Selection of defect structures in twist-grain-boundary-A phase of chiral liquid crystals

TL;DR

This paper investigates the structures of twist grain boundaries in chiral smectic liquid crystals, identifying conditions for different defect structures and comparing theoretical results with experiments.

Contribution

It introduces a Landau-de Gennes model to distinguish between MGBA and TGBA structures, improving understanding of defect stability and dislocation spacings.

Findings

MGBA structure is stable near cholesteric transition

Dislocation spacings match experimental data better than previous models

Cholesteric-like domains grow near phase transition

Abstract

We study the structure of the twist grain boundary in chiral smectic liquid crystals using the Landau-de Gennes model. By considering spatial variation of the smectic order, we distinguish the Melted-Grain-Boundary-A (MGBA) structure with cholesteric-like domains and the Twist-Grain-Boundary-A (TGBA) structure consisting of screw dislocations. The MGBA structure becomes stable near the transition to the cholesteric phase. On approaching the transition, the cholesteric-like domain grows outside the grain boundary. Also, the dislocation spacings of the TGBA structure agree better with experimental results than previous theories.