Sequence of Three-, Two-, and One-Dimensional Structures Formed from a Cholesteric Liquid Crystal at Change in the Chirality

Abstract

In this work the formation of modulated structures in chiral liquid crystals is studied. For different chiral nematics that at low temperature form the usual (with twist in one direction) cholesteric phase, we found that at high temperature in the vicinity of the phase transition into isotropic liquid a universal sequence of structural transformations is observed. Planar cholesteric transforms at short helical pitch into the three-dimensional phases with cubic symmetry (Blue Phases), in two-dimensional structure at intermediate helical pitch and in one-dimensional structure in the plane of the sample at large pitch. The structures possess periodic orientational and translational order on scales much larger than molecular scale. Optical measurements were made on ordered structures obtained near the transition temperature to the isotropic phase. Possible reasons of formation of the structures are discussed on the basis of existing experimental data and theoretical considerations.