Abstract
The presumed ground state of a nematic fluid confined in a cylindrical geometry with planar anchoring corresponds to that of an axial configuration, wherein the director, free of deformations, is along the long axis of the cylinder. However, upon confinement of lyotropic chromonic liquid crystals in cylindrical geometries, here we uncover a surprising ground state corresponding to a doubly twisted director configuration. The stability of this ground state, which involves significant director deformations, can be rationalized by the saddle-splay contribution to the free energy. We show that sufficient anisotropy in the elastic constants drives the transition from a deformation-free ground state to a doubly twisted structure, and results in spontaneous symmetry breaking with equal probability for either handedness. Enabled by the twist angle measurements of the spontaneous twist, we determine the saddle-splay elastic constant for chromonic liquid crystals for the first time.
Highlights
The presumed ground state of a nematic fluid confined in a cylindrical geometry with planar anchoring corresponds to that of an axial configuration, wherein the director, free of deformations, is along the long axis of the cylinder
disodium cromoglycate (DSCG) are shown in Fig. 2a,b, which correspond to the long axis of the capillary being parallel and at 45° with respect to the incident polarization direction, respectively
We demonstrate the emergence of spontaneous chirality when lyotropic chromonic liquid crystals (LCLCs) are confined to cylinders with degenerate planar anchoring conditions
Summary
The presumed ground state of a nematic fluid confined in a cylindrical geometry with planar anchoring corresponds to that of an axial configuration, wherein the director, free of deformations, is along the long axis of the cylinder. Upon confinement of lyotropic chromonic liquid crystals in cylindrical geometries, here we uncover a surprising ground state corresponding to a doubly twisted director configuration. The stability of this ground state, which involves significant director deformations, can be rationalized by the saddle-splay contribution to the free energy. The intricate nature of the coupling of curvature to the free energy and sufficient anisotropy of elastic constants drive the observed spontaneous reflection-symmetry breaking transition. We are unaware of any first principles study in the literature that addresses the reason for the twist elastic constant in these systems being curiously low These fascinating features of LCLCs distinguish them from small-molecule thermotropic nematics, conferring on confined LCLCs new and richer phenomenology
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