2D analysis of polydisperse core-shell nanoparticles using analytical ultracentrifugation - Walter, Johannes; Gorbet, Gary; Akdas, Tugce; Segets, Doris; Demeler, Borries; Peukert, Wolfgang (Analyst, 2017)
Accurate knowledge of the size, density and composition of nanoparticles (NPs) is of major importance for their applications. In this work the hydrodynamic characterization of polydisperse core-shell NPs by means of analytical ultracentrifugation (AUC) is addressed. AUC is one of the most accurate techniques for the characterization of NPs in the liquid phase because it can resolve particle size distributions (PSDs) with unrivaled resolution and detail. Small NPs have to be considered as core-shell systems when dispersed in a liquid since a solvation layer and a stabilizer shell will significantly contribute to the particle's hydrodynamic diameter and effective density. AUC measures the sedimentation and diffusion transport of the analytes, which are affected by the core-shell compositional properties. This work demonstrates that polydisperse and thus widely distributed NPs pose significant challenges for current state-of-the-art data evaluation methods. The existing methods either have insufficient resolution or do not correctly reproduce the core-shell properties. First, we investigate the performance of different data evaluation models by means of simulated data. Then, we propose a new methodology to address the core-shell properties of NPs. This method is based on the parametrically constrained spectrum analysis and offers complete access to the size and effective density of polydisperse NPs. Our study is complemented using experimental data derived for ZnO and CuInS NPs, which do not have a monodisperse PSD. For the first time, the size and effective density of such structures could be resolved with high resolution by means of a two-dimensional AUC analysis approac
Keywords: nanoparticles; centrifugation; resolution; core-shell; ZnO; analysis

2-photon fluorescence of quantum dots for investigations of nanoparticle formation and growth - Dinkel, Rebecca; Braunschweig, Björn; Peukert, Wolfgang (ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 2016)

3D printing of magnetic parts by laser powder bed fusion of iron oxide nanoparticle functionalized polyamide powders - Hupfeld, Tim; Salamon, Soma; Landers, Joachim; Sommereyns, Alexander; Donate-Buendia, Carlos; Schmidt, Jochen; Wende, Heiko; Schmidt, Michael; Barcikowski, Stephan; Goekce, Bilal (Journal of Materials Chemistry C, 2020)
The development of new feedstock materials is a central prerequisite for advances in Additive Manufacturing (AM). To increase the breadth of potential applications for 3D and 4D printing of polymers, micro- and nano-additives incorporated into the feedstock material play an important role. In this context, magnetic materials are of great interest. Our study describes a way to fabricate polymer powders for laser powder bed fusion (PBF-LB) with a homogeneous, well-dispersed coating of iron oxide nanoparticles. Without the addition of chemical precursors, spherical superparamagnetic FeO(x)nanoparticles with monomodal size distribution below 10 nm are generated from FeO(x)micropowder by laser fragmentation in liquid. The adsorption of the nanoparticles on polyamide (PA12) powder is conducted directly in an aqueous dispersion after laser fragmentation, followed by drying, powder analysis and PBF-LB processing.ViaMossbauer spectroscopy and magnetometry, we determined that the saturation magnetization and structure of the iron oxide nanoparticles were not influenced by PBF-LB processing, and the magnetic properties were successfully transferred to the final 3D-printed magnetic part.
CRIS-Team WoS Importer:2020-10-02

A 3D-Printed Wound-Healing Material Composed of Alginate Dialdehyde-Gelatin Incorporating Astaxanthin and Borate Bioactive Glass Microparticles - Monavari, Mahshid; Homaeigohar, Shahin; Medhekar, Rucha Shirish; Nawaz, Qaisar; Monavari, Mehran; Zheng, Kai; Boccaccini, Aldo R. (ACS Applied Materials and Interfaces, 2023)
In this study, a wound dressing composed of an alginate dialdehyde-gelatin (ADA-GEL) hydrogel incorporated by astaxanthin (ASX) and 70B (70:30 B2O3/CaO in mol %) borate bioactive glass (BBG) microparticles was developed through 3D printing. ASX and BBG particles stiffened the composite hydrogel construct and delayed its in vitro degradation compared to the pristine hydrogel construct, mainly due to their cross-linking role, likely arising from hydrogen bonding between the ASX/BBG particles and ADA-GEL chains. Additionally, the composite hydrogel construct could hold and deliver ASX steadily. The composite hydrogel constructs codelivered biologically active ions (Ca and B) and ASX, which should lead to a faster, more effective wound-healing process. As shown through in vitro tests, the ASXcontaining composite hydrogel promoted fibroblast (NIH 3T3) cell adhesion, proliferation, and vascular endothelial growth factor expression, as well as keratinocyte (HaCaT) migration, thanks to the antioxidant activity of ASX, the release of cell-supportive Ca2+ and B3+ ions, and the biocompatibility of ADA-GEL. Taken together, the results show that the ADA-GEL/BBG/ASX composite is an attractive biomaterial to develop multipurposed wound-healing constructs through 3D printing.
CRIS-Team WoS Importer:2023-06-02
Keywords: 3D printing; drug delivery; borate bioactive glass; astaxanthin. wound healing

A biphasic batch and continuous flow synthesis of hydrophobic gold and silver nanoparticles - Distaso, Monica; Peukert, Wolfgang (Reaction Chemistry & Engineering, 2023)
Plasmonic nanoparticles functionalized with hydrophobic ligands are required for several applications in flexible electronic, sensors and memory devices for their dispersability in polymeric matrices. In the current paper, we report a method for the batch and continuous synthesis of gold and silver nanoparticles (NPs) functionalized with oleylamine and oleic acid following a modified Brust-Schiffrin method. The role of key components of the reaction mixture in the phase transfer step is unravelled via(1)H and C-13 nuclear magnetic resonance (H-1 and C-13 NMR) spectroscopy. Gold and silver nanoparticles are characterized by Transmission and Scanning Electron Microscopy (TEM, SEM), Scanning TEM in High Angle Annular Dark Field mode (STEM-HAADF) coupled with X-ray Spectroscopy (STEM-EDX) analysis and UV-vis spectroscopy. Based on the findings for the synthesis in batch mode, we demonstrate the feasibility of the continuous flow synthesis for both gold and silver systems.
CRIS-Team WoS Importer:2023-06-02

Abrasion-Induced Acceleration of Melt Crystallisation of Wet Comminuted Polybutylene Terephthalate (PBT) - Tischer, Florentin; Düsenberg, Björn; Gräser, Timo; Kaschta, Joachim; Schmidt, Jochen; Peukert, Wolfgang (Polymers, 2022)
Within this contribution, the effect of grinding media wear on the melt crystallisation of polybutylene terephthalate (PBT) is addressed. PBT was wet ground in a stirred media mill in ethanol using different grinding media beads (silica, chrome steel, cerium-stabilised and yttrium-stabilised zirconia) at comparable stress energies with the intention to use the obtained particles as feed materials for the production of feedstocks for laser powder bed fusion additive manufacturing (PBF-AM). In PBF‑AM, the feedstock’s optical, rheological and especially thermal properties—including melt crystallisation kinetics—strongly influence the processability and properties of the manufactured parts. The influence of process parameters and used grinding media during wet comminution on the optical properties, crystal structure, molar mass distribution, inorganic content (wear) and thermal properties of the obtained powders is discussed. A grinding media-dependent acceleration of the melt crystallisation could be attributed to wear particles serving as nuclei for heterogeneous crystallisation. Yttrium-stabilised zirconia grinding beads proved to be the most suitable for the production of polymer powders for the PBF process in terms of (fast) comminution kinetics, unchanged optical properties and the least accelerated crystallisation kinetics.<br
Keywords: wet comminution; stirred media mills; abrasion; polymer; additive manufacturing; powder bed fusion; thermal properties; isothermal DSC

Accelerated grain refinement during accumulative roll bonding by nanoparticle reinforcement - Schmidt, Christian; Knieke, Catharina; Maier, Verena; Höppel, Heinz; Peukert, Wolfgang; Göken, Mathias (Scripta Materialia, 2011)
Ceramic nanoparticles produced by comminution are introduced homogeneously during accumulative roll bonding (ARB) in aluminium AA1050A by airgun spraying from a stabilized aqueous suspension. In the so-produced nanoparticle-reinforced ultrafine-grained material, acceleration of microstructural evolution during the early ARB cycles as well as reduced grain sizes at higher cycles are observed, both caused by additional local straining around the embedded nanoparticles and accompanied by further strengthening. The presented method of nanoparticle application allows homogeneous as well as graded particle distributio

Accurate Elemental Analysis of Metal-Containing Polymer Latexes Using ICP-Optical Emission Spectrometry - Vogel, Nicolas; et al. (Macromolecular Chemistry and Physics, 2010)
The use of ICP-OES to determine the metal content of metal-complex-containing colloidal dispersions is explored. Colloidal dispersions containing a defined amount of metal complex were produced by miniemulsion polymerization. It was found that simple ICP-OES measurements yielded apparent metal concentrations significantly below the expected value. To examine the behavior of the colloidal dispersions in the ICP spectrometer, a systematic study on measurement conditions was performed. It was found that the addition of a surfactant to both colloidal dispersions and standards led to measured metal contents close to the theoretical value. Most reliable results were obtained using SDS in concentrations above the cmc.
Keywords: colloids; hybrid nanoparticles; ICP-OES; miniemulsions; surfactants

A colloidoscope of colloid-based porous materials and their uses - Phillips, Katherine R.; England, Grant T.; Sunny, Steffi; Shirman, Elijah; Shirman, Tanya; Vogel, Nicolas; Aizenberg, Joanna (Chemical Society Reviews, 2016)
Nature evolved a variety of hierarchical structures that produce sophisticated functions. Inspired by these natural materials, colloidal self-assembly provides a convenient way to produce structures from simple building blocks with a variety of complex functions beyond those found in nature. In particular, colloid-based porous materials (CBPM) can be made from a wide variety of materials. The internal structure of CBPM also has several key attributes, namely porosity on a sub-micrometer length scale, interconnectivity of these pores, and a controllable degree of order. The combination of structure and composition allow CBPM to attain properties important for modern applications such as photonic inks, colorimetric sensors, self-cleaning surfaces, water purification systems, or batteries. This review summarizes recent developments in the field of CBPM, including principles for their design, fabrication, and applications, with a particular focus on structural features and materials' properties that enable these applications. We begin with a short introduction to the wide variety of patterns that can be generated by colloidal self-assembly and templating processes. We then discuss different applications of such structures, focusing on optics, wetting, sensing, catalysis, and electrodes. Different fields of applications require different properties, yet the modularity of the assembly process of CBPM provides a high degree of tunability and tailorability in composition and structure. We examine the significance of properties such as structure, composition, and degree of order on the materials' functions and use, as well as trends in and future directions for the development of CBPM.

A Combined SAXS/SANS Study for the in Situ Characterization of Ligand Shells on Small Nanoparticles: The Case of ZnO - Schindler, Torben; Schmiele, Martin; Schmutzler, Tilo; Kassar, Thaer; Segets, Doris; Peukert, Wolfgang; Radulescu, Aurel; Kriele, Armin; Gilles, Ralph; Unruh, Tobias (Langmuir, 2015)
ZnO nanoparticles (NPs) have great potential for their use in, e.g., thin film solar cells due to their electro-optical properties adjustable on the nanoscale. Therefore, the production of well-defined NPs is of major interest. For a targeted production process, the knowledge of the stabilization layer of the NPs during and after their formation is of particular importance. For the study of the stabilizer layer of ZnO NPs prepared in a wet chemical synthesis from zinc acetate, only ex situ studies have been performed so far. An acetate layer bound to the surface of the dried NPs was found; however, an in situ study which addresses the stabilizing layer surrounding the NPs in a native dispersion was missing. By the combination of small angle scattering with neutrons and X-rays (SANS and SAXS) for the same sample, we are now able to observe the acetate shell in situ for the first time. In addition, the changes of this shell could be followed during the ripening process for different temperatures. With increasing size of the ZnO core (dcore) the surrounding shell (dshell) becomes larger, and the acetate concentration within the shell is reduced. For all samples, the shell thickness was found to be larger than the maximum extension of an acetate molecule with acetate concentrations within the shell below 50 vol %. Thus, there is not a monolayer of acetate molecules that covers the NPs but rather a swollen shell of acetate ions. This shell is assumed to hinder the growth of the NPs to larger macrostructures. In addition, we found that the partition coefficient μ between acetate in the shell surrounding the NPs and the total amount of acetate in the solution is about 10% which is in good agreement with ex situ data determined by thermogravimetric analysis.
Keywords: nanoparticle; solar; cell; electroptical; property

A Comprehensive Brownian Dynamics Approach for the Determination of Non-ideality Parameters from Analytical Ultracentrifugation - Uttinger, Maximilian; Wawra, Simon; Guckeisen, Tobias; Walter, Johannes; Bear, Andreas; Thajudeen, Thaseem; Sherwood, Peter J.; Smith, Ana-Suncana; Wagemans, Anja M.; Stafford, Walter F.; Peukert, Wolfgang (Langmuir, 2019)
Brownian dynamics (BD) has been applied as a comprehensive tool to model sedimentation and diffusion of nanoparticles in analytical ultracentrifugation (AUC) experiments. In this article, we extend the BD algorithm by considering space-dependent diffusion and solvent compressibility. With this, the changes in the sedimentation and diffusion coefficient from altered solvent properties at increased pressures are accurately taken into account. Moreover, it is demonstrated how the concept of space-dependent diffusion is employed to describe concentration-dependent sedimentation and diffusion coefficients, in particular, through the Gralen coefficient and the second virial coefficient. The influence of thermodynamic nonideality on diffusional properties can be accurately simulated and agree with well-known evaluation tools. BD simulations for sedimentation equilibrium and sedimentation velocity (SV) AUC experiments including effects of hydrodynamic and thermodynamic nonideality are validated by global evaluation in SEDANAL. The interplay of solvent compressibility and retrieved nonideality parameters can be studied utilizing BD. Finally, the second virial coefficient is determined for lysozyme from SV AUC experiments and BD simulations and compared to membrane osmometry. These results are in line with DLVO theory. In summary, BD simulations are established for the validation of nonideal sedimentation in AUC providing a sound basis for the evaluation of complex interactions even in polydisperse systems.
CRIS-Team Scopus Importer:2019-09-17

A Comprehensive Brownian Dynamics-Based Forward Model for Analytical (Ultra)Centrifugation - Thajudeen, Thaseem; Walter, Johannes; Uttinger, Maximilian; Peukert, Wolfgang (Particle & Particle Systems Characterization, 2017)
In this study, it is demonstrated how Brownian dynamics (BD) simulations can be used as a comprehensive forward model for analytical ultracentrifugation (AUC) and analytical centrifugation experiments. BD simulations are a versatile alternative to the numerical solution of Lamm's equation. Time dependent concentration profiles can be accurately predicted by means of the BD simulations even for colloidal systems with multiple species. It is shown that in combination with Mie's theory for light scattering, BD simulations can be extended to generate data mimicking a multiwavelength detector for AUC. The forward model can be utilized as a comprehensive tool for developing and testing sophisticated data analyzing tools that can enhance the capabilities of using centrifugation-based techniques for characterizing nanoparticles. The model is validated using common analysis tools developed for the evaluation of sedimentation velocity data generated by a single wavelength extinction detector. The accuracy of the code is also proved using the recently developed and highly versatile High Dynamic Range-MULTIwavelength FITting tool for accurately predicting particle size distributions via gravitational sweep experiments performed in AUCs equipped with multiwavelength detectors.
Keywords: Brownian dynamics; analytical ultracentrifugation; Mie scattering; extinction coefficient; multiwavelength detectors

A comprehensive methodology to study double emulsion stability - Leister, Nico; Götz, Vanessa; Bachmann, Stephan Jan; Nachtigall, Stephanie; Hosseinpour, Saman; Peukert, Wolfgang; Karbstein, Heike (Journal of Colloid and Interface Science, 2022)
The stability of emulsions requires the fast formation of viscoelastic interfaces between water and oil phases. In double emulsions, two surfactant types (hydrophilic and lipophilic) are present and two interfacial films are involved. Understanding cooperative adsorption of these surfactants and its implication on properties of water/oil/water interfacial films will enable replacing the empirical methodologies used in designing double emulsion systems with a knowledge-based approach. The distribution of surfactants between the water/oil interfaces was investigated using single droplet diffusion experiments and simulation of equilibrium surfactant density profiles. The stability of the interfaces against coalescence was characterized by dye transport in a leach cell and coalescence time of single droplets in a model experiment. The conformation of the surfactants at an interface was then examined via surface rheology, sum frequency generation spectroscopy, and dissipative particle dynamics simulation. Two selected hydrophilic surfactants combined with a lipophilic surfactant induce very different properties at water/oil interfaces and different dye release behaviour from their corresponding double emulsions. Competitive adsorption of sodium dodecyl sulfate and lipophilic surfactant results in the improvement of encapsulation efficiency, elasticity of the interface, and resistance against coalescence due to the intercalation of surfactant alkyl chains into the oil chains.
Keywords: Coalescence; Diffusion; Double emulsions; Stability; Surfactants

A comprehensive study on the mechanism behind formation and depletion of Cu2ZnSnS4 (CZTS) phases - Ahmad, Rameez; Brandl, Marco; Distaso, Monica; Herre, Patrick; Spiecker, Erdmann; Hock, Rainer; Peukert, Wolfgang (Crystengcomm, 2015)
High efficiency kesterite based solar cells have vigorously raised the research interests in this material. The challenge lies in understanding the formation and co-existence of more than 10 possible by-products during and after the synthesis of Cu2ZnSnS4 (CZTS) and their various different structural and electronic defects. The present contribution shows an in-depth study on the stages of formation and depletion of nanoparticulate CZTS. Employing a hot injection synthesis method, we give direct experimental evidence of the co-existence of cubic, tetragonal and defected CZTS structures and different by-products as a function of time and temperature. SEM, (HR) TEM, XRD, EDX, ICP-OES, Raman spectroscopy and UV-Vis-NIR spectroscopy have been used in order to better evaluate and interpret data for crystal structures and compositions. The obtained understanding on the formation of different phases suggests 250 degrees C as the most favourable synthesis temperature. Based on our study, general strategies can be developed for controlling the amount of formed phases, the by-products and the defects in kesterite and other similar multicomponent nanoparticles as well as in bulk systems.

A Continuous Gradient Colloidal Glass - Schöttle, Marius; Lauster, Tobias; Römling, Lukas; Vogel, Nicolas; Retsch, Markus (Advanced Materials, 2022)
Colloidal crystals and glasses manipulate light propagation depending on their chemical composition, particle morphology, and mesoscopic structure. This light-matter interaction has been intensely investigated, but a knowledge gap remains for mesostructures comprising a continuous property gradient of the constituting particles. Here, a general synthetic approach to bottom-up fabrication of continuous size gradient colloidal ensembles is introduced. Firstly, the technique synthesizes a dispersion with a specifically designed gradual particle size distribution. Secondly, self-assembly of this dispersion yields a photonic colloidal glass with a continuous size gradient from top to bottom. Local and bulk characterization methods are used to highlight the significant potential of this mesostructure, resulting in vivid structural colors along, and superior light scattering across the gradient. The process describes a general pathway to mesoscopic gradients. It can expectedly be transferred to a variety of other particle-based systems where continuous gradients will provide novel physical insights and functionalities.
Keywords: colloidal self-assembly; gradient size distribution; light scattering; mesoscale gradient

A Convenient Method to Produce Close- and Non-close-Packed Monolayers using Direct Assembly at the Air-Water Interface and Subsequent Plasma-Induced Size Reduction - Vogel, Nicolas; et al. (Macromolecular Chemistry and Physics, 2011)
An extremely facile approach to produce close-packed colloidal monolayers over large areas using direct assembly at the air-water interface is presented. The influence of small amounts of sodium dodecyl sulfate (SDS) as well as the influence of the pH value of the subphase on the quality of the resulting monolayer is investigated. It is found that small amounts of SDS at the interface influence capillary forces and form a soft barrier that facilitates the crystallization process. Increased electrostatic repulsion arising from a higher pH of the subphase induced a higher order using carboxylic acid functionalized particles. The deposited close-packed monolayers were subjected to plasma treatment in order to shrink the colloids and produce non-close packed monolayers with lattice spacing and symmetry reflecting the order of the initial close-packed monolayer. A detailed examination of etching conditions and their influence on the shrinkage of the particles was performed, including effects of plasma power, composition, flow rates as well as polymeric-and substrate material. The monolayers exhibit vivid coloration, which is determined by their size and packing density. UV-Vis-NIR spectroscopy was used to investigate the change of monolayer color during the size reduction of the individual particles. A simple theoretical model was elaborated to explain the optical properties. Finally, the non-close-packed monolayers were used as masks to produce gold nanostructures to exemplify the versatility of the monolayer architectures in nanosphere lithography.
Keywords: colloid assembly; colloid monolayer; interference; monolayers; monolayer color; nanosphere lithography; non-close-packed monolayer

Acoustic Crystallization of 2D Colloidal Crystals - Menath, Johannes; Mohammadi, Reza; Grauer, Jens Christian; Deters, Claudius; Böhm, Maike; Liebchen, Benno; Janssen, Liesbeth M.C.; Löwen, Hartmut; Vogel, Nicolas (Advanced Materials, 2023)
2D colloidal crystallization provides a simple strategy to produce defined nanostructure arrays over macroscopic areas. Regularity and long-range order of such crystals is essential to ensure functionality, but difficult to achieve in self-assembling systems. Here, a simple loudspeaker setup for the acoustic crystallization of 2D colloidal crystals (ACDC) of polystyrene, microgels, and core–shell particles at liquid interfaces is introduced. This setup anneals an interfacial colloidal monolayer and affords an increase in average grain size by almost two orders of magnitude. The order is characterized via the structural color of the colloidal crystal, the acoustic annealing process is optimized via the frequency and the amplitude of the applied sound wave, and its efficiency is rationalized via the surface coverage-dependent interactions within the interfacial colloidal monolayer. Computer simulations show that multiple rearrangement mechanisms at different length scales, from the local motion around voids to grain boundary movements via consecutive particle rotations around common centers, collude to remove defects. The experimentally simple ACDC process, paired with the demonstrated applicability toward complex particle systems, provides access to highly defined nanostructure arrays for a wide range of research communitie
Keywords: structural color; monolayers; self-assembly; colloids; crystallization

Acoustic Crystallization of Two-dimensional Colloidal Crystals - Menath, Johannes; Mohammadi, Reza; Grauer, Jens Christian; Deters, Claudius; Böhm, Maike; Liebchen, Benno; Janssen, Liesbeth M.C.; Loewen, Hartmut; Vogel, Nicolas (Advanced Materials, 2022)
Two-dimensional colloidal crystallization provides a simple strategy to produce defined nanostructure arrays over macroscopic areas. Regularity and long-range order of such crystals is essential to ensure functionality, but difficult to achieve in self-assembling systems. Here, we introduce a simple loudspeaker setup for the acoustic crystallization of two-dimensional crystals (ACDC) of polystyrene, microgels, and core-shell colloidal particles at liquid interfaces. This setup anneals an interfacial colloidal monolayer and affords an increase in average grain size by almost two orders of magnitude. We characterize the order via the structural color of the colloidal crystal, optimize the acoustic annealing process via the frequency and the amplitude of the applied sound wave and rationalize its efficiency via the surface coverage-dependent interactions within the interfacial colloidal monolayer. Computer simulations show that multiple rearrangement mechanisms at different length scales, from the local rearrangement around voids to grain boundary movement via consecutive particle rotations around common centers, collude to remove defects. The experimentally simple ACDC process, paired with the demonstrated applicability towards complex particle systems, provides access to highly-defined nanostructure arrays for a wide range of research communities.
Keywords: colloids; crystallization; monolayer; self-assembly; structural color

Adaptive Behavior of Dynamic Orthoester Cryptands - Shyshov, Oleksandr; Brachvogel, Rene-Chris; Bachmann, Tobias; Srikantharajah, Rubitha; Segets, Doris; Hampel, Frank; Puchta, Ralph; Von Delius, Max (Angewandte Chemie International Edition, 2017)
The integration of dynamic covalent bonds into macrocycles has been a tremendously successful strategy for investigating noncovalent interactions and identifying effective host–guest pairs. While numerous studies have focused on the dynamic responses of macrocycles and larger cages to various guests, the corresponding constitutionally dynamic chemistry of cryptands remains unexplored. Reported here is that cryptands based on orthoester bridgeheads offer an elegant entry to experiments in which a metal ion selects its preferred host from a dynamic mixture of competing subcomponents. In such dynamic mixtures, the alkali metal ions Li+, Na+, K+, Rb+, and Cs+ exhibit pronounced preferences for the formation of cryptands of certain sizes and donor numbers, and the selection is rationalized by DFT calculations. Reported is also the first self-assembly of a chiral orthoester cryptate and a preliminary study on the use of stereoisomers as subcomponents.
Keywords: cryptands; dynamic combinatorial chemistry; supramolecular chemistry; host–guest chemistry; NMR spectroscopy

Addressing the plasmonic hotspot region by site-specific functionalization of nanostructures - Görlitzer, Eric; Speichermann, Lutz; Mirza, Talha Ahmed; Mohammadi, Reza; Vogel, Nicolas (Nanoscale Advances, 2020)
Strong electromagnetic fields emerge around resonant plasmonic nanostructures, focusing the light in tiny volumes, usually referred to as hotspots. These hotspots are the key regions governing plasmonic applications since they strongly enhance properties, signals or energies arising from the interaction with light. For a maximum efficiency, target molecules or objects would be exclusively placed within hotspot regions. Here, we propose a reliable, universal and high-throughput method for the site-specific functionalization of hotspot regions over macroscopic areas. We demonstrate the feasibility of the approach using crescent-shaped nanostructures, which can be fabricated using colloidal lithography. These structures feature polarization-dependent resonances and near-field enhancement at their tips, which we use as target regions for the site-selective functionalization. We modify the fabrication process and introduce a defined passivation layer covering the central parts of the gold nanocrescent, which, in turn, selectively uncovers the tips and thus enables a localized functionalization with thiol molecules. We demonstrate and visualize a successful targeting of the hotspot regions by binding small gold nanoparticles and show a targeting efficiency of 90%. Finally, we demonstrate the versatility of the method exemplarily by translating the principle to different nanostructure geometries and architectures.
CRIS-Team Scopus Importer:2020-02-04

Adhesion forces of spherical alumina particles on ceramic substrates - Peukert, Wolfgang; Götzinger, Martin (Journal of Adhesion, 2004)
Adhesion forces of spherical alumina particles on ceramic substrates were studied. Results of direct force measurements using an atomic force microscope (AFM) were compared with theoretical results of a new rod model and with molecular dynamic computer simulation. Spherical alumina particles were produced by a flame process. The particles were glued to cantilevers, and interaction forces were measured by the AFM. A significant reduction of adhesion forces due to adsorbed layers was observed. The interaction volumes were determined by AFM scanning using a soft cantilever. The measured interaction forces were compared with calculated forces using the Hamaker concept including an adsorbed surface layer and the determined interaction volume (rod model). It turned out that calculated adhesion forces, neglecting deformation, are smaller than measured ones. This problem can be overcome if deformation according to Hertz is included in the rod model. Even for such a hard material as alumina, deformation occurs in the contact zone, which was also observed in a molecular dynamic computer simulatio
UnivIS-Import:2015-03-09:Pub.2004.tech.ITC.mechve.adhesi
Keywords: Alumina; Molecular dynamics; Particle adhesion; Roughness

Adhesive force distribution of rough adhesive systems for the example of a ball-plate system - Peukert, Wolfgang; Götzinger, Martin (Chemie Ingenieur Technik, 2003)

