Confinement twists achiral liquid crystals and causes chiral liquid crystals to twist in the opposite handedness: Cases in and around sessile droplets

TL;DR

This study investigates how confinement and chiral dopants influence the twist and handedness of nematic liquid crystals, revealing mechanisms for creating and controlling chiral structures in confined geometries.

Contribution

It demonstrates how elastic anisotropy and topological defects induce twist deformations and how chiral dopants bias handedness, providing models for chiral symmetry breaking in confined nematic LCs.

Findings

Achiral LCLCs spontaneously twist, forming spiral textures in confinement.

Chiral dopants bias the handedness, but disfavored twists still occur with finite probability.

Director field models explain the energetics and metastability of chiral configurations.

Abstract

We study the chiral symmetry breaking and metastability of confined nematic lyotropic chromonic liquid crystal (LCLC) with and without chiral dopants. The isotropic-nematic coexistence phase of the LCLC renders two confining geometries: sessile isotropic(I) droplets surrounded by the nematic(N) phase and sessile nematic droplets immersed in the isotropic background. In the achiral system with no dopants, LCLC's elastic anisotropy and topological defects induce a spontaneous twist deformation to lower the energetic penalty of splay deformation, resulting in spiral optical textures under crossed polarizers both in the I-in-N and N-in-I systems. While the achiral system exhibits both handednesses with an equal probability, a small amount of the chiral dopant breaks the balance. Notably, in contrast to the homochiral configuration of a chirally doped LCLC in bulk, the spiral texture of the disfavored handedness appears with a finite probability both in the I-in-N and N-in-I systems. We propose director field models explaining how chiral symmetry breaking arises by the energetics and the opposite-twist configurations exist as meta-stable structures in the energy landscape. These findings help us create and control chiral structures using confined LCs with large elastic anisotropy.