Doubly-periodic instability pattern in a smectic A liquid crystal

TL;DR

This paper reports the discovery of a doubly-periodic surface defect pattern in a smectic A liquid crystal during phase transition, explained by a balance of surface anchoring, elastic energy, and saddle-splay distortion.

Contribution

It introduces a novel doubly-periodic defect pattern in smectic A liquid crystals and explains its formation using continuum Landau-deGennes theory.

Findings

Long period (~10 μm) results from surface anchoring and elastic energy balance.

Short period (~1 μm) caused by saddle-splay distortion and Gaussian curvature.

Pattern formation explained by theoretical modeling of defect interactions.

Abstract

We report the observation of a doubly-periodic surface defect-pattern in the liquid crystal 8CB, formed during the nematic--smectic A phase transition. The pattern results from the antagonistic alignment of the 8CB molecules, which is homeotropic at the surface and planar in the bulk of the sample cell. Within the continuum Landau-deGennes theory of smectic liquid crystals, we find that the long period (~10 \mu m) of the pattern is given by the balance between the surface anchoring and the elastic energy of curvature wall defects. The short period (~1 \mu m) we attribute to a saddle-splay distortion, leading to a non-zero Gaussian curvature and causing the curvature walls to break up.