Adipogenic, chondrogenic, osteogenic, and antimicrobial features of glass ceramic material supplemented with manganese - Rau, Julietta V.; De Stefanis, Adriana; Barbaro, Katia; Fosca, Marco; Yankova, Viktoriya G.; Matassa, Roberto; Nottola, Stefania Annarita; Nawaz, Qaisar; Ali, Muhammad Saad; Peukert, Wolfgang; Boccaccini, Aldo R. (Journal of Non-Crystalline Solids, 2021)
Innovative Mn-containing glass ceramic (Na2O[2.00]-K2O[0.09]-MgO[3.10]-MnO[2.07]-CaO[38.78]-CaF2[2.25]-P2O5[9.66]-SiO2[41.71] [wt%]) was obtained by sol-gel. It was investigated by High Resolution Field Emission Scanning Electron Microscopy, Energy Dispersive X-Ray Spectroscopy, X-Ray fluorescence, X-Ray Diffraction, and Fourier Transform Infrared Spectroscopy. Ion release characteristics of the glass ceramic powder were quantified via Inductively Coupled Plasma Optical Emission Spectroscopy. Biological tests were performed using equine adipose tissue mesenchymal stem cells (AMSCs). MTT assay demonstrated the cytocompatibility of the prepared material. AMSCs differentiation test showed that the glass ceramic favored the stem cell differentiation in adipogenic, chondrogenic, and osteogenic lineages, the last one being qualitatively more pronounced. The antimicrobial properties were evaluated against Escherichia coli, Enterococcus faecalis, Pseudomonas aeruginosa, Salmonella typhi, and Staphylococcus aureus bacteria strains and Candida albicans fungus. The inhibition of Gram-negative bacteria (S. tiphy, E. coli), Gram-positive (E. faecalis) and fungus (C. albicans) was detected, while the inhibition of P. aeruginosa and S. aureus was not significant.
CRIS-Team Scopus Importer:2021-02-19
Keywords: antimicrobial; bioactive glass; glass ceramic; manganese; osteogenic

A Dirty Story: Improving Colloidal Monolayer Formation by Understanding the Effect of Impurities at the Air/Water Interface - Rey, Marcel; Yu, Taotao; Guenther, Roman; Bley, Karina; Vogel, Nicolas (Langmuir, 2019)
Colloidal monolayers are important tools to fabricate surface structures at the nanoscale. A typical monolayer fabrication strategy involves the self-assembly of colloidal building blocks at liquid interfaces, which are subsequently deposited on a solid substrate. Even though this process is well established, the resulting order of the particles within the colloidal monolayer differs between batches of colloidal particles and can even change with the age of the dispersion. In this study, we investigate the origins of this variation of monolayer quality for polystyrene particles synthesized by surfactant-free emulsion polymerization. We correlate the interfacial behavior of the colloidal particles at the air/water interface on a Langmuir trough with the resulting quality of the monolayer after transfer to a solid substrate. We identify surface-active impurities as a major cause for a disturbed self-assembly of the colloidal particles. These impurities form during the particle synthesis and consist of copolymers of styrene, the comonomer acrylic acid, and sulfonate species from the initiator. We show that they can be removed by cleaning protocols to increase the monolayer quality. However, our experiments demonstrate that the impurities reappear over time even for cleaned dispersions, indicating desorption from the surface of the colloidal particles. We identify strategies to avoid the presence of the impurities at the air/water interface or to inhibit their effect on the self-assembly process. These simple guidelines improve the quality of the resulting colloidal monolayer, which is a prerequisite for the reliable fabrication of high-quality surface nanostructures from colloidal templates.
CRIS-Team Scopus Importer:2019-05-07

Adsorption isotherms and irreversible binding of proteins on commercially available hydrophobic adsorbents - Millitzer, Marcus; Wenzig, Edda; Peukert, Wolfgang (Chemical Engineering & Technology, 2005)
Quantitative data about the behavior of proteins in different downstream processing unit operations are needed. Adsorption isotherms that are usually used to design such process steps may not be sufficient as for protein binding there is to distinguish between an adsorbing and a desorbing branch of the isotherm, leading to different apparent adsorption coefcients for adsorption and desorption, respectively. It is demonstrated that two different proteins show simultaneously reversible as well as irreversible ”adsorption” in hydrophobic interaction protein chromatography and that the reversible and the irreversible part of the apparent ”adsorption” isotherm can be separated.
Keywords: Adsorption isotherm; Protein

Adsorption of CTAB on Sapphire- c at High pH: Surface and Zeta Potential Measurements Combined with Sum-Frequency and Second-Harmonic Generation. - Abdelmonem, Ahmed; Zhang, Yingchun; Braunschweig, Björn; Glikman, Dana; Rumpel, Armin; Peukert, Wolfgang; Begovic, Tajana; Liu, Xiandong; Lützenkirchen, Johannes (Langmuir, 2022)
The adsorption of cetyltrimethylammonium bromide (CTA+Br-) on sapphire-c surfaces was studied at pH 10 below the surfactants' critical micelle concentration. The evolution of interfacial potentials as a function of CTAB concentration was characterized by surface and zeta potential measurements and complemented by molecular dynamic (MD) simulations as well as by second-harmonic (SHG) and vibrational sum-frequency generation (SFG) spectroscopy. The changes in interfacial potentials suggest that the negative interfacial charge due to deprotonated surface aluminols groups is neutralized and can be even overcompensated by the presence of CTA+ cations at the interface. However, SFG intensities from strongly hydrogen-bonded interfacial water molecules as well as SHG intensities decrease with both increasing CTAB concentration and the magnitude of the surface potential. They do not suggest a charge reversal at the interface, while the change in zeta potential is actually consistent with an apparent charge inversion. This can be qualitatively explained by results from MD simulation, which reveal adsorbed CTA+ cations outside a first strongly bound hydration layer of water molecules, where they can locally distort the structural order and replace some of the interfacial water molecules adjacent to the first layer. This is proposed to be the origin for the significant loss in SFG and SHG intensities with increasing CTAB concentration. Moreover, we propose that CTA+ can act as a counterion and enhance the occurrence of deprotonated surface aluminols that is consistent with the decrease in surface potential.

Advanced Colloidal Sensors Enabled by an Out-of-Plane Lattice Resonance - Gupta, Vaibhav; Aftenieva, Olha; Probst, Patrick T.; Sarkar, Swagato; Steiner, Anja M.; Vogel, Nicolas; Fery, Andreas; Koenig, Tobias A. F. (Advanced Photonics Research, 2022)
The rational design and dispersion engineering of plasmonic colloid gratings are mainly responsible for advancing refractive index sensors. Herein, a 1D colloidal plasmonic lattice composed of nanoparticle dimer chains fabricated by a combination of interference lithography, soft molding, and colloidal self-assembly is studied. The bottom-up approach affords centimeter-scale arrays of high-quality colloidal nanoparticles with resonances in the visible range. Demonstrating a special case of collective plasmonic coupling called out-of-plane lattice resonance (OPLR) is focused on. Such OPLRs are excited, solely under oblique illumination with transverse magnetic polarization, and these findings with electromagnetic simulations are supported. In addition, it is experimentally found that such resonances are spectrally narrow with a linewidth of 8.08 +/- 0.6 nm and have a quality factor of 78.49 +/- 5.7, an enhancement by a factor of 11.62 compared with a single particle. The oblique incidence provides field enhancement outside the substrate plane, which is more accessible and sensitive to a surrounding analyte. A simple glycerol-water mixture as a model system to demonstrate this enhanced sensitivity and discuss the potential for a sensing application in an asymmetric refractive index environment is demonstrated. Beyond these sensing applications, this platform has the potential to enhance other processes, such as hot carrier injection or coherent energy transfer.
CRIS-Team WoS Importer:2023-05-05

Advanced Multiwavelength Detection in Analytical Ultracentrifugation - Pearson, Joseph; Walter, Johannes; Peukert, Wolfgang; Coelfen, Helmut (Analytical Chemistry, 2018)

Advanced processes for better materials-tape casting from nanoparticles - Peukert, Wolfgang; Knieke, Catharina; Vozdecky, Pavel; Roosen, Andreas (Chemie Ingenieur Technik, 2011)
It is shown by the example of a ceramic tape casting process, how advances in the field of process engineering lead to improved material properties. One great advance is the possibility of producing nanoparticles in stirred media mills. The nano-sized particle suspensions can be directly processed to ceramic tapes. The processing of nanoparticles requires specifically adjusted process conditions, but leads to a drastic improvement of the final product properties. Hence, dense and crack-free ceramic tapes with a higher mechanical strength, a lower surface roughness and a translucent character compared to tapes from micro-sized powders can be obtained. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Keywords: Ceramic tapes; Nano-milling; Stirred media mill

Advances in Colloidal Assembly: The Design of Structure and Hierarchy in Two and Three Dimensions - Vogel, Nicolas; Retsch, Markus; Fustin, Charles-Andre; Del Campo, Aranzazu; Jonas, Ulrich (Chemical Reviews, 2015)
No abstract available for this article

Aerosol synthesis of germanium nanoparticles supported by external seeding: Theoretical and experimental analysis - Wergen, Lukas; Domaschke, Maximilian; Herre, Patrick; Wu, Mingjian; Spiecker, Erdmann; Peukert, Wolfgang (Journal of Aerosol Science, 2019)

Aerosol synthesis of silicon nanoparticles with narrow size distribution-Part 1: Experimental investigations - Körmer, Richard; Jank, Michael; Ryssel, Heiner; Schmid, Hans-Joachim; Peukert, Wolfgang (Journal of Aerosol Science, 2010)
A study on the feasibility of aerosol processing of nearly monodisperse silicon nanoparticles via pyrolysis of monosilane in a hot wall reactor is presented. For optimal conditions silicon nanoparticles with a geometric standard deviation of 1.06 were synthesized at a production rate of 0.7 g/h. The size of the particles could be precisely controlled in the range of 20–40 nm, whilst maintaining a geometric standard deviation in the range of 1.06–1.08, by proper choice of the governing parameters temperature, residence time and precursor concentration. The results show that narrow particle size distributions can only be obtained in the temperature range between 900 and 1100 °C, as long as both the initial silane concentration (1 mbar silane partial pressure) and the reactor total pressure are low (25 mbar). This regime for the production of narrow particle size distributions has not been identified in prior work on the thermal decomposition of silane. Narrowly distributed particles can be obtained under conditions where nucleation and particle growth are separated and the agglomeration rates are negligible.

Aerosol synthesis of silicon nanoparticles with narrow size distribution-Part 2: Theoretical analysis of the formation mechanism - Körmer, Richard; Schmid, Hans-Joachim; Peukert, Wolfgang (Journal of Aerosol Science, 2010)
This work investigates the mechanisms which lead to the formation of silicon nanoparticles with narrow size distributions by means of population balance modeling. The model accounts for the full aerosol process, including chemical reaction, nucleation from supersaturated vapor, growth and agglomeration. The results are in good agreement with experimental data. The effects of the process parameters temperature, silane concentration and reactor total pressure are systematically investigated. The simulation allows an in-depth insight into the particle formation mechanism and reveals the key requirements which are necessary for the generation of narrow particle size distributions. In this mechanism, only a short nucleation burst occurs, while surface growth plays the dominant role in silane precursor consumption. A key role is attributed to condensation, because the numerical calculations can only reflect the experimental observations, if the condensation mechanism is included in the model.

A fast and improved tunable aggregation model for stochastic simulation of spray fluidized bed agglomeration - Singh, Abhinandan Kumar; Tsotsas, Evangelos (Energies, 2021)
Keywords: Polydisperse primary particles; Tunable aggregation model; Monte Carlo; Morphology; Agglomeration

Ageing mechanism of gold and silver nanorods in aqueous solution - Segets, Doris; Damm, Cornelia; Vieweg, Benito; Yang, Guang; Spiecker, Erdmann; Peukert, Wolfgang (Nanotechnology 2010: Advanced Materials, CNTs, Particles, Films and Composites - 2010 NSTI Nanotechnology Conference and Expo, NSTI-Nanotech 2010, 2010)
The current work addresses the understanding of the shape transformation of silver and gold nanorods towards more spherical nanostructures in aqueous suspension at ambient temperature. The shape transformation process was characterised using UV/Vis absorption spectroscopy, scanning electron microscopy (SEM), anodic stripping voltammetry and high resolution transmission electron microscopy (HRTEM). The increase in the particle number density during ageing indicates that the rods break spontaneously in smaller particles by surface defect induced ripening.
Keywords: Ageing; Gold nanorods; Optical characterization; Shape stability; Silver nanorods

A general approach for the characterization of fragmentation problems - Peukert, Wolfgang; Toneva, Petya Ivanova (Advanced Powder Technology, 2006)
A general approach for the quantitative and systematic characterization of fragmentation problems, which is based on the Weibull statistics, is presented. A model, initially developed for materials stressed under impact with respect to their breakage probability, has been successfully applied to the characterization of compressive comminution, fragmentation of nanoparticle agglomerates and destroying of adhesive bonds. The experimental results from the slow compression comminution and from the comminution by falling weight match for various materials and particle sizes exactly to the master curve deduced for impact comminution. However the material parameters determined for compression comminution are not identical for one and the same material to that determined by impact comminution. This indicates that the two model parameters are not pure material characteristics as assumed from the impact experiments but depend on the stress mechanism. The dependence of the fragmentation degree on the particle size and the energy input observed when impacting particles in the micrometer to millimetre range has been proven also for nanoparticle agglomerates. Furthermore a model analogical to that for breakage has been deduced for the quantification of the failure of adhesive bonds.
Keywords: Adhesion; Breakage probability; Fragmentation; Fragmentation degree; Modelling; Weibull statistics

A General Approach To Study the Thermodynamics of Ligand Adsorption to Colloidal Surfaces Demonstrated by Means of Catechols Binding to Zinc Oxide Quantum Dots - Lin, Wei; Walter, Johannes; Burger, Alexandra; Maid, Harald; Hirsch, Andreas; Peukert, Wolfgang; Segets, Doris (Chemistry of Materials, 2015)
A general strategy to study the thermodynamics of ligand adsorption to colloidal surfaces was established. The versatility of our approach is demonstrated by means of catechols binding to ZnO quantum dots (QDs). First, isothermal titration calorimetry (ITC) was used to extract all relevant thermodynamic parameters, namely association constant, enthalpy, entropy, and free energy of ligand binding. Noteworthy, the determined ΔG of −20.3 ± 0.4 kJ mol–1 indicates a strong, reproducible, and exothermic interaction between the catechol anchor group and the oxide particle surface. To confirm the characterization of ligand binding by measuring the heat of adsorption, the free energy was cross-validated by mass-based adsorption isotherms. A combination of inductively coupled plasma optical emission spectroscopy (ICP-OES) and UV/vis spectroscopy was developed to quantitatively determine the mass of bound catechols with respect to the available particle surface. The association constant K was determined by a Langmuir fit to be 2618 M–1 which leads to ΔG = −19.50 kJ mol–1 according to ΔG = −RTln K. To close the mass balance, analytical ultracentrifugation (AUC) was applied to detect the amount of the free, unbound catechol in solution. Finally, Raman spectroscopy and nuclear magnetic resonance spectroscopy (NMR) were performed to quantify the amount of remaining acetate from particle synthesis and to distinguish bound (chemisorbed) and unbound (physisorbed) catechol. Our results reveal that approximately 65 wt % of acetate is replaced, and physisorbed catechol will not affect the amount of remaining acetate on the ZnO surface. Moreover, no pronounced chemical shift peak as it would be expected for free catechol is observed by NMR at all. This indicates a highly dynamic adsorption–desorption equilibrium between the free and the physisorbed state of catechol on the particle surface. Our concept of combined analytics is seen to be a generally applicable strategy for particle-ligand interfacial studies. It gives detailed insight into thermodynamics, binding states, and ligand composition and is thus considered as an important step toward tailored colloidal surface properties.

Agglomeration and breakage of nanoparticles in stirred media mills - A comparison of different methods and models - Peukert, Wolfgang; Sommer, Marc; Stenger, Frank; Wagner, Norman (Chemical Engineering Science, 2006)
The increasing industrial demand for nanoparticles challenges the application of stirred media mills to grind in the sub-micron size range. It was shown recently [Mende et al., 2003. Mechanical production and stabilization of submicron particles in stirred media mills. Powder Technology 132, 64-73] that the grinding behavior of particles in the sub-micron size range in stirred media mills and the minimum achievable particle size is strongly influenced by the suspension stability and thus the agglomeration behavior of the suspension. Therefore, an appropriate modeling of the process must include a superposition of the two opposing processes in the mill i.e., breakage and agglomeration which can be done by means of population balance models. Modeling must now include the influence of colloidal surface forces and hydrodynamic forces on particle aggregation and breakup. The superposition of the population balance models for agglomeration and grinding with the appropriate kernels leads to a system of partial differential equations, which can be solved in various ways numerically. Here a modified h-p Galerkin algorithm which is implemented in the commercially available software package PARSIVAL developed by CiT (CiT GmbH, Rastede, Germany) and the moment methodology according to [Diemer and Olsen, 2002a. A moment methodology for coagulation and breakage problems: Part I - analytical solution of the steady-state population balance. Chemical Engineering Science 57 (12), 2193-2209; Diemer and Olsen, 2002b. A moment methodology for coagulation and breakage problems: Part II - moment models and distribution reconstruction. Chemical Engineering Science 57 (12), 2211-2288] are used and compared to explicit data on alumina. This includes a comparison of the derived particle size distributions, moments and its accuracy depending on the starting particle size distribution and the used agglomeration and breakage kernels. Finally, the computational effort of both methods in comparison to the prior mentioned parameters is evaluated in terms of practical application. © 2005 Elsevier Ltd. All rights reserved.
Keywords: Agglomeration; Breakage; Modeling; Population balance model; Stirred media mill; Suspensions

Agglomeration of Charged Nanopowders in Suspensions - Wirth, Karl-Ernst; Werth, Jochen; Linsenbühler, Markus; Dammer, S.M.; Farkas, Z.; Hinrichsen, H.; Wolf, D. E. (Powder Technology, 2003)
The aim of this work is to understand the agglomeration of charged powders suspended in nonpolar fluids. The concerted influence of electromagnetic, hydrodynamic and van der Waals forces as well as Brownian motion leads to a complex agglomeration behavior that depends on several parameters, e.g., the ratios of electric charges, particle sizes, temperatures and concentrations of the particles. Both experimental and theoretical considerations are presented. Hydrodynamic forces, especially the Brownian motion, effectively reduce the Coulomb repulsion. It is predicted that a suspension can only be stabilized at sufficiently low temperatures compared to the Coulomb barrier. Therefore, the aggregation of charged nanoparticles proceeds until a characteristic flake size is reached for which the effective Coulomb barrier equals the attraction forces and the suspension can be regarded as stable. The experimental verification of this result showed that the real agglomeration process starts with presintered aggregates - not primary particles - which agglomerate to larger flakes. © 2003 Elsevier B.V. All rights reserve
UnivIS-Import:2015-03-09:Pub.2003.tech.ITC.mechve.agglom
Keywords: Charged nanoparticles; Granular matter; Powders and suspensions

Agglomeration of Spray-Dried Milk Powder in a Spray Fluidized Bed: A Morphological Modeling - Singh, Abhinandan Kumar; Tsotsas, Evangelos (Processes, 2022)
The type of solid substrate plays a critical role in determining the kinetics of the spray fluidized bed (SFB) agglomeration process. In the case of porous (also soft) primary particles (PPs), droplet aging is due to imbibition and drying. The surface properties of the substrate also change due to imbibition. The focus of the present work is to simulate the agglomeration of the spray-dried milk powder using the Monte Carlo (MC) method coupled with a drying-imbibition model. In order to extract the morphology of the formed agglomerates, an aggregation model is employed. Further, this aggregation model is employed to predict the number of positions on the PPs (later agglomerates) for droplet deposition; previously, the ‘concept of positions’ was used. The transient growth of different milk powders (whole and skim) is depicted using the enhanced MC model. The enhancement in the droplet deposition model had a prominent influence on the overall kinetics of agglomeration. As expected, this enhanced MC model predicted that the agglomeration rate of skim milk powder is higher than that of whole milk powder.<br

Alkanethiols as inhibitors for the atmospheric corrosion of copper induced by formic acid: Effect of chain length - Hosseinpour, Saman; et al. (Journal of The Electrochemical Society, 2013)

Aluminum integral foam castings with microcellular cores by nano-functionalization - Hartmann, Johannes; Blümel, Christina; Ernst, Stefan; Fiegl, Tobias; Wirth, Karl-Ernst; Körner, Carolin (Journal of Materials Science, 2014)
The goal of the present work is the refinement of the pore morphology of aluminum integral foam castings. Integral foam molding, a modified high pressure die casting process, is used where a mixture of melt and blowing agent particles (magnesium hydride, MgH) is injected at high velocity into a permanent steel mold. At the mold surface, decomposition of the blowing agent and pore formation is suppressed due to the high solidification rate whereas solidification of the core is much slower allowing blowing agent decomposition, pore nucleation, and growth. Blowing agent particles not only act as gas suppliers but also represent pore nuclei. Thus, microcellular foam cores can be attained by increasing the number of MgH particles. But increasing the number of powder particles by powder milling strongly decreases the flowability and strong particle agglomeration as a result of the increasing cohesive forces leads to inhomogeneous foams. Flowability of the powder can be restored by coating it with SiO-nano-particles resulting in a homogeneous microcellular foam morphology. © 2013 Springer Science+Business Media New York.

A model-based precipitation study of copper-based catalysts - Peukert, Wolfgang; Hartig, Martin Andreas Johannes; Jacobsen, Nikolas; Leuthold, Alexander (AIChE Journal, 2015)
Numerical methods of particle technology are used to model the formation of catalyst precursors with the purpose to control disperse properties. A multicomponent and multiphase population balance model is applied to the precipitation of catalyst precursors in a T-mixer. Copper precursors are chosen to be investigated in detail as a basis for catalysts with a broad range of applications such as in methanol synthesis, water-gas shift and hydrogenation reactions. The simulations results could be validated by ex situ measurements such as the pH of the suspension, the solid dry weight of the precipitate, and the yield. Simulations show that dissociation reactions of copper and carbonate species in water control significantly the formation of Georgeite. Consumption of the copper component by solid formation can be controlled in a range of 20-100% by the adjustment of the pH of the copper nitrate reactant solution.
Keywords: Catalyst preparation; Methanol synthesis; Mixing; Population balance; Precursor chemistry

A model for the particle mass yield in the aerosol synthesis of ultrafine monometallic nanoparticles by spark ablation - Domaschke, Maximilian; Schmidt, Melanie; Peukert, Wolfgang (Journal of Aerosol Science, 2018)
Keywords: Nanoparticles; Scanning mobility particle sizer; Aerosol synthesis; Dimensional analysis; Spark ablation

Amphiphile-Induced Anisotropic Colloidal Self-Assembly - Rey, Marcel; Yu, Taotao; Bley, Karina; Landfester, Katharina; Buzza, D. Martin A.; Vogel, Nicolas (Langmuir, 2018)
Spherical colloidal particles typically self-assemble into hexagonal lattices when adsorbed at liquid interfaces. More complex assembly structures, including particle chains and phases with square symmetry, were theoretically predicted almost two decades ago for spherical particles interacting via a soft repulsive shoulder. Here, we demonstrate that such complex assembly phases can be experimentally realized with spherical colloidal particles assembled at the air/water interface in the presence of molecular amphiphiles. We investigate the interfacial behavior of colloidal particles in the presence of different amphiphiles on a Langmuir trough. We transfer the structures formed at the interface onto a solid substrate while continuously compressing, which enables us to correlate the prevailing assembly phase as a function of the available interfacial area. We observe that block copolymers with similarities to the chemical nature of the colloidal particles, as well as the surface-active protein bovine serum albumin, direct the colloidal particles into complex assembly phases, including chains and square arrangements. The observed structures are reproduced by minimum energy calculations of hard core–soft shoulder particles with experimentally realistic interaction parameters. From the agreement between experiments and theory, we hypothesize that the presence of the amphiphiles manipulates the interaction potential of the colloidal particles. The assembly of spherical colloidal particles into complex assembly phases on solid substrates opens new possibilities for surface patterning by enriching the library of possible structures available for colloidal lithograph

Amphiphilic invertible polyesters as reducing and stabilizing agents in the formation of metal nanoparticles - Kohut, Ananiy; Voronov, Andriy; Samaryk, Volodymyr; Peukert, Wolfgang (Macromolecular Rapid Communications, 2007)
Metal nanoparticles of various size and shape are prepared by the reduction of metal precursors in polymer micellar architectures (nanoreactors). The nanoreactors are developed from the amphiphilic invertible polyesters solved over a wide concentration range in solvents that strongly differ in polarity. In a non-polar medium, the micelle core contains hydrophilic [poly(ethylene oxide)] fragments, which acts as a reducing agent of metal ions. Nanoparticle stabilization occurs because of the presence of hydrophobic (polymethylene) fragments outside of the micelle structure. The size and shape of the nanoreactors may be altered by the polyester composition and molecular weight as well as by the solvent polarity and concentration of the amphiphilic polyester.
Keywords: amphiphilic polymers; invertibility; metals; nanoparticles; nanoreactors; synthesis

A multiwavelength emission detector for analytical ultracentrifugation - Wawra, Simon; Onishchukov, Georgy; Maranska, Maria; Eigler, Siegfried; Walter, Johannes; Peukert, Wolfgang (Nanoscale Advances, 2019)

An additive-free silicon anode in nanotube morphology as a model lithium ion battery material - Zhuo, Ying; Sun, Hong; Uddin, Md. Helal; Barr, Maissa; Wisser, Dorothea; Roßmann, Philip Kazys; Esper, Julian Duane; Tymek, Sarah; Döhler, Dirk; Peukert, Wolfgang; Hartmann, Martin; Bachmann, Julien (Electrochimica Acta, 2021)
Ordered arrays of parallel, cylindrical silicon nanotubes are obtained by aluminothermic reduction of SiO2 nanotubes generated by atomic layer deposition (ALD) on nanoporous aluminum oxide templates. The reduction to amorphous Si (a-Si) is characterized by a combination of X-ray diffraction (XRD), solid-state cross-polarization magic-angle spinning nuclear magnetic resonance (29Si CP-MAS NMR), ultraviolet-visible spectroscopy, attenuated total reflectance infrared spectroscopy (ATR-IR), and X-ray photoelectron spectroscopy (XPS). These a-Si nanotube arrays are electrochemically active in a lithium-ion battery environment when prepared on Cu current collectors without any additives. The absence of the traditional additive carbon black, which is an electrochemically inert conductor, increases the proportion of capacity associated with faradaic reactions (Li incorporation) with respect to the capacitive component. Electrochemical impedance spectroscopy (EIS) and charge-discharge tests demonstrate that the nanotube morphology yields an improved tolerance to fast cycling.
CRIS-Team Scopus Importer:2021-06-11
Keywords: Aluminothermic reduction; Anode material; Atomic layer deposition; Lithium ion battery; Si nanotube

Analogy Between the State Diagram of Segregated Vertical Gas-Solid Flows and the - Wirth, Karl-Ernst (Proceedings of 6.World Congress of Chemical Engineering, 2001)
UnivIS-Import:2015-04-16:Pub.2001.tech.ITC.mechve.analog
Keywords: segregation; gas; solid; flow

Analysis of bulk solids attrition in pneumatic conveying by distinguishing between process and material parameters - Peukert, Wolfgang; Frye, Lars (BHR Group Limited, 2004)
For the investigation of attrition, it is distinguished between process and material parameters. Therefore, attrition is regarded as a result of a process function determining the stress conditions the particles are subjected to and a material function summarizing the material specific response to these. The process function was determined by employing computational fluid dynamics (CFD) and by analyzing experimental results as well as discrete element simulations (DEM) carried out at Glasgow Caledonian University. The material function was determined by carrying out attrition experiments on varying scales and by measuring thermo-mechanical material properties with dynamic mechanical analysis (DMA).
Keywords: attrition; material; parameter; process; simulation

Analysis of optical absorbance spectra for the determination of ZnO nanoparticle size distribution, solubility, and surface energy - Segets, Doris; Gradl, Johannes; Klupp Taylor, Robin; Vassilev, Vassil; Peukert, Wolfgang (Acs Nano, 2009)
We present a model to calculate particle size distributions (PSDs) of colloidal ZnO nanoparticles from their absorbance spectra. Using literature values for the optical properties of bulk ZnO and correlating the measurement wavelengths in the UV−visible regime with distinct particle sizes by a tight binding model (TBM), an algorithm deconvolutes the absorbance spectra into contributions from size fractions. We find an excellent agreement between size distributions determined from TEM images and the calculated PSDs. For further validation, bimodal PSDs have been investigated and an approach to determine not only particle size but also solid concentration is introduced. We will show the applicability of our model by the determination of temperature-dependent ripening rates, which enables the calculation of solubilities, surface tensions, and the activation enthalpy of ripening. In principle, our methodology is applicable to different semiconductor nanoparticles in various solvents as long as their bulk properties are known and scattering is negligible.

