@article{PeppersackFlachPrziwaraetal.2023, author = {Peppersack, Christoph and Flach, Frederik and Prziwara, Paul and Damm, Cornelia and Breitung-Faes, Sandra and Peukert, Wolfgang and Kwade, Arno}, title = {Conceptual stabilizer selection for nanomilling based on dispersibility parameters}, series = {Advanced Powder Technology}, volume = {34}, journal = {Advanced Powder Technology}, number = {10}, publisher = {Elsevier BV}, issn = {0921-8831}, doi = {10.1016/j.apt.2023.104197}, pages = {12}, year = {2023}, abstract = {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.}, language = {en} } @article{PeppersackKwadeBreitungFaes2021, author = {Peppersack, Christoph and Kwade, Arno and Breitung-Faes, Sandra}, title = {Selective particle size analysis in binary submicron particle mixtures using density dependent differential sedimentation}, series = {Advanced Powder Technology}, volume = {32}, journal = {Advanced Powder Technology}, number = {11}, publisher = {Elsevier BV}, issn = {0921-8831}, doi = {10.1016/j.apt.2021.09.010}, pages = {4049 -- 4057}, year = {2021}, abstract = {Particle size characterization of heterogeneous mixtures is a challenging task, as it is not feasible to assign the measured signals to the individual components. Within this framework, the study proposes a method that applies the working principle of differential centrifugal sedimentation (DCS) in order to simultaneously separate and measure the denser component within a binary material mixture of submicron particles. The method was validated using a model system consisting of polyvinyl chloride (PVC) and diamond particles in a size range of 0.5 - 1.5 µm. The results proved that by applying a proper density gradient fluid, the diamond particles can be selectively analyzed by hindering the sedimentation of the lighter PVC component. Furthermore, a very promising application could be found with respect to wet fine grinding processes in stirred media mills. In fact, the approach was utilized to individually determine the particle size distribution of the grinding media wear within an ultrafine organic product. Despite the low quantity of wear particles, it was possible to separate them from the organic product under appropriate density conditions. The size distributions of both the wear and the product particles were validated with SEM images, confirming the feasibility of the method.}, language = {en} } @article{PeppersackWermbterKwadeetal.2022, author = {Peppersack, Christoph and Wermbter, Karsten and Kwade, Arno and Garnweitner, Georg and Breitung-Faes, Sandra}, title = {Top-Down Formulation of Goethite Nanosuspensions for the Production of Transparent, Inorganic Glass Coatings}, series = {Coatings}, volume = {12}, journal = {Coatings}, number = {3}, publisher = {MDPI AG}, issn = {2079-6412}, doi = {10.3390/coatings12030330}, pages = {18}, year = {2022}, abstract = {This study presents a simple but effective process route for the production of transparent coatings on glass substrates from inorganic pigment goethite. For this purpose, coating suspensions were prepared by wet milling with a stirred media mill. A water/ethanol mixture was used as the liquid medium to take advantage of the resulting low surface tension for the coating process. In this manner, stable suspensions with particles of down to 50 nm in size were obtained, which already showed a significant increase in transparency. With regard to grinding characteristics, particularly low stress energies proved to be energetically reasonable. The coating step was performed by wet film deposition, achieving coating thicknesses in a range of 0.5-2.5 µm via dip coating. Highly transparent coatings were obtained by applying small particles of 50 nm, which exhibited a significantly lower scattering loss of light (≈3\%) in comparison to particles of around 300 nm (70-80\%). Additionally, the film color could be adjusted through a variation of the drying temperature due to a conversion of goethite to hematite by dehydration. Since transparency was not affected, this provides an easy-to-implement process adaptation for controlling coating colors.}, language = {en} } @article{CaiPengSongetal.2022, author = {Cai, Yingying and Peng, Wentao and Song, Qingyuan and Pluta, Denis and Peppersack, Christoph and Breitung-Faes, Sandra and Kwade, Arno and Bigall, Nadja C. and Vana, Philipp}, title = {Nanoengineering of Egyptian Blue Nanosheets: Advantages and Limitations for Near-Infrared Photoluminescence Applications}, series = {ACS Applied Optical Materials}, volume = {1}, journal = {ACS Applied Optical Materials}, number = {1}, publisher = {American Chemical Society (ACS)}, issn = {2771-9855}, doi = {10.1021/acsaom.2c00114}, pages = {465 -- 472}, year = {2022}, abstract = {The ancient inorganic pigment Egyptian Blue is a fluorophore with outstanding near-infrared (NIR) performance and is thus considered as an emerging optical material that meets the current demand for cheap, efficient, and nontoxic NIR nanofluorophores. Herein, we present a protocol for the quick mass production of Egyptian Blue (CaCuSi4O10) nanosheets (EBNSs) with lateral size down to ∼100 nm by applying state-of-the-art ball-milling techniques. A systematic decay of the NIR photoluminescence behavior with decreasing size of the EBNSs was found, which challenges the desired application of EBNSs as bioimaging markers and other nanoapplications. To pave the way to surface modifications of EBNSs, we deposited a thin layer of silica on the surface of the EBNSs. Taking advantage of this modification, we subsequently performed surface-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization in order to grow both hydrophilic and hydrophobic polymer brushes from EBNSs, which enhanced dispersibility of the nanosheets and even delivered function. By matching the refractive index of the EBNS with its polymer shell, the quality of the NIR photoluminescence of the EBNS could significantly be improved, since disturbing light scattering at the interface could effectively be suppressed. Our results provide a clear picture of the advantages and limitations of EBNSs as optical nanomaterials for NIR fluorescence applications.}, language = {en} } @article{PeppersackKwadeBreitungFaes2025, author = {Peppersack, Christoph and Kwade, Arno and Breitung-Faes, Sandra}, title = {Selective Agglomeration and Separation from Heterogeneous Suspensions of Submicron Particles by Controlling Electrostatic Particle Interactions}, series = {Powders}, journal = {Powders}, number = {1}, edition = {4}, doi = {10.3390/powders4010008}, year = {2025}, abstract = {As part of the so-called interfacial separation techniques, selective particle ag- glomeration is one of the few options that are suitable for the separation of heterogeneous, multicomponent systems of particles smaller than 1 μm. In this regard, the component to be separated is exclusively transferred into a coarser size range, so that a material selective size separation by traditional mechanical methods can be achieved. In the presented study, this is demonstrated using heterogeneous suspensions of ceramic and organic particles, from which the separation of the inorganic material is pursued subsequent to the targeted control of the material-specific, electrostatic particle-particle interaction. Resulting from theoretical considerations on these interactions, favorable conditions for the selective agglomeration can be predicted. Experimental data reveal that for suitable param- eters, resulting from variations in interfacial particle properties, particle size, and the composition of the dispersions, a separation efficiency of up to 97\% can be obtained. Thereby, the importance of the particle-number fraction as an adjustable parameter needs to be clearly emphasized. Since a separation of the agglomerates can be achieved by simply using centrifugal forces, the shown technique is easy to apply and valuable for various industrial fields such as chemical and pharmaceutical engineering or recycling processes. In addition, no external additives are required for selective agglomeration, eliminating the risk of secondary contamination.}, language = {en} }