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

• Published in: Soft matter Vol. 15; no. 29; pp. 5835 - 5841
• Main Authors: Suh, Ahram, Gim, Min-Jun, Beller, Daniel, Yoon, Dong Ki
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 2019
• Subjects: Anchoring; Arrays; Configurations; Crystal defects; Domains; Liquid crystals; Melts; Microscopy; Nematic crystals; Optical microscopy; Phase transitions; Substrates; Surface defects; Thin films; Topology; Transformations (mathematics)
• ISSN: 1744-683X; 1744-6848
• DOI: 10.1039/c9sm00781d

We study transformations of self-organised 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 polarised 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 organised over large scales in patterns that retain a geometric memory of the nematic boojum configuration, which can be recovered with remarkable fidelity. We study transformations of self-organised 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.