Analysis of particle size distributions of quantum dots: From theory to application - Segets, Doris (KONA Powder and Particle Journal, 2016)
Small, quantum-confined semiconductor nanoparticles, known as quantum dots (QDs) are highly important material systems due to their unique optoelectronic properties and their pronounced structure-property relationships. QD applications are seen in the emerging fields of thin films and solar cells. In this review, different characterization techniques for particle size distributions (PSDs) will be summarized with special emphasis on strategies developed and suggested in the past to derive data on the dispersity of a sample from optical absorbance spectra. The latter use the assumption of superimposed individual optical contributions according to the relative abundance of different sizes of a colloidal dispersion. In the second part, the high potential of detailed PSD analysis to get deeper insights of typical QD processes such as classification by size selective precipitation (SSP) will be demonstrated. This is expected to lead to an improved understanding of colloidal surface properties which is of major importance for the development of assumption-free interaction models.
Keywords: Classification by size selective precipitation; Quantum dot; Particle size distribution; Structure-property relationship; Solubility parameters

Analysis of tribo-charging during powder spreading in selective laser sintering: Assessment of polyamide 12 powder ageing effects on charging behavior - Hesse, Nicolas; Dechet, Maximilian; Gomez Bonilla, Juan Sebastian; Lübbert, Christian; Roth, Stephan; Bück, Andreas; Schmidt, Jochen; Peukert, Wolfgang (Polymers, 2019)
Powder flowability is key to achieving high process stability and part quality by application of smooth and dense layers in selective laser sintering (SLS). This study sheds light on the rarely investigated effect of tribo-electric charge build-up during powder delivery in the SLS process. This is achieved by a novel approach to quantify electrostatic potentials during doctor blading. The presented model setup is used in combination with charge spectrometry and impedance spectroscopy to investigate the alterations in tribo-electric charging behavior for the most commonly used laser sintering material polyamide 12 in its virgin and aged, c.f. reused, states. We show that the electrostatic charge build-up is significantly enhanced for aged polymer powder material, likely contributing to altered performance in SLS processing.
CRIS-Team Scopus Importer:2019-05-28
Keywords: Additive manufacturing; Charge distribution; Electrostatics; Polyamide 12; Polymer ageing; Powder layer formation; Selective laser sintering; Surface potential; Tribo-charging

Analysis of ultrafine metal oxide particles in aerosols using mobility-resolved time-of-flight mass spectrometry - Domaschke, Maximilian; Lübbert, Christian; Peukert, Wolfgang (Journal of Aerosol Science, 2019)
In this work we present a powerful method to gain insight into the formation of inorganic nanoparticles from the gas phase by combining a high-resolution differential mobility analyzer with a time-of-flight mass spectrometer. Exemplary particles are generated by glowing-wire evaporation from tungsten, tantalum, rhenium, niobium and molybdenum and transferred via a new custom-made interface to the mobility classifier that is directly attached to the mass spectrometer. With only minor fragmentation occurring, clusters that represent early stages of particle formation from the gas phase can be detected. Regardless of the inert experimental conditions, only oxides were found for all tested precursor metals. Comparing the recorded mass-mobility data with theoretical predictions from a modified Mason-Schamp equation shows that produced materials possess densities smaller than those of the respective bulk materials. The maximum observed particle sizes were about 2 nm.
CRIS-Team Scopus Importer:2019-08-27
Keywords: Differential mobility analyzer; Glowing-wire evaporation; Multidimensional characterization; Nanoparticles; Time-of-flight mass spectrometry

Analytical Techniques for Corrosion-Related Characterization of Graphene and Graphene-Based Nanocomposite Coatings - Hosseinpour, Saman; Davoodi, Ali; Sedighi, Arash; Tofighi, Faeze (Corrosion Protection of Metals and Alloys Using Graphene and Biopolymer Based Nanocomposites, 2021)
The main aim of the present chapter is to review the various analytical and characterization tools which have been used recently to study graphene (G) and graphene-based nanocomposites, as corrosion protection layers and coatings, at macro-, micro-, and nano-scale. These methods include microscopy, spectroscopy, thermal stability evaluations and electrochemical tests. Most recent developments and achievements on each method are presented, including some detailed information about the techniques and experimental conditions in which they have been utilized. Examples of the application of imaging techniques, including scanning electron microscopy (SEM) and transmission electron microscopy (TEM) in the detection of microstructure of graphene-based composite coatings are provided. Applications of atomic force microscopy (AFM) in the assessment of the surface roughness and topography of graphene-based nanocomposite coatings are demonstrated. Concerning the spectroscopic methods, X-ray diffraction spectroscopy (XRD), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared reflection (FTIR) spectroscopy, Raman spectroscopy and confocal Raman microscopy (CRM) are discussed. Application of electrochemical techniques such as electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) tests in determining the corrosion protection efficiency is reviewed. Other corrosion assessment techniques, such as weight loss measurements and salt spray tests, are also briefly addressed. The chapter ends with some concluding remarks regarding the benefits and limitations of each technique, to provide a guide in choosing the appropriate set of complementary techniques for characterization of graphene-based coatings and their corrosion protection performanc

A Nanoparticle in a Nanoscale Volume of Solvent: Thermodynamic and Kinetic Considerations - Vogelsberger, Wolfram; Schmidt, Jochen (Journal of Physical Chemistry C, 2008)
The dissolution behavior of a nanoparticle in a nanoscale volume of solvent was theoretically investigated, using the Gibbs free energy calculation of the system nanoparticle-dissolved material - solvent, as a function of the size of the particle. The chemical nature of the particle is characterized by its surface tension in the solvent and the saturation concentration of the bulk material of the particle-forming species. The influence of both properties on the dissolution behavior was investigated, and the influence of the particle size and the size of the solvent volume was duly considered. The system nanoparticle-dissolved material-solvent is defined, therefore, by four properties. These include the number of molecules of the particle-forming species, the number of solvent molecules, surface tension of the interface particle-solution, and the saturation concentration of the particle-forming species bulk material. Depending on the numerical values of these quantities, a system can exhibit both a critical state (maximum value of Gibbs free energy) and a stable state (minimum value of Gibbs free energy). The dissolution process is finished at the minimum value. It is always possible to discover a system where the minimum and maximum values coincide for a given set of these four properties. These systems are known as first stable states. The first stable states separate regions where the initial particle can form a stable system, nanoparticle -dissolved material-solvent, by dissolution and regions where the nanoparticle dissolves completely. Concentrations of the dissolved material that overcome the equilibrium solubility of the bulk material by several orders of magnitude are possible. The small systems, even with such high concentrations as these, are stable. The results obtained have been confirmed experimentally in relation to multiparticle systems. They are of particular significance when one applies them to the synthesis of nanoscale materials and the valuation of possible toxicity of nanoscale particles.

An effective dialysis method for surface funtionalization of nanoparticles in liquid phase - Sample: Porphyrine derivatives @ ZnO-Nanorods - Klaumünzer, Martin; Münzel, C.; Burger, Alexandra; Mackovic, Mirza; Voigt, Michael; Spiecker, Erdmann; Hirsch, Andreas; Peukert, Wolfgang (Nanotechnology 2013: Advanced Materials, CNTs, Particles, Films and Composites - 2013 NSTI Nanotechnology Conference and Expo, NSTI-Nanotech 2013, 2013)
In order to optimize electron transfer and optoelectronic properties in nanoparticulate thin films for electronics we show the surface functionalization of ZnO nanorods by exchanging the stabilizing 2-[2-(2-Mefhoxyefhoxy)-ethoxy] acetic acid at the ZnO surface with redoxactive organic molecules. Surface functionalization is undertaken by an efficient dialysis method. Emission- and absorption-spectroscopy indicate an effective electronic interaction between the ZnO nanorods and the pophyrine derivatives. In addition, we discuss on the binding mechanism and the ligand exchange kinetics of the porphyrine molecules. Our experiments suggest a better and faster binding to the ZnO nanorod surface for porphyrine A than for porphyrine B. This can be explained by steric effects. Moreover we claim a fourfold anchored binding for porphyrine A and we shed light on entropic effects during ligand exchange.

An effective way to stabilize colloidal particles dispersed in polar and nonpolar media - Peukert, Wolfgang; Kohut, Ananiy; Voronov, Andriy (Langmuir, 2006)
This article 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 TiO has been functionalized with the aid of toluene diisocyanate (TDI) as a coupling agent. In the second step, the chains of amphiphilic oligoester have been covalently grafted to the titanium dioxide surface functionalized with isocyanate groups. It is shown that the titania modified in this way can form stable suspensions in both polar (water) and nonpolar (toluene) media. Multiple redispersion cycles show the ability of the modified titanium dioxide particles, after their removal from one type of dispersion and consequent drying, to be redispersed in dispersing media strongly differing by polarity from the previous. © 2007 American Chemical Society.
Keywords: polymer; particle; coating; self-adjustible; functional

A new approach for the stabilization of amorphous drug nanoparticles during continuous antisolvent precipitation - Trzenschiok, Holger; Distaso, Monica; Peukert, Wolfgang (Chemical Engineering Journal, 2019)
In this study a stabilization approach for the bottom-up production of drug nanoparticles was established and demonstrated for four commonly used drugs. The nanoparticles were produced by liquid antisolvent precipitation utilizing in-house build static mixers. The influence of the mixing conditions on the final particle size distributions was studied by variation of the energy input during precipitation. Multivalent cations of a non-toxic metal can be used to achieve superior electrostatic stabilization of the precipitated nanoparticles. For zirconium salts used as stabilizers in particular, the dependency of the resulting particle size on the pH and the salt concentration in the antisolvent was investigated. Remarkably, our approach allows the continuous production of drug nanoparticles down to a few 10 nm in diameter. A simple method to analyze the particle composition based on FTIR spectra is proposed and verified by thermogravimetric analysis. The amorphous character of the obtained particles was verified using X-ray diffraction and differential scanning calorimetry. To further demonstrate the broad applicability of our approach the solvent was varied and the stabilization applied to a different formation mechanism.
CRIS-Team Scopus Importer:2019-09-20
Keywords: Amorphous nanoparticles; Antisolvent precipitation; Ibuprofen; Micromixer; Poorly soluble drug; Stabilization

A new method to determine the synergistic effects of area ratio and microstructure on the galvanic corrosion of LAS A508/309 L/308 L SS dissimilar metals weld - Okonkwo, Bright O.; Ming, Hongliang; Wang, Jianqiu; Han, En Hou; Rahimi, Ehsan; Davoodi, Ali; Hosseinpour, Saman (Journal of Materials Science & Technology, 2021)
The synergistic effects of area ratio and microstructure on the galvanic corrosion of A508/309 L/308 L dissimilar metals weld (DMW) are studied by a multi-analytical approach. It was demonstrated that decreasing the anode/cathode surface area ratio obviously enhances the corrosion rate of A508, both locally and globally. Deeper analyses of the AFM results enabled quantitative comparison of the corrosion behaviour of the different surface constituents. It was revealed that in the galvanic interaction of the DMW, the grain refined region corrodes most, followed by the partial grain refined region and base metal matrix of the A508, respectively. The electrochemical localization index (LI) estimation method and AFM analysis both confirmed the presence of a mixed (localized and uniform) corrosion phenomenon occurring on the surface of the A508 anode metal in the galvanic interaction of the dissimilar metals. Finally, the degree of synergism equation was utilized to describe the synergistic effects of anode/cathode area ratio and the microstructure of the samples on the galvanic corrosion of LAS A508/309L/308L SS DMW.
CRIS-Team Scopus Importer:2020-12-11
Keywords: AFM; Galvanic corrosion; Inclusion; Low alloy steel; SEM; Stainless steel

An experimental study of ultrafiltration for sub-10nm quantum dots and sub-150 nm nanoparticles through PTFE membrane and Nuclepore filters - Peukert, Wolfgang; Segets, Doris; Chen, Sheng-Chieh; Ling, Tsz-Yan; Pui, David (Journal of Membrane Science, 2016)
Ultrafiltration techniques (pore size of membrane below 100nm) are widely used in chemical engineering, semiconductor, pharmaceutical, food and beverage industries. However, for small particles, which are more and more attracting interests, the pore size often does not correlate well with sieving characteristics of the ultra-membranes. This may cause serious issues during modeling and prediction of retention efficiencies. Herein, a series of liquid filtration experiments with unfavorable conditions were performed. PTFE membranes (50, 100nm) and Nuclepore filters (50, 400nm) were challenged with 1.7nm manganese doped ZnS and 6.6 nm ZnO quantum dots (QDs), 12.4, 34.4 and 50 nm Au and 150 nm SiO nanoparticles. For larger and medium sized particles, sieving and eventually pore blockage phenomena were observed. In comparison, for small QDs, a high initial retention efficiency (>0.4) in both filters was monitored, followed by a reduced efficiency with ongoing particle loading. This high initial retention of small nanoparticles was attributed to diffusion deposition rather than to sieving since the ratio of pore size to particle size was significantly high (up to 58). Our experimental results allow a basic understanding of the deposition mechanism of small nanoparticles (diffusion vs. sieving) in different filter structures.
Keywords: Diffusion deposition; Loading effect; Quantum dot; Surface interactions; Ultrafiltration

Angle-resolved second-harmonic light scattering of colloidal interfaces - Peukert, Wolfgang; Braunschweig, Björn; Sauerbeck, Christian (Proceedings of a meeting held 3-8 November 2013, San Francisco, California, USA. Core Programming Area at the 2013 AIChE Annual Meeting: Global Challenges for Engineering a Sustainable Future, 2013)

An improved generalized AMBER force field (GAFF) for urea - Özpinar, Gül; Peukert, Wolfgang; Clark, Timothy (Journal of Molecular Modeling, 2010)
We describe an improved force field parameter set for the generalized AMBER force field (GAFF) for urea. Quantum chemical computations were used to obtain geometrical and energetic parameters of urea dimers and larger oligomers using AM1 semiempirical MO theory, density functional theory at the B3LYP/6-31G(d,p) level, MP2 and CCSD ab initio calculations with the 6-311++G (d,p), aug-cc-pVDZ, aug-cc-pVTZ, and aug-cc-pVQZ basis sets, and with the CBS-QB3 and CBS-APNO complete basis set methods. Seven different urea dimer structures were optimized at the MP2/aug-cc-pVDZ level to obtain accurate interaction energies. Atomic partial charges were calculated at the MP2/aug-cc-pVDZ level with the restrained electrostatic potential (RESP) fitting approach. The interaction energies computed with these new RESP charges in the force field are consistent with those obtained from CCSD and MP2 calculations. The linear dimer structure calculated using the force field with modified geometrical parameters and the new RESP charge set agrees well with available experimental data.

An in situ study to shed light on the formation of goethite spindles by pseudomorphic transformation of intermediate phases - Michaud, Mark; Peukert, Wolfgang; Distaso, Monica (Powder Technology, 2023)
Size and shape control of nanoparticles is fundamental to tune their material properties and to identify structure property functions. Herein, the shape of goethite (α-FeOOH) particles is varied from needle to spindle upon sodium carbonate modulation. Our in-depth study sheds light on the formation path of goethite particles by in situ monitoring the pH, the dissolved oxygen concentration and Raman spectroscopy in the presence and in the absence of sodium carbonate. The pH evolution indicates two distinct plateaus, at 7–6.5, and 6–6.3, respectively: the time when the dissolved oxygen concentration vanishes is correlated with the time required to oxidize Fe(II) to Fe(III). Raman spectroscopy enabled the identification of the intermediate phases green rust at 500 cm−1 and siderite at 1080 cm−1. Their formation and depletion was correlated with the kinetics of goethite formation. The evolution of the olation reaction is monitored through the bending vibration of water at 1640 cm−1. Finally, goethite particles are characterized ex situ via X-ray diffraction to assess the crystalline phase, scanning electron microscopy (SEM) for evaluating the size and shape of particles and transmission electron microscopy (TEM) for the analysis of the three-dimensional arrangement of self-assembled layers. The evaluation of reflectance spectra with CIELAB color metrics show that goethite spindles have enhanced color properties in comparison to the needle-shaped particles.
CRIS-Team Scopus Importer:2023-06-23
Keywords: Nanoparticles; Precipitation; Raman spectroscopy; Shape-control; Structure property relationship

Anisometric engineering of particle interfaces: Multidimensional characterization and gram‐scale production - Klupp Taylor, Robin; Meincke, Thomas; Sadafi, Fabrizio-Zagros; Walter, Johannes; Pflug, Lukas; Watanabe, Shun; Peukert, Wolfgang; Stingl, Michael (Chemie Ingenieur Technik (Special Issue: ProcessNet‐Jahrestagung und 33. DECHEMA‐Jahrestagung der Biotechnologen 2018), 2018)
A simple continuous-flow liquid-phase approach for the partial coating of nanoscale particles with metal was established [1]. Unique to this is the surface conformal and morphology-tailored growth of the metal. Due to their anisotropic surface character, the resulting materials are potentially relevant as particulate surfactants or for the assembly of novel photonic, catalytic or theranostic materials. In this contribution, three significant challenges are described that have recently been tackled. Firstly, it is shown how the use of a KM type micromixer with very short characteristic mixing times facilitates the understanding of the metal coating growth process. Secondly, the application of multiwavelength analytical ultracentrifugation for the determination of yield, coating thickness, and coverage distribution of the metal patches is considered. The validity of the measurements through microscopy and spectroscopy is confirmed and it is demonstrated how this characterization method can be employed to support process design. Finally, it is illustrated how the continuous flow approach can be developed in order to produce anisotropic metal-coated particles on the gram scale, and a first analysis of the novel optical properties of the powders is provided. [1] T. Meincke, H. Bao, L. Pflug, M. Stingl, R. N. Klupp Taylor, Chem. Eng. J. 2016, 308, 89. DOI: https://doi.org/10.1016/j.cej.2016.09.0

Anisotropic Self-Assembly from Isotropic Colloidal Building Blocks - Rey, Marcel; Law, Adam D.; Buzza, D. Martin A.; Vogel, Nicolas (Journal of the American Chemical Society, 2017)

Anisotropic silicon nanowire arrays fabricated by colloidal lithography - Rey, Marcel; Wendisch, Fedja J.; Görlitzer, Eric; Tang, Julia; Bader, Romina; Bourret, Gilles Remi; Vogel, Nicolas (Nanoscale Advances, 2021)
The combination of metal-assisted chemical etching (MACE) and colloidal lithography allows for the affordable, large-scale and high-throughput synthesis of silicon nanowire (SiNW) arrays. However, many geometric parameters of these arrays are coupled and cannot be addressed individually using colloidal lithography. Despite recent advancements towards higher flexibility, SiNWs fabricated via colloidal lithography and MACE usually have circular, isotropic cross-sections inherited from the spherical templates. Here we report a facile technique to synthesize anisotropic SiNWs with tunable cross-sections via colloidal lithography and MACE. Metal films with an elliptical nanohole array can form from shadows of colloidal particles during thermal evaporation of the metal at tilted angles. The aspect ratio of these anisotropic holes can be conveniently controlled via the deposition angle. Consecutive MACE using these patterned substrates with or without prior removal of the templating spheres results in arrays of anisotropic SiNWs with either elliptical or crescent-shaped cross-sections, respectively. As a consequence of the anisotropy, long SiNWs with elliptical cross-sections preferentially collapse along their short axis, leading to a controlled bundling process and the creation of anisotropic surface topographies. These results demonstrate that a rich library of SiNW shapes and mesostructures can be prepared using simple spherical colloidal particles as masks.
CRIS-Team WoS Importer:2021-05-28
Keywords: Hierarchical structures; Wettability; Absorption; Interfaces; Monolayers; Microgels; Diameter; Size

Anodic Titanium Dioxide Nanotubes for Magnetically Guided Therapeutic Delivery - Hasanzadeh Kafshgari, Morteza; Kah, Delf-Thorge Eric; Mazare, Anca Valentina; Nguyen, Nhat Truong; Distaso, Monica; Peukert, Wolfgang; Goldmann, Wolfgang; Schmuki, Patrik; Fabry, Ben (Scientific Reports, 2019)
Hollow titanium dioxide (TiO2) nanotubes offer substantially higher drug loading capacity and slower drug release kinetics compared to solid drug nanocarriers of comparable size. In this report, we load TiO2 nanotubes with iron oxide nanoparticles to facilitate site-specific magnetic guidance and drug delivery. We generate magnetic TiO2 nanotubes (TiO2NTs) by incorporating a ferrofluid containing Ø ≈ 10 nm iron oxide nanoparticles in planar sheets of weakly connected TiO2 nanotubes. After thermal annealing, the magnetic tubular arrays are loaded with therapeutic drugs and then sonicated to separate the nanotubes. We demonstrate that magnetic TiO2NTs are non-toxic for HeLa cells at therapeutic concentrations (≤200 µg/mL). Adhesion and endocytosis of magnetic nanotubes to a layer of HeLa cells are increased in the presence of a magnetic gradient field. As a proof-of-concept, we load the nanotubes with the topoisomerase inhibitor camptothecin and achieve a 90% killing efficiency. We also load the nanotubes with oligonucleotides for cell transfection and achieve 100% cellular uptake efficiency. Our results demonstrate the potential of magnetic TiO2NTs for a wide range of biomedical applications, including site-specific delivery of therapeutic drugs.
CRIS-Team Scopus Importer:2019-09-27

A novel apparatus for in situ compression of submicron structures and particles in a high resolution SEM - Romeis, Stefan; Paul, Jonas; Ziener, Marc; Peukert, Wolfgang (Review of Scientific Instruments, 2012)
We report on the development and characterization of a novel in situ manipulation device to perform stressing experiments on the submicron scale inside a high resolution field emission scanning electron microscope. The instrument comprises two main assembly groups: an upper part for positioning and moving a mounted probe and a force sensor as well as a specimen support as lower part. The upper part consists of a closed loop tripod piezoelectric scanner mounted on a self-locking coarse positioning stage. Two interlocked steel springs and a linear variable differential transformer measuring the springs’ deflections compose the lower part of the instrument. This arrangement acts as force-sensor and sample support. In comparison to already well-established concepts a wide measuring range is covered by adjusting the spring constant between 30 N/m and 50000 N/m. Moreover, the new device offers striking advantages with respect to force calibration and sample deformation measurements. Force calibration is performed using the eigenfrequency of the force detection system directly inside the SEM. Deformation data are obtained with high accuracy by simultaneously recording displacements above and below the specimen. The detrimental apparatus compliance is determined, and the influence on measured data subsequently minimized: an easy to validate two-springs-in-series model is used for data correction. A force resolution in normal direction of 100 nN accompanied by a sample deformation resolution of 5 nm can be achieved with the instrument using an appropriate load cell stiffness. The capabilities and versatility of this instrument are exemplified by compression experiments performed on submicron amorphous silica particles.

