Lyotropic nematic liquid crystals: interplay between a small twist elastic constant and chirality effects under confined geometries

Abstract

ABSTRACT There are two classes of liquid crystals (LCs): Thermotropic LCs where the organic molecule represents the anisotropically shaped mesogen and lyotropic LCs, where the mesogens are non-spherical supramolecular assemblies dispersed in a solvent. Various kinds of lyotropic nematic liquid crystals (LLCs) exist, differing in shape and composition of the aggregates: Chromonic, polymeric or micellar LLCs.However, micellar LLCs are the most ubiquitous kind of LLCs, occurring in soaps and biological systems. Although these nematic lyotropics are so different, they exhibit – contrary to thermotropic nematics – spontaneous reflection symmetry breaking under confinement. We discuss spontaneous mirror symmetry breaking under capillary confinement for a standard micellar ND phase and give a detailed director field structure of the twisted polar configuration. Furthermore, we measure for the first time a complete set of viscoelastic properties of a micellar nematic LLC, finding a small twist elastic constant K 22, which is at least one order of magnitude smaller than K 11 and K 33. As demonstrated by the following work, a small K 22 and therefore spontaneous mirror symmetry breaking under confinement is rather the rule than the exception in lyotropic nematics and constitutes a unique difference between lyotropic and typical thermotropic nematics, for which the well-known one-constant approximation holds. Abbreviations: LC: Liquid Crystal; LLC: Lyotropic liquid crystal; TER: twisted escaped radial director configuration; TP: twisted polar director configuration; : director; K 11: splay elastic constant of the nematic phase; K 22: twist elastic constant of the nematic phase; K 33: bend elastic constant of the nematic phase; s: strength of a defect/disclination; ER: escaped radial director configuration; CDEAB: N,N-ethylhexadecylammonium bromide; DOH: decan-1-ol; ND: nematic phase of disk-shaped building blocks; NC: nematic phase of rod-shaped building blocks; H-field: magnetic field; PR: planar radial director configuration; PP: planar polar director configuration; RR: right handed – right handed; LL: left handed – left handed; RL: right handed – left handed; LR: left handed – right handed.