TY - JOUR A1 - Bartsch, Hendrik A1 - Bier, Markus A1 - Dietrich, S. T1 - The role of counterions in ionic liquid crystals JF - The Journal of Chemical Physics N2 - Previous theoretical studies of calamitic (i.e., rod-like) ionic liquid crystals (ILCs) based on an effective one-species model led to indications of a novel smectic-A phase with a layer spacing being much larger than the length of the mesogenic (i.e., liquid–crystal forming) ions. In order to rule out the possibility that this wide smectic-A phase is merely an artifact caused by the one-species approximation, we investigate an extension that accounts explicitly for cations and anions in ILCs. Our present findings, obtained by grand canonical Monte Carlo simulations, show that the phase transitions between the isotropic and the smectic-A phases of the cation–anion system are in qualitative agreement with the effective one-species model used in the preceding studies. In particular, for ILCs with mesogens (i.e., liquid–crystal forming species) carrying charged sites at their tips, the wide smectic-A phase forms, at low temperatures and within an intermediate density range, in between the isotropic and hexagonal crystal phases. We find that in the ordinary smectic-A phase, the spatial distribution of the counterions of the mesogens is approximately uniform, whereas in the wide smectic-A phase, the small counterions accumulate in between the smectic layers. Due to this phenomenology, the wide smectic-A phase could be interesting for applications, which hinge on the presence of conductivity channels for mobile ions. KW - Liquid crystals, Phase transitions, Electrostatics, Ions and properties, Crystal structure, Intermolecular forces, Monte Carlo methods, Classical statistical mechanics Y1 - 2021 UR - https://doi.org/10.1063/5.0034314 VL - 154 IS - 1 SP - 014901 ER - TY - JOUR A1 - Bier, Markus A1 - Mußotter, Maximilian A1 - Dietrich, S. T1 - Structure of electrolyte solutions at nonuniformly charged surfaces on a variety of length scales JF - Physical Review E N2 - The structures of dilute electrolyte solutions close to nonuniformly charged planar substrates are systematically studied within the entire spectrum of microscopic to macroscopic length scales by means of a unified classical density functional theory approach. This is in contrast to previous investigations, which are applicable either to short or to long length scales. It turns out that interactions with microscopic ranges, e.g., due to the hard cores of the fluid molecules and ions, have a negligible influence on the formation of nonuniform lateral structures of the electrolyte solutions. This partly justifies the Debye-Hückel approximation schemes applied in previous studies of that system. In general, a coupling between the lateral and the normal fluid structures leads to the phenomenology that, upon increasing the distance from the substrate, fewer details of the lateral nonuniformities contribute to the fluid structure, such that ultimately only large-scale surface features remain relevant. It can be expected that this picture also applies to other fluids characterized by several length scales. KW - Classical statistical mechanics, Electrostatic interactions, Interface & surface thermodynamics, Complex fluids, Ionic fluids, Liquid-solid interfaces, Polymers & Soft Matter, Statistical Physics Y1 - 2022 UR - https://doi.org/10.1103/PhysRevE.106.054801 VL - 106 IS - 5 SP - 054801 ER - TY - JOUR A1 - Mußotter, Maximilian A1 - Bier, Markus A1 - Dietrich, S. T1 - Heterogeneous surface charge confining an electrolyte solution JF - The Journal of Chemical Physics N2 - The structure of dilute electrolyte solutions close to a surface carrying a spatially inhomogeneous surface charge distribution is investigated by means of classical density functional theory within the approach of fundamental measure theory. For electrolyte solutions, the influence of these inhomogeneities is particularly strong because the corresponding characteristic length scale is the Debye length, which is large compared to molecular sizes. Here, a fully three-dimensional investigation is performed, which accounts explicitly for the solvent particles, and thus provides insight into effects caused by ion–solvent coupling. The present study introduces a versatile framework to analyze a broad range of types of surface charge heterogeneities even beyond the linear response regime. This reveals a sensitive dependence of the number density profiles of the fluid components and of the electrostatic potential on the magnitude of the charge as well as on the details of the surface charge patterns at small scales. KW - Density functional theory, Fundamental measure theory, Electrostatics, Partial differential equations, Elementary particle interactions, Electrochemistry, Electrolytes, Interfaces Y1 - 2020 UR - https://doi.org/10.1063/5.0006208 VL - 152 IS - 23 ER - TY - JOUR A1 - Zarubin, Grigorii A1 - Bier, Markus A1 - Dietrich, S. T1 - A ferronematic slab in external magnetic fields JF - Soft Matter N2 - The behavior of a uniformly magnetized ferronematic slab is investigated numerically in a situation in which an external magnetic field is applied parallel and antiparallel, respectively, to its initial magnetization direction. The employed numerical method allows one to determine hysteresis curves from which a critical magnetic field strength (i.e., the one at which the ferronematic sample becomes distorted) as a function of the system parameters can be inferred. Two possible mechanisms of switching the magnetization by applying a magnetic field in the antiparallel direction are observed and characterized in terms of the coupling constant between the magnetization and the nematic director and in terms of the coupling strength of the nematic liquid crystal and the walls of the slab. Suitably prepared walls allow one to combine both switching mechanisms in one setup, such that one can construct a cell, the magnetization of which can be reversibly switched off. Y1 - 2018 UR - https://doi.org/10.1039/C8SM01813H VL - 14 SP - 9806 EP - 9818 ER - TY - JOUR A1 - Schmitt, Jan A1 - Posselt, G A1 - Dietrich, F A1 - Thiede, S A1 - Raatz, A A1 - Herrmann, C A1 - Dröder, K T1 - Technical performance and energy intensity of the electrode-separator composite manufacturing process JF - Procedia CIRP Y1 - 2015 U6 - https://doi.org/10.1016/j.procir.2015.02.016 VL - 29 SP - 269 EP - 274 ER -