A novel approach for preparation and in situ tensile testing of silica glass membranes in the TEM - Mackovic, Mirza; Przybilla, Thomas; Dieker, Christel; Herre, Patrick; Romeis, Stefan; Stara, Hana; Schrenker, Nadine; Peukert, Wolfgang; Spiecker, Erdmann (Frontiers in Materials, 2017)
The mechanical behavior of glasses in the micro- and/or nanometer regime increasingly gains importance in nowadays modern technology. However, suitable small scale preparation and mechanical testing approaches for a reliable assessment of the mechanical properties of glasses still remain a big challenge. In the present work, a novel approach for site-specific preparation and quantitative in situ tensile testing of thin silica glass membranes in the transmission electron microscope is presented. Thereby, advanced focused ion beam techniques are used for the preparation of nanoscale dog bone shaped silica glass specimens suitable for in situ tensile testing. Small amounts of gallium are detected on the surface of the membranes resulting from redeposition effects during the focused ion beam preparation procedure. Possible structural changes of silica glass upon irradiation with electrons and gallium ions are investigated by controlled irradiation experiments, followed by a structural analysis using Raman spectroscopy. While moderate electron beam irradiation does not alter the structure of silica glass, ion beam irradiation results in minor densification of the silica glass membranes. In situ tensile testing of membranes under electron beam irradiation results in distinctive elongations without fracture confirming the phenomenon of superplasticity. In contrast, in situ tensile testing in the absence of the electron beam reveals an elastic/plastic deformation behavior, and finally leads to fracture of the membranes. The Young’s moduli of the glass membranes pulled at beam off conditions in the TEM are comparable with values known for bulk fused silica, while the tensile strength is in the range of values reported for silica glass fibers with comparable dimensions. The impact of electron beam irradiation on the mechanical properties of silica glass membranes is further discussed. The results of the present work open new avenues for dedicated preparation and nanomechanical characterization of silica glasses, and further contribute to a fundamental understanding of the mechanical behavior of such glasses when being scaled down to the nanometer regim
Keywords: Silica glass; in situ TEM; in situ nanomechanical testing; Mechanical Properties; Electron beam irradiation; superplasticity; FIB; Raman spectroscopy

A novel, precipitated polybutylene terephthalate feedstock material for powder bed fusion of polymers (PBF): Material development and initial PBF processability - Dechet, Maximilian; Gomez Bonilla, Juan Sebastian; Grünewald, Moritz; Popp, Kevin; Rudloff, Johannes; Lang, Marieluise; Schmidt, Jochen (Materials & Design, 2021)
The development of a novel polybutylene terephthalate (PBT) feedstock material for powder bed fusion of polymers with laser beam (PBF-LB/P) by means of liquid-liquid phase separation (LLPS) and precipitation is outlined. Appropriate solvents for precipitation have been identified by a screening approach based on solubility parameters. Feasible system compositions, and solution and cloud point temperatures were determined. For the most promising solvent cyclopentanone, a parameter study on the influence of stirring conditions during precipitation was performed. The obtained products were characterized with respect to their particle size distribution, particle shape, phase morphology, thermal properties and melt viscosity. Under optimized process conditions, PBT particles of high degree of crystallinity with narrow size distribution and a mean diameter of 36 μm were obtained; flowability was improved by dry coating. The initial PBF-LB/P processability was assessed by building single layers in a parameter study using a Formiga P110 machine. Dense single layers were obtained at laser power PL = 11.5 W, scanning speed vS = 4000 mm/s, hatch distance hS = 0.24 mm and layer thickness dS = 0.1 mm. Best to the authors' knowledge, this is the first study in the open literature reporting on a PBT feedstock material obtained by liquid-liquid phase separation and crystallizatio
Keywords: Polybutylene terephthalate (PBT); Powder bed fusion (PBF); Liquid-liquid phase separation (LLPS); Powder characterization; Spreadability; Processability

A novel process chain for the production of spherical sls polymer powders with good flowability - Schmidt, Jochen; Sachs, Marius; Blümel, Christina; Winzer, Bettina; Toni, Franziska; Wirth, Karl-Ernst; Peukert, Wolfgang (Proceedings of the 7th World Congress on Particle Technology, WCPT 2014, 2015)
Rapid prototyping has been applied so far in the production of special parts at low piece numbers. Currently, rapid prototyping gradually is transferred to additive manufacturing opening new applications. Especially selective laser sintering (SLS) applying polymer powder systems is promising. In the case of SLS basically only polyamide is available as an optimized powder material showing satisfying behavior during processing. Other types of polymer powders produced by cryogenic grinding show poor powder flowability as well as an unfavorable particle habitus resulting in poor device quality. In fact, it is challenging to produce laser sintering powders with small particle size, good flowability and processability. Within this account we present a novel process route for the production of spherical polymer micron-sized particles of good flowability. The feasibility of the process chain is demonstrated for polystyrene (PS) and poly butylene terephthalate (PBT) and the increase of powder flowability after the consecutive process steps has been monitored using a tensile strength tester. The influence of particle habitus and surface functionalization on powder flowability and its properties is discussed. In a first step polymer microparticles are produced by a wet grinding method at reduced temperatures. By this approach the mean particle size and the particle size distribution can be tuned between a few microns and several 10 microns and adapted to specific needs. The dependencies of mean product particle size, particle size distribution and grinding kinetics on stressing conditions, system composition and especially process temperature (increase of the brittleness of the polymer vs. increase of dampening of grinding bead motion with decreasing temperature) will be extensively discussed for the polymers PS, PBT, poly oxo methylene (POM) and Poly ether ether ketone (PEEK). The comminution products obtained typically consist of microparticles of irregular shape and poor powder flowability, i.e. these intermediate products are cohesive and thus will show poor SLS processability. An improvement of flowability of the ground polymer particles is achieved in a second step by changing their shape. The irregular particles are rounded using a heated downer reactor. It will be demonstrated that the 'degree' of rounding can be controlled by changing the temperature profile or the residence time. To further improve the flowability of the cohesive spherical polymer microparticles nanoparticles are adhered to the microparticles' surface in a third step. The improvement of powder flowability after the consecutive process steps is remarkable: rounded and dry-coated PS powders exhibit a strongly reduced tensile strength (by a factor 5) in comparison to the tensile strength of the edged PS comminution product. The improved flowability and packing behavior of the polymer powders open new options in SLS processing including the usage of much smaller polymer bead
Keywords: downer reactor; dry particle coating; polymers; selective laser sintering; wet grinding

A novel process for production of spherical PBT powders and their processing behavior during laser beam melting - Schmidt, Jochen; Sachs, Marius; Zhao, Meng; Fanselow, Stephanie; Wudy, Katrin; Drexler, Maximilian; Drummer, Dietmar; Wirth, Karl-Ernst; Peukert, Wolfgang (31st International Conference of the POLYMER PROCESSING SOCIETY, 2016)
Additive manufacturing processes like laser beam melting of polymers are established for production of prototypes and individualized parts. The transfer to other areas of application and to serial production is currently hindered by the limited availability of polymer powders with good processability. Within this contribution a novel process route for the production of spherical polymer micron-sized particles of good flowability has been established and applied to produce polybutylene terephthalate (PBT) powders. Moreover, the applicability of the PBT powders in selective laser beam melting and the dependencies of process parameters on device properties will be outlined. First, polymer micro particles are produced by a novel wet grinding method. To improve the flowability the produced particles the particle shape is optimized by rounding in a heated downer reactor. A further improvement of flowability of the cohesive spherical PBT particles is realized by dry coating. An improvement of flowability by a factor of about 5 is achieved by subsequent rounding of the comminution product and dry-coating as proven by tensile strength measurements of the powders. The produced PBT powders were characterized with respect to their processability. Therefore thermal, rheological, optical and bulk properties were analyzed. Based on these investigations a range of processing parameters was derived. Parameter studies on thin layers, produced in a selective laser melting system, were conducted. Hence appropriate parameters for processing the PBT powders by laser beam melting, like building chamber temperature, scan speed and laser power have been identified.
Keywords: downer reactor; dry coating; polybutylene terephthalate (PBT); selective laser beam melting of polymers; wet grinding

A novel process route for the production of spherical LBM polymer powders with small size and good flowability - Schmidt, Jochen; Sachs, Marius; Blümel, Christina; Winzer, Bettina; Toni, Franziska; Wirth, Karl-Ernst; Peukert, Wolfgang (Powder Technology, 2014)
Rapid prototyping has been applied so far in the production of special parts at low piece numbers. Currently, 'rapid prototyping' gradually is transferred to additive manufacturing opening new applications. At present basically only polyamide (PA) is available as an optimized powder material showing satisfying behavior during processing in laser beam melting (LBM). Other types of polymer powders produced by cryogenic grinding show poor powder flowability as well as an unfavorable particle habitus resulting in poor device quality. In fact, it is challenging to produce laser sintering powders with small particle size, good flowability and processability. We present a novel process chain for the production of spherical polymer micron-sized particles of good flowability that can be applied to a large variety of polymers: in a first step polymer particles are produced by a wet grinding method that are rounded in a second step using a heated downer reactor. To increase the flowability of the cohesive spherical polymer particles further nanoparticles are adhered to the particle surface in the third step. We demonstrate an increase of powder flowability by a factor of 5. The influence of particle habitus and nanoparticle functionalization on powder flowability is discussed in detail. © 2014 Elsevier B.V.
Keywords: Downer reactor; Dry particle coating; Flowability; Laser beam melting (LBM); Polymers; Wet grinding

A novel process route for the production of spherical SLS polymer powders - Schmidt, Jochen; Sachs, Marius; Blümel, Christina; Winzer, Bettina; Toni, Franziska; Wirth, Karl-Ernst; Peukert, Wolfgang (Proceedings of PPS-30 : the 30th International Conference of the Polymer Processing Society : conference papers : 6-12 June 2014, Cleveland, Ohio, USA, 2015)
Currently, rapid prototyping gradually is transferred to additive manufacturing opening new applications. Especially selective laser sintering (SLS) is promising. One drawback is the limited choice of polymer materials available as optimized powders. Powders produced by cryogenic grinding show poor powder flowability resulting in poor device quality. Within this account we present a novel proceb route for the production of spherical polymer micron-sized particles of good flowability. The feasibility of the proceb chain is demonstrated for polystyrene e. In a first step polymer microparticles are produced by a wet grinding method. By this approach the mean particle size and the particle size distribution can be tuned between a few microns and several 10 microns. The applicability of this method will be discubed for different polymers and the dependencies of product particle size distribution on strebing conditions and proceb temperature will be outlined. The comminution products consist of microparticles of irregular shape and poor powder flowability. An improvement of flowability of the ground particles is achieved by changing their shape: they are rounded using a heated downer reactor. The influence of temperature profile and residence time on the product properties will be addrebed applying a viscous-flow sintering model. To further improve the flowability of the cohesive spherical polymer particles nanoparticles are adhered onto the microparticles' surface. The improvement of flowability is remarkable: rounded and dry-coated powders exhibit a strongly reduced tensile strength as compared to the comminution product. The improved polymer powders obtained by the proceb route proposed open new pobibilities in SLS procebing including the usage of much smaller polymer bead
Keywords: Downer reactor; Poly butylene terephthalate (PBT); Poly oxo methylene (POM); Polystyrene (PS); Rounding; Selective laser sintering (SLS); Wet grinding; rounding

A population balance model of quantum dot formation: Oriented growth and ripening of ZnO - Segets, Doris; Hartig, Martin Andreas Johannes; Gradl, Johannes; Peukert, Wolfgang (Chemical Engineering Science, 2012)
The precipitation of zinc oxide (ZnO) semiconductor quantum dots was investigated throughout the whole particle formation process, namely reaction, nucleation, growth and ripening and described by means of population balance equations (PBE). Regarding nucleation, the simulation revealed that the mechanism for the solid formation is by orders of magnitude lower than predicted by classical homogeneous nucleation theory. Thus, the earliest stages of particle formation were described by a combination of reaction kinetics determined by experiments for the formation of preformed clusters and subsequent oriented cluster aggregation. Finally, slow Ostwald ripening, i.e. the growth of larger structures at the expense of smaller particles, was modeled in good agreement with the already experimentally determined particle sizes for ripening temperatures between 10 and 50 °C.

A Powder on the move - Wirth, Karl-Ernst; Linsenbühler, Markus (European Coatings Journal, 2002)
There is a rising demand on powder coatings towards ever finer particles. However, such fine powders are more difficult to fluidise. This problem can be overcome by coating the powder coating particles themselves with spacer-nanoparticles, thus reducing the attractive van der Waals forces. Here, an innovative process for this particle coating is presented: The spacer particles and powder coating particles are given opposite electric charges and then mixed - both in a medium of liquid nitrogen. The procedure is promising also as a general method for mixing fine solid powders as well.
UnivIS-Import:2015-03-09:Pub.2002.tech.ITC.mechve.apowde
Keywords: powder; technology

Application of Printable ITO/PEDOT Nanocomposites as Transparent Electrodes in Optoelectronic Devices - Maksimenko, Ilja; Kilian, Daniel; Mehringer, Christian; Voigt, Michael; Peukert, Wolfgang; Wellmann, Peter (Conference on Lasers and Electro-Optics, 2012)
Printable transparent hybrid composites consisting of indium tin oxide (ITO) nanoparticles and conducting polymer 3,4-polyethylenedioxythiophene: polystyrene sulfonic acid (PEDOT:PSS)) as matrix material were developed and used as transparent electrodes in all-printed flexible electroluminescent lamps and electrochromic display
Keywords: optical devices; electro-optical devices; thin films; transparent conductive coatings

Approximate Moment Methods for Population Balance Equations in Particulate and Bioengineering Processes - Duerr, Robert; Bück, Andreas (Processes, 2020)
Population balance modeling is an established framework to describe the dynamics of particle populations in disperse phase systems found in a broad field of industrial, civil, and medical applications. The resulting population balance equations account for the dynamics of the number density distribution functions and represent (systems of) partial differential equations which require sophisticated numerical solution techniques due to the general lack of analytical solutions. A specific class of solution algorithms, so-called moment methods, is based on the reduction of complex models to a set of ordinary differential equations characterizing dynamics of integral quantities of the number density distribution function. However, in general, a closed set of moment equations is not found and one has to rely on approximate closure methods. In this contribution, a concise overview of the most prominent approximate moment methods is given.
CRIS-Team WoS Importer:2020-06-19

Aqueous Long-Term Solubility of Titania Nanoparticles and Titanium(IV) Hydrolysis in a Sodium Chloride System Studied by Adsorptive Stripping Voltammetry - Schmidt, Jochen; Vogelsberger, Wolfram (Journal of Solution Chemistry, 2009)
The solubility of industrially produced titanium dioxide nanoparticles has been studied in aqueous sodium chloride media in the pH range 1 to 13 at 25 °C by using adsorptive stripping voltammetry (AdSV). Kinetic dissolution curves have been obtained as well as long-term solubilities that provide an approximation of the equilibrium solubilities. The titania nanoparticles used in the dissolution experiments have been characterized by nitrogen sorption measurements, XRD and colloid titration. The equilibrium solubilities and titanium(IV) speciation and their dependences on pH have been modelled by assuming the formation of the mononuclear titanium hydroxo complexes [Ti(OH) n ](4−n)+ (n=2 to 5) to be the only titanium species present. The solubility product of titanium dioxide and equilibrium constants for titanium(IV) hydrolysis, calculated from the AdSV solubility data, are presente

A review of models for single particle compression and their application to silica microspheres - Paul, Jonas; Romeis, Stefan; Tomas, Jürgen; Peukert, Wolfgang (Advanced Powder Technology, 2014)
We report on the deformation behavior of single silica microspheres. For the first time a detailed discussion on the quantitative evaluation of force–deformation data in the elastic and plastic regime is given. The microspheres are compressed between two flat plates of a custom built manipulation device supported by a scanning electron microscope. The device allows a high sample throughput enabling full statistical evaluation of force–deformation data of single microspheres. Existing theories describing the deformation behavior of single spheres are discussed and applied to the elastic and plastic deformation regime of silica microspheres. The results obtained from the theories are compared between each other and values reported in literature. The silica microspheres exhibit a significantly different deformation behavior than expected from bulk fused silica, i.e. a distinct plastic deformation behavior. Furthermore, a significant decrease in Young’s modulus and hardness was observed caused by high porosity and reduced crosslinking of silicon atoms, respectively, that is inherent to silica produced by Stöber synthesis. However, the calculated contact pressures exceed the compressive strength of bulk fused silica by at least a factor of two as an effect of a reduced amount of material flaws in microstructures.

A Rhodium Triphenylphosphine Catalyst for Alkene Hydrogenation Supported on Neat Superparamagnetic Iron Oxide Nanoparticles - Dehe, Daniel; Wang, Lei; Mueller, Melanie K.; Doerr, Gunder; Zhou, Zhou; Klupp-Taylor, Robin N.; Sun, Yu; Ernst, Stefan; Hartmann, Martin; Bauer, Matthias; Thiel, Werner R.; Klupp Taylor, Robin (ChemCatChem, 2015)
A phosphonic acid functionalized triphenylphosphine rhodium complex was synthesized and grafted onto neat superparamagnetic iron oxide nanoparticles. The material was investigated by elemental analysis, IR spectroscopy, thermogravimetric analysis, XRD, N-2-physisorption analyses, and TEM measurements. The obtained hybrid material could be used as a catalyst for the hydrogenation of alkenes with excellent yields and a broad substrate scope. The catalyst can be reused ten times without any loss of activity. According to the results from X-ray absorption spectroscopy, it is likely that formation of Rh nanoparticles occurs during the reaction.
Keywords: hydrogenation; iron; magnetic properties; phosphonate; rhodium

Arrays of size and distance controlled platinum nanoparticles fabricated by a colloidal method - Vogel, Nicolas; et al. (Nanoscale, 2011)
Based on emulsion polymerization in the presence of a Pt complex, polystyrene (PS) particles were prepared exhibiting a well defined average diameter with narrow size-distribution. Furthermore, the colloids contain a controlled concentration of the Pt precursor complex. Optimized coating of Si substrates with such colloids leads to extended areas of hexagonally ordered close-packed PS particles. Subsequent application of plasma etching and annealing steps allows complete removal of the PS carriers and in parallel nucleation and growth of Pt nanoparticles (NPs) which are located at the original center of the PS colloids. In this way, hexagonally arranged spherical Pt NPs are obtained with controlled size and interparticle distances demonstrating variability and precision with so far unknown parameter scalability. This control is demonstrated by the fabrication of Pt NP arrays at a fixed particle distance of 185 nm while systematically varying the diameters between 8 and 15 nm. Further progress could be achieved by seeded emulsion polymerization. Here, Pt loaded PS colloids of 130 nm were used as seeds for a subsequent additional emulsion polymerization, systematically enlarging the diameter of the PS particles. Applying the plasma and annealing steps as above, in this way hexagonally ordered arrays of 9 nm Pt NPs could be obtained at distances up to 260 nm. To demonstrate their stability, such Pt particles were used as etching masks during reactive ion etching thereby transferring their hexagonal pattern into the Si substrate resulting in corresponding arrays of nanopillars.

A self-assembled metamaterial for Lamb waves - Khanolkar, Amey; Wallen, Samuel; Ghanem, M. Abi; Jenks, J.; Vogel, Nicolas; Boechler, N. (Applied Physics Letters, 2015)
We report the design and characterization of a self-assembled, locally resonant acoustic metamaterial for Lamb waves, composed of a monolayer of 1.02 extgreekmm polystyrene microspheres adhered to a 1.27 extgreekmm thick free-standing silicon membrane. A laser-induced transient grating technique is used to generate Lamb waves in the metamaterial and to measure its acoustic response. The measurements reveal a microsphere contact resonance and the lowest frequency spheroidal microsphere resonance. The measured dispersion curves show hybridization of flexural Lamb waves with the microsphere contact resonance. We compare the measured dispersion with an analytical model using the contact resonance frequency as a single fitting parameter, and find that it well describes the observed hybridization. This study may lead to an improved understanding of microscale contact mechanics and to the design of new types of acoustic metamaterials.

A Self‐Ordered Nanostructured Transparent Electrode of High Structural Quality and Corresponding Functional Performance - Döhler, Dirk; Triana Merlo, Andres Dario; Büttner, Pascal; Scheler, Florian; Görlitzer, Eric; Harrer, Johannes; Vasileva, Anna A.; Ali, Ezzeldin; Gruber, Wolfgang; Unruh, Tobias; Manshina, Alina A.; Vogel, Nicolas; et al. (Small, 2021)
The preparation of a highly ordered nanostructured transparent electrode based on a combination of nanosphere lithography and anodization is presented. The size of perfectly ordered pore domains is improved by an order of magnitude with respect to the state of the art. The concomitantly reduced density of defect pores increases the fraction of pores that are in good electrical contact with the underlying transparent conductive substrate. This improvement in structural quality translates directly and linearly into an improved performance of energy conversion devices built from such electrodes in a linear manne
Keywords: nanosphere lithography; anodic alumina; antimony sulfide

As flat as it gets: ultrasmooth surfaces from template-stripping procedures - Vogel, Nicolas; et al. (Nanoscale, 2012)
In an experimentally simple replica process, the natural flatness of mica or polished silicon wafers can be transferred to metal films, resulting in metal surfaces with topographic features in Angstrom dimensions over large areas. Two decades after its invention, the template-stripping process continues to appeal to scientists from diverse research backgrounds primarily due to its simplicity, cost-effectiveness and ability to yield high quality substrates and structures. This article introduces the basic construction process for template-stripped substrates, and reports on a variety of extensions of the process, including the generation of materials contrasts and the design of tailored topographies. It also highlights the use of such substrates in a variety of research fields in nanoscience and technology ranging from surface force measurement and high definition imaging to the self-assembly of model membranes and plasmonics.

A single-molecule approach to systematically study the narrow escape problem in micro-patterned model membranes - Meiser, Elisabeth; Mohammadi, Reza; Vogel, Nicolas; Holcman, David; Fenz, Susanne (EUROPEAN BIOPHYSICS JOURNAL WITH BIOPHYSICS LETTERS, 2021)
CRIS-Team WoS Importer:2021-08-13

A solution-based ALD route towards (CH3NH3)(PbI3) perovskite via lead sulfide films - Koch, Vanessa; Barr, Maissa; Büttner, Pascal; Mínguez-Bacho, Ignacio; Döhler, Dirk; Winzer, Bettina; Reinhardt, Elisabeth; Segets, Doris; Bachmann, Julien (Journal of Materials Chemistry A, 2019)
We present a procedure to grow thin films of lead sulfide (PbS) with 'solution Atomic Layer Deposition' (sALD), a technique which transfers the principles of ALD from the gas phase (gALD) to liquid processing. PbS thin films are successfully deposited on planar and porous substrates with a procedure that exhibits the unique ALD characteristics of self-limiting surface chemistry and linear growth at room temperature. The polycrystalline p-type PbS films are stoichiometric and pure. They are converted to the hybrid perovskite methylammonium iodoplumbate (methylammonium lead iodide, MAPI, CH3NH3PbI3) by annealing to 150 °C in the presence of vapors from methylammonium iodide (MAI).
CRIS-Team Scopus Importer:2019-11-19

Assessing stress conditions and impact velocities in fluidized bed opposed jet mills - Strobel, Alexander; Köninger, Benedikt; Romeis, Stefan; Schott, Florian; Wirth, Karl Ernst; Peukert, Wolfgang (Particuology, 2020)
Fluidized bed opposed jet mills are capable of meeting the continuously growing demand for contamination-free fine particles. In this type of jet mill, the solid material is entrained and accelerated by expanding gas jets that are focused onto a focal point inside a fluidized bed. The resulting particle collisions induce breakage. The process is affected by the relative particle velocities and the number of particle–particle collisions. Clearly, both quantities are distributed. However, to date, neither relative particle velocities nor collision frequencies in such units have been determined. The present work introduces an innovative method to assess the stressing conditions in jet mills experimentally. To this end, mixtures of glass and ductile metal microspheres were used, with the latter employed in small amounts. Inter-particle collisions between the aluminum and glass spheres lead to the formation of dents on the microparticles. The size and number of these dents are associated with the individual collision velocities and overall collision frequencies. The correlation between dent size and collision velocity was obtained from finite element calculations based on empirical data. The proposed approach was validated using particle image velocimetry during secondary gas injection into a fluidized bed reactor. In this case the effect of the distance between two opposed nozzles was examined. For a lab-scaled fluidized bed opposed jet mill the effects of gas pressure and hold-up were investigated. Relative particle velocities were found to be significantly lower than the gas velocities, while the number of contacts per particle was determined to be extremely high.
CRIS-Team Scopus Importer:2020-07-03
Keywords: Finite element modeling; Fluidized bed opposed jet mill; Relative velocity distribution; Single particle probes; Stress number distribution

Assessing the influence of viscosity and milling bead size on the stressing conditions in a stirred media mill by single particle probes - Strobel, Alexander; Schwenger, Jan; Wittpahl, Sandra; Schmidt, Jochen; Romeis, Stefan; Peukert, Wolfgang (Chemical Engineering Research & Design, 2018)
Keywords: Fluid viscosity; Grinding media size; Stress number and energy distribution; Single particle probes; Stirred media milling

Assessment of Tribological behavior of nickel-nano Si3N4 composite coatings fabricated by pulsed electroplating process - Sajjadnejad, Mohammad; Karimi Abadeh, Hossein; Omidvar, Hossein; Hosseinpour, Saman (Surface Topography: Metrology and Properties, 2020)
Pure nickel and nano-composite nickel-silicon nitride (Si3N4) coatings were fabricated using pulsed current electrodeposition technique.Acontrol sample for each coatingwas created and the effect of current density, duty cycle, and pulse frequency on the tribological properties of the electrodeposited coatings was investigated by altering these parameters.X-ray diffraction, scanning electronmicroscopy and pin-on-disk testswere performed to assess the properties of the fabricated coatings.X-ray diffraction results indicated that both pure and nano-composite coatings possess preferential growth of (111) crystallite planes,which results in the formation of binary symmetrical shaped grains.However, incorporating particles into the coating hindered the growth on other planes, specially (200) growth plane. Incorporation of Si3N4 particles into the coating reduced crystallite size and increased grain refinement; both ofwhich resulted in the increased microhardness of the deposited coatings through dispersion strengtheningmechanism.Complementary atomic forcemicroscopy investigations indicated that the roughness of all nano-composite sampleswas higher than that for the pure nickel coating. After incorporation of Si3N4 particles the wear behavior of all coatingswas improved as a result of the improved hardness.Measured wear rates indicate that increasing the current density, during electrodeposition, is themost influencing parameter in reducing thewear coefficient. Furthermore, implementing particles changes thewearmechanismfromhigh plastic deformation, gouging, and delamination to ploughing. Although nano-composite coatings exhibitwider grooves on the surface compared to those on pure nickel coatings, they tend to adhere better to the substrate.The friction coefficient for all nano-composite coatingsweremarginally higher than that for pure nickel coating, to our understanding, as a result of inadequate load carrying effect of silicon nitride particles.<br
Keywords: nickel; pulsed electrodeposition; silicon nitride; wear; tribology

Assigning Electronic States in Carbon Nanodots - Strauß, Volker; Kahnt, Axel; Zolnhofer, Eva; Meyer, Karsten; Maid, Harald; Placht, Christian; Bauer, Walter; Nacken, Thomas; Peukert, Wolfgang; Etschel, Sebastian; Halik, Marcus; Guldi, Dirk Michael (Advanced Functional Materials, 2016)
Luminescent carbon nanodots exhibit enormous potential to be used as functional building blocks in energy conversion devices. Their intrinsic heterogeneity, however, hinders a thorough characterization and subsequently their applicability. In this work, the spectroscopic and electrochemical properties of prototype carbon nanodots were thoroughly studied in solution. Spectro-electrochemical experiments revealed information on the spectral features of several oxidized and reduced species of our carbon nanodots. Therefore, these experiments were complemented with pulse radiolysis where the spectral signature of the one-electron oxidized and reduced forms were identified. Both, electrochemically and radiolytically reduced and oxidized products show high reactivity in solution which correlates with an open-shell character, detected by paramagnetic resonance spectroscopy. The herein presented studies help to understand the complex nature of carbon nanodots and serve to overcome difficulties in device fabrication.

A step closer to continuous buffer preparation from solids: Predicting powder compaction and how to prevent it - Komuczki, D.; Hesse, Nicolas; Schmidt, Jochen; Satzer, P. (New Biotechnology, 2023)
The preparation of buffer solutions used in the biopharmaceutical industry is typically performed manually by the addition of one or multiple buffering reagents to water. Recently, the adaptation of powder feeders for continuous solid feeding was demonstrated for continuous buffer preparation. However, the intrinsic characteristics of powders can change the stability of the process, due to the hygroscopic nature of some substances and humidity-induced caking and compaction behavior, but there is no simple and easy methodology available for predicting this behavior for buffer species. To predict which buffering reagents are suitable without special precautions and investigate their behavior, force displacement measurements were conducted with a customized rheometer over 18 h. While most of the eight investigated buffering reagents indicated uniform compaction, especially sodium acetate and dipotassium hydrogen phosphate (K2HPO4) showed a significant increase in yield stress after 2 h. Experiments conducted with a 3D printed miniaturized screw conveyor confirmed the increased yield stress measurements by visible compaction and failure of the feeding. By taking additional precautions and adjusting the design of the hopper, we demonstrated a highly linear profile of all buffering reagents over a duration of 12 and 24 h. We showed that force displacement measurements accurately predict the behavior of buffer components in continuous feeding devices for continuous buffer preparation and are a valuable tool to identify buffer components that need special precautions. Stable, precise feeding of all tested buffer components was demonstrated, highlighting the importance of identifying buffers that need a specialized setup with a rapid methodology.
CRIS-Team Scopus Importer:2023-06-02
Keywords: Ball indentation; Buffers; Chromatography; Pharmaceutical; Powder

A study of adhesion forces of oxide particles by molecular modeling and AFM-measurements - Peukert, Wolfgang; Götzinger, Martin (Proceedings 26th Annual Meeting of The Adhesion Society, 2003)
UnivIS-Import:2015-04-16:Pub.2003.tech.ITC.mechve.astudy
Keywords: adhesion; surface; afm

A test of improved force field parameters for urea: molecular-dynamics simulations of urea crystals - Ozpinar, Gul Altinbas; Beierlein, Frank; Peukert, Wolfgang; Zahn, Dirk; Clark, Timothy (Journal of Molecular Modeling, 2012)
Molecular-dynamics (MD) simulations of urea crystals of different shapes (cubic, rectangular prismatic, and sheet) have been performed using our previously published force field for urea. This force field has been validated by calculating values for the cohesive energy, sublimation temperature, and melting point from the MD data. The cohesive energies computed from simulations of cubic and rectangular prismatic urea crystals in vacuo at 300 K agreed very well with the experimental sublimation enthalpies reported at 298 K. We also found very good agreement between the melting points as observed experimentally and from simulations. Annealing the crystals just below the melting point leads to reconstruction to form crystal faces that are consistent with experimental observations. The simulations reveal a melting mechanism that involves surface (corner/edge) melting well below the melting point, and rotational disordering of the urea molecules in the corner/edge regions of the crystal, which then facilitates the translational motion of these molecules.

