, initial bed mass) were realized. Moisture content, particle size distribution and apparent density of the particles were measured, as well as the thickness and porosity of the layer created on the initial particles. Similar results can be obtained by both heating methods, advantages of inductive heating are discussed as well as limitation
Keywords: Inductive heating of fluiized beds; Coating; Layer porosity; MAGNETIC-FIELD

Industrially scalable and cost-effective Mn2+ doped ZnxCd1-xS/ZnS nanocrystals with 70% photoluminescence quantum yield, as efficient down-shifting materials in photovoltaics - Levchuk, Ievgen; Wuerth, C.; Krause, F.; Osvet, Andres; Batentschuk, Miroslaw; Resch-Genger, Ute; Kolbeck, Claudia; Herre, Patrick; Steinrück, Hans-Peter; Peukert, Wolfgang; Brabec, Christoph (Energy and Environmental Science, 2016)
We present colloidally stable and highly luminescent ZnxCd1-xS:Mn/ZnS core–shell nanocrystals (NCs) synthesized via a simple non-injection one-pot, two-step synthetic route, which can be easily upscaled. A systematic variation of the reaction component, parameters and thickness of the ZnS shell yielded doped nanocrystals with a very high photoluminescence quantum yield ( extgreekFpl) of 70%, which is the highest value yet reported for these Mn-doped sulfide-semiconductor NCs. These materials can be synthesized with high reproducibility in large quantities of the same high quality, i.e., the same extgreekFpl using accordingly optimized reaction conditions. The application of these zero-reabsorption high quality NCs in the light conversion layers, deposited on top of a commercial monocrystalline silicon (mono-Si) solar cell, led to a significant enhancement of the external quantum efficiency (EQE) of this device in the ultraviolet spectral region between 300 and 400 nm up to ca. 12%. EQE enhancement is reflected by an increase in the power conversion efficiency (PCE) by nearly 0.5 percentage points and approached the theoretical limit (0.6%) expected from down-shifting for this Si solar cell. The resulting PCE may result in a BoM (bill of materials) cost reduction of app. 3% for mono-Si photovoltaic modules. Such small but distinct improvements are expected to pave the road for an industrial application of doped semiconductor NCs as cost-effective light converters for silicon photovoltaic (PV) and other optoelectronic applications.
EAM Import::2019-03-14

Inferential control of product properties for fluidized bed spray granulation layering - Dürr, Robert; Neugebauer, Christoph; Palis, Stefan; Bück, Andreas; Kienle, Achim (21st IFAC World Congress 2020, 2020)
Fluidized bed layering granulation has found application in a wide range of industrial processes, e.g. food, pharmaceutical or fertilizer manufacturing. The quality of the produced granules is a critical factor for subsequent processing steps and depends on individual particle properties like characteristic size, porosity or mechanical stability. Therefore, these properties have to be monitored closely during the process to enable accurately timed intervention by plant operators or the application of suitable feedback control algorithms. In case certain properties are not measurable due to financial or technical limitations, observer techniques can fill the gap and provide reliable estimates for these properties. In this manuscript, observer design is demonstrated and validated for a fluidized bed layering granulation process model represented by a complex set of partial and ordinary differential equations. Furthermore, an inferential integral state feedback controller is designed and applied to the complex nonlinear mode
Keywords: Continuous fluidized bed layering granulation; Model-based control; Distributed parameter systems; State estimation

Infiltration behavior of liquid thermosets in thermoplastic powders for additive manufacturing of polymer composite parts in a combined powder bed fusion process - Setter, Robert; Riedel, Florentin; Peukert, Wolfgang; Schmidt, Jochen; Wudy, Katrin (Polymer Composites, 2021)
Polymer-based multimaterial additive manufacturing (AM) has developed into one of the most promising technologies of recent times. A processing concept was developed in previous studies, which targets the implementation of reactive liquids in a thermoplastic powder-bed for the creation of multimaterial polymer composite parts. This process aims to be the first AM process of its kind to fully utilize the potentials of both thermoplastic and thermoset polymers simultaneously. A highly important aspect for this process is the investigation of the infiltration behavior of the reactive liquids within the powder bed, since premature or delayed curing of the liquids could lead to deviations from the intended geometry as well as process errors due to material protrusions. This investigation presents an experimental and a mathematical approach to describe and predict the time which a droplet needs to completely infiltrate the powder bed. The results showed, that the experimental setup is viable to observe the droplet height over time at temperatures of up to 105°C and infiltration times below 500 ms. The mathematical model proved to be a powerful approximation to describe the infiltration behavior of a reactive liquid within a thermoplastic powder bed once a material-specific form factor is determined for each powder material. Through the process of elimination, the independence of the form factor was demonstrated for different powder parameters like the particle size. A theory is presented, which correlates the form factor to the microstructural shape and surface condition of the particles based on SEM images.
Keywords: additive manufacturing; reinforcement; 3D printing; thermoplastics; thermosets

Inflow boundary conditions determine T-mixer efficiency - Schikarski, Tobias; Trzenschiok, Holger; Peukert, Wolfgang; Avila, Marc (Reaction Chemistry & Engineering, 2019)
We report on a comprehensive experimental-computational study of a simple T-shaped mixer for Reynolds numbers up to 4000. In the experiments, we determine the mixing time by applying the Villermaux-Dushman characterization to a water-water mixture. In the numerical simulations, we resolve down to the smallest (Kolmogorov) flow scales in space and time. Excellent agreement is obtained between the experimentally measured mixing time and numerically computed intensity of segregation, especially in the turbulent regime, which validates both approaches. We confirm that the mixing time is mainly determined by the specific power input, as assumed in most mixing-models. However, we show that by suitably manipulating the inflow conditions, the power input necessary to achieve a given mixing time can be reduced by a factor of six. Our study enables detailed investigations of the influence of hydrodynamics on chemical reactions and precipitation processes, as well as the detailed testing of turbulence and micromixing models.
CRIS-Team WoS Importer:2019-03-15

Influence of annealing temperature and measurement ambient on TFTs based on gas phase synthesized ZnO nanoparticles - Walther, Sabine; Schäfer, Stefan; Jank, M. P. M.; Thiem, H.; Peukert, Wolfgang; Frey, Lothar; Ryssel, Heiner (Microelectronic Engineering, 2010)
In this paper, we report on the applicability of gas phase synthesized ZnO nanoparticles for printed electronics. Electrical characteristics of thin film transistors with an active layer based on ZnO nanoparticle dispersions are presented. A low charge carrier mobility and a low Ion/Ioff ratio are found for the devices when measured in nitrogen atmosphere. The mobility is limited by the rough interface between semiconductor and dielectric. Additional electrical measurements in dry air reveal a dependency of the Ion/Ioff ratio on surface states of the ZnO particles. It is shown that adsorption of oxygen on ZnO nanoparticles leads to improved transistor characteristics.
Keywords: Nanoparticle; Printable electronics; Thin film transistor; Zinc oxide

Influence of carbon-coated iron nanoparticles on the Raman spectrum of liquid ethanol - Kiefer, Johannes; Toni, Franziska; Wirth, Karl-Ernst (Journal of Raman Spectroscopy, 2015)
Raman spectroscopy is applied to study the interactions between carbon‐coated iron nanoparticles and ethanol. The spectra reveal changes in the vibrational structure of ethanol, despite dispersion of only a very small amount of nanoparticles. The hydrogen bonding network of ethanol is significantly affected in the presence of the particles. This is revealed by frequency shifts throughout the spectrum as well as the modification of the OH stretching band of the alcohol. The carbon shell of the nanoparticles does not exhibit polar groups, and hence the non‐polar interactions in the system are strengthened and the hydrogen bonding is weakene
Keywords: elastic scattering; composite; Raman scattering; molecular interactions

Influence of drying conditions on process properties and parameter identification for continuous fluidized bed spray agglomeration - Strenzke, G.; Golovin,; Wegner, M.; Palis, S.; Bück, Andreas; Kienle, A.; Tsotsas, E. (IDS'2018: 21ST INTERNATIONAL DRYING SYMPOSIUM, 2018)
CRIS-Team WoS Importer:2019-08-16

Influence of mechanical properties on impact fracture: Prediction of the milling behaviour of pharmaceutical powders by nanoindentation - Meier, Matthias; John, Edgar; Wieckhusen, Dierk; Wirth, Wolfgang; Peukert, Wolfgang (Powder Technology, 2009)
The impact grinding behaviour of materials can be characterized by the two breakage parameters f(Mat) and xW(m,min) [Vogel and Peukert, Powder Technol. 129 (2003) 101-110]. These parameters are usually determined by single particle milling tests. The parameters are useful for predicting the selection function and the breakage function and thus enable modelling of impact milling processes. So far, no detailed correlations have been established between the breakage parameters f(Mat) and xW(m,min) In and intrinsic material properties. In this work, we study the correlation between the breakage parameters of pharmaceutical powders and their mechanical properties (hardness, Young's modulus and fracture toughness) that are determined from indentation experiments. It will be shown that f(Mat) and xW(m,min) can be expressed in terms of the brittleness index (defined as the ratio of hardness to fracture toughness H/K-c). This correlation allows the prediction of the breakage probability of a material by using only a small number of crystals. (c) 2008 Elsevier B.V. All rights reserved.
Keywords: Comminution; Grinding; Breakage probability; Material properties; Nanoindentation; Single particle tests

Influence of mixing on precipitation of nanoparticles - Peukert, Wolfgang; Schwarzer, Hans-Christoph (Chemie Ingenieur Technik, 2002)
Precipitation is a promising method for the economic production of commercial amounts of nanoparticles because it is fast, and operable at ambient temperature. However, process control – due to the rapidity of the involved processes of mixing, nucleation, growth, and agglomeration – and stabilization against agglomeration represent challenges. This paper shows how these challenges can be successfully handled. The focus of this work is therefore set on how to tailor the particle-size distribution in continuous precipitation. Precipitation experiments with barium sulfate in a T-mixer are presented. It was found that the size of the precipitated primary particles is strongly dependent on the mixing intensity. On increasing the mixing intensity, it was possible to generate particles of approximately 50 nanometers in diameter. The second challenge, to stabilize the particles against agglomeration, was successfully met by adsorbing potential-determining ions on the particle surfaces, i.e., by increasing repulsive particle interactions. Thus, stable suspensions of barium sulfate nanoparticles were obtained.
UnivIS-Import:2015-03-09:Pub.2002.tech.ITC.mechve.influe
Keywords: precipitation; nanoparticle; mixing

Influence of Mixing on the Precipitation of Organic Nanoparticles: A Lagrangian Perspective on Scale-up Based on Self-Similar Distributions - Schikarski, Tobias; Trzenschiok, Holger; Avila, Marc; Peukert, Wolfgang (Chemical Engineering & Technology, 2019)
Precipitation of nanoparticles is applied in various fields with a rising interest in the formulation of poorly soluble drugs. The impact of fluid mixing on the precipitation of organic nanoparticles is analyzed. Direct numerical simulations are applied to determine the spatiotemporal evolution of the liquid phase composition and to estimate the particle evolution along Langragian trajectories. The simulation results are compared with laboratory experiments of mixing and particle size evolution, which use a recently developed approach to rapidly stabilize the precipitated nanoparticles. The impact of mixing on precipitation is revealed, thereby enabling a parameter-free estimation of the mean particle sizes and the particle size distributions. The distributions of residence time, supersaturation time, and particle size are self-similar for Reynolds numbers in the turbulent regime and allow the derivation of scale-up rules.
CRIS-Team Scopus Importer:2019-06-25
Keywords: Direct numerical simulations; Ibuprofen; Lagrangian mixing; Nanoparticle precipitation; T-micromixer

Influence of moisture control on activity in continuous fluized bed drying of baker’s yeast pellets - Dürr, Robert; Bück, Andreas (Drying Technology, 2020)
This work investigates how process control of moisture content in continuously operated convective dryers for particulate bio-materials influences the product’s activity. As case study drying of baker’s yeast in a fluidized bed dryer is considered. Superiority of controlled process operation over un-controlled operation with respect to uncertainties in the falling-rate drying period as well as process disturbances is demonstrated simulation studies. Furthermore, limitations in controllability of activity are pointed out and future actions are proposed.
CRIS-Team Scopus Importer:2020-10-30
Keywords: activity; Convective drying; fluidized bed; process control; yeast

Influence of Nanoparticle Reinforcement on the Mechanical Properties of Ultrafine-Grained Aluminium Produced by ARB - Schmidt, Christian; Knieke, Catharina; Maier, Verena; Höppel, Heinz Werner; Peukert, Wolfgang; Göken, Mathias (Materials Science Forum, 2011)
Dispersed nanoparticles are introduced from stabilized suspensions during the accumulative roll bonding process in aluminium AA1050A by air gun spraying up to a final volume fraction of 0.1 % after eight cycles. Additional strengthening caused by particle insertion is observed and strongly depends on the suspension medium and stabilizing agent as both influence interfacial bonding of the particles to the matrix. The particle insertion furthermore results in reduced peel strength of the sheets irrespective of particle material and size caused by a reduction of effective metal to metal bonding area during rolling through the presence of the particle

