TY - JOUR A1 - Schürings, Marco-Philipp A1 - Nevskyi, Oleksii A1 - Eliasch, Kamill A1 - Michel, Ann-Katrin A1 - Liu, Bing A1 - Pich, Andrij A1 - Böker, Alexander A1 - von Plessen, Gero A1 - Wöll, Dominik T1 - Diffusive Motion of Linear Microgel Assemblies in Solution JF - Polymers N2 - Due to the ability of microgels to rapidly contract and expand in response to external stimuli, assemblies of interconnected microgels are promising for actuation applications, e.g., as contracting fibers for artificial muscles. Among the properties determining the suitability of microgel assemblies for actuation are mechanical parameters such as bending stiffness and mobility. Here, we study the properties of linear, one-dimensional chains of poly(N-vinylcaprolactam) microgels dispersed in water. They were fabricated by utilizing wrinkled surfaces as templates and UV-cross-linking the microgels. We image the shapes of the chains on surfaces and in solution using atomic force microscopy (AFM) and fluorescence microscopy, respectively. In solution, the chains are observed to execute translational and rotational diffusive motions. Evaluation of the motions yields translational and rotational diffusion coefficients and, from the translational diffusion coefficient, the chain mobility. The microgel chains show no perceptible bending, which yields a lower limit on their bending stiffness. KW - microgels KW - linear assemblies KW - in situ fluorescence microscopy KW - shape analysis KW - rotational diffusion KW - translational diffusion KW - bending stiffness KW - actuation Y1 - 2016 U6 - https://doi.org/10.3390/polym8120413 SN - 2073-4360 VL - 8 PB - MDPI CY - Basel ER - TY - JOUR A1 - Petreska, Irina A1 - Pejov, Ljupco A1 - Sandev, Trifce A1 - Kocarev, Ljupčo A1 - Metzler, Ralf T1 - Tuning of the dielectric relaxation and complex susceptibility in a system of polar molecules: a generalised model based on rotational diffusion with resetting JF - Fractal and fractional N2 - The application of the fractional calculus in the mathematical modelling of relaxation processes in complex heterogeneous media has attracted a considerable amount of interest lately. The reason for this is the successful implementation of fractional stochastic and kinetic equations in the studies of non-Debye relaxation. In this work, we consider the rotational diffusion equation with a generalised memory kernel in the context of dielectric relaxation processes in a medium composed of polar molecules. We give an overview of existing models on non-exponential relaxation and introduce an exponential resetting dynamic in the corresponding process. The autocorrelation function and complex susceptibility are analysed in detail. We show that stochastic resetting leads to a saturation of the autocorrelation function to a constant value, in contrast to the case without resetting, for which it decays to zero. The behaviour of the autocorrelation function, as well as the complex susceptibility in the presence of resetting, confirms that the dielectric relaxation dynamics can be tuned by an appropriate choice of the resetting rate. The presented results are general and flexible, and they will be of interest for the theoretical description of non-trivial relaxation dynamics in heterogeneous systems composed of polar molecules. KW - rotational diffusion KW - memory kernel KW - Fokker-Planck equation KW - non-exponential relaxation KW - autocorrelation function KW - complex KW - susceptibility Y1 - 2022 U6 - https://doi.org/10.3390/fractalfract6020088 SN - 2504-3110 VL - 6 IS - 2 PB - MDPI AG, Fractal Fract Editorial Office CY - Basel ER -