Atmospheric corrosion of Cu, Zn, and Cu–Zn alloys protected by self-assembled monolayers of alkanethiols - Hosseinpour, Saman; et al. (Surface Science, 2016)

Atomization of Superheated Liquids - Wirth, Karl-Ernst; Rossmeissl, Markus (Proceedings International Conference for Particle Technology, 2004)
UnivIS-Import:2015-04-16:Pub.2004.tech.ITC.mechve.atomiz

Atomization of Superheated suspensions with different solids and solid concentrations - Wirth, Karl-Ernst; Wellner, Sabine (Proceedings of the seventeenth international conference on liquid atomization and spray systems, 2001)
The effect of the superheated atomization of water-solid-suspensions is investigated with two different solids, aluminia  and  zeolith.  The  particle  size  distributions  of  the  powders  seems  to  have  no  influence  for  the  droplet size  distributions  of  the  suspension  sprays.  The  shapes  of  the  solid  particles  intensify  the  atomization  by disintegration of the jet to smaller droplets if surface roughness and crevice are given. The concentration of the solid in the suspension influences the spray geometry. The volume of the spray cone increases with an increase of solid concentration. It was perceived that internal scattering of the jet is given for all superheating, ∆T_S. The nucleation is assumed to be heterogeneous. Particles in a fluid increase the probability for heterogeneous nucleus and an influence of the particle concentration and surface shape is verified in the region near the dense core
UnivIS-Import:2015-04-16:Pub.2001.tech.ITC.mechve.atomiz
Keywords: supercritical Fluid; Spray; PIV

Attractive particle interaction forces and packing density of fine glass powders - Ribeiro Parteli, Eric Josef; Schmidt, Jochen; Blümel, Christina; Wirth, Karl-Ernst; Peukert, Wolfgang; Pöschel, Thorsten (Scientific Reports, 2014)
We study the packing of fine glass powders of mean particle diameter in the range (4-52)μm both experimentally and by numerical DEM simulations. We obtain quantitative agreement between the experimental and numerical results, if both types of attractive forces of particle interaction, adhesion and non-bonded van der Waals forces are taken into account. Our results suggest that considering only viscoelastic and adhesive forces in DEM simulations may lead to incorrect numerical predictions of the behavior of fine powders. Based on the results from simulations and experiments, we propose a mathematical expression to estimate the packing fraction of fine polydisperse powders as a function of the average particle size.

Attrition of polymeric bulk materials in pneumatic conveying: mechanisms and material properties - Peukert, Wolfgang; Frye, Lars (Pneumatic and hydraulic conveying systems III, 2002)
UnivIS-Import:2015-04-16:Pub.2002.tech.ITC.mechve.attrit
Keywords: transport; conveyer

Attrition of polymeric bulk materials in pneumatic conveying: mechanisms and material properties - Peukert, Wolfgang; Frye, Lars (Particulate Science and Technology, 2003)
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). The paper focuses on dilute phase conveying (homogeneous flow) and in the first part describes the determination of the process function by employing computational fluid dynamics (CFD). In the second part, experimental results for the determination of the material function by means of simulating the previously identified stress modes of impact and friction under well-defined stress conditions are presented. Contrary to what was expected initially, the numerical simulations as well as experimental results indicate that sliding friction is apparently of importance in dilute phase conveying. This conclusion can be drawn from the low calculated impact angles in a pipe bend (r B /D=5; D=80 mm), which lie between 10 and 35°. Consequently, the tangential impact velocity components ranging from 32 to 40 m/s are considerably higher than the normal ones (5 to 22 m/s). These results are confirmed by observations made in experiments to determine the material function. The relative attrition behavior of four different polypropylenes 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 condition
UnivIS-Import:2015-03-09:Pub.2003.tech.ITC.mechve.attrit_5
Keywords: Attrition; Pneumatic Conveying; Polymers; Process Function; Material Function; Computational Fluid Dynamics (CFD)

Attrition of polymeric bulk solids in pneumatic conveying: determination of process and material function - Peukert, Wolfgang; Frye, Lars (4th International Conference on Bulk Solids Handling, 2003)
UnivIS-Import:2015-04-16:Pub.2003.tech.ITC.mechve.attrit
Keywords: polymer; process; function

A tunable aggregation model incorporated in Monte Carlo simulations of spray fluidized bed agglomeration - Singh, Abhinandan Kumar; Tsotsas, Evangelos (Powder Technology, 2020)
Keywords: Morphological descriptors; Tunable aggregation model; Aggregation models; Fractal dimension; Agglomeration

Automated synthesis of quantum dot nanocrystals by hot injection: Mixing induced self-focusing - Salaheldin, Ahmed M.; Walter, Johannes; Herre, Patrick; Levchuk, Ievgen; Jabbari, Yasaman; Kolle, Joel; Brabec, Christoph; Peukert, Wolfgang; Segets, Doris (Chemical Engineering Journal, 2017)
The hot injection technique for the synthesis of quantum dots (QDs) is a well-established and widely used method in the lab. However, scale-up rules do not exist. One reason is that in particular the role of process parameters like mixing on particle formation is largely unknown, as systematic examination of the latter is impossible for the laborious and complex manual synthesis. Herein we studied the mixing induced self-focusing of particle size distributions (PSDs) of CdSe QDs using automation in combination with a defined stirrer geometry. Basis for our study is a platform that allows parallelization with inline temperature monitoring, defined injection rate, accurate sampling times as well as controlled stirring. Reproducibility in terms of optical product properties was analyzed by absorption and emission whereas reproducibility in terms of the PSD was verified by deconvolution of UV/Vis absorbance spectra and especially by analytical ultracentrifugation (AUC) complemented by transmission electron microscopy (TEM). In line with previous results, AUC confirmed that even QDs made by hot injection in an automated setup are polydisperse with multimodal size distributions. Finally, reproducibility in combination with early stage sampling and controlled mixing allowed us for the first time to analyze the influence of stirring on focusing and defocusing of PSDs, that has been expressed in terms of the evolution of the relative standard deviation (RSD). Our work paves the way to gain in-depth understanding of often forgotten process-structure relationships of colloidal nanoparticles which eventually is a first step in the direction of the development of scalable synthesis and reliable application of high-quality QDs in technical application

A widely applicable method to stabilize nanoparticles comprising oxygen-rich functional groups - Distaso, Monica; Lautenbach, Vanessa; Uttinger, Maximilian; Walter, Johannes; Lübbert, Christian; Thajudeen, Thaseem; Peukert, Wolfgang (Powder Technology, 2022)
Colloidal stability of nanoparticle suspensions is fundamental to apply nanomaterials in functional devices and to develop new methodologies in nanoscience. Herein, a versatile method is described to disperse and stabilize various solids with technological applications in pharmaceutical industry, batteries and fuel cells, dye sensitized solar cells, pigments and coatings. The method is based on the use of Zr(IV) hydroxo-complexes that interact with carboxylic- and hydroxo- functional groups at the solid-liquid interfaces of active pharmaceutical ingredients (API), carbon black (CB) and Pt-CB, metal oxide and metal oxy-hydroxide nanoparticles. The colloidal stability is assessed via sedimentation analysis, electrophoretic measurements, ultraviolet-visible spectroscopy (UV–Vis), attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) and isothermal titration calorimetry (ITC). The effect of the anion and pH are studied in depth. Finally, the current work enables liquid phase length and diameter characterization of rod-like goethite (α-FeOOH) particles without relying on tedius counting the particles from electron micrographs.
CRIS-Team Scopus Importer:2022-07-08
Keywords: Functional devices; Nanoparticles; Nanoparticulate inks; Stability; Surface

A widely applicable tool for modeling precipitation processes - Haderlein, Michael; Güldenpfennig, Andreas; Segets, Doris; Peukert, Wolfgang (Computers & Chemical Engineering, 2017)
This work presents a generalized tool for modeling precipitation processes for the parallel formation of multiple solid phases. A symmetric mixing model for T-mixers is presented which mimics the mixing process in a numerically highly efficient way. This model can easily be extended to other reactor types such as stirred tank reactors following the implementation given in this work. Modelling ion activities and ion complexation is strongly accelerated by the analytical formulation of the Jacobian of the corresponding system of equations. Solid formation processes are described via the numerically efficient Direct Quadrature Method of Moments (DQMOM) which is parallelized for treating multiple solid phases simultaneously. Expressions for agglomeration of multiple solid phases and for particle transfer between different mixer zones are given. Both the models of the individual processes and the entire precipitation tool are validated and tested in multiple scenarios proving the flexibility of the tool.
Keywords: Ion complexation; Mixing; Multi-phase; Population Balance Equation; Precipitation; T-Mixer

Axial Pressure Profile in Circulating Fluidized Beds - Wirth, Karl-Ernst (Chemical Engineering & Technology, 1988)
The axial pressure profile was measured for a variety of solids, as a function of the superficial gas velocity, in a cylindrical circulating fluidized bed with an inner diameter of 0. 19 m and an overall height of 11. 5 m. Depending on the solids content and superficial gas velocity, two or one sections can be observed in the plant where the pressure gradient is constant. A pressure profile with one pressure gradient exists only at high gas velocities, so long as the acceleration pressure drop immediately above the gas distributor is negligible. Comparisons of measured pressure drops in circulating fluidized beds with those measured in vertical pneumatic conveying led to a state diagram for vertical gas-solid flows. The operation behavior of different types of circulating fluidized bed plants can be explained with the aid of this diagram.
UnivIS-Import:2015-03-05:Pub.1988.tech.ITC.mechve.axialp
Keywords: pressure; profile; fluidization

Balancing ballistic and hopping light transport by purposive arraying of colloidal particles - Romanov, Sergei G.; Orlov, Sergej; Vogel, Nicolas; Bley, Karina; Landfester, Katharina; Weiss, Clemens K.; Peschel, Ulf (Photonic Crystal Materials and Devices XI, 2014)
Keywords: 2-dimensional slab photonic crystal; Diffraction; Disorder; Etching; Mie resonance; Optical spectra; Photon hopping

BaO Clusters on MgO Nanocubes: A Quantitative Analysis of Optical-Powder Properties - Sternig, Andreas; Mueller, Markus; Mccallum, Mark; Bernardi, Johannes; Diwald, Oliver (Small, 2010)
Uniformly sized and shaped nanoparticles are well suited for the quantitative characterization of optical-powder properties. For the first time, quantum yields related to photoluminescence emissions that originate from the photoexcitation of MgO nanocube corners and edges are measured. In addition, the surfaces of these nanoparticles are doped with submonolayer barium, which oxidizes during adsorption onto the MgO nanocrystal surfaces and transforms in O_2atmosphere into BaO. UV–Vis diffuse reflectance and photoluminescence spectroscopy is employed to explore whether 10-3 monolayer equivalents of these dopants affect the MgO specific optical properties. Surface-admixed BaO produces additional absorption and photoluminescence emission features but does not significantly affect those specific to MgO nanocubes. On this basis the number of optically active sites that can be sampled inside a powder of alkaline earth oxide nanoparticles using a standard spectrometer system is estimated.
EAM Import::2019-03-13

Benchmarking of Gas-Assisted Atomization Systems for Liquid Disintegration - Günther, Astrid; Lampa, Aljoscha; Fritsching, Udo; Schröder, Jewe; Kleinhans, Agnes; Gaukel, Volker; Schuchmann, Heike; Loth, Jan-Martin; Petermann, Marcus; Wirth, Karl-Ernst (Chemical Engineering & Technology, 2016)
Four different gas-assisted atomizer systems are compared to assess their atomization performance for water and polymer solution feeds. An external mixing twin-fluid atomizer serving as standard atomization configuration is compared to three rather unconventional atomization techniques. An internal mixing atomization system is represented by an effervescent atomizer that can be operated at lower air-to-liquid ratio than the conventional gas atomizers. Superheated atomization is an innovative technique to enhance the atomization of liquids by a phase change within the emerging spray. CO2-assisted atomization takes the same line by releasing a liquid saturated with CO2 into a lower pressure environment. The atomization configurations were used to disintegrate the model fluid water and more challenging polymer solutions with higher viscosities. Resulting spray configurations and drop sizes distributions were compared.
Keywords: Complex viscosity; Gas-assisted atomization; Polymer solution feeds; Spray morphology

Berechnung des Druckverlustes bei horizontaler pneumatischer Strähnenförderung - Wirth, Karl-Ernst (Preprints "The Modern Trends in the Development of Pneumatic Conveying", 1986)
UnivIS-Import:2015-04-16:Pub.1986.tech.ITC.mechve.berech
Keywords: pneumatic; conveying

Berechnung pneumatischer Förderanlagen im Bereich der Flug- und Strähnenförderung - Wirth, Karl-Ernst (Aufbereitungs-Technik/Mineral Processing, 1982)
UnivIS-Import:2015-03-05:Pub.1982.tech.ITC.mechve.berech_85

Bestimmung des Druckverlustes bei pneumatischer Strähnenförderung - Wirth, Karl-Ernst; Molerus, Otto (Chemie Ingenieur Technik, 1981)
UnivIS-Import:2015-03-05:Pub.1981.tech.ITC.mechve.bestim

Betriebsverhalten von zirkulierenden Wirbelschichtfeuerungen - Wirth, Karl-Ernst (Preprints VGB-Konferenz "Wirbelschichtsysteme 1990", 1990)
UnivIS-Import:2015-04-16:Pub.1990.tech.ITC.mechve.betrie
Keywords: wirbelschicht

Binary Indium-Zinc Oxide Photoanodes for Efficient Dye-Sensitized Solar Cells - Peukert, Wolfgang; Stanzel, Melanie; Kunzmann, Andreas; Guldi, Dirk Michael; Costa Riquelme, Rubén Dario (Advanced Energy Materials, 2016)
The benefits of incorporating binary metal-oxide electrodes en route toward efficient dye-sensitized solar cells (DSSCs) have recently emerged. The current work aims at realizing efficient indium-doped zinc oxide based DSSCs by means of enhancing charge transport processes and reducing recombination rates. Electrochemical impedance spectroscopic assays corroborate that low amounts of indium reduce charge transport resistances and increase electron recombination resistances. The latter are in concert with a remarkable enhancement of the charge collection efficiency from 33% to 83% for devices with ZnO and InZnO photoanodes, respectively. Going beyond 15 mol% of indium, an effective electron trapping increases the charge transport resistance and, in turn, dramatically reduces charge collection efficiency. Upon implementing InZnO into an electron cascade photoanode architecture featuring an InZnO bottom layer and a ZnO top layer, a device efficiency of 5.77% and a significantly high current density of 20.4 mA cm in binary ZnO DSSCs are achieved.
Keywords: binary oxides; charge collection efficiency; flame spray pyrolysis; indium-zinc oxide photoanodes; n-type DSSCs

Bioactive Glass Flakes as Innovative Fillers in Chitosan Membranes for Guided Bone Regeneration - Zhang, Huijun; Wu, Jingjing; Wan, Ying; Romeis, Stefan; Esper, Julian Duane; Peukert, Wolfgang; Zheng, Kai; Boccaccini, Aldo R. (Advanced Engineering Materials, 2021)
Herein, novel bioactive glass flakes (BGFs) (45S5 composition), obtained by compression in the liquid phase in a stirred media mill, are combined with chitosan (CS) to develop composite membranes using solvent casting for guided bone regeneration (GBR). The incorporation of BGFs endows CS membranes with superior bioactivity as evidenced by rapid hydroxyapatite formation after 3 days of immersion in simulated body fluid (SBF). Moreover, the addition of BGFs reduces the swelling ratio of CS membranes, beneficial for GBR applications. The swelling behavior can also be modulated by tuning the added amount of BGFs. In vitro cell studies indicate the noncytotoxicity of composite membranes toward osteoblast cell line MC3T3-E1, although the presence of BGFs slightly reduces the cell viability compared to pure CS membranes. The incorporation of BGFs also improves the osteogenic differentiation of MC3T3-E1 cells as indicated by the enhanced alkaline phosphatase activity. The results show the feasibility of BGFs as anisotropic bioactive fillers in polymeric matrices. In conclusion, the developed CS-BGF composite membranes show promising potential as a novel material for GBR.
CRIS-Team Scopus Importer:2021-10-08
Keywords: bioactive fillers; bioactive glass flakes; chitosan; composites; guided bone regeneration

Biocompatibility of submicron Bioglass® powders obtained by a top-down approach - Dörfler, Anja; Detsch, Rainer; Romeis, Stefan; Schmidt, Jochen; Eisermann, Claudia; Peukert, Wolfgang; Boccaccini, Aldo R. (Journal of Biomedical Materials Research Part B: Applied Biomaterials, 2014)
In this study in vitro bioactivity and biocompatibility of two submicron 45S5 Bioglass powders obtained by top-down processing have been evaluated and are compared to the as-received powder. Both submicron powders exhibited flake-like morphologies with lateral extensions of only a few microns; the flake thickness accounted for a few tens of nanometers. Enhanced in vitro bioactivity was found for the comminuted powders upon immersion in simulated body fluid. In vitro biocompatibility was evaluated by incubation of MG-63 osteoblast-like cells with various amounts (0-200 μg/mL) of the glass powders. Neither LDH-activity nor mitochondrial activity (WST-8) tests indicated cell toxicity. Increased mitochondrial activity was found for the submicron powders: incubation with high amounts revealed up to a threefold increase of osteoblast activity (ALP-activity). An overgrowth of the formed mineralized phase with phenotypical MG-63 cells was found by staining only for the submicron glasses. A distance ring is formed for the as-received powder. Superior bioactivity markers are found for shorter process times, that is, lower mass specific surface areas. This is attributed to the formation of carbonates during the comminution process. © 2013 Wiley Periodicals, Inc.
Keywords: in vitro bioactivity and biocompatibility; MG-63 cells; sub-micron particles; top-down production

Biodegradabiliy of spherical mesoporous silica particles (MCM-41) in simulated body fluid (SBF) - Boccardi, Elena; Philippart, Anahi; Beltran, Ana M.; Schmidt, Jochen; Liverani, Liliana; Peukert, Wolfgang; Boccaccini, Aldo R. (American Mineralogist, 2018)
Keywords: Mesoporous silica particles; Simulated body fluid; Bone tissue engineering; Drug carriers; Biomaterials - Mineralogy Meets Medicine; Biodegradability

Biodegradable Polylactide Supraparticle Powders with Functional Additives for Biomedical Additive Manufacturing - Canziani, Herbert; Hanschmann, Benedikt; Tischer, Florentin; Sommereyns, Alexander; Distler, Thomas; Schramm, Jonas; Hesse, Nicolas; Schmidt, Jochen; Grünewald, Alina; Detsch, Rainer; Boccaccini, Aldo R.; Maskos, Michael; et al. (Advanced Functional Materials, 2022)
Additive manufacturing, in particular powder bed-based fabrication processes hold promise to revolutionize biomedical engineering for the ability to provide customized, functional implants, for example as bone replacement materials. However, providing functional powder particles that unify material requirements for biodegradable and bioactive biomaterials and process requirements to enable successful powder bed fusion remains an unmet challenge. Here, a supraparticle-based approach to create biodegradable poly(lactic acid) and composite powders for the additive manufacturing of bone replacement materials is introduced. Colloidal binary Ca-SiO2 glasses and hydroxyapatite are incorporated as bioactive functional additives to support the formation of bone-like calcium phosphate. The supraparticle powders are prepared by a scalable spray-drying process, which offers control of particle size, shape, and composition. All process-relevant powder characteristics are analyzed as a function of composition and structure, including flowability, thermal, and melt rheological properties. The optimized supraparticle powders are successfully used in the process of laser powder bed fusion of polymers to prepare macroscopic specimens via additive manufacturing. It is demonstrated that the material combination of the composites provides relevant functional properties, including biodegradation and bioactivity. The process provides a flexible and adjustable toolbox for the design of functional powders toward biomedical additive manufacturing.<br
Keywords: 3D printing; additive manufacturing; biomaterials; PLA; powder bed fusion; spray drying; supraparticles

Bioinspired Photonic Pigments from Colloidal Self-Assembly - Görlitzer, Eric; Klupp Taylor, Robin; Vogel, Nicolas (Advanced Materials, 2018)
Keywords: structural color; photonic pigments; self-assembly; colloids; bioinspired

Bottom-Up Assembly of Silica and Bioactive Glass Supraparticles with Tunable Hierarchical Porosity - Egly, Steffen; Fröhlich, Christina; Vogel, Stefanie; Grünewald, Alina; Wang, Junwei; Detsch, Rainer; Boccaccini, Aldo R.; Vogel, Nicolas (Langmuir, 2018)
We investigate the formation of spherical supraparticles with controlled and tunable porosity on the nanometer and micrometer scales using the self-organization of a binary mixture of small (nanometer scale) oxidic particles with large (micrometer scale) polystyrene particles in the confinement of an emulsion droplet. The external confinement determines the final, spherical structure of the hybrid assembly, while the small particles form the matrix material. The large particles act as templating porogens to create micropores after combustion at elevated temperatures. We control the pore sizes on the micrometer scale by varying the size of the coassembled polystyrene microspheres and produce supraparticles from both silica- and calcium-containing CaO/SiO2 particles. Although porous supraparticles are obtained in both cases, we found that the presence of calcium ions substantially complicated the fabrication process since the increased ionic strength of the dispersion compromises the colloidal stability during the assembly process. We minimized these stability issues via the addition of a steric stabilizing agent and by mixing bioactive and silica colloidal particles. We investigated the interaction of the porous particles with bone marrow stromal cells and found an increase in cell attachment with increasing pore size of the self-assembled supraparticles.

Bottom-Up Design of Composite Supraparticles for Powder-Based Additive Manufacturing - Canziani, Herbert; Chiera, Salvatore; Schuffenhauer, Thomas; Kopp, Sebastian-Paul; Metzger, Florian; Bück, Andreas; Schmidt, Michael; Vogel, Nicolas (Small, 2020)
Additive manufacturing promises high flexibility and customized product design. Powder bed fusion processes use a laser to melt a polymer powder at predefined locations and iterate the scheme to build 3D objects. The design of flowable powders is a critical parameter for a successful fabrication process that currently limits the choice of available materials. Here, a bottom-up process is introduced to fabricate tailored polymer- and composite supraparticles for powder-based additive manufacturing processes by controlled aggregation of colloidal primary particles. These supraparticles exhibit a near-spherical shape and tailored composition, morphology, and surface roughness. These parameters can be precisely controlled by the mixing and size ratio of the primary particles. Polystyrene/silica composite particles are chosen as a model system to establish structure–property relations connecting shape, morphology, and surface roughness to the adhesion within the powder, which is accessed by tensile strength measurements. The adhesive properties are then connected to powder flowability and it is shown that the resulting powders allow the formation of dense powder films with uniform coverage. Finally, successful powder bed fusion is demonstrated by producing macroscopic single layer specimens with uniform distribution of nanoscale silica additives.
CRIS-Team Scopus Importer:2020-07-10
Keywords: additive manufacturing; composite powders; nanoscale; spray drying; supraparticles

Boxes fabricated from plate-stabilized liquid marbles - Fujiwara, Junya; Yokoyama, Ai; Seike, Musashi; Vogel, Nicolas; Rey, Marcel; Oyama, Keigo; Hirai, Tomoyasu; Nakamura, Yoshinobu; Fujii, Syuji (Materials Advances, 2021)
Polyhedral liquid marbles were fabricated using hydrophobic polymer plates in the shape of a circle, a heart and a star as a stabilizer and water as an inner liquid phase. Boxes could be fabricated by the evaporation of the inner water from the liquid marbles. The fabrication efficiency and stability of these boxes as a function of the plate shape were investigated. Functional materials such as polymers and colloidal particles were successfully introduced into the boxes.
CRIS-Team WoS Importer:2021-07-09

Breakage behaviour of different materials - construction of master curve for the breakage probability - Peukert, Wolfgang; Vogel, Lutz (Powder Technology, 2003)
An approach to quantify the grinding behaviour of different materials is presented. Based on a dimensional analysis and on fracture mechanical considerations, two material parameters, fMat. and Wm,min, are derived theoretically. fMat. characterises the resistance of particulate material against fracture in impact comminution. fMat. comprises the effect of particle size on fracture and the resistance against the external load which is quantified by the specific impact energy. Wm,min characterises the specific energy which a particle can take up without fracture. Values for fMat. and Wm,min which determine the grindability of different materials are given. Both the dimensional analysis and the fracture mechanical considerations lead to the same influence of initial particle size, mass-specific impact energy and newly derived material parameters on the comminution result. Experimentally, the material parameters are determined by single-particle impact tests. Together with the initial particle size and the impact energy, they allow for a quantitative description of the breakage probability of different materials in the form of a mastercurve and can also be applied for the qualitative description of the breakage function. The results for five polymers, limestone and glass spheres of different sizes are shown.
UnivIS-Import:2015-03-09:Pub.2003.tech.ITC.mechve.breaka
Keywords: Breakage probability; Breakage function; Single-particle tests; Grinding; Comminution; Material properties; Mastercurve

Bronze corrosion protection by long-chain phosphonic acids - Mikić, Dajana; Otmačić Ćurković, Helena; Hosseinpour, Saman (Corrosion Science, 2022)
Bronze surfaces were modified by methyl, carboxyl and amino terminated phosphonic acids films to assess the impact of the terminal group and the film thickness on the corrosion resistance of coated samples. The structure of the adsorbed films was characterized by goniometry, specular IR, and SFG spectroscopy. Corrosion studies were conducted for three weeks of continuous immersion in acid rain solution using polarization measurements and electrochemical impedance spectroscopy. Films formed in 1 mM solutions of phosphonic acids provided better corrosion protection than those formed in 0.1 mM solutions. Carboxyl terminated phosphonic acid films exhibited the least protective film on bronze.
CRIS-Team Scopus Importer:2022-07-08
Keywords: Acid inhibiton; Alloy; EIS; IR spectroscopy; SEM

Brownian dynamics simulations of analytical ultracentrifugation experiments exhibiting hydrodynamic and thermodynamic non-ideality - Uttinger, Maximilian; Walter, Johannes; Thajudeen, Thaseem; Wawra, Simon; Peukert, Wolfgang (Nanoscale, 2017)

Bulk and Surface Excitons in Alloyed and Phase-Separated ZnO-MgO Particulate Systems - Zhang, Huanjun; Gheisi, Amirreza; Sternig, Andreas; Mueller, Knut; Schowalter, Marco; Rosenauer, Andreas; Diwald, Oliver; Maedler, Lutz (ACS Applied Materials and Interfaces, 2012)
The rational design of composite nanoparticles with desired optical and electronic properties requires the detailed analysis of surface and bulk contributions to the respective overall function. We use flame spray pyrolysis (FSP) to generate nanoparticles of the ternary Zn–Mg–O system the compositions of which range from solid solutions of Zn2+ ions in periclase MgO to phase separated particle mixtures which consist of periclase (cubic) MgO and wurtzite (hexagonal) ZnO phases. The structure and composition of the composite ZnxMg1–xO (0 łeq x łeq 0.3) particles are investigated using X-ray diffraction and high-resolution transmission electron microscopy, whereas UV diffuse reflectance and photoluminescence (PL) spectroscopy are used for the investigation of their optical properties. Vacuum annealing has been carried out to track the effects of stepwise elimination of surface adsorbates on the photoexcitation and PL emission properties. We demonstrate that for Zn0.1Mg0.9O particles, the admixed ZnO suppresses the MgO specific surface excitons and produces a PL emission band at 470 nm. Although gaseous oxygen partially reduces the emission intensity of hydroxylated particles, it leads to entire quenching in completely dehydroxylated samples after vacuum annealing at 1173 K. Consequently, surface hydroxyls at the solid–gas interface play a significant role as protecting groups against the PL-quenching effects of O2. The obtained results are relevant for the characterization of ZnO-based devices as well as for other metal oxide materials where the impact of the surface composition on the photoelectronic properties is usually neglected.
EAM Import::2019-03-13

Can spray freeze-drying improve the re-dispersion of crystalline nanoparticles of pure naproxen? - Braig, Veronika; Konnerth, Christoph-Günther; Peukert, Wolfgang; Lee, Geoffrey (International Journal of Pharmaceutics, 2019)
Spray freeze drying (SFD) was used to prepare re-dispersible powders of crystalline, pure-drug nanodispersions of naproxen in lactose and stabilized with hydroxypropyl cellulose. The particle size of the rehydrated powders was determined using static light scattering/Mie analysis. The nanoparticles present in the SFD powders were aggregated but could be dispersed on re-dispersion with water and stirring either with or without additional ultrasonic treatment. The disaggregation of the SFD nanoparticles was superior to that reported in the literature for spray dried nanoparticles of the same composition. It appears that the moderately-rapid freezing of the large spray droplets in LN2 during SFD produces less aggregation than does evaporative drying of the much smaller droplets during spray drying. Re-dispersion was also found to depend strongly on the pH of the original nanodispersion. The solubility of this weak acid is greater at higher pH which resulted in formation of a dissolved fraction of drug in the nanodispersions during media milling. After SFD, the dissolved naproxen fraction formed an amorphous solid which re-dissolves on re-hydration whereas the crystalline nanoparticles disaggregate.
CRIS-Team Scopus Importer:2019-05-02
Keywords: Nanoparticles; Particle size; Poorly soluble drug; Re-dispersion; Spray freeze drying

Carbon Nanodots: Toward a Comprehensive Understanding of Their Photoluminescence - Strauß, Volker; Margraf, Johannes; Dolle, Christian; Butz, Benjamin; Nacken, Thomas; Walter, Johannes; Bauer, Walter; Peukert, Wolfgang; Spiecker, Erdmann; Clark, Timothy; Guldi, Dirk Michael (Journal of the American Chemical Society, 2014)
We report the characterization of carbon nanodots (CNDs) synthesized under mild and controlled conditions, that is, in a microwave reactor. The CNDs thus synthesized exhibit homogeneous and narrowly dispersed optical properties. They are thus well suited as a testbed for studies of the photophysics of carbon-based nanoscopic emitters. In addition to steady-state investigations, time-correlated single-photon counting, fluorescence up-conversion, and transient pump probe absorption spectroscopy were used to elucidate the excited-state dynamics. Moreover, quenching the CND-based emission with electron donors or acceptors helped shed light on the nature of individual states. Density functional theory and semiempirical configuration-interaction calculations on model systems helped understand the fundamental structure-property relationships for this novel type of material.