Influence of operating parameters on process behavior and product quality in continuous spray fluidized bed agglomeration - Strenzke, G.; Dürr, R.; Bück, Andreas; Tsotsas, E. (Powder Technology, 2020)
The present work investigates continuous spray fluidized bed agglomeration with internal separation using glass primary particles and sprayed solution of cellulosic binder. Different fluidization and thermal parameters were investigated with respect to their influences on process behavior and product quality. Product quality is characterized with respect to particle size, sphericity and porosity. Trends between operation parameters and product characteristics are established, especially in view of the drying potential of the fluidization gas. In addition to the successful identification of the parameter influences, this study has detected general relationships between drying potential and agglomerate porosity, as well as between agglomerate size and porosity.
CRIS-Team Scopus Importer:2020-08-14
Keywords: Continuous operation; Fluidized bed; Internal separation; Spray agglomeration

Influence of particle size and concentration on the second-harmonic signal generated at colloidal surfaces - Schneider, L.; Schmid, Hans-Joachim; Peukert, Wolfgang (Applied Physics B-Lasers and Optics, 2007)
Second harmonic generation (SHG) spectroscopy is a recently developed technique for the investigation of surface properties of particles. To apply the method to technical colloidal systems, the dependences of several experimental parameters on the signal have to be studied. In this work the influence of particle concentration on the SHG signal from the surfaces of colloids (polystyrene beads in a size range of 0.1 mu m to 2.9 mu m) is investigated. A simple model, based on Lambert-Beer's law, to describe the measured dependences is derived. The model agrees with the experimental observations for particles smaller 1.1 mu m and with a small modification also for larger particles. Based on the new model an analytical equation for determining the optimum concentration, where highest signals in colloidal SHG spectroscopy measurements are obtained, is derived.

Influence of polydispersity and breakage on stochastic simulations of spray fluidized bed agglomeration - Singh, Abhinandan Kumar; Tsotsas, Evangelos (Chemical Engineering Science, 2022)
Keywords: Polydisperse primary particles; Tunable sequential algorithm; Constant volume Monte Carlo; Morphological descriptors; Breakage

Influence of process conditions on the product properties in a continuous fluidized bed spray granulation process - Diez, E.; Meyer, K.; Bück, Andreas; Tsotsas, Evangelos; Heinrich, Stefan (Chemical Engineering Research & Design, 2018)
This work focuses on continuously operated spray granulation processes in horizontal fluidized beds highlighting the influence of process conditions on the particle properties of the resulting product granules. The drying process has a decisive influence on the kinetics of the growth rate and thus also on the properties of the particles, such as the morphological structure, particle moisture content and porosity as well as density, compression strength and the wetting behavior. This influence has been considered in this study in more detail on the basis of the model material sodium benzoate. In order to compare the produced granules at different drying conditions and spray rates of the suspension an external product classification was used to achieve a certain product granule size. The obtained experimental results show a deep influence of the thermal conditions onto granule morphology and structural properties, which is in qualitative agreement with recent experimental observations (Rieck et al., 2015; Hoffmann et al., 2015a, Schmidt et al., 2017b). The overall trend of the results reveal smoother product granules with decreasing spray rates of the suspension and increasing drying temperatures. These smoother surface morphologies lead to a more homogeneous layering which has as a consequence that the internal particle porosity is decreasing while the solids density and the compression strength of the particles are increasing at the same time. In this study the purely qualitative classification of the surface texture from previous experimental studies was extended by the topographic analysis of the product granules, giving the possibility to quantify the morphological structure by means of roughness measurements. This makes the morphological design accessible as product property and permits the utilization of models that describe the morphology according to the process condition
Keywords: Fluidized bed; Spray granulation; Granule morphology; Particle properties

Influence of process parameters on breakage kinetics and grinding limit at the nanoscale - Knieke, Catharina; Romeis, Stefan; Peukert, Wolfgang (Aiche Journal, 2011)
In long-term milling experiments, in a stirred media mill, a grinding limit where no further particle breakage occurs was identified. During mechanical stressing of the particles, defects are generated in the crystalline lattice, which allows real fracture of nanoparticles. Below a critical size, defects cannot be stored or generated in the crystallites and the overall limit of grinding is reached. This limit is strongly influenced by material properties and hardly affected by most of the process conditions. However, the breakage kinetics strongly depend on the process parameters and suspension conditions as long as the grinding limit is not reached. Based on these findings, two mechanisms of nanoparticle breakage are proposed. Proper choice of process parameters saves not only up to 90% of the energy input to reach the grinding limit but also leads to a higher product quality in terms of crystallinity and less milling bead wear.

Influence of process variables on spray agglomeration process in a continuously operated horizontal fluidized bed - Du, J.; Bück, Andreas; Tsotsas, E. (Powder Technology, 2020)
Experiments on continuously operated spray fluidized bed agglomeration are presented in this work. The process is conducted with glass beads and water-based binder hydroxypropylmethylcellulose (HPMC). By varying the process parameters, the results show that by the decrease of air temperature or feed rate and by the increase of binder concentration, larger particles can be achieved. Larger particle size also results in higher bed mass and more fluctuations in the process. Besides parameters variations, different internal and outlet weir configurations are used. Tracers are used in the experiments to characterize the particle residence time distribution. The separation effect can be decreased and the particle residence time can be optimized by the installation of internal weirs and lower height of outlet weir. The results show that the jets from the spray nozzles are increasing the motion and mixing of particles significantly.
CRIS-Team Scopus Importer:2020-01-24
Keywords: Continuous process; Horizontal fluidized bed; Residence time distribution; Spray agglomeration

Influence of separation properties and processing strategies on product characteristics in continuous fluidized bed spray granulation - Mueller, Daniel; Bück, Andreas; Tsotsas, Evangelos (Powder Technology, 2019)
The realization of continuous operation in fluidized bed spray granulation raises issues of process stability and product specification. It requires an appropriate process control strategy and a suitable granulator design. In previous work, a two-zone population balance (PB) model was developed and simulated product size distributions were evaluated by experiments in a Wurster granulator with external straight-duct air classification, however only regarding the process stability. The present contribution extends this population balance model with further equations for the purpose of product size control whereby the parameter setting of the former investigation serves as basis of the shown simulation study. Three process control strategies have been developed, implemented into the PB-model and investigated for diverse desired particle growth ratios and various separation sharpnesses. The simulation results show that only one of these strategies is able to provide the targeted requirements of both, process stability and product specification, but only for sufficiently good separation performance.
CRIS-Team Scopus Importer:2020-02-21
Keywords: Continuous spray granulation; Fluidized bed; Population balances; Process control; Simulation; Straight-duct air classification; Wurster equipment

Influence of Surfactant-Mediated Interparticle Contacts on the Mechanical Stability of Supraparticles - Wang, Junwei; Kang, Eunsoo; Sultan, Umair; Merle, Benoit; Inayat, Alexandra; Graczykowski, Bartlomiej; Fytas, George; Vogel, Nicolas (Journal of Physical Chemistry C, 2021)
Colloidal supraparticles are micron-scale spherical assemblies of uniform primary particles, which exhibit emergent properties of a colloidal crystal, yet exist as a dispersible powder. A prerequisite to utilize these emergent functionalities is that the supraparticles maintain their mechanical integrity upon the mechanical impacts that are likely to occur during processing. Understanding how the internal structure relates to the resultant mechanical properties of a supraparticle is therefore of general interest. Here, we take the example of supraparticles templated from water/fluorinated oil emulsions in droplet-based microfluidics and explore the effect of surfactants on their mechanical properties. Stable emulsions can be generated by nonionic block copolymers consisting of a hydrophilic and fluorophilic block and anionic fluorosurfactants widely available under the brand name Krytox. The supraparticles formed in the presence of both types of surfactants appear structurally similar, but differ greatly in their mechanical properties. While the nonionic surfactant induces superior mechanical stability and ductile fracture behavior, the anionic Krytox surfactant leads to weak supraparticles with brittle fracture. We complement this macroscopic picture with Brillouin light spectroscopy that is very sensitive to the interparticle contacts for subnanometer-thick adsorbed layers atop of the nanoparticle. While the anionic Krytox does not significantly affect the interparticle bonds, the amphiphilic nonionic surfactant drastically strengthens these bonds to the point that individual particle vibrations are not resolved in the experimental spectrum. Our results demonstrate that seemingly subtle changes in the physicochemical properties of supraparticles can drastically impact the resultant mechanical propertie
Keywords: Ductile fracture; Emulsification; Fracture mechanics; Nonionic surfactants; Ostwald ripening; Physicochemical properties; Colloidal crystals; Emergent functionality; Emergent property; Internal structure; Interparticle contacts; Mechanical impacts; Mechanical integrity; Micron scale; Primary particles; Spherical assembly; Mechanical stability

Influence of Tail Groups during Functionalization of ZnO Nanoparticles on Binding Enthalpies and Photoluminescence - Segets, Doris; Lin, Wei; Schmidt, Jochen; Peukert, Wolfgang; Mahler, Michael; Schindler, Torben; Unruh, Tobias; Meyer, Bernd (Langmuir, 2017)
We report on the tailoring of ZnO nanoparticle (NP) surfaces by catechol derivatives (CAT) with different functionalities: tert-butyl group (tertCAT), hydrogen (pyroCAT), aromatic ring (naphCAT), ester group (esterCAT), and nitro group (nitroCAT). The influence of electron-donating/-withdrawing properties on enthalpy of ligand binding (ΔH) was resolved and subsequently linked with optical properties. First, as confirmed by ultraviolet/visible (UV/vis) and Fourier transform infrared (FT-IR) spectroscopy results, all CAT molecules chemisorbed to ZnO NPs, independent of the distinct functionality. Interestingly, the ζ-potentials of ZnO after functionalization shifted to more negative values. Then, isothermal titration calorimetry (ITC) and a mass-based method were applied to resolve the heat release during ligand binding and the adsorption isotherm, respectively. However, both heat- and mass-based approaches alone did not fully resolve the binding enthalpy of each molecule adsorbing to the ZnO surface. This is mainly due to the fact that the Langmuir model oversimplifies the underlying adsorption mechanism, at least for some of the tested CAT molecules. Therefore, a new, fitting-free approach was developed to directly access the adsorption enthalpy per molecule during functionalization by dividing the heat release measured via ITC by the amount of bound molecules determined from the adsorption isotherm. Finally, the efficiency of quenching the visible emission caused by ligand binding was investigated by photoluminescence (PL) spectroscopy, which turned out to follow the same trend as the binding enthalpy. Thus, the functionality of ligand molecules governs the binding enthalpy to the particle surface, which in turn, at least in the current case of ZnO, is an important parameter for the quenching of visible emission. We believe that establishing such correlations is an important step toward a more general way of selecting and designing ligand molecules for surface functionalization. This allows developing strategies for tailored colloidal surfaces beyond empirically driven formulation on a case by case basi
Keywords: functionalization; nanoparticle; photoluminesence

Influence of the counterion on the synthesis of ZnO mesocrystals under solvothermal conditions - Klupp Taylor, Robin; Distaso, Monica; Taccardi, Nicola; Wasserscheid, Peter; Peukert, Wolfgang (Chemistry - A European Journal, 2011)
Polymers and coordinating solvents have been shown to serve as templating agents to assist the precipitation of ZnO nanoparticles and address their morphology. In this work we show for the first time that a difference in the coordination strength between the polymer (poly-N-vinylpyrrolidone (PVP)) and the two Zn precursor salts (nitrate and acetate) is able to promote or suppress the formation of mesocrystalline structures and even more importantly to tune their three-dimensional organization. On the basis of FTIR and C NMR spectroscopic studies, we propose that not only the polymer (PVP) but also the solvent (DMF) play a key role as directing agents. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Keywords: NMR spectroscopy; optical properties; oriented attachment; poly-N-vinylpyrrolidone; ZnO mesocrystals

Influence of the number of flights on the dilute phase ratio in flighted rotating drums by PTV measurements and DEM simulations - Zhang, Lanyue; Jiang, Zhaochen; Mellmann, Jochen; Weigler, Fabian; Herz, Fabian; Bück, Andreas; Tsotsas, Evangelos (Particuology, 2020)
Particle distribution in the cross-section of the flighted rotating drum (FRD) is critical to the analysis of heat and mass transfer between gas and solids. In this work, the particle tracking velocimetry (PTV) method is applied to study the influence of the number of flights on the particle motion in FRDs. The drum, installed with 1, 4, 8, or 12 rectangular flights, is filled with plastic balls to 15% and operated at various rotating speeds ranging from 10 rpm to 30 rpm. The results show that the number of flights has different effects on the holdup ratio and cascading rate of single flight and active flights. With 8 and 12 flights, the FRD produces a larger and more stable particle ratio of the dilute phase. Moreover, DEM simulations agree with PTV measurements, whereas literature models show significant deviations. © 2020 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Scienc
Keywords: Flighted rotating drum; Number of flights; DEM; Dilute phase; PTV

