Helmut R. Brand

Landau model of the smectic C-isotropic phase transition

We propose a Landau model to describe the smectic C–isotropic phase transition. A general Landau theory for the coupled orientational and translational order parameters and including the tilt angle is developed. The conditions for the smectic C–isotropic phase transition and the stability conditions of the smectic C phase are calculated. On the basis of this model it is argued that the smectic C–isotropic phase transition is always first order. We present a detailed analysis of the question under which conditions a direct smectic C–isotropic phase transition prevails in comparison to smectic A–isotropic and nematic–isotropic transitions. The theoretical results are found to be in qualitative agreement with all published experimental results.

Macroscopic behavior of systems with an axial dynamic preferred direction

We present the derivation of the macroscopic equations for systems with an axial dynamic preferred direction. In addition to the usual hydrodynamic variables, we introduce the time derivative of the local preferred direction as a new variable and discuss its macroscopic consequences including new cross-coupling terms. Such an approach is expected to be useful for a number of systems for which orientational degrees of freedom are important including, for example, the formation of dynamic macroscopic patterns shown by certain bacteria such a Proteus mirabilis. We point out similarities in symmetry between the additional macroscopic variable discussed here, and the magnetization density in magnetic systems as well as the so-called

Dielectric Degrees of Freedom in Chiral Smectic C Liquid Crystals

hat l

Nonlinear Hydrodynamics of Strongly Deformed Smectic C and C* Liquid Crystals

vector in superfluid 3He-A. Furthermore we investigate the coupling to a gel-like system for which one has the strain tensor and relative rotations between the new variable and the network as additional macroscopic variables.

Cholesteric Liquid Crystals: Flow Properties, Thermo- and Electromechanical Coupling

The statics and dynamics of smectic C (and C∗) liquid crystals has been a long-standing topic for investigations. All the previous descriptions, however, have been restricted in some sense. Either the theories were linear, or flat layers were assumed, or the layer thickness was taken to be constant, or only statics was considered, or the description (in the chiral case) included terms not compatible with layering. Here we will give a nonlinear hydrodynamic theory, which applies to strongly curved layers, non-flat ‘ground’ states, strongly compressed layers as well as strongly deformed director orientations. Some discrepancies between previous theories are resolved.

Simple Landau model of the smectic- A-isotropic phase transition

Abstract We show that there are only three low frequency relaxation modes in the dielectric spectrum of smectic C* liquid crystals due to the symmetry of that phase. Two additional symmetry violating dielectric modes may exist at very high frequencies. We refute a recent criticism of that picture expressed in this journal.

A phenomenological theory of the isotropic to chiral smectic-C phase transition.

Abstract We discuss flexoelectricity in cholesteric liquid crystals. In particular we point out that experimental results obtained by Patel and Meyer can be understood as surface effects. In addition we discuss similarities and differences between static and dynamic effects associated with flexoelectricity in cholesteric and nematic liquid crystals.

Macroscopic Dynamics Near the Isotropic-Smectic-A Phase Transition

The statics and dynamics of smectic C (and C) liquid crystals has been a long-standing topic for investigations. All the previous descriptions, however, have been restricted in some sense. Either the theories were linear, or flat layers were assumed, or the layer thickness was taken to be constant, or only statics was considered, or the description (in the chiral case) included terms not compatible with layering. Here we will give a nonlinear hydrodynamic theory, which applies to strongly curved layers, non-flat ground states, strongly compressed layers as well as strongly deformed director orientations. Some discrepancies between previous theories are resolved.