Carbon nano-onions: Individualization and enhanced water dispersibility - Lucherelli, Matteo Andrea; Stiegler, Lisa; Steiger, Florian; Åhlgren, E. Harriet; Requena-Ramírez, Julia; Castro, Edison; Echegoyen, Luis; Hirsch, Andreas; Peukert, Wolfgang; Kotakoski, Jani; Walter, Johannes; Perez-Ojeda Rodriguez, Maria Eugenia; et al. (Carbon, 2024)
Carbon nano-onions (CNOs) are a unique class of carbon nanomaterials, with a concentric fullerene-like structure and sp2-hybridized carbon atoms. Onions present high mechanical strength, good conductivity, the capability to intercalate alkali metals, showing promising applications in diverse fields, such as tribology, energy storage, and nanomedicine. Their production has been developed by several techniques, with the most interesting being the thermal annealing of carbon nanodiamonds because of the easy scalability (gram-scale) and morphologic control (size and shape form perfectly spherical to polygonal). However, this synthesis is commonly affected by the formation of strong aggregates larger than 100 nm, attributed to carbon soot formation or strong van der Waals interactions, hindering the work with small and individual particles, leading to an altered yield of functionalization. In this study we propose a method for CNO individualization based on strong acid treatment, yielding highly water dispersible nanoparticles. Analytical ultracentrifugation (AUC) analysis is employed as a technique to investigate the particle dimensions directly in dispersion, permitting an ensemble analysis free from further sample preparation bias. Moreover, we also provide a comprehensive evaluation of the common post-synthetic treatment methods, and their effects. By means of scanning transmission electron microscopy with medium angle annular dark field detector and electron energy loss spectroscopy (STEM-MAADF and EELS) we have shown images of individual CNOs. Their successful separation achieved in this study is significant for future research and applications in nanomedicine, electrochemistry, and materials composites, where sample homogeneity is critical.<br
CRIS-Team Scopus Importer:2024-01-12
Keywords: Analytical ultracentrifugation; Carbon materials; Carbon nano-onions; Exfoliation; Materials chemistry

Carboxylate Ion Pairing with Alkali-Metal Ions for β-Lactoglobulin and Its Role on Aggregation and Interfacial Adsorption - Beierlein, Frank; Clark, Timothy; Braunschweig, Björn; Engelhardt, Kathrin; Glas, Lena; Peukert, Wolfgang (Journal of Physical Chemistry B, 2015)
We report a combined experimental and computational study of the whey protein extgreekb-lactoglobulin (BLG) in different electrolyte solutions. Vibrational sum-frequency generation (SFG) and ellipsometry were used to investigate the molecular structure of BLG modified air-water interfaces as a function of LiCl, NaCl, and KCl concentrations. Molecular dynamics (MD) simulations and thermodynamic integration provided details of the ion pairing of protein surface residues with alkali-metal cations. Our results at pH 6.2 indicate that BLG at the air-water interface forms mono- and bilayers preferably at low and high ionic strength, respectively. Results from SFG spectroscopy and ellipsometry are consistent with intimate ion pairing of alkali-metal cations with aspartate and glutamate carboxylates, which is shown to be more effective for smaller cations (Li(+) and Na(+)). MD simulations show not only carboxylate-alkali-metal ion pairs but also ion multiplets with the alkali-metal ion in a bridging position between two or more carboxylates. Consequently, alkali-metal cations can bridge carboxylates not only within a monomer but also between monomers, thus providing an important dimerization mechanism between hydrophilic surface patches.
EAM Import::2019-03-13
Keywords: electrolyte; solution; molecular; dynamics; surface

Cell Interactions with Size-Controlled Colloidal Monolayers: Toward Improved Coatings in Bone Tissue Engineering - Walter, Teresa; Grünewald, Alina; Detsch, Rainer; Boccaccini, Aldo R.; Vogel, Nicolas (Langmuir, 2020)
The surface structure of biomaterials is of key importance to control its interactions with biological environments. Industrial fabrication and coating processes often introduce particulate nanostructures at implant surfaces. Understanding the cellular interaction with particle-based surface topologies and feature sizes in the colloidal length scale therefore offers the possibility to improve the biological response of synthetic biomaterials. Here, surfaces with controlled topography and regular feature sizes covering the relevant length scale of particulate coatings (100-1000 nm) are fabricated by colloidal templating. Using fluorescent microscopy, WST assay, and morphology analysis, results show that adhesion and attachment of bone-marrow derived murine stromal cells (ST2) are strongly influenced by the surface feature size while geometric details play an insignificant role. Quantitative analysis shows enhanced cell adhesion, spreading, viability, and activity when surface feature size decreases below 200 nm compared to flat surfaces, while larger feature sizes are detrimental to cell adhesion. Kinetic studies reveal that most cells on surfaces with larger features lose contact with the substrate over time. This study identifies colloidal templating as a simple method for creating highly defined model systems to investigate complex cell functions and provides design criteria for the choice of particulate coatings on commercial implant materials.
CRIS-Team Scopus Importer:2020-03-17

Cellulose-biotemplated silica nanowires coated with a dense gold nanoparticle layer - Klupp Taylor, Robin; Scheel, Hannelore; Greil, Peter; Zollfrank, Cordt; et al. (Materials Chemistry and Physics, 2011)
Keywords: Cellulose; Biotemplating; Transmission electron microscopy; Gold nanoshells

Centrifugation | Analytical Ultracentrifugation - Peukert, Wolfgang; Walter, Johannes (Encyclopedia of Analytical Science, 2019)
Analytical ultracentrifugation is a highly accurate, reproducible and versatile technique to characterize the molecular weight, size, shape anisotropy, density and association of macromolecules and nanoparticles in solution. As a well-accepted analytical method, it has been applied widely in biology, biochemistry and polymer science to characterize (bio-)macromolecules and gains increasing interest in particle technology due to recent hard- and software developments. Multiwavelength detection providing access to spectral properties is one of the most important developments of the recent years. Experiments in the analytical ultracentrifuge are performed in sector shaped cells to measure the spatial and temporal concentration gradients using extinction, interference or fluorescence detectors. A moving boundary forms in sedimentation velocity experiments where high centrifugal forces are present. The rate of movement and shape of the boundary are determined by sedimentation and diffusion properties, respectively. The sedimentation depends on the analyte’s mass and frictional properties whereas diffusion is solely determined by frictional effects. Equilibrium studies are performed at lower rotor speeds where the mass transport due to sedimentation and diffusion balances, thus providing access to molecular weight distributions and interaction parameters. A variety of data analysis algorithms have been developed. Recently, multidimensional analysis has been established.
CRIS-Team Scopus Importer:2020-02-21
Keywords: Analytical ultracentrifugation; Association; Centrifugation; Density; Diffusion; Interactions; Lamm equation; Macromolecule; Mass; Multidimensional properties; Nanoparticle; Sedimentation; Shape; Size; Spectrum

CFD simulation of particle residence time distribution in industrial scale horizontal fluidized bed - Chen, K.; Bachmann, P.; Bück, Andreas; Jacob, M.; Tsotsas, E. (Powder Technology, 2019)
This work investigates the applicability of two conceptually different methods for simulation of particle residence time distributions (RTDs): the species method and the multi-solid method. Both are Eulerian methods; their key difference is found in the specification of the macroscopic particle dispersion coefficient and its relation to micro scale particle diffusivity. The intricate interrelation between particle diffusivity and dispersion coefficient was investigated. It is shown and discussed that, if a-priori knowledge on macroscopic dispersion is available, e.g. from correlations, the species method, which by definition requires data on microscale particle diffusivity, can be used directly with the macroscopic data in both, transient and steady-state simulation. If no such data is available, the multi-solid method has to be used which computes the dispersion coefficient directly, at greater computational expense. Additional advantages of the species model over well-known dispersion model are presented and discussed for the example of an industrial multi-chamber horizontal fluidized bed. (C) 2018 Published by Elsevier B.V.
CRIS-Team WoS Importer:2019-04-18

Changes within the stabilizing layer of ZnO nanoparticles upon washing - Schindler, Torben; Schmutzler, Tilo; Schmiele, Martin; Lin, Wei; Segets, Doris; Peukert, Wolfgang; Appavou, Marie-Sousia; Kriele, Armin; Gilles, Ralph; Unruh, Tobias (Journal of Colloid and Interface Science, 2017)
In detail, it was observed that the diffuse acetate shell shrinks to the size of a monolayer upon washing but the acetate content of this monolayer is higher than within the diffuse shell of the particles of the native dispersion. A second washing cycle reduces the acetate concentration within the stabilizing shell and the stability of the dispersion drops accordingly. After another (third) washing cycle strong agglomeration was observed for all investigated samples. (C) 2017 Elsevier Inc. All rights reserved.
Keywords: Small angle scattering; Stabilization; Quantum dots; Purification; Stabilizing shell

Chapter 13 Enabling Nanomilling through Control of Particulate Interfaces - Peukert, Wolfgang; Sommer, Marc (Elsevier B.V., 2007)
The postulated grinding limit at around half a micron that has existed for decades does not exist. Particle sizes down to 10 nm can be obtained. Nanomilling in aqueous and non-aqueous media becomes possible when the particulate interfaces are carefully controlled to prevent agglomeration of the broken fragments. Particle stability ensures also low suspension rheology. Any influence of the type of mill is not pronounced, if it exists at all. Important features are small milling beads, a high energy density in the mill, i.e. stirrer speeds in the range of 6-12 m/s and inhibition of agglomeration. Stabilization must be faster than the breakage kinetics. The latter can be estimated from population balance models. Ionic stabilization is preferable wherever it works because this mechanism is rather simple and can be detected on-line during milling by means of electro-acoustic spectroscopy. Even though stabilization can be achieved by the steric mechanism more research is necessary to understand details of the stabilization process. Nanomilling is a neat example which shows that real breakthroughs become possible even in very old and traditional technologies by fundamental studies of the underlying mechanisms. Nanomilling became, thus, an option for those who look for simple and versatile processes to nanoparticles. © 2007.
Keywords: nano; particle; milling; interface; interaction; energy

Chapter 20 Modelling of Mills and Milling Circuits - Peukert, Wolfgang; Toneva, Petya Ivanova (2007)
This chapter provides an overview of the existing mathematical models for the simulation of grinding and classification in mill–classifier circuits not only for ball mills but also for other mill types. Examples of the simulation of closed circuits are divided according to the mill type and the level of sophistication introduced into the models. Milling circuits are used in various industrial sectors to achieve desired product size distributions and product properties. The optimization and control of milling circuits is of high technological importance. Various models of mills and milling circuits are published in the literature with different precision and degree of sophistication. Mostly the grinding and classification are investigated separately and then both unit operations are connected into a mathematical model by the recirculation feed. To provide cost and time savings as well improvement of productivity through optimization of a grinding circuit a mathematical simulation of the process can be applied.
Keywords: milling; modeling; mathematical; grinding; classification; ball; mill; optimization

Characterisation of grinding-relevant particle properties by inverting of a population balance model - Vogel, Lutz; Peukert, Wolfgang (Particle & Particle Systems Characterization, 2002)
An approach for the quantitative characterisation of feed materials in impact grinding is presented. With the help of dimensional reasoning and a fracture mechanic model two material parameters can be derived which describe the breakage probability quantitatively. The influence of stress intensity (impact energy), stress number, initial particle size and material are separated clearly. The two derived material parameters can be determined by single particle impact experiments with narrow size fractions of the feed material. A single mastercurve for the selection function of five different polymers, limestone and glass describes the breakage behaviour for two decades of initial particle size. The procedure using narrow feed size fractions can be simplified by using feed material with a broad particle size distribution. Then the appropriate population balance has to be inverted in order to determine the particle properties. Both, the population balance and the inversion are presented and validated with experimental results.
UnivIS-Import:2015-03-09:Pub.2002.tech.ITC.mechve.charac_6
Keywords: Breakage probability; Comminution; Mastercurve; Population balance

Characterization of a downer reactor for particle rounding - Sachs, Marius; Friedle, Maximilian; Schmidt, Jochen; Peukert, Wolfgang; Wirth, Karl-Ernst (Powder Technology, 2016)
The gradual shift of rapid prototyping towards additive manufacturing (AM) implies higher demands on the available material. So far, most of the processes as laser beam melting (LBM) rely on polyamide as PA12. To overcome limitations and to address this lack of suitable polymer material with a fine particle size, Schmidt et al. [1] have established a wet-grinding process which allows the production of very fine polymer particles. Since the ground product shows a rather bad flowability, further treatment is necessary to enable the use of this material in AM. A rounding of the chiseled particles can improve the flowability [2]. This treatment changes the morphology of the particles by surface tension forces in the molten state [3]. To accomplish rounding of the polymer powder, a downer reactor in semi-industrial scale has been established and will be characterized in this article. Main topics are the powder dispersion, the inlet geometry and its influence on the gas flow behavior inside the downer. This was achieved by combining basic simulation and experimental data. Furthermore, the heat distribution and agglomeration in the gas phase were investigated as important parameters of the process. Finally, a proof of concept by rounding wet ground PBT material was successfully conducted. The product was investigated to obtain data about a change in particle size and polymeric structure.
Keywords: CFD; Downer reactors; Laser beam melting; Particle rounding; Polymers

Characterization of complex particle properties by mobility-classified mass spectrometry – A case study for glutathione capped gold nanoclusters - Lübbert, Christian; Peukert, Wolfgang (Journal of Aerosol Science, 2024)
CRIS-Team Scopus Importer:2024-03-29

Characterization of Electrospray Drop Size Distributions by Mobility-Classified Mass Spectrometry: Implications for Ion Clustering in Solution and Ion Formation Pathways - Lübbert, Christian; Peukert, Wolfgang (Analytical Chemistry, 2021)
One of the outcomes of electrospray ionization is the size distribution of the droplets, which determines, together with the solvent composition and the source gas temperature, the minimum distance from the sprayer tip to the mass spectrometer inlet and therefore the ion transfer efficiency. Even more importantly, the average number of analyte molecules and, if present, contaminant species per droplet depend on the drop size. Consequently, the drop size distribution is a key parameter in nonspecific ion clustering in solution and ion suppression. The finding that small droplet sizes improve the mass spectral quality led to the development of nanoelectrospray sources, which dispense liquid flow rates below 0.1 μL/min and can generate drops with diameters smaller than 100 nm. However, current discussions on the effect of drop size on ion formation pathways and efficiencies remain qualitative because the exact drop size distributions are unknown. Here, we show that ion mobility-classified mass spectrometry of raffinose cluster ions allows us to determine very precisely the drop size distribution generated by the electrospray source in positive- and negative-ion modes. Based on the derived drop size distributions, we can quantitatively predict nonspecific ion clustering and can extract accurate probabilities for emission of species from parent drops upon Coulomb fission.

Characterization of gas phase temperatures in dependence of particle presence in the flame spray pyrolysis process - Peukert, Wolfgang; Gao, Yi; Kögler, Andreas; Kilian, Daniel; Seeger, Thomas; Leipertz, Alfred; Engel, Sascha (CLEO: Applications and Technology, CLEO_AT 2012, 2012)
We introduce a novel strategy to acquire gas phase temperatures by O2 pure rotational CARS during flame spray pyrolysis (FSP) for silica production. RCARS benefits from a polarization filtering technique that is essential in particle and droplet environments. Particle containing regions were located by correlating laser-induced breakdown (LIB) in a particle-laden and a particle-free flame at different heights. Measured temperatures in the particle regime show significantly lower flame temperatures for particle-laden flames since energy is dissipated rapidly by radiation heat transfer in the presence of particles. ©2011 Optical Society of Americ
Keywords: gas; phase; flame; spray; pyrolysis; polarization; laser

Characterization of gold films by surface plasmon spectroscopy: Large errors and small consequences - Vogel, Nicolas; et al. (Surface Science, 2009)
Evaporated gold films have a smooth interface with their substrate and a rougher top surface. We investigate the optical response of such a film by excitation of surface plasmons both on the tough and on the smooth side. The smooth side, although polycrystalline, has an optical response that is very similar to a monocrystalline surface. The film can be modeled as two-layers with significantly different optical constants. For investigations on thin dielectric films though, this heterogeneity introduces only a negligible error. (C) 2008 Elsevier B.V. All rights reserved.
Keywords: Thin gold films; Surface plasmons; Roughness; Template stripping

Characterization of mixing in a T-mixer: A combined experimental and numerical study - Peukert, Wolfgang; Schwarzer, Hans-Christoph; Manhart, Michael (European Conference on Mixing, 2003)
UnivIS-Import:2015-04-16:Pub.2003.tech.ITC.mechve.charac
Keywords: mixing; simulation

Characterization of nanofluids in evaporating droplets by dynamic light scattering - Wu, Wenchang; Panduro Vela, David; Bück, Andreas; Fröba, Andreas Paul (Measurement, 2023)
The diffusion of nanoparticles in nanofluids in form of pendant drops and levitated droplets is characterized by dynamic light scattering. In combination with a heterodyne detection scheme, particle diffusivity in pendant drops can be determined by this method. The diffusivities therein correspond well to the values measured inside a cuvette. During evaporation, crust formation in the drop can also be identified by the method. Dynamic light scattering experiments for levitated droplets are performed with an ultrasonic acoustic levitator. Again, the dynamics of the particle number density fluctuations inside the droplet can be characterized, but the derivation of particle diffusivities is not yet possible. In both cases, the evolution of the characteristic time reflecting the diffusive process of nanoparticles can be determined until the point of crust formation. In summary, the applicability and limitation of dynamic light scattering for the characterization of diffusion of particles in evaporating drops are identifie
Keywords: Drying; Diffusion; Levitation; Dynamic light scattering; Pendant drop; Nanofluid

Characterization of particle surfaces - Peukert, Wolfgang; Götzinger, Martin (World Congress Particle Technology 4, 2002)
UnivIS-Import:2015-04-16:Pub.2002.tech.ITC.mechve.charac_34
Keywords: particle; surface

Characterization of Polymer Powders for Selective Laser Sintering - Schmidt, Jochen; Dechet, Maximilian; Gomez Bonilla, Juan Sebastian; Hesse, Nicolas; Bück, Andreas; Peukert, Wolfgang (Proceedings of the 30th Annual International Solid Freeform Fabrication Symposium 2019, 2019)

Characterization of Pulse and Direct Current Methods for Electrodeposition of Ni-Co Composite Coatings Reinforced with Nano and Micro ZnO Particles - Ghazanlou, Siavash Imanian; Farhood, A. H. S.; Ahmadiyeh, Somayeh; Ziyaei, Ehsan; Rasooli, Ali; Hosseinpour, Saman (Metallurgical and Materials Transactions A-Physical Metallurgy and Materials Science, 2019)
Ni-Co composite coatings reinforced with ZnO particles are prepared by either pulsed current (PC) or direct current (DC) electrodeposition methods. X-ray diffraction, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and EDX mapping are employed to investigate phase structure, surface morphology, elemental composition, and elemental distribution of coating, respectively. The effects of electrodeposition parameters such as stirring rate, average current density, and ZnO particles concentration on the microhardness of electrodeposited composite coating reinforced with nano and micro ZnO particles are investigated. Optimal values are determined for all of the above-mentioned parameters, which result in the maximum hardness of the coating. Any deviation from the optimal parameters leads to a reduction of the coating's microhardness. The SEM, atomic force microscopy (AFM), wear test, and electrochemical examinations revealed that changing the electrodeposition method from DC to PC and varying the size of ZnO particles from micro to nano affect the surface morphology from rough to smooth and reduce the surface friction coefficient, both of which enhanced the wear resistance of the coating and improved its corrosion resistance. The SEM results from worn surfaces illustrated that the size of reinforcing ZnO particles and the electroplating method change the wear mechanisms and worn surface morphology.
CRIS-Team WoS Importer:2019-03-15

Characterization of stressing conditions in mills – A comprehensive research strategy based on well-characterized model particles - Strobel, Alexander; Romeis, Stefan; Wittpahl, Sandra; Herre, Patrick; Schmidt, Jochen; Peukert, Wolfgang (Powder Technology, 2017)
Despite the abundant industrial use of various wet mills a detailed understanding of the mechanisms involved is far from being complete. During comminution stress distributions are applied to the individual particles of a processed suspension. In fact, the type of stressing and the acting stress energies are distributed. The distributions of acting stress energy and number of stress events per product particle are governed by the used mill and its operational conditions. Mill functions link the stress energy and stress number distributions to the operating parameters and are so far unknown. We introduce a new methodology to directly characterize the effective stress energy and effective stress number distributions within stirred media mills: Mechanically fully characterized spherical particles are used as particulate probes. The underlying finite element model for the energetic behavior of the probes during uniaxial compression is supported by manipulation experiments on the single particle level. The deformation behavior of individual particles and the respective changes of the particles’ shapes are used to determine the stressing history of the particles and hence the stress energy and stress number distributions in the mill. Experimental limitations and prospects of the proposed methodology are outlined in detail. The new approach is comprehensively discussed for a lab-scale stirred media mill operated at exemplary process conditions. The transfer to other mills or unit operations, however, is straightforward.
Keywords: Finite element modelling; Single particle compression; Single particle probes; Stress energy distribution; Stress number distribution

Characterization of surface properties of carbon black and graphite - Peukert, Wolfgang; Götzinger, Martin (Annales Universitatis Mariae Curie-Sklodowska, Sectio AA Chemia, 2002)
Carbon black is used in several technical applications. Fillers in tires, black pigments in printing technology or synthetic cloth fibers are only a few examples. Because of the small particle size of carbon blacks, the surface properties have a great influence on the product property . We studied two different carbon black that show a large difference up to 20% in rolling drag when used as filler in tires. Different roughness or diverse polar groups on the surfaces are possible reasons for this. Morphology, surface structure and chemical surface composition of carbon black are not well defined. For such systems, TGA-MS and gas adsorption are powerful tools to analyze surface properties. We use adsorption equilibria in the Henry-region that reflect the interaction of molecules with the particle surfaces. From measured Henry-coefficients and known atomic surface structure, dispersive interaction parameters of the solid, e.g. a Hamaker-constant, can be determined by inversely solving the applied adsorption model. This method can be used to characterize carbon black if the interactions of different molecules with carbon atoms are calibrated on a defined surface like graphite. From known interaction potentials of various probe molecules, structural information like surface roughness of carbon black can be determined
UnivIS-Import:2015-04-16:Pub.2002.tech.ITC.mechve.charac

Characterization of the Flow Pattern of a Gas/Solids Flow in a Downer Reactor - Wirth, Karl-Ernst; Lehner, Peter (Chemical Engineering Science, 1999)
The downer reactor is discussed in the literature as a new type of gas/solids reactor. Due to the cocurrent movement of gas and solids in the direction of gravity, it is expected that a narrow residence time distribution and a flow regime close to plug flow can be established in this reactor. Recent studies show, that the gas/solids distributor on the top of the downer greatly influences the flow conditions. However, the influence of the physical properties of the solids and the plant setup on the flow behavior is still ambiguous. Therefore, experimental investigations concerning the local and cross-sectional solids distribution have been carried out under different operating conditions (variation of superficial gas velocity and solids circulation rate) and with different solids (glass beads, d/p= 60 and 130 l/m). An X-ray computed tomography system has been used to obtain the solids concentration distribution in the entire cross-section at different axial positions of the downer. Pressure poles can provide additional information about the overall behavior of the gas/solids flow. Results show a signifcant infuence of the entrance conditions of the gas/solids flow on the flow pattern in the region below the gas/solids distributor. After a signicant length, depending on solids properties and superficial gas velocity, the flow behavior becomes independent of the entrance conditions. Superficial gas velocity not only influences the entrance length, but also the solids distribution in the entire cross-section of the downer.
UnivIS-Import:2015-04-20:Pub.1999.tech.ITC.mechve.charac_61
Keywords: Fluidization; Hydrodynamics; Multiphase flow; Process tomography; Downer; Circulating fluidized bed

Characterization of the grinding behaviour in a single particle impact device: studies on pharmaceutical powders. - Peukert, Wolfgang; Meier, Matthias; John, Edgar; Wirth, Karl Ernst; Wieckhusen, Dierk (European Journal of Pharmaceutical Sciences, 2008)
The grinding behaviour of different materials can be described by the two material parameters fMat and Wm,min [Vogel, L., Peukert, W., 2003. Breakage behaviour of different materials-construction of a mastercurve for the breakage probability. Powder Technol. 129, 101-110]. fMat describes the resistance of particulate material against fracture in impact comminution, Wm,min characterizes the specific energy which a particle can take up without comminution. The material parameters are determined experimentally by single particle impact tests. This concept is also applicable to pharmaceutical powders, as will be shown in this work. A device is presented for the characterization of particles with sizes down to a few 10 microm. Particles are dispersed and accelerated in an air stream which is flowing against an impact plate. The impact velocity is controlled by the air flow. An LDA system enables the measurement of particle velocities. The results obtained with this jet mill are in accordance to those obtained from another single particle impact device used by Vogel and Peukert, in which the influence of fluid flow is completely avoided. Since the new device is especially designed for finer powders, it will allow a more detailed analysis of the material parameters at smaller particle sizes. Additionally, a new analysis method has been developed in order to determine the breakage probability not from sieve analysis but from laser light diffraction (LLD) data by using a population balance.
Keywords: grinding; comminution; particle

Characterization of the Local Flow Structures in a High Loaded Riser-Reactor at Elevated Temperatures - Wirth, Karl-Ernst; Strabel, Michael (Proceedings Fluidization XI, 2004)
UnivIS-Import:2015-04-16:Pub.2004.tech.ITC.mechve.charac_1
Keywords: Fluidization; bed