Influence of the Particle Size Distribution on the Operation Behaviour of Circulating Fluidized Beds - Wirth, Karl-Ernst (Preprints 2nd International Conference on the Multiphase Flow, 1995)
UnivIS-Import:2015-04-16:Pub.1995.tech.ITC.mechve.influe

Influence of the polydispersity of pH 2 and pH 3.5 beta-lactoglobulin amyloid fibril solutions on analytical methods - Heyn, Timon R.; Garamus, Vasil M.; Neumann, Hendrikje R.; Uttinger, Maximilian; Guckeisen, Tobias; Heuer, Monique; Selhuber-Unkel, Christine; Peukert, Wolfgang; Keppler, Julia K. (European Polymer Journal, 2019)
It is well known that amyloid beta-lactoglobulin (BLG) fibril solutions contain a heterogeneous mixture of amyloid aggregates and non-amyloid material. However, few information are available on how strongly separated fractions of different morphologies (straight fibrils at pH 2 and worm-like aggregates at pH 3.5) vary with respect to physicochemical properties and building blocks as most analyses are conducted with unfractionized solutions where superposition effects occur. The pH-value shift resulted in an altered degree of acid hydrolysis which led to dissimilar building blocks of the aggregates (peptides at pH 2, non-hydrolyzed protein at pH 3.5). The respective separated amyloid and non-amyloid fractions showed significantly different size (SAXS, SEC, AUC) and charge properties (Zeta potential) than the whole samples. Strong superposition effects were evident with common analyses such as FTIR, TRP fluorescence and Thioflavin-T. At the same time, structural differences of pH 2 and pH 3.5 aggregates could be presented more clearly.
CRIS-Team Scopus Importer:2019-09-17
Keywords: Amyloid aggregates; AUC; Beta-lactoglobulin; Building-blocks; Fibrils; Polydispersity; SAXS; Superposition effects; Whey-protein; Worm-like fibrils

Influence of thermal conditions on particle properties in fluidized bed layering granulation - Neugebauer, Christoph; Bück, Andreas; Palis, Stefan; Mielke, Lisa; Tsotsas, Evangelos; Kienle, Achim (Processes, 2018)
Fluidized bed layering granulation is frequently used to formulate particles of high quality. From previous studies, it is well known that the dynamic behavior of the process, as well as the product properties depend on operating parameters. The process is characterized by heat and mass transfer between fluidized particles and the surrounding fluidization medium. To investigate the mutual influence between particle phase and fluidization medium, a dynamic model is introduced. The model comprises two parts: a population balance model to describe the evolution of the particle sizes and a system of ordinary differential equations to account for thermal conditions. For the first time, the dynamic model considers the bidirectional coupling of particles and fluidization medium in fluidized bed layering granulation. By means of simulations, it is shown that the derived model is capable of reproducing the experimental finding
Keywords: Layering granulation; Population balance; Drying; Fluidized bed; Dynamics

Influence of Ti3+ defect-type on heterogeneous photocatalytic H2 evolution activity of TiO2 - Mohajernia, Shiva; Andryskova, Pavlina; Zoppellaro, Giorgio; Hejazi, Seyedsina; Kment, Stepan; Zboril, Radek; Schmidt, Jochen; Schmuki, Patrik (Journal of Materials Chemistry A, 2020)
Reduced titanium dioxide has recently attracted large attention, particularly for its unique co-catalyst-free heterogeneous photocatalytic application for H2 generation. The enhanced photocatalytic activity of the reduced TiO2 was previously ascribed to the introduction of point crystal defects (mainly Ti3+ centers), which result in the formation of intrinsic co-catalytic centers and enhanced visible light absorption. In this work, we systematically investigate the effect of different defects in the TiO2-x lattice on photocatalytic H2 evolution. To introduce different types of defects, thermal annealing in air (oxidative), Ar (inert), Ar/H2 (reducing), and H2 (reducing) atmospheres was performed on commercially available anatase nanopowder. Then, the powders were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM) to clarify the effect of treatment on material properties. Furthermore, the defect types were characterized by electron paramagnetic resonance (EPR) spectroscopy. We show that thermal annealing in different atmospheres can form different amounts of different defect types in the TiO2 structure. The highest photocatalytic activation is achieved by annealing the anatase powder in a reducing atmosphere for an appropriate temperature/annealing time. By combining the results from H2 generation and EPR analysis we show that the simultaneous presence of two types of defects, i.e. surface exposed Ti3+ and lattice embedded Ti3+ centers in an optimum low concentration is the determining factor for an optimized photocatalytic H2 evolution rate. In fact, annealing anatase powder under the so-reported optimized conditions in reducing atmosphere leads to the generation of a considerable amount of H2, with rates as high as 338 μmol h-1 g-1
CRIS-Team Scopus Importer:2020-02-07

Inhibitive effect of Clopidogrel as a green corrosion inhibitor for mild steel; statistical modeling and quantum Monte Carlo simulation studies - Naseri, Ehsan; Hajisafari, Mahmoud; Kosari, Ali; Talari, Mahla; Hosseinpour, Saman; Davoodi, Ali (Journal of Molecular Liquids, 2018)
In this work, response surface method (RSM) is employed to design electrochemical experiments for assessment of a green organic molecule, namely Clopidogrel from cardiovascular drugs class, as a corrosion inhibitor for mild steel in sulfuric acid solution. Mathematical models based on multiple regressions are generated to estimate the influence of the affecting factors like acid concentration, solution temperature and inhibitor concentration on the inhibitive performance of Clopidogrel. The corrosion rates are measured experimentally using potentiodynamic polarization technique. The calculated Langmuir adsorption energy reveals that Clopidogrel adsorbs both physically and chemically onto the mild steel surface and the adsorption type is almost independent of the environmental factors. The adsorption mechanism of Clopidogrel is computed through quantum chemical calculations, confirming that this compound can replace water molecules from the surface upon its adsorption to the metal substrate. The simulation results are approved experimentally using an inherently surface sensitive tool, sum frequency generation spectroscopy (SFG).
Keywords: Clopidogrel; Green corrosion inhibitor; Mild steel; Sulfuric acid; Surface response method; Monte Carlo simulation; Sum frequency generation (SFG) spectroscopy

Initial Oxidation of Alkanethiol-Covered Copper Studied by Vibrational Sum Frequency Spectroscopy - Hosseinpour, Saman; et al. (Journal of Physical Chemistry C, 2011)

Inorganic layers on polymeric films - influence of defects and morphology on barrier properties - Peukert, Wolfgang; Hanika, Markus; Langowski, Horst-Christian; Moosheimer, Ulrich (Chemical Engineering & Technology, 2003)
Flexible polymeric films are not only widely used in conventional packaging as substitute for glass and aluminum foil packaging but are also proposed as encapsulation for novel products, like flexible solar cells or organic light-emitting devices. The two essential properties of the polymeric packaging are flexibility and good permeation barrier properties against gases and vapors. This article deals with vacuum web coating as a common way of increasing barrier properties of polymeric films and the problems related to this procedure. Defects caused by particles and surface imperfections are found to dominate the permeation rate for such coated polymeric films. Atomic force microscopy, electron and also optical microscopy was used for analysis of the coating layer. Three-dimensional numerical simulations were performed for modeling of the influence of defect size, spacing and film thickness. Results of numerical modeling and of many practical experiments show that the permeability is almost independent of the substrate film thickness when a critical thickness is exceeded. In most cases the defects can be treated as independent of each other. The gas permeability of vacuum web-coated polymeric films can be quantitatively predicted by a simple formula. For gases, like oxygen, it is shown that a statistic analysis of the defect sizes by optical microscopy is sufficient. For water vapor transmission, however, the structure of the coating layer itself has also to be taken into account.
UnivIS-Import:2015-03-09:Pub.2003.tech.ITC.mechve.inorga
Keywords: layer; polymer; film; morphology

Insights into galvanic corrosion behavior of Ti-Cu dissimilar joint: Effect of microstructure and volta potential - Rahimi, Ehsan; Rafsanjani-Abbasi, Ali; Imani, Amin; Hosseinpour, Saman; Davoodi, Ali (Materials, 2018)
Keywords: SKPFM; Ti-Cu dissimilar welding; Electrochemical measurements; Microstructure; Galvanic corrosion

In situ cracking of silica beads in the SEM and TEM - Effect of particle size on structure-property correlations - Paul, Jonas; Romeis, Stefan; Mackovic, Mirza; Marthala, Venkata; Herre, Patrick; Przybilla, Thomas; Hartmann, Martin; Spiecker, Erdmann; Schmidt, Jochen; Peukert, Wolfgang (Powder Technology, 2015)
Stöber Fink Bohn (SFB) silica is a well-known colloidal system: monodisperse spherical particles are readily obtained by this wet chemical synthesis route. Despite the frequent application of SFB silica, its mechanical properties are not comprehensively understood. Within this account, size dependent mechanical properties of single SFB particles are systematically investigated using in situ SEM and TEM techniques: particle properties are addressed in the size range of 1.5 μm down to 200 nm. Both, untreated particles and heat treated particles densified at 1000 °C are investigated. Structural characterization by vibrational spectroscopy, by solid state nuclear magnetic resonance spectroscopy, by scanning electron microscopy and by focused ion beam machining allows correlating mechanical properties and the internal particle structure. For untreated particles comprised of a weakly cross-linked silica network a high degree of plasticity associated with low Young’s moduli and hardness values is found. At large strains only cracking without full fracture of the particles occurs, whereby the crack path is clearly linked to the synthesis conditions: for larger particles obtained from a multistep growth process cracks propagate along weak intraparticle interfaces and are deflected around an inner core structure. After the thermal treatment cross-linking of the silica network is significantly enhanced and Young’s moduli comparable to vitreous silica accompanied by increased hardness values are found. Only the smallest particles exhibit cracking; fracture into two or more pieces is distinguished for particles above 500 nm. It is found by SEM imaging that the relative occurrence of cracking into several pieces is increasing with size - a behaviour associated with the brittle to ductile transition of silica. By testing a large quantity of particles, statistical significance is ensured.

In situ deformation and breakage of silica particles inside a SEM - Romeis, Stefan; Paul, Jonas; Herre, Patrick; Hanisch, Mathias; Klupp Taylor, Robin; Schmidt, Jochen; Peukert, Wolfgang (7th World Congress on Particle Technology, WCPT 2014, 2015)
Mechanical properties and particle breakage behavior in the submicron size range are of fundamental importance for many particle related processes and applications. Although many (in situ) studies have been dedicated to materials' size dependent mechanical characterization, particles as free standing structures have been omitted widely. An important, yet open question is the structure property relationship at small scales. Within this account, the application of a custom built manipulator for particle compression inside a scanning electron microscope (SEM) is presented: Stöber-Fink-Bohn (SFB) particles with mean diameters of 500 nm and 1000 nm are subjected to heat treatments and their mechanical properties are directly correlated to the internal structure. The as-synthesized SFB particles exhibit a complex and size dependent internal structure. Mechanical properties undermatching the values of fused silica are found and only plastic cracking at large strains is observed: cracks are formed at the surface and propagate in radial direction towards the particle center. Heat treatment leads to densification. The degree of changes is controlled by temperature and treatment time. Starting from initially low values, Young's modulus and hardness are increasing with treatment temperature. Properties of fused silica are approached or even exceeded after a treatment at 1000°C. A significant level of plasticity and high sustained deformations are still found. Whereas small particle show ductile cracking, the heat treated micron sized particles show a brittle behavior. A brittle to ductile transition in the size range of 500 nm to 1000 nm is thus identified.
Keywords: heat treatment; in situ manipulation; mechanical properties; Stöber silica; Submicron particles

In situ investigations on the amorphous to crystalline phase transformation of precursors for methanol synthesis catalysts - Güldenpfennig, Andreas; Distaso, Monica; Peukert, Wolfgang (Chemical Engineering Journal, 2019)
Two in situ methods are presented to study phase transformations in the synthesis of Cu/Zn hydroxycarbonates as catalyst precursors for industrial methanol production. In contrast to the well-established application of in situ FTIR probes in the detection of liquid phase concentrations, we evaluated spectra arising from the structural changes in the solid phase during the transformation of amorphous georgeite to nanocrystalline zincian malachite. Further, a novel microreaction system is employed to gain statistical insight on the scattering of the reaction time as a function of various process parameters. The obtained transformation kinetics during aging are described by a model based on the theory of solvent-mediated phase transformations showing excellent agreement with experimental results. The quantitative impact of temperature, concentration and zinc content on dissolution, nucleation and growth of the respective phases is discussed.
CRIS-Team WoS Importer:2019-04-23

