arXiv subjects

Andreas Wierschem

Publications and source records attributed to Andreas Wierschem.

3 recordsLinked to original sources

arXiv2026

Functional trends and rheological evaluation of polyurethane microcapsules in dermato-cosmetic applications

To date, natural and synthetic polymer-based microcapsules have been used extensively in various dermato-cosmetic applications, with an emphasis on the targeted delivery of active ingredients, including therapeutic and aesthetic interventions. Although numerous polymer candidates have been comprehensively investigated, polyurethane based microcapsules have received comparatively minor attention, despite possessing a multitude of intrinsic benefits. However, in recent years, although there has been an upsurge of studies involving polyurethane, predominantly as a capsule wall or shell component, towards tangible dermato-cosmetic applications, these are only intermittently documented. In the current review, we target this lacuna, explore, and collate only the most contemporary trends and advances (2017-to date) in the field. In addition, despite the significance, and pertaining to the acute deficiency of rheological studies targeting polyurethane-based microcapsules in dermato-cosmetic applications, we critically examine and lay a comprehensive interpretation, based on the current state-of-the-art, inevitability for systematic inquiries, and identification of several target domains that need urgent attention. Finally, we deliberate on the challenges and the impending projections from a diverse outlook. We focus on a steady and more sustainable path forward via incorporation of green raw materials, cumulative domain-optimized and customer-focused applications, and a significantly improved understanding of the microcapsule mechanical behavior via implementation of novel rheological characterization procedures.

cond-mat.soft↗

arXiv2026

Concentration regimes in salt-free aqueous xanthan solutions under shear

Concentration regimes in polymer and polyelectrolyte solutions can be identified by scaling laws for the relation between specific zero-shear viscosity and concentration. Recently, we have shown that the same is true for the infinite-shear viscosity plateau. The shear-thinning range is usually accessed by focusing on the viscosity functions for the respective concentration regime. For salt-free aqueous xanthan solutions, we find power-law dependencies of the specific viscosity on concentration throughout the entire shear-rate range. We distinguish six different concentration regimes. Apart from those already known for the zero-shear viscosity of polyelectrolyte solutions, i.e. dilute, semidilute unentangled, semidilute entangled and neutral semidilute entangled, we identify a linear regime for low shear rates at high concentrations, where the solution gels and a regime at both, higher concentrations and higher shear rates. Within some regimes, the power-law exponents change smoothly with shear rate, particularly, when deviating from the zero-shear viscosity plateau before the power-law of the viscosity function. Some regimes merge as their power-law exponents approach each other. The fact that the regimes extend smoothly from the zero-shear regime into finite shear rates, i.e. away from thermodynamic equilibrium, shows that indicators such as critical concentrations remain valid at finite shear rates. This motivates us to interpret the data in the light of existing scaling laws and current knowledge about shear-rate dependent interaction mechanisms in polyelectrolyte solutions, particularly in xanthan solutions. It allows to follow the shift of relevant interaction mechanisms with shear rate. We think that the consideration of scaling laws under shear can be particularly helpful for identifying, for instance, thresholds for shear-induced disentanglement or disaggregation.

cond-mat.soft↗

arXiv2017

Focus on Imaging Methods in Granular Physics

Granular materials are complex multi-particle ensembles in which macroscopic properties are largely determined by inter-particle interactions between their numerous constituents. In order to understand and to predict their macroscopic physical behavior, it is necessary to analyze the composition and interactions at the level of individual contacts and grains. To do so requires the ability to image individual particles and their local configurations to high precision. A variety of competing and complementary imaging techniques have been developed for that task. In this introductory paper accompanying the Focus Issue, we provide an overview of these imaging methods and discuss their advantages and drawbacks, as well as their limits of application.

physics.ins-det↗