Characterization of the Native Passive Film on Ferrite and Austenite Phases of Sensitized 2205 Duplex Stainless Steel - Rahimi, Ehsan; Rafsanjani-Abbasi, Ali; Davoodi, Ali; Hosseinpour, Saman (Journal of The Electrochemical Society, 2019)
The influence of isothermal sensitization of 2205 duplex stainless steel (DSS) in 850°C was quantified using double-loop electrochemical potentiodynamic reactivation test. We assessed the microstructure, Volta potential distribution, and semiconductive properties of the native passive film on individual austenite and ferrite phases of solution annealed and sensitized DSS, using optical and scanning electron microscopy, scanning Kelvin probe force microscopy, and scanning tunneling spectroscopy. Beside conventionally used line profile scans, we used a multi-modal Gaussian distribution method for analyzing the Volta potential distribution over the entire scanned area. The Volta potential distribution evaluations indicated that the driving force for preferential corrosion at the ferrite/austenite interface in DSS increases after sensitization. Scanning tunneling spectroscopy revealed that the formation of intermetallic phases and depleted zones in DSS after sensitization, decrease the surface energy bandgap in both austenite and ferrite phases, whereas the density of electronic states in these phases increases, compared to those of solution annealed DSS. The multi-analytical approach that is used in this research provides complementary evidence for the detrimental effects of sensitization on corrosion resistance of DSS.
Keywords: Corrosion; Surface Science; Duplex Stainless Steel; scanning tunneling spectroscopy; Sensitization

Characterization of the passive layer on ferrite and austenite phases of super duplex stainless steel - Rahimi, E.; Kosari, Ali; Hosseinpour, Saman; Davoodi, Ali; Zandbergen, H.; Mol, Johannes M.C. (Applied Surface Science, 2019)
In this study, we report on a combined microscopic, analytical and electrochemical characterization of the nanoscopic passive layer on a tungsten‑molybdenum-containing super duplex stainless steel. We used scanning transmission electron microscopy/energy dispersive X-ray spectroscopy, scanning Kelvin probe force microscopy, scanning tunneling spectroscopy, and Mott–Schottky electrochemical impedance spectroscopy analysis to correlate the local chemical composition and electronic properties of passive layers on austenite and ferrite phases. The passive layer on the ferrite phase contains a higher amount of Mo, W, and Cr, which accommodates a higher nobility of ferrite and a higher local energy of the band gap compared to those on the austenite. The two aforementioned phases exhibit a different composition and semi-conductive properties of their passive layers leading to dissimilar local corrosion susceptibility. These findings are of pivotal importance in further studies of austenite and ferrite phase resolved corrosion resistance of duplex stainless steel demanding a dedicated alloying strategy.
CRIS-Team Scopus Importer:2019-08-30
Keywords: A. Stainless steel; B. SKPFM; B. STEM/EDS; B. STS; C. Passive film

Characterizations of drug carrying magnetic nanoparticles for tumor therapy: Biological outcome and first immunological aspects - Dürr, Stephan; Tietze, Rainer; Lyer, Stefan; Janko, Christina; Schreiber, Eveline; Mann, Johannes; Turcu, R.; Gitter, K.; Odenbach, S.; Vasylyev, Serhiy; Herrmann, Martin; Peukert, Wolfgang; et al. (Magnetohydrodynamics, 2013)
Nanosized magnetic drug carriers offer a splendid prospect for directed drug application. The increased drug concentration in cancer tissue reached for this kind of application enables therapeutic effects on tumors that cannot be achieved using conventional chemotherapeutic treatment. Characterizing the drug targeting system and its behavior in vitro is necessary for understanding the biological outcome. In our studies, IRspectroscopy shows covalent binding of the biocompatible fatty acid layer. Although binding of mitoxantrone (MTO) to particles is hardly defined, considerable amounts of drug can be carried by nanoparticles. Furthermore, the nanosized drug carrier complex has to be investigated due to its biological outcome. Real-time cell analysis is useful to observe the therapeutic particles concerning their outcome in cell culture time-resolved up to several days. First experiments in concordance to a conventional assay show that the effectivity of nanoparticle bound MTO in cell culture is higher than treatment with pure MTO. A preliminary study demonstrates that the burden of the immune system is reduced by Magnetic Drug Targeting (MDT) vs. conventional chemotherapy. For a better understanding of MDT for cancer treatment, further studies have to be done to explain especially the binding behavior of superparamagnetic iron oxide nanoparticles to the respective chemotherapeutic agent.
Keywords: nano; magnetic; characterization; particle; agent

Characterizing a Vertical Gas-Solid-Flow by Means of Gamma-Absorption-Tomographie - Wirth, Karl-Ernst; Schiewe, Thilo (Preprints Frontiers in Industrial Process Tomography II, 1997)
UnivIS-Import:2015-04-16:Pub.1997.tech.ITC.mechve.charac

Chemisorbed and Physisorbed Water at the TiO2/Water Interface - Hosseinpour, Saman; Tang, Fujie; Wang, Fenglong; A. Livingstone, Ruth; Schlegel, Simon; Ohto, Tatsuhiko; Bonn, Mischa; Nagata, Yuki; Backus, Ellen (Journal of Physical Chemistry Letters, 2017)
The interfacial structure of water in contact with TiO2 is the key to understand the mechanism of photocatalytic water dissociation as well as photoinduced superhydrophilicity. We investigate the interfacial molecular structure of water at the surface of anatase TiO2, using phase-sensitive sum frequency generation spectroscopy together with spectra simulation using ab initio molecular dynamic trajectories. We identify two oppositely oriented, weakly and strongly hydrogen-bonded subensembles of O-H groups at the superhydrophilic UV irradiated TiO2 surface. The water molecules with weakly hydrogen-bonded O-H groups are chemisorbed, i.e. form hydroxyl groups, at the TiO2 surface with their hydrogen atoms pointing toward bulk water. The strongly hydrogen-bonded O-H groups interact with the oxygen atom of the chemisorbed water. Their hydrogen atoms point toward the TiO2. This strong interaction between physisorbed and chemisorbed water molecules causes superhydrophilicity.
Keywords: NaN

Chiral Plasmonic Shells: High-Performance Metamaterials for Sensitive Chiral Biomolecule Detection - Yang, Xiu; Huang, Shanshan; Chikkaraddy, Rohit; Görlitzer, Eric; Chen, Feiliang; Du, Jinglei; Vogel, Nicolas; Weiss, Thomas; Baumberg, Jeremy; Hu, Yidong (ACS Applied Materials and Interfaces, 2022)
Low-cost and large-area chiral metamaterials (CMs) are highly desirable for practical applications in chiral biosensors, nanophotonic chiral emitters, and beyond. A promising fabrication method takes advantage of self-assembled colloidal particles, onto which metal patches with defined orientation are created using glancing angle deposition (GLAD). However, using this method to make uniform and well-defined CMs over macroscopic areas is challenging. Here, we fabricate a uniform large-area colloidal particle array by interface-mediated self-assembly and precisely control the structural handedness of chiral plasmonic shells (CPSs) using GLAD. Strong chiroptical signals arise from twisted currents at the main, corner, and edge of CPSs, allowing a balance between strong chiroptical and high transmittance properties. Our shell-like chiral geometry shows excellent sensor performance in detecting chiral molecules due to the formation of uniform superchiral fields. Systematic investigations optimize the interplay between peak and null point resonances in different CPSs and result in a record consistency chiral sensor parameter U, i.e., 3.77 for null points and 0.0867 for peaks, which are about 54 and 1.257 times larger than the highest value (0.068) of previously reported CMs. The geometrical chirality, surface plasmonic resonance, chiral surface lattice resonance, and chiral sensor performance evidence the chiroptical effect and the excellent chiral sensor performance.
Keywords: chiral field; chiral metamaterials; chiral sensor; chiroptical effect; glancing angle deposition; microsphere self-assembly

Chiral Surface Lattice Resonances - Görlitzer, Eric; Mohammadi, Reza; Nechayev, Sergey; Volk, Kirsten; Rey, Marcel; Banzer, Peter; Karg, Matthias; Vogel, Nicolas (Advanced Materials, 2020)
Collective excitation of periodic arrays of metallic nanoparticles by coupling localized surface plasmon resonances to grazing diffraction orders leads to surface lattice resonances with narrow line width. These resonances may find numerous applications in optical sensing and information processing. Here, a new degree of freedom of surface lattice resonances is experimentally investigated by demonstrating handedness-dependent excitation of surface lattice resonances in arrays of chiral plasmonic crescents. The self-assembly of particles used as mask and modified colloidal lithography is applied to produce arrays of planar and 3D gold crescents over large areas. The excitation of surface lattice resonances as a function of the interparticle distance and the degree of order within the arrays is investigated. The chirality of the individual 3D crescents leads to the formation of chiral lattice modes, that is, surface lattice resonances that exhibit optical activity.
CRIS-Team Scopus Importer:2020-05-02
Keywords: chirality; colloidal lithography; optical activity; plasmonics; surface lattice resonances

Choosing the right nanoparticle size-designing novel ZnO electrode architectures for efficient dye-sensitized solar cells - Pfau, Markus; Kunzmann, Andreas; Segets, Doris; Peukert, Wolfgang; Wallace, Gordon G.; Officer, David L.; Clark, Timothy; Costa, Ruben Dario; Guldi, Dirk Michael (Journal of Materials Chemistry A, 2017)
A novel concept for constructing optimized ZnO-based photoanodes as integrative components of dye-sensitized solar cells (DSSCs) is realized by deploying differently sized nanoparticles, ranging from 2 to 10 nm, together with commercially available 20 nm nanoparticles. The 2 nm nanoparticles were used to construct an efficient buffer layer for transparent electrodes based on 10 nm nanoparticles, resulting in a relative increase of device efficiency from 1.8 to 3.0% for devices without and with a buffer layer, respectively. A mixture of 10 and 20 nm nanoparticles was optimized to maximize the diffuse reflection and to minimize the charge transport resistance in a light-scattering layer. This optimization resulted in a homogenous layer of more than 15 mm that provided a device efficiency of 3.3%. The buffer layer, transparent electrode, and light-scattering electrode, were then combined to give an overall efficiency of around 5%. Thus, this work demonstrates that varying the electrode architecture with nanoparticles of different diameters is a powerful strategy for improving the overall efficiency of ZnO-based DSSCs.

Chromatographic property classification of narrowly distributed ZnS quantum dots - Süß, Sebastian; Bartsch, Katja; Wasmus, Christina; Damm, Cornelia; Segets, Doris; Peukert, Wolfgang (Nanoscale, 2020)
Although optimized synthesis methods for nanoparticles (NPs) on small scale can lead to narrow particle size distributions (PSDs) and thus defined optical properties, in particular during scale-up, an additional classification step must be applied to adjust the particle properties according to the needs of the later application. NP chromatography is a promising separation method, which can be potentially transferred to preparative and industrial scale. Herein, we demonstrate that remarkable classification of ZnS quantum dots (QDs) with respect to the fundamental band gap energy is achieved by chromatography although the PSD of the feed material is already very narrow (1.5-3.0 nm). We investigated the interactions of ZnS QDs with stationary and mobile phase materials in order to select a proper material couple so that irreversible NP adhesion, agglomeration, decomposition or dissolution of the ZnS QDs during the chromatographic experiments are avoided and highly reproducible chromatograms are obtained. Using a fraction collector, the already narrowly size distributed feed material was separated into coarse and fine fractions with distinct band gap energies. For characterization of the chromatographic fractionation, quantities known from particle technology, i.e. separation efficiency, cut size and yield, were adapted to the band gap energy distributions accessible from UV/Vis spectroscopy. The optimization of process conditions (flow rate, temperature, switching time of the fraction collector) allows fine-tuning of the property classification and therefore of the optical properties within the narrow distribution of the ZnS QDs. Our study shows the strength and high potential of chromatography for preparative and continuous separation of NPs even in case of narrow size-distributed sub-10 nm semiconductor QDs.
CRIS-Team Scopus Importer:2020-06-19

Classification and characterization of multimodal nanoparticle size distributions by size-exclusion chromatography - Gromotka, Lukas; Uttinger, Maximilian; Schlumberger, Carola; Thommes, Matthias; Peukert, Wolfgang (Nanoscale, 2022)
Size-exclusion chromatography (SEC) is a well-known, versatile and scalable technique for the separation of molecules according to their hydrodynamic size in solution as well as for the determination of molecular weight distributions of polymers. In this paper we demonstrate and generalize the applicability of SEC to the classification and characterization of multimodal distributions of nanoparticles over a broad size range. After calibration with gold standards from 5 nm to 80 nm, the calibration curve is used to determine the particle size distributions (PSDs) of the standards which are in agreement with comprehensive nanoparticle size analysis by analytical ultracentrifugation. Universal calibration curves independent of the core material and surface functionality can be constructed if the pore diameter of the stationary phase exceeds the particle diameter by a factor of 2-3. Mixtures of gold standards are separated by SEC and evaluated in terms of peak resolution and size-dependent separation curves depending on how well the individual peaks are resolved. Baseline separation of a multimodal mixture is observed and its PSD is determined. Mixtures can be fractionated into coarse and fine fractions with nm precision at different switching times of the fraction collector. Our study demonstrates the strength of SEC to classify multimodal PSDs as well as to accurately determine size distributions of complex nanoparticle dispersions over a broad size range.

Classification of Different Zones in a Flame Spray Pyrolysis Process - Münsterjohann, Bettina; Engel, Sascha; Kilian, Daniel; Will, Stefan; Peukert, Wolfgang (International Workshop Nucleation and Early Stages of Particle Formation, 2014)

Classification of Nanoparticles by Size-Selective Precipitation: The Role of Solubility Parameters - Süß, Sebastian; Sobisch, T.; Lerche, D.; Mori, Y.; Peukert, Wolfgang; Segets, Doris (Chemie Ingenieur Technik, 2016)

Classification of Zinc Sulfide Quantum Dots by Size: Insights into the Particle Surface–Solvent Interaction of Colloids - Peukert, Wolfgang; Lutz, Christian; Yamamoto, Kyoko; Komada, So; Süß, Sebastian; Mori, Yasushige; Segets, Doris (Journal of Physical Chemistry C, 2015)
We present a detailed study on the classification of ZnS quantum dots (QDs) by size selective precipitation (SSP). SSP allows the postsynthetic narrowing of a given feed distribution and is usually realized by titration of a poor solvent into a suspension of dispersed particles. Thereby preferred flocculation of larger structures is induced. Our results confirm that SSP is a highly robust process, following a law of mass action. That means a certain solvent composition always leads to the same ratio between coarse and fines particles with respect to a specific particle size xi. This ratio is independent of the particle size distribution (PSD) of the feed, the washing history of the particles, and the solid concentration of the particles. Regarding the illustration of our findings, we established a combined approach that takes Hansen solubility parameters (HSP) of solvent mixtures as well as changing van der Waals interactions into account. Relating both to each other, a size-dependent region of enhanced solubility is clearly identified. Our concept allows a differentiation between volume-related effects like van der Waals interactions and surface-related effects like the interaction of a ligand with a solvent mixture. A comprehensive interpretation of classification results obtained with different good solvents and poor solvents enables to deduce a general strategy for the demanding determination of HSP for small colloids. Our work makes an important contribution to the design of an appropriate colloidal postprocessing which is applicable to larger quantitie
Keywords: ZnS; quantum; dot; selctive; precipitation; flocculation; structure; hansen; solubitlity; size

Classifier performance during dynamic fine grinding in fluidized bed opposed jet mills - Köninger, Benedikt; Spoetter, Christian; Romeis, Stefan; Weber, Alfred P.; Wirth, Karl-Ernst (Advanced Powder Technology, 2019)
Dry grinding of particles to sizes below 10 µm can be realized in fluidized bed opposed jet mills. In these mills the energy for comminution is supplied by pressurized gas, which is introduced through focused nozzles. The gas transports the material towards an internal classifier, which separates the fines from the coarse material. The fines are discharged whereas the coarse material is recycled. Within this study special attention is paid to separation at the classifying wheel. Limestone batch grinding experiments were performed in a fluidized bed opposed jet mill equipped with on-line and in-line probes: The particle size distributions (PSDs) of the product flow and the solid concentration below the classifier were determined on-line. The flow field around the classifier was recorded by a high-speed camera and off-line measurements of the mill inventory and its PSD were performed. Our measurements reveal that the solid transport from the milling zone to the classifier and the classifier performance strongly depend on solid concentration. Increasing the solid feed concentration or the classifier wheel speed leads to unwanted accumulation of product-sized particles inside the mill. In particular, we find high solid loadings of up to 1.05 g⋅g−1 and strong cluster formation (local zones of high solid concentration) in the vicinity of the classifier blades. Estimated separation efficiency curves of the classifier show a strong “fish-hook effect” which increases with the solid concentration. Our findings are relevant for future process optimization by careful tuning of grinding performance, holdup and classifier speed.
CRIS-Team Scopus Importer:2019-06-21
Keywords: Classification; Fluidized bed opposed jet mill; High-speed imaging; Internal separation curve; Process dynamics

Cleaning matters! - Mahmoud, Ahmed Salaheldin Abdelhamid; Segets, Doris (ACS Combinatorial Science, 2019)
Translation of a manual process to high throughput for research and development requires special consideration. One important and often unreported aspect is the establishment of an efficient cleaning routine. This becomes significant, as precious time and in particular material would be lost, i.e., when low-quality high throughput experimentation is involved. We present a fully automated cleaning routine of the challenging synthesis of cadmium selenide quantum dots. Manual, semi-automated and fully automated cleaning protocols were executed and compared in terms of spectral similarities of the synthesized colloids. Only the fully automated protocol enabled true 24/7 operation.
CRIS-Team Scopus Importer:2019-10-18
Keywords: Automation; Cleaning; High throughput experimentation; Nanocrystals; Quantum dots

Coaten von Lebensmitteln/Pharmazeutika - Wirth, Karl-Ernst (-, 2001)
UnivIS-Import:2015-04-16:Pub.2001.tech.ITC.mechve.coaten

Cobalt-Releasing 1393 Bioactive Glass-Derived Scaffolds for Bone Tissue Engineering Applications - Hoppe, Alexander; Jokic, Bojan; Janackovic, Djordje; Fey, Tobias; Greil, Peter; Romeis, Stefan; Schmidt, Jochen; Peukert, Wolfgang; Lao, Jonathan; Jallot, Edouard; Boccaccini, Aldo R. (ACS Applied Materials and Interfaces, 2014)
Loading biomaterials with angiogenic therapeutics has emerged as a promising approach for developing superior biomaterials for engineering bone constructs. In this context, cobalt-releasing materials are of interest as Co is a known angiogenic agent. In this study, we report on cobalt-releasing three-dimensional (3D) scaffolds based on a silicate bioactive glass. Novel melt-derived "1393" glass (53 wt % SiO2, 6 wt % Na2O, 12 wt % K2O, wt % MgO, 20 wt % CaO, and 4 wt % P2O5) with CoO substituted for CaO was fabricated and was used to produce a 3D porous scaffold by the foam replica technique. Glass structural and thermal properties as well as scaffold macrostructure, compressive strength, acellular bioactivity, and Co release in simulated body fluid (SBF) were investigated. In particular, detailed insights into the physicochemical reactions occurring at the scaffold-fluid interface were derived from advanced micro-particle-induced X-ray emission/Rutherford backscattering spectrometry analysis. CoO is shown to act in a concentration-dependent manner as both a network former and a network modifier. At a concentration of 5 wt % CoO, the glass transition point (T-g) of the glass was reduced because of the replacement of stronger Si-O bonds with Co-O bonds in the glass network. Compressive strengths of >2 MPa were measured for Co-containing 1393-derived scaffolds, which are comparable to values of human spongy bone. SBF studies showed that all glass scaffolds form a calcium phosphate (CaP) layer, and for 1393-1Co and 1393-5Co, CaP layers with incorporated traces of Co were observed. The highest Co concentrations of similar to 12 ppm were released in SBF after reaction for 21 days, which are known to be within therapeutic ranges reported for Co2+ ions.
Keywords: cobalt; hypoxia; bioglass; bioactive; scaffold; bone tissue engineering; angiogenesis

Collapse-induced phase transitions in binary interfacial microgel monolayers - Harrer, Johannes; Ciarella, Simone; Rey, Marcel; Loewen, Hartmut; Janssen, Liesbeth M. C.; Vogel, Nicolas (Soft Matter, 2021)
Microgels, consisting of a swollen polymer network, exhibit a more complex self-assembly behavior compared to incompressible colloidal particles, because of their ability to deform at a liquid interface or collapse upon compression. Here, we investigate the collective phase behavior of two-dimensional binary mixtures of microgels confined at the air/water interface. We use stimuli-responsive poly(N-isopropylacrylamide) microgels with different crosslinking densities, and therefore different morphologies at the interface. We find that the minority microgel population introduces lattice defects in the ordered phase of the majority population, which, in contrast to bulk studies, do not heal out by partial deswelling to accommodate in the lattice. We subsequently investigate the interfacial phase behavior of these binary interfacial assemblies under compression. The binary system exhibits three distinct isostructural solid-solid phase transitions, during which the coronae between two small particles collapse first, followed by the collapse between small-large and large-large microgel pairs. A similar hierarchy of phase transitions is found for mixtures of microgels and core-shell particles. Simulations based on augmented potentials qualitatively reproduce the experimentally observed phase transitions. We rationalize the presence of this hierarchy in phase transitions from differences in the interfacial morphology between the species: the larger coronae of softer (and therefore larger) microgels provide a higher resistance to phase transitions compared to the smaller coronae of the more crosslinked microgels and core-shell particles. The control of phase transitions via the molecular architecture further allows the formation of characteristic, flower-like defects by introducing particles with "weaker"coronae that are more prone to collapse with their neighboring particles. Our findings underline the dominating role of the corona for interfacial microgel assemblies, which acts as an energy barrier, shifting the collapse to higher surface pressures. This journal is
CRIS-Team Scopus Importer:2021-05-21

Colloidal Analysis of Particles Extracted from Microalloyed Steels - Hegetschweiler, Andreas; Jochem, Aljosha Rakim; Zimmermann, Anna; Walter, Johannes; Staudt, Thorsten; Kraus, Tobias (Particle & Particle Systems Characterization, 2021)
Different colloidal particle characterization methods are examined for their suitability to determine the particle size distribution of particles extracted from steels. Microalloyed steels are dissolved to extract niobium and titanium carbonitride particles that are important for the mechanical properties of these steels. Such particles have sizes ranging from several nanometers to hundreds of nanometers depending on the precipitation stage during the thermomechanically controlled rolling process. The size distribution of the particles is analyzed by dynamic light scattering (DLS), analytical ultracentrifugation (AUC), and hollow fiber flow field-flow fractionation (HF5) and compared to data obtained for reference particles as well as data from electron microscopy, the standard sizing technique used in metallurgy today. AUC and HF5 provide high-quality size distributions, average over large particle numbers that enables statistical analysis, and yield useful insights for alloy design; however, DLS fails due to a lack of resolution. Important aspects in the conversion and comparison of size distributions obtained for broadly distributed particle systems with different measurement principles and the role of surfactants used in sample preparation are discussed.
CRIS-Team Scopus Importer:2021-06-18
Keywords: colloidal analysis; microalloyed steels; niobium carbonitrides; precipitate analysis; titanium carbonitrides

Colloid process engineering - Peukert, Wolfgang; Kind, Matthias; Rehage, Heinz; Schuchmann, Heike (Springer International Publishing, 2015)
This book deals with colloidal systems in technical processes and the influence of colloidal systems by technical processes. It explores how new measurement capabilities can offer the potential for a dynamic development of scientific and engineering, and examines the origin of colloidal systems and its use for new products. The future challenges to colloidal process engineering are the development of appropriate equipment and processes for the production and obtainment of multi-phase structures and energetic interactions in market-relevant quantities. The book explores the relevant processes and for controlled production and how they can be used across all scales.
Keywords: colloid; multi-phase; process

Coloration in Supraparticles Assembled from Polyhedral Metal-Organic Framework Particles - Wang, Junwei; Liu, Yang; Bleyer, Gudrun; Peukert, Wolfgang; Görlitzer, Eric; Englisch, Silvan; Przybilla, Thomas; Mbah Chrameh, Fru; Engel, Michael; Spiecker, Erdmann; Imaz, Inhar; Maspoch, Daniel; et al. (Angewandte Chemie International Edition, 2022)
Supraparticles are spherical colloidal crystals prepared by confined self-assembly processes. A particularly appealing property of these microscale structures is the structural color arising from interference of light with their building blocks. Here, we assemble supraparticles with high structural order that exhibit coloration from uniform, polyhedral metal–organic framework (MOF) particles. We analyse the structural coloration as a function of the size of these anisotropic building blocks and their internal structure. We attribute the angle-dependent coloration of the MOF supraparticles to the presence of ordered, onion-like layers at the outermost regions. Surprisingly, even though different shapes of the MOF particles have different propensities to form these onion layers, all supraparticle dispersions show well-visible macroscopic coloration, indicating that local ordering is sufficient to generate interference effects.
CRIS-Team Scopus Importer:2022-03-04
Keywords: Emulsion; Metal–Organic Frameworks; Self-Assembly; Structural Color; Supraparticles

Color from hierarchy: Diverse optical properties of micron-sized spherical colloidal assemblies - Vogel, Nicolas; Utech, Stefanie; England, Grant T.; Shirman, Tanya; Phillips, Katherine R.; Koay, Natalie; Burgess, Ian B.; Kolle, Mathias; Weitz, David A.; Aizenberg, Joanna (Proceedings of the National Academy of Sciences of the United States of America, 2015)
Materials in nature are characterized by structural order over multiple length scales have evolved for maximum performance and multifunctionality, and are often produced by self-assembly processes. A striking example of this design principle is structural coloration, where interference, diffraction, and absorption effects result in vivid colors. Mimicking this emergence of complex effects from simple building blocks is a key challenge for man-made materials. Here, we show that a simple confined self-assembly process leads to a complex hierarchical geometry that displays a variety of optical effects. Colloidal crystallization in an emulsion droplet creates micron-sized superstructures, termed photonic balls. The curvature imposed by the emulsion droplet leads to frustrated crystallization. We observe spherical colloidal crystals with ordered, crystalline layers and a disordered core. This geometry produces multiple optical effects. The ordered layers give rise to structural color from Bragg diffraction with limited angular dependence and unusual transmission due to the curved nature of the individual crystals. The disordered core contributes nonresonant scattering that induces a macroscopically whitish appearance, which we mitigate by incorporating absorbing gold nanoparticles that suppress scattering and macroscopically purify the color. With increasing size of the constituent colloidal particles, grating diffraction effects dominate, which result from order along the crystal's curved surface and induce a vivid polychromatic appearance. The control of multiple optical effects induced by the hierarchical morphology in photonic balls paves the way to use them as building blocks for complex optical assemblies-potentially as more efficient mimics of structural color as it occurs in nature.
Keywords: Colloids; Hierarchy; Photonic crystal; Self-assembly; Structural color

Color-PTV measurement and CFD-DEM simulation of the dynamics of poly-disperse particle systems in a pseudo-2D fluidized bed - Jiang, Zhaochen; Hagemeier, Thomas; Bück, Andreas; Tsotsas, Evangelos (Chemical Engineering Science, 2018)
In a pseudo-2D fluidized bed, a new color particle tracking velocimetry (PTV) method, integrating the Voronoi tracking algorithm and the relaxation probability tracking algorithm, is proposed to measure velocities of individual particles with different sizes marked by distinguishable colors. Thorough verification of the color-PTV methodology is conducted based on synthetic images generated from CFD-DEM simulation data, in terms of segmentation bias, segmentation ratio, recovery ratio and error ratio. The novel color-PTV methodology shows very good performance in simultaneously tracking a large number of different individual particles in poly-disperse systems. Experimental results are used to compare with CFD-DEM simulations using different drag models. Simulations with correction for the effect of particle size dispersity in the drag model show significantly better agreement with respect to the mixing index, time-averaged volumetric particle flux, distributions of individual particle velocity as well as distributions of particle granular temperatur
Keywords: CFD-DEM; Color-PTV; Mixing; Size dispersity; Fluidized bed; Granular temperature