In Situ Monitoring of Particle Formation with Spectroscopic and Analytical Techniques Under Solvothermal Conditions - Embrechts, Heidemarie; Hartmann, Martin; Peukert, Wolfgang; Distaso, Monica (Chemical Engineering & Technology, 2020)
The formation of multifunctional materials involves various simultaneous and closely entangled physicochemical processes including nucleation, growth, aggregation, and in some cases also growth by oriented aggregation. These elementary particle formation processes occur in broad size ranges from the molecular to micrometer level and time scales ranging from seconds to hours. This contribution demonstrates that the in situ monitoring of reaction mixtures and dispersions with several simultaneous analytical and spectroscopic techniques is an effective and widely applicable strategy to achieve an in-depth understanding of the formation of complex particulate structures and to move towards the rational design of materials.
CRIS-Team Scopus Importer:2020-04-21
Keywords: Carbon nanodots; Mesocrystals; Metal-organic frameworks; Oriented attachment; Particle formation

In situ Raman and FTIR spectroscopic study on the formation of the isomers MIL-68(Al) and MIL-53(Al) - Embrechts, Heidemarie; Kriesten, Martin; Ermer, Matthias; Peukert, Wolfgang; Hartmann, Martin; Distaso, Monica (RSC Advances, 2020)
The topological metal-organic framework isomers MIL-53 and MIL-68 form from similar educts but differ in their pore geometries. They have been known for several years, but their synthesis is always reported separately. In consequence, the underlying mechanism and decisive synthesis parameters leading to the formation of either MIL-53 or MIL-68 are not understood. The present study shows how to induce the formation of MIL-68(Al) rather than MIL-53(Al) at low synthesis temperatures in N,N-dimethylformamide (DMF) using a modulated synthesis approach. MIL-68(Al) is identified as the intermediate product of formic acid modulated synthesis, which converts into the thermodynamically stable MIL-53(Al) product at longer synthesis times. The interactions of formic acid with the synthesis precursors responsible for inducing MIL-68(Al) formation are investigated with in situ Raman and FTIR spectroscopy. In contrast to the commonly assumed modulation mechanism of competitive coordination of linker and modulator with the metal node, formic acid is shown to form hydrogen bonds via the carboxylic group of the terephthalic acid (H2BDC) linker, slowing prenucleation building unit and subsequent crystal growth. MIL-68(Al) formation is favored by the combination of a deficiency of terephthalic acid in solution and a slow MOF growth rate. Dissolved H2BDC in solution is proposed to hinder MIL-68(Al) formation by serving as a molecular template for the rhombic MIL-53(Al) pore channels.
CRIS-Team Scopus Importer:2020-03-17

In situ spectroscopy of ligand exchange reactions at the surface of colloidal gold and silver nanoparticles. - Peukert, Wolfgang; Dinkel, Rebecca; Braunschweig, Björn (Journal of Physics: Condensed Matter, 2017)
Gold and silver nanoparticles with their tunable optical and electronic properties are of great interest for a wide range of applications. Often the ligands at the surface of the nanoparticles have to be exchanged in a second step after particle formation in order to obtain a desired surface functionalization. For many techniques, this process is not accessible in situ. In this review, we present second-harmonic scattering (SHS) as an inherently surface sensitive and label-free optical technique to probe the ligand exchange at the surface of colloidal gold and silver nanoparticles in situ and in real time. First, a brief introduction to SHS and basic features of the SHS of nanoparticles are given. After that, we demonstrate how the SHS intensity decrease can be correlated to the thiol coverage which allows for the determination of the Gibbs free energy of adsorption and the surface coverage.
Keywords: nanoparticle; property; second; harmonic; scattering

In situ spectroscopy of the ligand exchange at the surface of colloidal Au nanoparticles - Dinkel, Rebecca; Braunschweig, Björn; Peukert, Wolfgang (ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 2016)

In Situ Study on the Evolution of Multimodal Particle Size Distributions of ZnO Quantum Dots: Some General Rules for the Occurrence of Multimodalities - Schindler, Torben; Walter, Johannes; Peukert, Wolfgang; Segets, Doris; Unruh, Tobias (Journal of Physical Chemistry B, 2015)
Properties of small semiconductor nanoparticles (NPs) are strongly governed by their size. Precise characterization is a key requirement for tailored dispersities and thus for high-quality devices. Results of a careful analysis of particle size distributions (PSDs) of ZnO are presented combining advantages of UV/vis absorption spectroscopy, analytical ultracentrifugation, and small-angle X-ray scattering (SAXS). Our study reveals that careful cross-validation of these different methods is mandatory to end up with reliable resolution. PSDs of ZnO NPs are multimodal on a size range of 2-8 nm, a finding that is not yet sufficiently addressed. In the second part of our work the evolution of PSDs was studied using in situ SAXS. General principles for the appearance of multimodalities covering a temperature range between 15 and 45 °C were found which are solely determined by the aging state indicated by the size of the medium-sized fraction. Whenever this fraction exceeds a critical diameter, a new multimodality is identified, independent of the particular time-temperature combination. A fraction of larger particles aggregates first before a fraction of smaller particles is detected. Fixed multimodalities have not yet been addressed adequately and could only be evidenced due to careful size analysis.

In-Situ surface characterization of nano- and microparticles by optical Second Harmonic Generation - Schürer, Benedikt; Wunderlich, Sarina; Peschel, Ulf; Peukert, Wolfgang (Nanotechnology 2010: Advanced Materials, CNTs, Particles, Films and Composites, 2010)
Nonlinear optical spectroscopic techniques, namely Second Harmonic Generation (SHG) spectroscopy and Sum Frequency Generation (SFG), are highly interface sensitive and can be used to obtain information exclusively from the surface of particles. Second Harmonic Generation (SHG) has proven to be a versatile technique that can be used to probe different kinds of surface properties of dispersed particle systems in in-situ. Prominent examples are the direct study of molecular adsorption at the surface of particles and the determination of surface potentials of nano- and microparticles. However, in most of these studies well-defined spherical and monodisperse particles with low number densities were used. Here we demonstrate the application of the SHG technique for the study of more complex and technically relevant particle systems. We discuss the influence of particle concentration and particle size distribution. Moreover, we apply a novel nonlinear Mie Model that is capable to simulate the SH scattering from the surface of spherical particles and we show that the model can be used to extract information about molecules at the particle liquid interfac
Keywords: Nonlinear Mie model; Nanoparticles; Second Harmonic Generation; Optics; Surface characterization

In Situ Surface Characterization of Polydisperse Colloidal Particles by Second Harmonic Generation - Schürer, Benedikt; Peukert, Wolfgang (Particulate Science and Technology, 2010)
Optical second harmonic generation (SHG) has a high potential for studying surface properties of colloidal particles in situ with a high temporal resolution. In the past the SHG technique has been applied successfully to determine the surface potential of colloidal particles and emulsion droplets and to study adsorption processes at the interface of solid and liquid particles. However, in previous studies mainly monodisperse particles were used. Here we demonstrate that it is also possible to study adsorption processes on polydisperse particle systems with SHG by comparing in situ adsorption measurements on monodisperse and on polydisperse mixtures of polystyrene (PS) particles. In addition, the results suggest that SHG is also applicable for surface characterization of polydisperse samples at high particle concentrations, where absorption and scattering of the particles is dominant.

In-situ X-ray diffraction analysis of the recrystallization process in Cu2ZnSnS4nanoparticles synthesised by hot-injection - Brandl, Marco; Ahmad, Rameez; Distaso, Monica; Azimi, Seyed Hamed; Hou, Yi; Peukert, Wolfgang; Brabec, Christoph; Hock, Rainer (Thin Solid Films, 2015)
Kesterite CuZnSnS(CZTS) is a promising material for thin film solar cell applications. The biggest advantages of this compound lie in the abundance and non-toxicity of the contained elements. Low temperature hot injection synthesis can provide an economic way to produce CZTS nanoparticles for application in solution processed solar cells. Powder X-ray diffraction (PXRD) measurements on the as-synthesised particles suggest that the crystal structure is cubic and can be best described as sphalerite-like. This means that the cations in the CZTS are statistically distributed on the cation sites of the crystal lattice rather than well-ordered like in the tetragonal kesterite structure. An in-situ PXRD measurement while annealing the particles up to 550 °C revealed a recrystallization process that transforms the structure from cubic to tetragonal meaning an ordering of the cations.
Keywords: Copper zinc tin sulphide; Cubic phase; Hot-injection synthesis; In-situ; Phase transition; Tetragonal phase; X-ray diffraction

In-Situ X-ray Diffraction Analysis of the Recrystallization Process in Cu2ZnSnS4 Nano Particles Synthesized by Hot-Injection - Brandl, Marco; Ahmad, Rameez; Distaso, Monica; Azimi, Hamed; Hou, Yi; Peukert, Wolfgang; Brabec, Christoph; Hock, Rainer (Thin Solid Films, 2015)
Kesterite Cu2ZnSnS4 (CZTS) is a promisingmaterial for thin film solar cell applications. The biggest advantages of this compound lie in the abundance and non-toxicity of the contained elements. Low temperature hot injection synthesis can provide an economic way to produce CZTS nanoparticles for application in solution processed solar cells. Powder X-ray diffraction (PXRD) measurements on the as-synthesised particles suggest that the crystal structure is cubic and can be best described as sphalerite-like. This means that the cations in the CZTS are statistically distributed on the cation sites of the crystal lattice rather than well-ordered like in the tetragonal kesterite structure. An in-situ PXRD measurement while annealing the particles up to 550 °C revealed a recrystallization process that transforms the structure from cubic to tetragonal meaning an ordering of the cations.
EAM Import::2019-03-13

Integrated processes for nanoscale products with new application properties Integrierte Prozesse für nanoskalige Produkte mit neuen Anwendungseigenschaften - Peukert, Wolfgang; et al. (Chemie Ingenieur Technik, 2005)

Integration of quartz crystal microbalance with vibrational sum frequency spectroscopy-quantification of the initial oxidation of alkanethiol-covered copper - Hosseinpour, Saman; et al. (Journal of Physical Chemistry C, 2012)

Interaction of light with hematite hierarchical structures: Experiments and simulations - Distaso, Monica; Zhuromskyy, Oleksandr; Seemann, Benjamin; Pflug, Lukas; Mackovic, Mirza; Encina, Ezequiel Roberto; Klupp Taylor, Robin; Müller, Rolf; Leugering, Günter; Spiecker, Erdmann; Peschel, Ulf; Peukert, Wolfgang (Journal of Quantitative Spectroscopy & Radiative Transfer, 2017)
Mesocrystalline particles have been recognized as a class of multifunctional materials with potential applications in different fields. However, the internal organization of nanocomposite mesocrystals and its influence on the final properties have not yet been investigated. In this paper, a novel strategy based on electrodynamic simulations is developed to shed light on how the internal structure of mesocrystals influences their optical properties. In a first instance, a unified design protocol is reported for the fabrication of hematite/PVP particles with different morphologies such as pseudo-cubes, rods-like and apple-like structures and controlled particle size distributions. The optical properties of hematite/PVP mesocrystals are effectively simulated by taking their aggregate and nanocomposite structure into consideration. The superposition T-Matrix approach accounts for the aggregate nature of mesocrystalline particles and validate the effective medium approximation used in the framework of the Mie theory and electromagnetic simulation such as Finite Element Method. The approach described in our paper provides the framework to understand and predict the optical properties of mesocrystals and more general, of hierarchical nanostructured particles.
Keywords: Effective medium approximation; FEM; Maxwell-Garnett theory; Mesocrystals; Scattering; T-Matrix

