Chiral symmetry breaking and surface faceting in chromonic liquid crystal droplets with giant elastic anisotropy

Significance Lyotropic chronomic liquid crystals (LCLCs) are water-based systems consisting of planar molecules that form aligned stacks in the nematic phase that develop two-dimensional crystalline order upon cooling to the columnar phase. They are characterized by an unusually small resistance to twist distortions. This work explores the interplay of giant elastic anisotropy and geometrical frustration imposed by boundary conditions in droplets, demonstrating, in particular, spontaneous formation in the nematic phase of chiral patterns from achiral building blocks and of central line defects and surface faceting in the columnar phase. Because LCLCs are water-loving, these findings about the combined effects of anisotropic elasticity, confinement, and frustration take steps toward tapping applications for liquid crystals in aqueous environments. Confined liquid crystals (LC) provide a unique platform for technological applications and for the study of LC properties, such as bulk elasticity, surface anchoring, and topological defects. In this work, lyotropic chromonic liquid crystals (LCLCs) are confined in spherical droplets, and their director configurations are investigated as a function of mesogen concentration using bright-field and polarized optical microscopy. Because of the unusually small twist elastic modulus of the nematic phase of LCLCs, droplets of this phase exhibit a twisted bipolar configuration with remarkably large chiral symmetry breaking. Further, the hexagonal ordering of columns and the resultant strong suppression of twist and splay but not bend deformation in the columnar phase, cause droplets of this phase to adopt a concentric director configuration around a central bend disclination line and, at sufficiently high mesogen concentration, to exhibit surface faceting. Observations of director configurations are consistent with Jones matrix calculations and are understood theoretically to be a result of the giant elastic anisotropy of LCLCs.