Combination of a dielectric continuum model with inverse gas chromatography for the characterization of solid surfaces - Peukert, Wolfgang; Mehler, Carsten; Thielmann, Frank (Adsorption Science & Technology, 2002)
The use of dielectric continuum model for the characterization of solid surfaces was combined for the first time with inverse gas chromatography. Extension of dielectric continuum models to adsorption from the gaseous phase allowed the distributed surface properties of solid surfaces to be determined. An inverse gas chromatograph was used for the measurement of adsorption equilibria as a quick alternative to time-consuming measurements by gravimetric or volumetric set-ups. Combination of the two techniques allowed the rapid determination of the distributed properties of solid surfaces to be effected and the results were interpreted in a fundamental physical sense. This led to a novel and promising way for the rapid and exact characterization of solid surfaces.
UnivIS-Import:2015-03-09:Pub.2002.tech.ITC.mechve.combin
Keywords: dielectric; gas; chromatography; characterization; solid; surface

Combined continuous nanoparticle synthesis with chromatographic size classification - Gromotka, Lukas; Biegel, Markus; Damm, Cornelia; Traore, Nabi; Drobek, Dominik; Spiecker, Erdmann; Peukert, Wolfgang (Advanced Powder Technology, 2024)
In this paper, we report a combination of the continuous flow synthesis of gold nanoparticles (AuNPs) with subsequent purification and narrowing of the particle size distribution (PSD) by size-exclusion chromatography (SEC) by adapting the flow rates of synthesis and classification. First, we show scalability of chromatographic classification with respect to column dimension and the absence of irreversible nanoparticle adhesion on the column material. Two different syntheses lead to a large and widely distributed and a small and narrowly distributed AuNP dispersion, which are classified by a semipreparative column. The PSDs of individual fractions are characterized by analytical SEC. The broadly distributed AuNP dispersion was classified into three fractions with distinct PSDs. For the narrowly distributed AuNPs, the separation is almost independent of the mobile phase flow rate: coarse and fine fractions with almost identical PSDs and separation efficiency curves are observed irrespective of the flow rate. Even NP samples with narrow PSDs can be classified into multiple fractions with tailored PSDs while simultaneously removing dissolved impurities from the dispersion. With our study, we demonstrate the potential of a direct combination of continuous NP synthesis with chromatographic classification for the optimization of final PSDs and the simultaneous purification of nanoparticulate dispersions.
CRIS-Team Scopus Importer:2023-12-15
Keywords: Continuous flow synthesis; Gold nanoparticles; Purification; Size classification; Size-exclusion chromatography

Combined experimental/numerical study on the precipitation of nanoparticles - Peukert, Wolfgang; et al. (Aiche Journal, 2004)
Nanoparticle precipitation in a T-mixer was investigated experimentally as well as through simulations based on the population balance equation coupled with a global mixing model using barium sulfate as the substance under investigation. A detailed predictive precipitation model is presented and the important model parameters are identified: the mixing kinetics, the interfacial energy, and the physicochemical calculation of supersaturation. Furthermore, the capability of the global mixing model was evaluated, achieving good agreement of the mean particle sizes between experimental and simulation results. Many insights into the kinetics and the relevant time scales of the competing steps such as micromixing (mixing at the molecular level), nucleation, growth, and aggregation are obtained. However, some discrepancies in the width of the particle size distributions remain that are attributed to spatial and temporal fluctuations in the flow field and, consequently, in the mixing kinetics that cannot be resolved by the applied global mixing model. © 2004 American Institute of Chemical Engineers.
UnivIS-Import:2015-03-09:Pub.2004.tech.ITC.mechve.combin
Keywords: Barium sulfate; Interfacial energy; Micromixing; Nanoparticle; Population balance equation; Precipitation

Combined in situ quartz crystal microbalance with dissipation monitoring, indirect nanoplasmonic sensing, and vibrational sum frequency spectroscopic monitoring of alkanethiol-protected copper corrosion - Hosseinpour, Saman; et al. (Langmuir, 2013)
In this study, we have applied three techniques to simultaneously and in situ study the initial stage of corrosion of copper protected by a self-assembled monolayer of octadecanethiol (ODT). We combined quartz crystal microbalance with dissipation monitoring (QCM-D), indirect nanoplasmonic sensing (INPS), and vibrational sum frequency spectroscopy (VSFS) and obtained complementary information about mass uptake and optical and spectroscopic changes taking place during the initial corrosion phase. All three techniques are very sensitive to the formation of a corrosion film (thickness in the range 0-0.41 nm) under mildly corrosive conditions (dry air, <0.5% relative humidity). The three techniques yield information about the viscoelasticity of the corrosion film (QCM-D), the homogeneity of the corrosion reaction on the surface (INPS), and the stability of the ODT protection layer (VSFS). Furthermore, by also studying the corrosion process in humid air (ca. 70% relative humidity), we illustrate how the combination of these techniques can be used to differentiate between simultaneously occurring processes, such as water adsorption and corrosion product formation.

Combining Bottom-Up Self-Assembly with Top-Down Microfabrication to Create Hierarchical Inverse Opals with High Structural Order - Schaffner, Manuel; England, Grant; Kolle, Mathias; Aizenberg, Joanna; Vogel, Nicolas (Small, 2015)
Colloidal particles can assemble into ordered crystals, creating periodically structured materials at the nanoscale without relying on expensive equipment. The combination of small size and high order leads to strong interaction with visible light, which induces macroscopic, iridescent structural coloration. To increase the complexity and functionality, it is important to control the organization of such materials in hierarchical structures with high degrees of order spanning multiple length scales. Here, a bottom-up assembly of polystyrene particles in the presence of a silica sol-gel precursor material (tetraethylorthosilicate, TEOS), which creates crack-free inverse opal films with high positional order and uniform crystal alignment along the (110) crystal plane, is combined with top-down microfabrication techniques. Micrometer scale hierarchical superstructures having a highly regular internal nanostructure with precisely controlled crystal orientation and wall profiles are produced. The ability to combine structural order at the nano- and microscale enables the fabrication of materials with complex optical properties resulting from light-matter interactions at different length scales. As an example, a hierarchical diffraction grating, which combines Bragg reflection arising from the nanoscale periodicity of the inverse opal crystal with grating diffraction resulting from a micrometer scale periodicity, is demonstrated.
Keywords: hierarchy; inverse opals; photolithography; photonic crystals; self-assembly; structural color

Communication via electron and energy transfer between zinc oxide nanoparticles and organic adsorbates - Gnichwitz, Jan-Frederik; Hirsch, Andreas; Guldi, Dirk Michael; Peukert, Wolfgang; Werner, Fabian; Marczak, Renata (Journal of Physical Chemistry C, 2009)
Stable ZnO nanoparticles suitable for further surface functionalization were synthesized in the liquid phase from homogeneous ethanolic solutions of the precursors lithium hydroxide and zinc acetate. It was found that the growth of the particles was governed by temperature as well as the presence of the reaction byproduct lithium acetate during the aging process. In particular, the reaction could be almost completely arrested by removal of this byproduct. The washing consisted of repeated precipitation of the ZnO particles by addition of alkanes such as heptane, removal of the supernatant, and redispersion in ethanol. Furthermore, the surface of the colloidal ZnO nanoparticles was successfully modified by catechol-anchoring group containing dye molecules, i.e., 5-(N-(3,4-dihydroxyphenethyl)-2-phenoxyacetamide)-10,15,20-(p-tert- butyltriphenyl)porphyrinatozinc (DOPAZ) and 5-(3,4-dihydroxy-N-phenylbenzamide)- 10,15,20-tris(4-tert-butylphenyl)porphyrinatozinc (CAMIZ), for the study of photochemical properties. Thermogravimetric analysis proved the stability of the catechol anchor groups. Steady-state absorption spectroscopy as well as steady-state and time-resolved emission studies confirmed the electronic communication between the ZnO nanoparticles in their excited state and both of the porphyrins. More than 96% emission quenching of ZnO can be achieved by addition of the porphyrins, proving that the visible emission of the ZnO is caused by surface states, since only the surface of the particles was altered by the grafting experiments. Moreover, with increasing porphyrin concentrations the lifetimes changed from 46.0 to 15.3 ns. The shortened lifetimes prompt a new deactivation pathway, namely, through the electronic coupling of the porphyrins to the ZnO nanoparticle. Assuming that the decrease in lifetime is entirely due to electron transfer to the porphyrins, a rate constant of 0.35 × 10 s could be determined for this process. When testing the excited state of the porphyrin in comparative assays between ZnO and Al O , we conclude a similar electron transfer deactivation. © 2009 American Chemical Society.
Keywords: Nanoparticle; electron; functionalization

Comparison of the effects of 45S5 and 1393 bioactive glass microparticles on hMSC behavior - Qazi, Taimoor H.; Hafeez, Shahzad; Schmidt, Jochen; Duda, Georg N.; Boccaccini, Aldo R.; Lippens, Evi (Journal of Biomedical Materials Research Part A, 2017)
Keywords: bioactive glass; cell function; hMSCs; ion release; microparticles

Comparison of the sputtered TiO2 anatase and rutile thin films as electron transporting layers in perovskite solar cells - Shahvaranfard, Fahimeh; Li, Ning; Hosseinpour, Saman; Hejazi, Seyedsina; Zhang, Kaicheng; Altomare, Marco; Schmuki, Patrik; Brabec, Christoph (Nano Select, 2021)
We examine comparatively the performance of sputtered TiO2 rutile and anatase thin films as an electron transport layer (ETL) inMAPbI3-based perovskite solar cells. Both anatase and rutile TiO2 ETLs are deposited (on fluorine-doped tin oxide [FTO] substrates) by magnetron sputtering in the form of nanocrystalline thin films. We systematically investigate the role of crystallographic phase composition of TiO2 ETLs on the photovoltaic performance of perovskite solar cells. The champion power conversion efficiencies (PCEs) of 18.4% and 17.7% under reverse scan mode are obtained for perovskite solar cells based on TiO2 anatase and TiO2 rutile ETL, respectively. The results show that the magnetron sputtering deposited ETLs differ from each other only in their phase composition while the overall performance of the devices is not greatly affected by the crystallographic phase of the TiO2 ETLs. Our results point to an important fact that for a proper and reliable comparison between the performance of TiO2 anatase and rutile ETLs, it is crucial to investigate films of similar morphology and structure that are synthesize under similar condition
Keywords: magnetron sputtering; perovskite solar cell; TiO2 anatase; TiO2 rutile

Compatibility of fabrication of superhydrophobic surfaces and addition of inhibitors in designing corrosion prevention strategies for electrodeposited nickel in saline solutions - Noorbakhsh Nezhad, Amir Hossein; Arefinia, Reza; Kashefi, Mehrdad; Davoodi, Ali; Hosseinpour, Saman (Applied Surface Science, 2019)
The aim of this study is to assess the synergistic effect of two corrosion control strategies: application of an inhibitor and enhancing the surface superhydrophobicity, for protection of electrodeposited nickel in saline solutions. For this purpose, 4-Mercaptopyridine (C5H5NS) was added to the synthetic sea water solution and its corrosion inhibition efficiency was evaluated on electrodeposited smooth bright nickel layer and nickel films with hierarchical micro/nano structure. Stearic acid was used to tune the wetting properties of nickel films, from hydrophilic to superhydrophobic. Contact angle measurement, scanning electron microscopy, and Fourier-transform infrared spectroscopy were utilized in the characterization of deposited nickel layers. Potentiodynamic polarization and electrochemical impedance spectroscopy were employed to assess the corrosion inhibition performance of inhibitor on different nickel films. Our results indicate that simultaneous increase in the surface hydrophobicity and adsorption of corrosion inhibitor strategies does not yield a better corrosion resistance and that the most effective corrosion inhibition can be obtained on the bright smooth sample after a prolonged immersion in the corrosive solution. Furthermore, we show that the contact angle alone cannot be used to indicate the corrosion inhibition capability of an inhibitor. <br
Keywords: Superhydrophobicity; Inhibitor; 4-Mercaptopyridine; Nickel; Corrosion; Contact angle

Computational and experimental investigations into N2O decomposition over MgO nanocrystals from thorough molecular mechanism to ab initio microkinetics - Piskorz, Witold; Zasada, Filip; Stelmachowski, Pawel; Diwald, Oliver; Kotarba, Andrzej; Sojka, Zbigniew (Journal of Physical Chemistry C, 2011)
In this article a comprehensive molecular modeling of the reaction mechanism complemented by ab initio microkinetic modeling of the catalytic decomposition of N2O on MgO nanocrystals is discussed. The density functional level of theory was used to study the molecular mechanism of conceivable elementary steps of the deN2O reaction over the most stable (100) surface, including the effect of surface morphology. It is shown that terrace sites are responsible for steady state reactivity, whereas the more basic and reactive sites located on edges and corners are involved only in the initial stages of the reaction because of poisoning. Detailed analysis of the reaction progress in terms of the energy profiles and the evolution of partial charges and bond orders for each step allowed for an in-depth insight at the atomic scale into the nature of the catalytic N2O decomposition over anionic redox active sites constituted by surface O2– ions. The harmonic transition state theory along with the calculated free enthalpies of activation were used to model the reaction progress in pulse (transient) and steady state regimes as well as to predict the kinetic isotopic effects (KIE) for 15N and 18O labeled reactants. The proposed kinetic scheme was able to reproduce the results of temperature-programmed surface reaction and KIE experiments with high accuracy without fitting of any parameter

Conceptual stabilizer selection for nanomilling based on dispersibility parameters - Peppersack, C.; Flach, Frederik; Prziwara, P.; Damm, Cornelia; Breitung-Faes, S.; Peukert, Wolfgang; Kwade, A. (Advanced Powder Technology, 2023)
The choice of stabilizers to prevent particle agglomeration during nanomilling is an elaborate process which is often based on empirical rules and experience. Usually, extensive screening studies are required to find an appropriate stabilizing additive. The present study shows how the selection of polymeric stabilizers can be narrowed down to a couple of additives based on Hansen solubility parameters. The stabilizing capability was found to be a function of the difference between solubility parameters of additive and particulate species. Solubility parameters of different additives and two particle species were determined by inverse gas chromatography and the stabilization performance was evaluated by nanomilling experiments conducted with a stirred media mill. It is shown that a certain difference of solubility parameters between particle and additive is necessary in order to provide colloidal stability of small particles after milling. On the one hand, the additive needs a certain affinity to the particle surface, while on the other hand it also has to be compatible with the solvent. Based on experimental data, a solubility parameter difference in the range of 7.5–10 MPa0.5 was identified as a good measure for a proper stabilizer selection. The approach was proved for two organic particle species and represents a promising tool for a more efficient formulation development of drug nanosuspensions.
CRIS-Team Scopus Importer:2023-09-01
Keywords: Colloidal stability; Hansen solubility parameter; Inverse gas chromatography; Nanomilling

Conduction Mechanisms and Environmental Sensitivity of Solution-Processed Silicon Nanoparticle Layers for Thin-Film Transistors - Weis, Sebastian; Körmer, Richard; Jank, Michael; Lemberger, Martin; Otto, Michael; Ryssel, Heiner; Peukert, Wolfgang; Frey, Lothar (Small, 2011)
Room-temperature, solution-processed, silicon nanoparticle thin films show significant gating with distinct hysteresis in their current–voltage characteristics. Device performance strongly depends on measurement environment and charge transport is determined by particle surfaces. Particle encapsulation with polymethyl methacrylate or Al2O3 reduces hysteresis and device sensitivity against environmental influences. Both Al2O3 coating and UV exposure during measurements alter current transport and enhance conductivity, providing evidence for surface-dominated transpor
UnivIS-Import:2015-03-09:Pub.2011.tech.IE.LEB.conduc
Keywords: silicon; nanoparticle; thin; film

Conductivity in nonpolar media: Experimental and numerical studies on sodium AOT-hexadecane, lecithin-hexadecane and aluminum(III)-3,5-diisopropyl salicylate-hexadecane systems - Peschka, Dirk; Schmidt, Jochen; Wagner, Barbara; Bänsch, Eberhard; Münch, Andreas; Peukert, Wolfgang; Prignitz, Rodolphe (Journal of Colloid and Interface Science, 2012)
The conductivity behavior of doped hydrocarbon systems is studied by applying impedance spectroscopy. In the case of 3,5-diisopropyl salicylato aluminum (III) the charge carriers are formed by dissociation of the compound and their concentration is proportional to the square root of the solute concentration. In hydrocarbon systems that consist of micelle forming compounds (sodium AOT/lecithin) a linear dependence of charge carrier concentration on solute concentration is observed in the concentration regime where micelles are present. The conduction mechanisms are studied by numerical solution of a Poisson-Nernst-Planck system that describes the charge transport. We follow two different approaches to extract the degree of micelle dissociation from the impedance data. Firstly, by computing the response of a linear approximation of the Poisson-Nernst-Planck model, and secondly by computing the fully nonlinear response from direct numerical simulations using finite elements. For high and moderate frequencies both approaches agree very well with the experimental data. For small frequencies the response becomes nonlinear and the concept of impedance fails. Furthermore, the numerically computed values for the degree of dissociation are of the same order of magnitude as the values obtained with classical formulas, but still differ by a factor of about 1/3. The direct numerical simulation allows new insight into the conduction mechanisms for different frequency regimes. © 2012 Elsevier In
Keywords: Degree of dissociation; Direct numerical simulation; Electrochemical impedance spectroscopy; Finite element analysis; Poisson-Nernst-Planck model; Reverse micelles

Congratulations to Prof. Dr.-Ing. Otto Molerus on the occasion of his 70th birthday on June 18th 2004 - Peukert, Wolfgang; Wirth, Karl-Ernst (Powder Technology, 2005)
On behalf of the editors of this special issue of Powder Technology and of the colleagues who contributed to this issue, we congratulate Prof. Dr.-Ing. Otto Molerus on the occasion of his 70th birthday. Birthdays, particularly b round Q ones, invite one to sit back for a moment. We remember things from the past and look into the future. Dear Prof. Molerus, colleagues from all over the world have been motivated by your birthday to dedicate a paper to you. You are connected with many of the scientists here through numerous contacts, discussions and joint projects.
Keywords: Congratulation; birthday; molerus; particle; technology

Conservative finite volume schemes for multidimensional fragmentation problems - Saha, Jitraj; Bück, Andreas (Mathematics, 2021)
In this article, a new numerical scheme for the solution of the multidimensional fragmentation problem is presented. It is the first that uses the conservative form of the multidimensional problem. The idea to apply the finite volume scheme for solving one-dimensional linear fragmentation problems is extended over a generalized multidimensional setup. The derivation is given in detail for two-dimensional and three-dimensional problems; an outline for the extension to higher dimensions is also presented. Additionally, the existing one-dimensional finite volume scheme for solving conservative one-dimensional multi-fragmentation equation is extended to solve multidimensional problems. The accuracy and efficiency of both proposed schemes is analyzed for several test problems.
CRIS-Team Scopus Importer:2021-04-19
Keywords: Conservative formulation; Finite volume scheme; Multidimensional fragmentation equation; Weight functions

Consider the home research environments of international students - Hosseinpour, Saman; Sareh, Pooya; Ameli Hajebi, Saya; Mahmoudi, Morteza (Nature Human Behaviour, 2023)
CRIS-Team Scopus Importer:2023-03-31

Continuous, crystalline Sb2S3 ultrathin light absorber coatings in solar cells based on photonic concentric p-i-n heterojunctions - Büttner, Pascal; Scheler, Florian; Döhler, Dirk; Barr, Maissa; Bosch, Michael; Rey, Marcel; Yokosawa, Tadahiro; Hinz, Sandra; Maultzsch, Janina; Spiecker, Erdmann; Vogel, Nicolas; Minguez Bacho, Ignacio; et al. (Nano Energy, 2022)
Many modern types of solar cells that rely exclusively on earth-abundant non-toxic materials include interfaces between a heavier metal chalcogenide and another type of semiconductor. Often, the chemical (adhesion) and physical (charge transfer) characteristics of those interfaces are the defining factors for the final device performance. Here, we describe that a ZnS adhesion layer is not sufficient to prevent the dewetting of Sb2S3 upon annealing a thin layer of it on an oxidic surface if the substrate is not planar and features highly curved surfaces. An ALD-coated sacrificial capping layer of ZnO prevents the morphological rearrangements of Sb2S3 during thermal crystallization and can be removed subsequently. When implemented towards a photovoltaic p-i-n heterojunction, this strategy furnishes perfect conformality of the layer stack but unsatisfactory performance. The correlation of interface chemistry with the electrical properties and the device performance identifies a reducing effect of ZnO atomic layer deposition chemistry on the Sb2S3 surface as the cause of Zn diffusion into the light absorbing semiconductor. This deleterious doping can be prevented by a preliminary oxidative treatment of the Sb2S3 surface with ozone. When applied to a structured substrate consisting of ordered arrays of nanospheres, this approach yields the first ever concentric p-i-n heterojunction solar cells with photonic light trapping effect—a geometry which in comparison with standard scattering layers'on top’ inherently generates a very large refractive index contrast. In the red part of the visible spectrum, light absorption amounts to the value expected with four passes through a planar layer of the thickness used here (35 nm Sb2S3). This effect allows us to demonstrate >5% overall solar energy conversion efficiency with only 35 nm of a simple light absorber phase that uses no toxic, rare materials
CRIS-Team Scopus Importer:2022-10-14
Keywords: Atomic layer deposition; Concentric semiconductor junctions; Antimony chalcogenides; Interfacial layers; Photonic structures; Gradient doping; Interface chemistry

Continuous flow synthesis of plasmonic gold patches and nearly-complete nanoshells on polystyrene core particles - Meincke, Thomas; Klupp Taylor, Robin (Particuology, 2023)
We describe the development of a T-mixer based continuous flow process for the coating of 86-500 nm diameter spherical polystyrene particles with thin gold patches by heterogeneous nucleation and growth. After establishing a suitable flow rate for good mixing and sufficiently uniform product morphology we systematically investigate the main reaction parameters. This reveals a considerable tunability of the patch morphology and, by virtue of the localized surface plasmon resonance of gold, the optical properties of the product dispersions. In order to further widen the range of nanostructures accessible by our process, a second T-mixer was added. This introduced new gold precursor, leading to further growth of the patches that were formed after the first mixer. By this approach nearly complete gold nanoshells could be produced in high yield on both small and large core particles, without the unwanted production of free-standing gold nanoparticles. Due to the pronounced optical properties of nearly complete gold nanoshells on small core particles, we could estimate from electrodynamic simulations the equivalent shell thickness to be as low as 8.6 nm. This is significantly thinner than can be routinely achieved using the standard seeded growth approach to synthesise gold nanoshells. Our results are therefore highly promising for the gram-scale synthesis of plasmon resonant nanostructures with designed optical propertie
Keywords: Continuous flow; core-shell particles; patchy particles; nucleation; diffusion limited growth

Continuous synthesis of CuInS2 quantum dots - Akdas, Tugce; Haderlein, Michael; Walter, Johannes; Apeleo Zubiri, Benjamin; Spiecker, Erdmann; Peukert, Wolfgang (RSC Advances, 2017)
In colloidal semiconductor nanocrystal synthesis, many activities have been focused on the control over the mean particle size of the product. However, for device applications additional requirements apply, e.g. the necessity for a narrow particle size distribution (PSD). In the present work, we investigate the impact of reactor characteristics on the synthesis of CuInS2 quantum dots (QDs). Therefore, the synthesis is carried out in three different reactors, namely in a fully scalable and continuous tubular reactor, in a commercial microreactor and in a batch three-neck round-bottom flask. All reaction products from the three reactor types have the same crystal structure and inorganic composition. Slight differences in optical properties are mainly ascribed to differences in the PSD, which is confirmed by sedimentation velocity experiments. Furthermore, the necessity for using different post-processing routines coupled with our findings by analytical ultracentrifugation (AUC) hint at changes in the organic matrix surrounding the CuInS2 QDs. Our study demonstrates the massive impact of heat transfer on the synthesis and the final PSD of CuInS2 QDs synthesized via heating-up and allows us to draw conclusions on their formation.

Controlled mixing during colloidal quantum dot synthesis: A proxy-concept based on equivalent parameters - Salaheldin, Ahmed M.; Segets, Doris (Chemical Engineering Journal, 2023)
Mixing is a key process parameter during liquid phase particle synthesis that requires special attention, in particular for scalable process and reactor development. This issue is especially pressing for advanced materials where on the one hand multifunctional properties require products of utmost quality, while on the other hand only few strategies for process design are yet developed. One material class in this context is quantum dot (QD) nanocrystals. By making use of automation and high throughout (HT) experimentation, we could recently demonstrate qualitatively the role of mixing on focusing and defocusing during QD synthesis by hot injection. In this work, we demonstrate the application of HT methodologies to investigate the effect of mixing as an important process parameter during process optimization and scale up. We performed reaction optimization by screening a multi-parameter design space using design of experiments (DoE) and machine learning (ML). We developed a so-called cold model as proxy that is based on equivalent mixing times (EMTs) derived from a competing parallel reaction system. Experimentally, we realized a fully automated approach using a HT platform for particle synthesis. The final dataset (128 experiments for model development including repeats and 29 experiments for prediction testing) was combined with DoE and complimented with machine learning. By doing so, with DoE, we could reduce the number of experiments required to develop a predictive, statistical knowledge base for EMTs at ambient conditions. Finally, we demonstrated the applicability of EMTs for two defined stirrer geometries to fine tune the widths of the particle size distribution and photoluminescence of QDs at increasing reaction volumes from 20 mL to 80 mL. This opens the door towards scalable processes for QDs at increased reaction volumes while maintaining product quality.
CRIS-Team Scopus Importer:2023-10-06
Keywords: Design of experiments; High-throughput experimentation; Hot injection; Machine learning; Mixing time; Quantum dots

Controlled synthesis of reactive polymeric architectures using 5-norbornene-2-carboxylic acid pentafluorophenyl ester - Vogel, Nicolas; et al. (Macromolecular Symposia, 2007)
Keywords: Active ester monomers; Functionalization of polymers; Living polymerization; Ring-opening metathesis polymerization (ROMP)

Control of aggregation in production and handling of nanoparticles - Peukert, Wolfgang; Schwarzer, Hans-Christoph; Stenger, Frank (4th International Conference on Bulk Solids Handling, 2003)
In product engineering of particulate systems, the property function relates the dispersity to the product properties, whereas the process function shows how to produce the required dispersity. These principles are applied to the production of nanoparticles. Nanoparticles are controlled by surface forces. Due to their high mobility nanoparticles are unstable and may coagulate rapidly if the particles are not stabilized. Stabilization is achieved by tailoring the particulate surfaces, e.g. through repulsive double layer forces. Macroscopic properties are thus controlled by microscopic control of the interfaces, i.e. we bridge the gap between the molecular level and material properties. These principles are generally valid and are thus applied to precipitation and to nanomilling in stirred ball mills. The mean particle size in precipitation can be controlled by either the mixing intensity or the surface charge density of the particles. In stirred media mills oxide particles as small as 10 nm can be achieved by stabilizing the particles appropriately.
UnivIS-Import:2015-04-16:Pub.2003.tech.ITC.mechve.contro
Keywords: nanoparticle; aggregation; handling