Interface-induced hysteretic volume phase transition of microgels: simulation and experiment - Kolker, Jannis; Harrer, Johannes; Ciarella, Simone; Rey, Marcel; Ickler, Maret; Janssen, Liesbeth M.C.; Vogel, Nicolas; Löwen, Hartmut (Soft Matter, 2021)
Thermo-responsive microgel particles can exhibit a drastic volume shrinkage upon increasing the solvent temperature. Recently we found that the spreading of poly(N-isopropylacrylamide) (PNiPAm) microgels at a liquid interface under the influence of surface tension hinders the temperature-induced volume phase transition. In addition, we observed a hysteresis behavior upon temperature cycling, i.e. a different evolution in microgel size and shape depending on whether the microgel was initially adsorbed to the interface in expanded or collapsed state. Here, we model the volume phase transition of such microgels at an air/water interface by monomer-resolved Brownian dynamics simulations and compare the observed behavior with experiments. We reproduce the experimentally observed hysteresis in the microgel dimensions upon temperature variation. Our simulations did not observe any hysteresis for microgels dispersed in the bulk liquid, suggesting that it results from the distinct interfacial morphology of the microgel adsorbed at the liquid interface. An initially collapsed microgel brought to the interface and subjected to subsequent swelling and collapsing (resp. cooling and heating) will end up in a larger size than it had in the original collapsed state. Further temperature cycling, however, only shows a much reduced hysteresis, in agreement with our experimental observations. We attribute the hysteretic behavior to a kinetically trapped initial collapsed configuration, which relaxes upon expanding in the swollen state. We find a similar behavior for linear PNiPAm chains adsorbed to an interface. Our combined experimental - simulation investigation provides new insights into the volume phase transition of PNiPAm materials adsorbed to liquid interfaces.
CRIS-Team WoS Importer:2021-05-28
Keywords: Responsive microgels; Soft particles; Temperature; Poly(n-isopropylacrylamide); Suspensions; Behavior; Water; Deformation; Adsorption; Dendrimers

Interfacial Activity of Metal beta-Diketonato Complexes: In Situ Generation of Amphiphiles by Water Coordination - Vogel, Nicolas; et al. (Langmuir, 2011)
Symmetric transition metal complexes of 2,4-pentanedione (acetyl acetone) are interfacially active: Spinning drop tensiometry reveals lowering of the interfacial tension at the water-organic interface, most pronounced for [Cr(acac)(3)], [Fe(acac)(3)], [Zr(acac)(4)], and [Hf(acac)(4)]. The interfacial activity is explained by the in situ generation of amphiphilic species. Based on tensiometry and (1)H and diffusion-ordered NMR spectroscopy (DOSY NMR), hydrogen bonding of the organically dissolved complexes with water, in some cases in combination with inner-sphere hydrolytic coordination, is identified as the primary origin of this amphiphilicity. The complexes are a rare example of symmetric molecules that turn amphiphilic only upon interfacial interaction with water.

Interfacial arrangement and phase transitions of PNiPAm microgels with different crosslinking densities - Rey, Marcel; Hou, Xunan; Tang, Jo Sing; Vogel, Nicolas (Soft Matter, 2017)
Microgels are colloidal hydrogel particles that exhibit a pronounced softness, which arises from the swollen nature of the constituent polymer network. This softness leads to a substantial deformability of such particles at liquid interfaces, which, in turn translates into a complex phase behaviour that can exhibit a phase transition between a non-close packed and a close packed arrangement. Here, we explore how the degree of swellability and deformability - and therefore the softness of the particles - affects the phase behaviour of microgels at the air/water interface upon compression. We use precipitation polymerization to synthesize poly(N-isopropylacrylamide) microgels with similar hydrodynamic radii in the collapsed state and systematically vary the degree of swellability by changing the crosslinking density. We spread these microgels onto the air/water interface of a Langmuir trough and characterize their interfacial properties by surface pressure - area isotherms. Furthermore, we continuously transfer the interfacial microgel monolayer during compression onto a solid substrate, thus encoding the complete phase diagram of the microgels with increasing particle density as a function of the position on the solid substrate. We investigate the microgel arrangement by atomic force microscopy and scanning electron microscopy and use image analysis to extract quantitative information on the interparticle distance and degree of order. We find that the phase transition is very sensitive to the crosslinking density and occurs at much lower surface pressures for less deformable particles. The softest microgels do not undergo any phase transition. Instead, the system exhibits pronounced local conformation changes around point defects with local five- and sevenfold symmetries, indicating that the geometry of the assembled structure effectively controls the local pressure experienced by the microgels.

Interfacial energy estimation in a precipitation reaction using the flatness based control of the moment trajectories - Vassilev, Vassil; Gröschel, Michael; Schmid, Hans-Joachim; Peukert, Wolfgang; Leugering, Günter (Chemical Engineering Science, 2010)
In this paper, we consider a model for precipitation experiments based on the population balance equation. The study revealed a high sensitivity of the system with respect to the modeling of intrinsic parameters, motivating a comprehensive validation of the estimates. In the forward simulation the impact of the influencing parameters including surface energy, nucleus size and distribution is investigated. Subsequently we construct a simplified model of the precipitation process in such a way that it is orbitally flat in terms of control theory, which enables the inverse calculation of the parameters. The numerical results of the inverse simulation for the interfacial energy have been compared to a physical model. The possibility of solving the inverse problem provides a promising way of estimating hardly measurable quantities for more complex molecules.

Interfacial self-assembly of SiO2-PNIPAM core-shell particles with varied crosslinking density - Ickler, Maret; Menath, Johannes; Holstein, Laura; Rey, Marcel; Buzza, D. Martin A.; Vogel, Nicolas (Soft Matter, 2022)
Spherical particles confined to liquid interfaces generally self-assemble into hexagonal patterns. It was theoretically predicted by Jagla two decades ago that such particles interacting via a soft repulsive potential are able to form complex, anisotropic assembly phases. Depending on the shape and range of the potential, the predicted minimum energy configurations include chains, rhomboid and square phases. We recently demonstrated that deformable core-shell particles consisting of a hard silica core and a soft poly(N-isopropylacrylamide) shell adsorbed at an air/water interface can form chain phases if the crosslinker is primarily incorporated around the silica core. Here, we systematically investigate the interfacial self-assembly behavior of such SiO2-PNIPAM core-shell particles as a function of crosslinker content and core size. We observe chain networks predominantly at low crosslinking densities and smaller core sizes, whereas higher crosslinking densities lead to the formation of rhomboid packing. We correlate these results with the interfacial morphologies of the different particle systems, where the ability to expand at the interface and form a thin corona at the periphery depends on the degree of crosslinking close to the core. We perform minimum energy calculations based on Jagla-type pair potentials with different shapes of the soft repulsive shoulder. We compare the theoretical phase diagram with experimental findings to infer to which extent the interfacial interactions of the experimental system may be captured by Jagla pair-wise interaction potentials.
CRIS-Team WoS Importer:2022-07-29

Interplay between size, morphology, microstructure defects and optoelectronic properties of CdSe nanocrystals - Neumann, S.; Rudolph, M.; Menter, Christina; Mahmoud, Ahmed Salaheldin Abdelhamid; Segets, D.; Rafaja, D. (ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 2021)
CRIS-Team WoS Importer:2022-04-01

Interplay of Internal Structure and Interfaces on the Emitting Properties of Hybrid ZnO Hierarchical Particles - Distaso, Monica; Bertoni, Giovanni; Todisco, Stefano; Marras, Sergio; Gallo, Vito; Manna, Liberato; Peukert, Wolfgang (ACS Applied Materials and Interfaces, 2017)
The design of hybrid organic/inorganic nanostructures with controlled assembly drives the development of materials with new or improved properties and superior performances. In this paper, the surface and internal structure of hybrid ZnO poly-N-vinylpyrrolidone (ZnO/PVP) mesocrystals are investigated in detail and correlated with their emitting properties. A photoluminescence study at room temperature reveals that the as-synthesized particles show a remarkable ultraviolet (UV) emission, whereas an emission from defects in the visible region is not observed. On the other hand, a visible emission is achieved upon calcination of the hybrid ZnO/PVP particles in air, and its intensity is found to increase with the calcination temperature and, in some cases, to overwhelm the UV emission. A molecular description is proposed for the absence of a visible emission from defects in the as-synthesized ZnO/PVP mesocrystals on the basis of Fourier transform infrared (FTIR) and solid-state (13)C NMR (SSNMR) spectroscopy. An in-depth electron microscopy study sheds light on the internal organization of mesocrystals and reveals the formation of nanoreactors, that is, particles with enclosed porosity, upon thermal treatment.
Keywords: structure-function relationship; nanoreactors; postprocessing; coordination; nanocomposites; mesocrystals

Interplay of Mie and Bragg resonances in partly ordered monolayers of colloidal spheres - Vogel, Nicolas; et al. (Photonic Crystal Materials and Devices X, 2012)
Keywords: 2-dimensional slab photonic crystal; Diffraction; Hopping; Lattice disorder; Mie resonance; Optical spectra

Intracellular Drug Delivery with Anodic Titanium Dioxide Nanotubes and Nanocylinders - Hasanzadeh Kafshgari, Morteza; Mazare, Anca Valentina; Distaso, Monica; Goldmann, Wolfgang; Peukert, Wolfgang; Fabry, Ben; Schmuki, Patrik (ACS Applied Materials and Interfaces, 2019)
Titanium dioxide (TiO 2 ) holds remarkable promises for developing current theranostic strategies. Anodic TiO 2 nanostructures as a porous scaffold have offered a broad range of useful theranostic properties; however, previous attempts to generate single and uniform TiO 2 one-dimensional nanocarriers from anodic nanotube arrays have resulted in a broad cluster size distribution of arbitrarily broken tubes that are unsuitable for therapeutic delivery systems due to poor biodistribution and the risk of introducing tissue inflammation. Here, we achieve well-separated, uniformly shaped anodic TiO 2 nanotubes and nanocylinders through a time-varying electrochemical anodization protocol that leads to the generation of planar sheets of weakly connected nanotubes with a defined fracture point near the base. Subsequent sonication cleanly detaches the nanotubes from the base. Depending on the position of the fracture point, we can fabricate single-anodic nanocylinders that are open on both ends and nanotubes that are closed on one end. We proceed to show that anodic nanotubes and nanocylinders are nontoxic at therapeutic concentrations. When conjugated with the anticancer drug doxorubicin using a pH-responsive linker, they are readily internalized by cells and subsequently release their drug cargo into acidic intracellular compartments. Our results demonstrate that uniformly sized anodic TiO 2 nanotubes and nanocylinders are suitable for subcellular delivery of therapeutic agents in cancer therapy.
CRIS-Team Scopus Importer:2019-05-09
Keywords: electrochemical anodization; intracellular drug delivery; nanocylinders; nanotubes; titanium dioxide

Intrinsically stable dispersions of silicon nanoparticles. - Reindl, Armin; Peukert, Wolfgang (Journal of Colloid and Interface Science, 2008)
Stable suspensions of silicon nanoparticles (SiNP) were fabricated by dispersion in 1-butanol as well as ethanol without the application of an additive. In order to achieve an in-depth insight into the stabilizing mechanism, the particle-particle interactions need to be considered. In this respect the total interaction energy of the silicon nanoparticles in 1-butanol and ethanol was calculated for three model systems according to the DLVO theory: (1) two solid silicon spheres, (2) two spheres with a silicon core and an amorphous silicon dioxide shell, and (3) two spheres with a silicon core, an amorphous silicon dioxide shell and a monolayer of adsorbed solvent molecules. The results of the calculations are evaluated and discussed with regard to experimental data obtained by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), high resolution transmission electron microscopy (HRTEM), and zeta potential measurements.

