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The approaches developed for studying the polarization of molecules and the dynamics of ions in dielectric materials are usually considered separately. The two effects are often believed to take place in different frequency ranges. The low frequency response is usually dominated by ionic migration, whereas the high frequency response is played by molecular polarization. The goal here is to clarify the interplay between free and bound charge densities and their influences on permittivity and impedance profiles by proposing a version of the Poisson-Nernst-Planck (PNP) model that allows to include the effect of a frequency-dependent (and thus not instantaneous) polarizability.

The complex arrangement of layered structures in curved geometries is a ubiquitous problem in soft condensed matter systems. In general, cholesteric liquid crystals (CLCs) in spherical droplets have been studied in the literature by means of the Landau-de Gennes (LdG) simulation method, which often need Ansatz structures to reach stable states. In this paper, we successfully achieved different organizations of CLC droplets by performing thermal quenches under several combinations of elastic constants and anchoring energy as chirality is increased by using a chiral pairwise additive potential interpreted in terms of Monte Carlo (MC) simulations. We describe well-known structures for planar and homeotropic alignment that were quenched from random states, including some high chirality regime droplets. The method proposed here represents an easier to implement and faster to execute simulation method, that demands considerably low computational power, to study the complex arrangement of layered structures such as CLCs in complex geometries. It has the advantage, when compared to the LdG method for example, of naturally contemplating the role played by thermal fluctuations and elastic anisotropy. Furthermore, it finally allows studies involving thermal quenching of CLC droplets, starting from a random state, to reach stable states.

The recent experimental observation of twist-bend nematic phases has kindled interest on this new class of materials. The natural twist-bend deformations of the director results in a nanoscale pitch (pseudo-layers) probed by freeze-fracture transmission electron microscopy (FFTEM) and very recently it was verified by resonant soft x-ray scattering (RSoXS) technique. It is pivotal that other mechanisms arise to certify the recent experiments and corroborate the theoretical models. Impedance spectroscopy is a method commonly used to investigate the dynamics of bound or mobile charge in the bulk or interfacial regions of materials in the vast field of condensed matter. Here we use impedance spectroscopy technique to investigate the electrical transport properties of twist-bend nematic phase in a dimeric liquid crystal mixture. The experimental data is analyzed in the framework of an anomalous diffusion equation coupled with Poisson’s equation where bulk and surface contributions are taken into account. Our fitting results agree well with the impedance measurements in the nematic (N) and the twist-bend ( N tb ) phase and indicate that strong subdiffusive regimes take place in the system. We also find a large diffusion anisotropy depending on the imposed orientation, which is associated with motions along or through the pseudo-layers, showing that the impedance technique can be used to explore the molecular arrangement of N tb phases.

This work focuses on the striped pattern formation of cholesteric liquid crystals confined in a hybrid aligned cell. The study is performed by means of Monte Carlo simulations. This pattern formati...

General diffusion processes involve one or more diffusing species and are usually modelled by Fick’s law, which assumes infinite propagation velocity. In this article, searching for the effect of finite propagation speeds in a system with two reacting species, we investigate diffusing and reacting particles governed by a hyperbolic diffusion equation, that is, the Cattaneo equation, which describes a diffusion process with finite propagation velocity, in the presence of a constant external field and reaction terms. These reaction terms are linear and may be related to irreversible and reversible processes, including memory effects, depending on the choices of the reaction rates. We obtain exact solutions for the equilibrium concentrations and explore the rich variety of behaviours exhibited by the species involved in reaction processes. Our results may shine new light into systems with more than one kind of diffusing and reacting particles, as is the case in several industrial and biological process, when finite speeds and memory effects are involved.

Surface driven pattern formation is an intriguing phenomenon in the liquid crystal field. Owing to its ability to transmit torque, one can generate different patterns by propagating distortions on the optical wavelength scale in the sample from the surface. Here, we theoretically investigate (from the elasticity point of view) twist deformations induced by a rotating easy axis at one surface, by considering the anchoring energy and surface viscosity of nematic and chiral nematic samples. The model is solved analytically in the limit of strong anchoring and numerically for a low anchoring strength situation. Such rotation could be induced, in principle, by light-controlling the orientation of an azobenzene monolayer coated at one of the glass substrates or by an in-plane rotating field. We discuss the role of the surface parameters and the different distortions, and calculate light transmission using the Jones method. Three different regimes are identified: free twist, stick-slip twist, and constrained twist. The results obtained here may be relevant for liquid crystal active waveplates and for determining surface viscosity and the azimuthal anchoring energy.