Visualizing Invisible Phase Transitions in Blue Phase Liquid Crystals Using Early Warning Indicators

• Published in: Small (Weinheim an der Bergstrasse, Germany) Vol. 18; no. 25; pp. e2200113 - n/a
• Main Authors: Matsui, Takayuki, Matsumori, Tadayoshi, Ito, Yuji, Hase, Yoko, Yoshida, Hiroyuki
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 01.06.2022
• Subjects: blue phase liquid crystals; critical transitions; early warning; Free energy; Indicators; Liquid crystals; martensitic transitions; Materials science; Nanotechnology; Phase transitions; Skewness; skewness mapping; blue phase liquid crystals; martensitic transitions; critical transitions; skewness mapping; early warning
• ISSN: 1613-6810; 1613-6829
• DOI: 10.1002/smll.202200113

Changes in the statistical properties of data as a system approaches a critical transition is studied intensively as early warning signals, but their application to materials science, where phase transitions—a type of critical transition—are of fundamental importance, are limited. Here, a critical transition analysis is applied to time‐series data from a microscopic 3D ordered soft material—blue phase liquid crystals (BPLC)—and demonstrates that phase transitions that are invisible under ambient conditions can be visualized through the choice of appropriate early warning indicators. After discussing how a phase transition affects the statistical properties in a system with a Landau–de Gennes type free energy potential, the predicted changes are experimentally observed at the two types of phase transitions that occur in a BPLC: the isotropic to simple cubic, and simple cubic to body‐centered cubic transitions. In particular, it is shown that the skewness of the intensity distribution inverts its sign at the phase transition, enabling temporally and spatially resolved mapping of phase transitions. This approach can be easily adapted to a wide variety of material systems and microscopy techniques, providing a powerful tool for studying complex critical transition phenomena. Skewness images achieve quasi‐quantitative visualization of where and when phase transitions occur by statistical calculations, especially skewness. Collective phase transition of blue phase liquid crystals, martensitic transition, is successfully visualized. Generic statistical variables used in diverse fields as early warning signals can be a powerful tool for visualizing phase transitions in optically featureless soft materials.