Intrinsic and Extrinsic Incorporation of Indium and Single-Walled Carbon Nanotubes for Improved ZnO-Based DSSCs - Schol, Peter; Zhang, Wen Shan; Scharl, Tobias; Kunzmann, Andreas; Peukert, Wolfgang; Schröder, Rasmus R.; Guldi, Dirk Michael (Advanced Energy Materials, 2022)
A common goal in renewable energy research is the production of semiconductor layers with matching additives to gain desirable effects and advantages. Important examples are adjustment of the band gap, enhancing the conductivity, tailoring roughness of the semiconductor, or reducing the recombination rate of charge carriers. In this work a twofold approach is demonstrated. First, the intrinsic incorporation of indium into zinc oxide tunes the band gap of the semiconductor layer of the DSSCs. Second, single-walled carbon nanotubes (SWCNT) as an extrinsic additive improves the charge transport capabilities. To better combine the SWCNTs with the semiconductor layer a protective ZnO shell is grown on the SWCNTs. A combination of current–voltage, incident photon to current efficiency, and electrochemical impedance spectroscopic assays corroborates the positive effects of both additives on the cell performance. The effective charge-carrier diffusion lengths are enhanced from 0.52 µm for pure ZnO to 5.12 µm for low SWCNT concentrations and 15 mol% of indium. This, as well as the increase in collection efficiency from 30.3% to 62.3% enables enhanced transport in these novel devices. A final device utilizing 0.1 wt% SWCNT@ZnO20nm and In15Zn85O yields a current density of 16.49 mA cm−2 and an efficiency of 4.46%.
CRIS-Team Scopus Importer:2022-03-11
Keywords: indium–zinc oxide photoanodes; n-type DSSCs; semiconductor doping; single-wall carbon nanotubes

Invertible architectures from amphiphilic polyesters. - Peukert, Wolfgang; Voronov, Andriy; Kohut, Ananiy; Gevus, O.; Tokarev, Victor; Voronov, Stanislav (Langmuir, 2006)
We synthesized and characterized novel amphiphilic polyesters with both hydrophilic and hydrophobic functionalities. The polyesters are soluble in organic and aqueous media and reveal the formation of inverse architectures whose behavior could be correlated to their chemical structure. We foresee that the amphiphilic properties of the polyesters reported here are obviously the basis of new architectures both in solution and on the solid surfaces, which could be used in a broad range of applications. The described synthesis of the copolymers is very simple and is based on commercially available products. That makes this approach attractive in various uses.
Keywords: synthesis; characterization; polymer; functionality

Invertible polymers for the stabilization of nanoparticles - Peukert, Wolfgang; Kohut, Ananiy; Voronov, Andriy (NSTI-Nanotech 200, 2007)
Novel amphiphilic polyesters with both hydrophilic and hydrophobic functionalities being alternately distributed along polymer backbones have been synthesized and characterized. The polyesters are soluble in organic and aqueous media and reveal the formation of inverse architectures whose behavior could be correlated to their chemical structure. This work offers a new approach to building up self-adjustable invertible polymer coatings at solid surfaces. The approach is based on a two-step process. In the first step, the surface of dispersed titania or silicon wafers has been functionalized with the aid of a reactive copolymer, viz., poly(styrene-alt-maleic anhydride) (PSM), to which, in the second step, the chains of amphiphilic polyester have been tethered. The modified titania can form stable suspensions in both polar and nonpolar media. An environmentally induced switching of the surface properties has been observed via the AFM of silicon wafers with tethered polyester chains.
Keywords: Colloidal stability; Invertible polymers; Synthesis

Investigating the Surface of Nanoparticles by Second Harmonic Generation - Wunderlich, Sarina; Peschel, Ulf; Schürer, Benedikt; Peukert, Wolfgang (Conference on Lasers and Electro-Optics (CLEO)/Quantum Electronics and Laser Science Conference (QELS), 2010)
We investigate Second Harmonic Generation at the surface of nanoparticles both by modeling and experiment. We present an ab initio simulation method, which allows deducing surface properties as well as the nature of adsorbed molecules. (C) 2010 Optical Society of America

Investigation and mitigation of reagent ageing during the continuous flow synthesis of patchy particles - Völkl, Andreas; Klupp Taylor, Robin (Chemical Engineering Research & Design, 2022)
Patchy particles, which comprise a core particle of one material partially covered by a thin layer of another, offer great promise for tailored particle-based materials and devices in the future. This study concerns the investigation and improvement of a potentially gram-scalable continuous flow process based on a cascade of two T-mixers for the synthesis of thin, conformal silver patches on colloidal silica particles. The starting point of the work is the observation that on seemingly random occasions the process results in patches having undesired spiky protrusions. Through a systematic study of reagent ageing supported by scanning electron microscopy, optical spectroscopy and chemical equilibrium calculations it can be ascertained that the desired product morphology is only obtained through carbon dioxide absorption by the dilute ammonia solution used in the reaction. It is shown that the ageing process can be emulated for fresh reagents by addition of ammonium nitrate or nitric acid. <br
Keywords: Continuous flow synthesis; Static T-mixer; Heterogeneous nucleation and growth; Absorption of carbon dioxide by aqueous ammonia; Localized surface plasmon resonance; Chemical equilibrium

Investigation of a flame spray pyrolysis process using several optical measurement techniques - Münsterjohann, Bettina; Huber, Franz; Stanzel, Melanie; Peukert, Wolfgang; Will, Stefan (International Congress Engineering of Advanced Materials, 2017)
The flame spray pyrolysis (FSP) process is one of the mostly used gas-phase techniques in industry and research to produce a broad spectrum of complex and functional nanoparticles on acommercial scale. Nanoparticulate oxides, including zinc oxide (ZnO), gallium(III)-oxide (Ga2O3) or indium(III)-oxide (In2O3) are low cost and promising materials for electronic and optical devices. To cover the high demand of these interesting materials, FSP turned out to be an economic, energy- and cost-efficient syntheses method. In the flame droplet formation, evaporation, combustion, nanoparticle formation and finally particle growth, agglomeration and sintering takes place. For the production of nanoparticles with well-defined properties, a detailed understanding of the interplay between these different particle formation steps and the influence of varying process conditions on the resulting nanoparticles is essential. However, due to the highly turbulent and multiphase character of the spray flame it is still limited.As the droplet formation and evaporation is one of the first crucial steps in the FSP process, it was characterized by Mie-scattering, Phase-Doppler Anemometry (PDA) and shadowgraphymeasurements under different process conditions. PDA allows for pointwise droplet velocity and droplet size measurements whereas the spray geometry with its spray angle and height was analyzed by shadowgraphy measurements and Mie-scattering. The ethanol spray was investigatedat both conditions with and without a flame so that the influence of evaporation and combustion on the droplet formation can be analyzed. In order to localize the nucleation zone where particle formation takes place, chemiluminescence measurements were performed for different material systems like pure metal oxides (ZnO, TiO2, SnO, Ga2O3, In2O3) and mixed oxides (ITO, indium zinc oxide, gallium zinc oxide). Furthermore the influence of varying precursor flow rates (2.5 l/min to 10 l/min) and precursor concentrations (0.1 mol/l to 0.5 mol/l) on the size and location of the nucleation zone was investigated. As temperature is one of the most important factors influencing particle size, morphology and crystallinity initial tests for measurements of temperature fields by Two-Line Atomic Fluorescence (TLAF) were performed. Finally, the sizes of the aggregates formed were determined by wide-angle light scattering (WALS
Keywords: PDA; shadowgraphy; Mie-scattering; chemiluminescence; TLAF; WALS

Investigation of interfacial processes leading to anisotropic silver nanostructures on 2D monolayers of silica spheres - Klupp Taylor, Robin; Hanisch, Mathias; Spies, Ines (Investigation of Interfacial Processes Leading to Anisotropic Silver Nanostructures On 2D Monolayers of Silica Spheres, 2013)
One-dimensional nanostructures comprising noble metals are promising materials for a range of electronic, photonic, biomedical and catalysis applications. In particular, their anisotropic morphology opens up possibilities for charge or photonic transport as well as providing a means for the self- or directed-orientation of the building blocks during  fabrication of a functional structure e.g. using electrical fields or fluid forces. In order to enable widespread exploitation of one-dimensional nanostructures, there needs to be more effort to develop and understand simple and scalable routes to achieve them. In this contribution we describe how one-dimensional silver nanoparticle assemblies can be formed at a solid-air interface in the absence of explicitly added reducing and templating agents. We show that in this extremely simple but highly sensitive process, dynamic and strongly anisotropic effects occur during aging of a 2D monolayer of silica nanospheres that had been treated with the ammoniacal silver complex (Ag(NH3)2+). Electron microscopy reveals that 5 – 10 nm silver nanoparticles are arranged in necklace-like assemblies on the silica spheres and up to a certain distance from them on the substrate. We investigate the formation of the nanoparticle necklaces by varying simple parameters of the liquid phase and aging treatments. We also describe attempts to scale-up the process from a few mm2 to cm2, particularly focussing on the formation of the nanostructures on 2D silica nanoparticle monolayers deposited by dip-coating on silicon wafers. We show that together with the simple chemical treatments, dynamic effects at the silica particle monolayer-air interface can lead to a number of interesting morphologies being produced, included the nanoparticle necklaces seen in the smaller scale work. These findings, as well as studies of the interfacial properties of silica help us to narrow down our  mechanistic understanding of the nanostructure formation by the synergistic chemical behavior of the used materials, namely Ag(NH3)2+ and amorphous silica particles. In particular, the presence of dissolved silicates, a result of the high pH of the ammoniacal silver complex appear to be critical. Besides potential uses in transparent electrical conductive coatings, substrates for surface-enhanced Raman spectroscopy (SERS) or for electromagnetic shielding the 1D nanostructures produced by our process  could be particularly interesting for possible novel optical properties of the structures. In the latter case we believe that mesh-coated silica particles formed by their further metallization may display resonances in their magnetization at optical frequencies and thus meets requirements for the formation of, for example, negative index metamaterials.
Keywords: nanostructure; metal; monolayer; surface; particle; noble; assembly

Investigation of spray agglomeration process in continuously operated horizontal fluidized bed - Du, J.; Bück, Andreas; Tsotsas, E. (IDS'2018: 21ST INTERNATIONAL DRYING SYMPOSIUM, 2018)
CRIS-Team WoS Importer:2019-08-16

Investigation of the comminution process in pendular roller mills - Wirth, Karl-Ernst; Wheeldon, Markus; Galk, Joachim (International Journal of Mineral Processing, 2015)
In the dry grinding industry the demand for very fine particle size distributions is increasing rapidly. At the same time a growing awareness for an economical management of our planet's resources has raised the demand for energy efficient processes. Roller mills in general and specifically pendular roller mills are best suited to meet these conflictive demands, since they can, up to this day, produce particle size distributions with a D < 10 μm while evidencing comparatively low power consumption values and high solids throughputs. The design of the pendular roller mill is thus far based on the experience gathered from industrially utilized mills. Due to the aforementioned development of roller mill applications this experience will no longer be sufficient for guaranteeing a successful scale-up process. In order to find valid scale-up rules for fine grinding pendular mills the operating behavior of such mills must first be fully understood. The grinding process in roller mills can be subdivided into the following steps: comminution between the rollers and the grinding ring, classification and solids transport between milling zone and classifier. In order to verify and improve the existing scale-up methods all process steps must be completely characterized. In order to characterize the comminution process a new measuring method was developed with which the milling gap between the rollers and the grinding ring and the rotation speed of the rollers can be determined simultaneously. This method was used on a pilot scale pendular roller mill during course and fine grinding processes to investigate the influence of process settings on the comminution conditions. As a result of measuring the milling gap, it is now possible for the first time to measure the relationships between parameters such as energy input, solids throughput, solids hold-up or pressure loss on the one hand and the milling gap on the other hand. These relationships can be used to establish a physical model of the comminution process, from which a scale-up rule for the comminution process can be derived. This publication will show and assess the relation between process parameters and the milling gap for course and fine grinding processes respectively.
Keywords: Classifier mills; Comminution; Dry grinding; Pendular roller mills

Investigation of the Relationship between the 2D and 3D Box-Counting Fractal Properties and Power Law Fractal Properties of Aggregates - Wang, Rui; Singh, Abhinandan Kumar; Kolan, Subash Reddy; Tsotsas, Evangelos (Multimodal Technologies and Interaction, 2022)
The fractal dimension has been widely used to describe the structural and morphological characteristics of aggregates. Box-counting (BC) and power law (PL) are the most common methods to calculate the fractal dimension of aggregates. However, the prefactor , as another important fractal property, has received less attention. Furthermore, there is no relevant research about the BC prefactor ( ). This work applied a tunable aggregation model to generate a series of three-dimensional aggregates with different input parameters (power law fractal properties: and , and the number of primary particles ). Then, a projection method is applied to obtain the 2D information of the generated aggregates. The fractal properties ( and ) of the generated aggregates are estimated by both, for 2D and 3D BC methods. Next, the relationships between the box-counting fractal properties and power law fractal properties are investigated. Notably, 2D information is easier achieved than 3D data in real processes, especially for aggregates made of nanoparticles. Therefore, correlations between 3D BC and 3D PL fractal properties with 2D BC properties are of potentially high importance and established in the present work. Finally, a comparison of these correlations with a previous one (not considering ) is performed, and comparison results show that the new correlations are more accurate<br

Investigation of the size-property relationship in CuInS2 quantum dots - Akdas, Tugce; Walter, Johannes; Segets, Doris; Distaso, Monica; Winter, Benjamin; Birajdar, Balaji; Spiecker, Erdmann; Peukert, Wolfgang (Nanoscale, 2015)
In this work we investigated fundamental properties of CuInS2 quantum dots in dependence of the particle size distribution (PSD). Size-selective precipitation (SSP) with acetone as poor solvent was performed as an adequate post-processing step. Our results provide deep insight into the correlation between particle size and various optical characteristics as bandgap energy, absorption and emission features and the broadness of the emission signal. These structure-property relationships are only achieved due to the unique combination of different analytical techniques. Our study reveals that the removal of 10 wt% of smallest particles from the feed results in an enhancement of the emission signal. This improvement is ascribed to a decreased quenching of the emission in larger particles. Our results reveal the impact of PSDs on the properties and the performance of an ensemble of multicomponent QDs and anticipate the high potential of controlling PSDs by well-developed post-processing.

