Topological defects and geometric memory across the nematic-smectic A liquid crystal phase transition

TL;DR

This study investigates how defect structures in liquid crystals transform and retain geometric memory across the nematic-smectic A phase transition, combining experimental observations with numerical modeling.

Contribution

It reveals the topological and geometrical rules governing defect transformations and demonstrates the preservation of geometric memory during phase transitions.

Findings

Defect configurations are correlated across phase transition.

Focal conic domains retain geometric memory of nematic boojum configurations.

Numerical modeling elucidates topological rules of defect transformations.

Abstract

We study transformations of self-organized defect arrays at the nematic-smectic A liquid crystal phase transition, and show that these defect configurations are correlated, or "remembered", across the phase transition. A thin film of thermotropic liquid crystal is subjected to hybrid anchoring by an air interface and a water substrate, and viewed under polarized optical microscopy. Upon heating from smectic-A to nematic, a packing of focal conic domains melts into a dense array of boojums---nematic surface defects---which then coarsens by pair-annihilation. With the aid of Landau-de Gennes numerical modeling, we elucidate the topological and geometrical rules underlying this transformation. In the transition from nematic to smectic-A, we show that focal conic domain packings are organized over large scales in patterns that retain a geometric memory of the nematic boojum configuration, which can be recovered with remarkable fidelity.