Investigation of toner adhesion in the electrophotographic process - Zhou, Hongben (Friedrich-Alexander-Universität Erlangen-Nürnberg, 2008)
Adhesion between particles and surfaces is an essential phenomenon for many industrial applications. For example, the key to optimize the electrophotographic process is to understand the adhesion forces between charged toner particles and the photoconductive drum surface. The relevant adhesion forces in this process are the van der Waals, the capillary and the electrostatic forces. In the frame of this work these forces and their dependence on various parameters are investigated by means of AFM, centrifugal detachment and electric field detachment methods. The results are compared with each other and further with model calculations and numerical simulations. The van der Waals force is identified as the dominating adhesion force in the observed systems. This force is mainly depending on the Hamaker constants and the structure of the contact region. In case of deformable adhesion partners their mechanical properties and the applied load have strong impacts on the van der Waals force as well. The capillary force amounts to the same order of magnitude as the van der Waals force, if the surfaces of the adhesion partners are smooth, while it is negligible between rough adhesion partners. The electrostatic force is usually significantly smaller than the van der Waals force. However, it can result in the relocation of particles and may thus lead to a significant increase of the van der Waals forc

In vitro reactivity of Cu doped 45S5 Bioglass® derived scaffolds for bone tissue engineering - Hoppe, Alexander; Meszaros, Robert; Staehli, Christoph; Romeis, Stefan; Schmidt, Jochen; Peukert, Wolfgang; Marelli, Benedetto; Nazhat, Showan N.; Wondraczek, Lothar; Lao, Jonathan; Jallot, Edouard; Boccaccini, Aldo R. (Journal of Materials Chemistry B, 2013)
Cu-doped 45S5 bioactive glasses with varying Cu contents were fabricated and used to process 3D porous scaffolds via the foam replica technique. Cu-doping results in the weakening of the glass network and a decrease in its glass transition temperature. Acellular in vitro studies revealed very high bioactivity independent of Cu doping as indicated by the fast formation of a carbonated hydroxyapatite layer (CHA) on scaffold surfaces after immersion in simulated body fluid (SBF). The kinetics of the glass-ceramic scaffold's transition to an amorphous calcium phosphate layer (ACP) and the crystallisation of CHA were explored by FT-IR and SEM analyses. The elemental distribution in the scaffold/fluid interface region was monitored by the advanced micro-PIXE-RBS (particle induced X-ray emission/Rutherford backscattering spectrometry) method. Cu-containing glasses showed slower release of Si, Ca and P from the scaffold periphery, whereas traces of Cu were found incorporated in the CaP layer on the scaffold surface. Cu release kinetics from the scaffolds in SBF were found to depend on culturing conditions while highest Cu concentrations of ∼3.1 ppm and ∼4.6 ppm under static and quasi-dynamic conditions, respectively, were observed. Since Cu exhibits potential angiogenic and osteogenic properties, the Cu-containing scaffolds are suggested as promising materials for bone tissue engineering applications. © 2013 The Royal Society of Chemistry.
UnivIS-Import:2015-03-09:Pub.2013.tech.IW.LM.invitr_2

Ionic-Liquid-Infused Nanostructures as Repellent Surfaces - Galvan, Yaraset; Phillips, Katherine R.; Haumann, Marco; Wasserscheid, Peter; Zarraga, Ramon; Vogel, Nicolas (Langmuir, 2018)
In order to prepare lubricant-infused repellent coatings on silica nanostructures using low vapor pressure ionic liquids as lubricants, we study the wetting behavior of a set of imidazolium-based ionic liquids with different alkyl side chains as a function of the applied surface functionalities. We take advantage of the structural color of inverse opals prepared from a colloidal coassembly technique to study the infiltration of ionic liquids into these nanoporous structures. We find that the more hydrophobic ionic liquids with butyl and hexyl side chains can completely infiltrate inverse opals functionalized with mixed self-assembled monolayers composed of imidazole groups and aliphatic hydrocarbon chains, which we introduce via silane chemistry. These molecular species reflect the chemical nature of the ionic liquid, thereby increasing the affinity between the liquid and solid surface. The mixed surface chemistry provides sufficiently small contact angles with the ionic liquid to infiltrate the nanopores while maximizing the contact angle with water. As a result, the mixed monolayers enable the design of a stable ionic liquid/solid interface that is able to repel water as a test liquid. Our results underline the importance of matching chemical affinities to predict and control the wetting behavior in complex, multiphase systems
Keywords: Coating materials; Salts; Liquids; Wetting; Solvents

Ionomer and protein size analysis by analytical ultracentrifugation and electrospray scanning mobility particle sizer - Wawra, Simon; Thoma, Martin; Walter, Johannes; Lübbert, Christian; Thajudeen, Thaseem; Damm, Cornelia; Peukert, Wolfgang (European Biophysics Journal, 2018)
Keywords: Analytical ultracentrifugation; Scanning mobility particle sizer; Combined analysis; Multiwavelength detector

Iron Precursor Decomposition in the Magnesium Combustion Flame: A New Approach for the Synthesis of Particulate Metal Oxide Nanocomposites - Gheisi, Amirreza; Niedermaier, Matthias; Tippelt, Gerold; Lottermoser, Werner; Bernardi, Johannes; Diwald, Oliver (Particle & Particle Systems Characterization, 2017)
Powders of Fe–Mg–O nanocomposite particles have been grown using a novel chemical vapor synthesis approach that employs the decomposition of a metalorganic precursor inside the metal combustion flame. After annealing in controlled gas atmospheres composition distribution functions, structure and phase stability of the obtained magnesiowüstite nanoparticles are measured with a combination of techniques such as inductively coupled plasma‐optical emission spectroscopy, energy dispersive X‐ray spectroscopy, X‐ray diffraction, and scanning and transmission electron microscopy. Complementary Mössbauer spectroscopy measurements reveal that depending on Fe loading and temperature of annealing either metastable and superparamagnetic solid solutions of Fe3+ ions in periclase (MgO) or phase separated mixtures of MgO and ferrimagnetic magnesioferrite (MgFe2O4) nanoparticles can be obtained. The described combustion technique represents a novel concept for the production of mixed metal oxide nanoparticles. Adressing the impact of selected annealing protocols, this study underlines the great potential of vapor phase grown non‐equilibrium solids, where thermal processing provides means to trigger phase separation and, concomitantly, the emergence of new magnetic propertie
Keywords: metal oxide nanoparticles; metastability; ferrimagnetism; iron admixture; phase separation; combustion synthesis

Isoelectric Point of Proteins at Hydrophobic Interfaces - Lautenbach, Vanessa; Hosseinpour, Saman; Peukert, Wolfgang (Frontiers in Chemistry, 2021)
Structural and colloidal stability of proteins at different surfaces and interfaces is of great importance in many fields including medical, pharmaceutical, or material science. Due to their flexibility, proteins tend to respond to their environmental conditions and can undergo structural and conformational changes. For instance, alterations in physiological factors such as temperature, ions concentration, or pH as well as the adsorption to an interface can initiate protein aggregation. Therefore, at different surfaces and interfaces the characterization of the structural and colloidal stability of proteins, which is mainly influenced by their electrostatic and hydrophobic interactions, is of fundamental importance. In this study, we utilized sum frequency generation (SFG) spectroscopy to assess the role of solution pH on the polarity and magnitude of the electric field within the hydration shell of selected model proteins adsorbed to a hydrophobic surface. We used polystyrene (PS) as a model hydrophobic surface and determined the isoelectric point (IEP) of four structurally different model proteins. Comparing the measured IEP of proteins at the PS/solution or air/solution interface with that determined in the bulk solution via zeta potential measurement, we found significant similarities between the IEP of surface adsorbed proteins and those in the bulk aqueous phase. The pH dependence behavior of proteins was correlated to their amino acid composition and degree of hydrophobicit
Keywords: proteins; isoelectric point; sum frequency generation spectroscopy; surface hydrophobicity; zeta potential

Isoelectric points of proteins at the air/liquid interface and in solution - Guckeisen, Tobias; Hosseinpour, Saman; Peukert, Wolfgang (Langmuir, 2019)
Electrostatic interactions play essential roles in determining the function, colloidal stability, and adsorption of proteins on different surfaces and interfaces. Therefore, a molecular level understanding of the charge state of the proteins under different conditions is required to explain their macroscopic properties. In this study we have employed an inherently surface sensitive spectroscopic tool, sum frequency generation spectroscopy, to determine the charge state of a wide range of proteins as a function of pH at the liquid/air interface via measurement of the degree of orientation of water molecules. We compared the isoelectric point of the 12 investigated proteins at the liquid/air interface with that in the bulk solution obtained through zeta potential measurements. Ellipsometry is performed to determine the film thickness at the liquid/air interface at different charge states. In particular, protein aggregation at the isoelectric point is reflected by increased film thickness. For all proteins, the interfacial point of zero charge is close (with less than 1 pH unit variation) to that in the bulk solution.
Keywords: protein; potential; charge; surface

Isolation and Purification of Single Gold Nanoclusters by Alternate Pumping Chromatography - Supper, Malvina; Birner, Virginia; Gromotka, Lukas; Peukert, Wolfgang; Kaspereit, Malte (Separations, 2023)
Alternate pumping chromatography is applied to obtain atomically precise glutathione-stabilized gold nanoclusters in high purity from synthesized mixtures. On the basis of anion exchange chromatography, the feasibility of isolating a single cluster, Au10 GSH10, as well as two different clusters simultaneously (Au25 GSH18 and Au29 GSH20) is demonstrated. In addition, Au18 GSH14, which is present only in trace amounts, is successfully enriched. A simple design procedure is proposed that allows using columns with different retention behavior. Successful experiments with large injection amounts confirm the potential of the concept for preparative-scale productions of high-quality nanoparticulate product

Kernel identification in continuous fluidized bed spray agglomeration from steady state data - Otto, Eric; Dürr, Robert; Strenzke, Gerd; Palis, Stefan; Bück, Andreas; Tsotsas, Evangelos; Kienle, Achim (Advanced Powder Technology, 2021)
Fluidized bed spray agglomeration is an important industrial particle formation process. In particular, the continuous operation mode is able to provide a constant stream of product particles with constant quality in terms of particle properties. Mathematical process modeling represents a valuable tool for a thorough analysis of the involved mechanistic processes and can further be used for process intensification and control. Sophisticated models describing the quantitative effect of process conditions on particle properties are particularly important. Therefore, in this contribution the influence of the seven most important operational parameters on the particle size distribution is modeled, including fluidization and binder properties. To this end, a population balance process model with the three-parametric Kapur kernel is fitted to experimental data. The first main result of this contribution is the quantitative description of the dependency between the agglomeration rate and the process conditions by multidimensional paraboloids. The second main result is the introduction of a general method by which this quantitative formulation is obtained.
CRIS-Team Scopus Importer:2021-06-18
Keywords: Agglomeration kernel; Continuous spray agglomeration; Kapur kernel; Parameter identification; Population balance equation

Kinetics of radical formation during the mechanical activation of quartz - Damm, Cornelia; Peukert, Wolfgang (Langmuir, 2009)
The kinetics of radical formation during the mechanical activation of quartz by wet grinding or sonication was investigated using 2,2-diphenyl-1- picrylhydrazyl (DPPH) as a scavenger. The consumption of DPPH during the sonication of quartz in an ethanol suspension is a zeroth-order process. A linear relationship between the rate constant of the DPPH consumption and the quartz concentration in the suspension indicates that radical formation under sonication increases with the growing total surface area of the quartz particles. Sonication leads to the formation of free radicals by the mechanical activation of the particle surface. The kinetics of the DPPH consumption during wet grinding of quartz in a stirred media mill is described successfully by a modified zeroth-order rate law taking the total surface area of the quartz particles into account. The surface-normalized rate constant of the DPPH consumption decreases from 1.8 × 10 mol L h m to 4.8 × 10 mol L h m if the specific surface area of the feed material increases from 0.5 to 84 m/g. This finding indicates that the breakage of the quartz particles contributes much more to radical formation than does the mechanical activation of the particles in the mill because the breakage rate increases with growing particle diameter. Ethanol but not DPPH was found on the surface of the ground quartz particles. From this finding, it can be concluded that radicals on the surface of the quartz particles react with ethanol, leading to the formation of ethanol radicals and H radicals. DPPH reacts with the H radicals. As a side reaction, radicals can react with oxygen, leading to the formation of peroxides. © Copyright 2009 American Chemical Society.

Kunststoffpulver für die Additive Fertigung: Vorhersage des Prozessverhaltens mittels prozessangepasster Analyse / Plastic powder for Additive Manufacturing: Prediction of process behavior based on process adapted characterization - Wudy, Katrin; Schmidt, Jochen; Lanzl, Lydia; Zhao, Meng; Jaksch, Andreas; Dechet, Maximilian; Hesse, Nicolas; Drummer, Dietmar; Peukert, Wolfgang (Vom Pulver zum multifunktionalen Bauteil, 2019)

Large-Area 3D Plasmonic Crescents with Tunable Chirality - Görlitzer, Eric; Mohammadi, Reza; Nechayev, Sergey; Banzer, Peter; Vogel, Nicolas (Advanced Optical Materials, 2019)
Chiral plasmonic nanostructures hold promise for enhanced chiral sensing and circular dichroism spectroscopy of chiral molecules. It is therefore of interest to fabricate chiral plasmonic nanostructures with tailored chiroptical properties over large areas with reasonable effort. Here, a colloidal lithography approach is used to produce macroscopic arrays of sub-micrometer 3D chiral plasmonic crescent structures over areas >1 cm 2 . The chirality originates from symmetry breaking by the introduction of a step within the crescent structure. This step is produced by an intermediate layer of silicon dioxide onto which the metal crescent structure is deposited. It is experimentally demonstrated that the chiroptical properties in such structures can be tailored by changing the position of the step within the crescent. These experiments are complemented by finite element simulations and the application of a multipole expansion to elucidate the physical origin of the circular dichroism of the crescent structures.
CRIS-Team Scopus Importer:2019-06-04
Keywords: chirality; colloidal lithography; multipole decomposition; plasmonics; split-ring resonator

Large-Scale Synthesis of Highly Uniform Silicon Nanowire Arrays Using Metal-Assisted Chemical Etching - Wendisch, Fedja J.; Rey, Marcel; Vogel, Nicolas; Bourret, Gilles Remi (Chemistry of Materials, 2020)
The combination of metal-assisted chemical etching (MACE) with colloidal lithography has emerged as a simple and cost-effective approach to nanostructure silicon. It is especially efficient at synthesizing Si micro- and nanowire arrays using a catalytic metal mesh, which sinks into the silicon substrate during the etching process. The approach provides a precise control over the array geometry, without requiring expensive nanopatterning techniques. Although MACE is a high-throughput solution-based approach, achieving large-scale homogeneity can be challenging because of the instability of the metal catalyst when the experimental parameters are not set appropriately. Such instabilities can lead to metal film fracture, significantly damaging the substrate and thus compromising the nanowire array quality. Here, we report on the critical parameters that influence the stability of the metal catalyst layer for achieving large-scale homogeneous MACE: etchant composition, metal film thickness, adhesion layer thickness, nanowire diameter and pitch, metal film coverage, Si/Au/etchant interface length, and crystalline quality of the colloidal template (grain size and defects). Our results investigate the origin of the catalyst film fracture and reveal that MACE experiments should be optimized for each Si wire array geometry by keeping the etch rate below a certain threshold. We show that the Si/Au/etchant interface length also affects the etch rate and should thus be considered when optimizing the MACE experimental parameters. Finally, our results demonstrate that colloidal templates with small grain sizes (i.e., <100 μm2) can yield significant problems during the pattern transfer because of a high density of defects at the grain boundaries that negatively affects the metal film stability. As such, this work provides guidelines for the large-scale synthesis of Si micro- and nanowire arrays via MACE, relevant for both new and experienced researchers working with MAC
Keywords: Etching; Metals; Gold; Nanowire arrays; Silicon

Laser-Activated Self-Assembled Thermoplasmonic Nanocavity Substrates for Intracellular Delivery - Madrid, Marinna; Saklayen, Nabiha; Shen, Weilu; Huber, Marinus; Vogel, Nicolas; Mazur, Eric (ACS Applied Bio Materials, 2018)
Intracellular delivery is crucial for cellular engineering and the development of therapeutics. Laser-activated thermoplasmonic nanostructured surfaces are a promising platform for high-efficiency, high-viability, high-throughput intracellular delivery. Their fabrication, however, typically involves complicated nanofabrication techniques, limiting the approach's applicability. Here, colloidal self-assembly and templating are used to fabricate large arrays of thermoplasmonic nanocavities simply and cost-effectively. These laser-activated substrates are used to deliver membrane-impermeable dye into cells at an efficiency of 78% and throughput of 30â»000 cells min-1 while maintaining 87% cell viability. Proof-of-concept data show delivery of large cargoes ranging from 0.6 to 2000 kDa to cells without compromising viability.
CRIS-Team Scopus Importer:2023-03-29
Keywords: colloidal templating; intracellular delivery; pulsed lasers; self-assembly; thermoplasmonics

Laser Beam Melting in Powder Bed of nonspherical aluminium microparticles dry coated with metal nanoparticles - Karg, Michael; Ahuja, Bhrigu; Schmidt, Jochen; Winzer, Bettina; Wirth, Karl-Ernst; Peukert, Wolfgang; Schmidt, Michael (Proceedings [Elektronski vir] / 6th International Conference on Additive Technologies iCAT2016, 2016)
Out of all Al alloys, Laser Beam Melting in Powder Bed (LBM) is almost exclusively used to process Al-Si cast alloys today. Feasibility of LBM of high-performance Al-Cu wrought alloys was published previously by the authors. Prealloyed powders are used for LBM. Small amounts or less common application-specific alloys must be atomized on request which is expensive, time consuming and of varying quality. Instead, during LBM alloys might form from mixtures of few basic powders. If density differs strongly as e. g. with Al and Cu, powders de-mix uncontrollably due to gravity. In LBM, spherical inert gas atomized powders are used. Cheaper non-spherical air atomized Al powders deposit insufficiently homogeneous in thin powder layers. LBM of Metal Matrix Composites (MMC) was shown using mechanical alloying that was time-consuming, affected particle size and shape. The goal of this contribution is to investigate the feasibility of an approach towards larger freedom of choice in LBM regarding all aforementioned dimensions of alloy composition, MMC creation and non-spherical base powders. Metal nanoparticles (np) were dry coated onto air atomized Al alloy micro particles. Powders with adhering np and LBM products were analyzed and compared to previous results.</
Keywords: metal nanoparticle adhesion; air atomized aluminium powder Metal Matrix Composite MMC; in-situ alloying; Selective Laser Melting SLM; powder bed fusion

Lasergestützte Verbindungstechnik für räumliche, spritzgegossene Schaltungsträger (3D-MID) für Gebrauchstemperaturen über 150°C - Eßer, Gerd; Horn, Michael (PLUS-Produktion von Leiterplatten und Systemen, 2003)
LFT Import::2019-07-15 (988)

Laser Spot Welding and Soldering of Micro Components to 3-Dimensional Circuit Substrates - Ostendorf, A.; Kulik, C.; Zeadan, M.; Schmidt, Michael; Horn, Michael (5th International Congress on Molded interconnect Devices (MID), 2002)
LFT Import::2019-08-05 (1716)

Laterally patterned ultraflat surfaces - Vogel, Nicolas; et al. (Small, 2009)
Keywords: Electrodes; Lithography; Patterning; Self-assembled monolayers; Surfaces

Layer-by-Layer Assemblies of Catechol-Functionalized TiO2 Nanoparticles and Porphyrins through Electrostatic Interactions - Burger, Alexandra; Costa, Ruben Dario; Lobaz, Volodymyr; Peukert, Wolfgang; Hirsch, Andreas; Guldi, Dirk Michael (Chemistry - A European Journal, 2015)
In the current work, we present the successful functionalization and stabilization of P-25 TiO2 nanoparticles by means of N1,N7-bis(3-(4-tert-butyl-pyridium-methyl)phenyl)-4-(3-(3-(4-tert-butyl-pyridinium-methyl)phenylamino)-3-oxopropyl)-4-(3,4-dihydroxybenzamido)heptanediamide tribromide (1). The design of the latter is aimed at nanoparticle functionalization and stabilization with organic building blocks. On one hand, 1 features a catechol anchor to enable its covalent grafting onto the TiO2 surface, and on the other hand, positively charged pyridine groups at its periphery to prevent TiO2 agglomeration through electrostatic repulsion. The success of functionalization and stabilization was corroborated by thermogravimetric analysis, dynamic light-scattering, and zeta potential measurements. As a complement to this, the formation of layer-by-layer assemblies, which are governed by electrostatic interactions, by alternate deposition of functionalized TiO2 nanoparticles and two negatively charged porphyrin derivatives, that is, 5,10,15,20-(phenoxyacetic acid)-porphyrin (2) and 5,10,15,20-(4-(2-ethoxycarbonyl)-4-(2-phenoxyacetamido)heptanedioic acid)-porphyrin (3), is documented. To this end, the layer-by-layer deposition is monitored by UV/Vis spectroscopy, scanning electron microscopy, ellipsometry, and profilometry techniques. The resulting assemblies are utilized for the construction and testing of novel solar cells. From stable and repeatable photocurrents generated during several ön-offc̈ycles of illumination, we derive monochromatic incident photo-to-current conversion efficiencies of around 3 \

Ligand-assisted thickness tailoring of highly luminescent colloidal CH3NH3PbX3 (X = Br and I) perovskite nanoplatelets - Levchuk, Ievgen; Herre, Patrick; Brandl, Marco; Osvet, Andres; Hock, Rainer; Peukert, Wolfgang; Schweizer, Peter; Spiecker, Erdmann; Batentschuk, Miroslaw; Brabec, Christoph (Chemical Communications, 2017)
Quantum size-confined CHNHPbX (X = Br and I) perovskite nanoplatelets with remarkably high photoluminescence quantum yield (up to 90%) were synthesized by ligand-assisted re-precipitation. Thickness-tunability was realized by varying the oleylamine and oleic acid ligand ratio. This method allows tailoring the nanoplatelet thickness by adjusting the number of unit cell monolayers. Broadly tunable emission wavelengths (450-730 nm) are achieved via the pronounced quantum size effect without anion-halide mixing.

Light interaction between gold nanoshells plasmon resonance and planar optical waveguides - Lal, Surbhi; Westcott, Sarah; Klupp Taylor, Robin; Jackson, Joseph; Nordlander, Peter; Halas, Naomi (Journal of Physical Chemistry B, 2002)
We have studied the experimental and theoretical aspects of the interaction of gold nanoshells on a waveguiding structure. Gold nanoshells are core−shell particles consisting of a silica core surrounded by a thin gold shell. The waveguiding structure consists of a 2 μm thick layer of gold with a dielectric layer of varying thickness deposited on it. Light scattering experiments performed on gold nanoshells randomly deposited on the dielectric layer show a change in the scattering spectrum of the nanoshells because of coupling of light with the waveguide modes. Comparison of experimental data with theoretical calculations based on the classic theory of point dipoles placed over a conducting surface shows a significant shift in the dipole resonance position. A simple image charge calculation taking into consideration finite size effects explains the red shift observed in the experimental data for the smallest dielectric layer thickness. Observed deviations from the theoretical models are attributable to nanoshell aggregate
Keywords: plasmon; nanoparticle; optics; shell; core; particle

Liquid filtration of nanoparticles through track-etched membrane filters under unfavorable and different ionic strength conditions: Experiments and modeling - Peukert, Wolfgang; Segets, Doris; Süß, Sebastian; Chen, Sheng-Chieh; Pui, David; Lee, Handol (Journal of Membrane Science, 2017)
Nanoparticle deposition experiments under unfavorable conditions were conducted experimentally and theoretically. The 0.2 and 0.4 µm rated track-etched membrane filters were challenged with 60, 100, 147, 220, 350 and 494 nm polystyrene latex (PSL) particles with different ionic strengths ranging from 0.005 to 0.05 M. The capillary tube model, with replacing the viscosity of air to water, was used to estimate the initial efficiency, or the transport efficiency of the particles to the filter surface, which was corrected in a second step by allowing the detachment of the nanoparticles according to the sum of adhesive and hydrodynamic torques. The adhesive torques were derived from surface interactions accessed by the extended DLVO theory. Calculation results showed that the adhesive torque of a particle located in the calculated primary minimum was slightly larger than the hydrodynamic torque, resulting in particle deposition. However, experimental data clearly indicated that detachment occurred. This could only be explained by the presence of additional hydration forces, leading to a larger separation which became relevant at high ionic strengths. By including hydration into our theoretical framework, experiment and theory were in very good agreement under all different ionic strength conditions. The findings allow a basic understanding of surface interactions between nanoparticles and membranes in micro- and ultra-filtration applications for drinking water production, wastewater treatment and particle free water production in industries.
Keywords: Adhesive and hydrodynamic torque; Derjaguin-Landau-Verwey-Overbeek (DLVO) theory; Microfiltration; Short range hydration effects; Track-etched polycarbonate membrane filter

Liquid phase temperature determination in dense water sprays using linear Raman scattering - Hankel, Robert; Günther, Astrid; Wirth, Karl-Ernst; Leipertz, Alfred; Bräuer, Andreas (Optics Express, 2014)

Local densification of a single micron sized silica sphere by uniaxial compression - Romeis, Stefan; Paul, Jonas; Herre, Patrick; de Ligny, Dominique; Schmidt, Jochen; Peukert, Wolfgang (Scripta Materialia, 2015)