Fukuoka and Tsukuba, Japan—Researchers have uncovered key insights about how liquid crystals, materials capable of forming complex ordered structures, transform between different phases. Published in PNAS, the study provides a clearer understanding of how these materials change their structures at the microscopic level. This research could provide a means to give a deeper insight into the transformation between different structures in a wider variety of materials.
Liquid crystals are materials that exhibit properties of both liquids and solids. They flow like liquids but can also form ordered structures like solids. Liquid crystals are widely used in devices such as digital displays, light-responsive materials, and sensors. However, despite their widespread use, understanding how they reorganize at the microscopic level has long been a scientific challenge, and the underlying mechanisms have remained unclear.
Professor Jun-ichi Fukuda from Kyushu University's Department of Physics, in collaboration with Dr. Kazuaki Z. Takahashi from the National Institute of Advanced Industrial Science and Technology (AIST) and the Japan Science and Technology Agency (JST), performed a study focusing on cholesteric blue phases, a specific type of liquid crystal characterized by its unique cubic symmetry. These blue phases form complex three-dimensional structures with distinctive properties, making them a subject of great interest in both basic science and materials engineering.
The team investigated the transition from one blue phase, BP II, to another, BP I. As BP II changes into BP I, the liquid crystal forms twin boundaries—regions where two parts of the material align differently. Previous experimental studies fail to capture the detailed mechanism of transformation of blue phases involving the formation of twin structures.
To gain a deeper understanding of this process, the team employed computer simulations performed by Fukuda, and MALIO, a machine learning tool Takahashi designed to analyze and distinguish the local structures of BP I and BP II liquid crystal phases. The exploitation of the latter machine learning approach makes it possible to distinguish between the BP II and BP I structures, and to analyze their evolution over time. The strategy developed by the team allowed the tracking of the transformation in real time, revealing key stages in the transition such as the formation of small BP I domains, which grow and eventually form twin boundaries. Their approach provides valuable insights into the formation and growth of twin structures during the transformation.
"The dynamics of soft materials like liquid crystals are highly complex," says Fukuda. "This work has given us a deeper understanding of how these materials transform at a microscopic level."
The approach presented in this study could also reveal how hierarchical structures in soft materials, such as polymers and biological systems, undergo similar phase transitions. "Our method is not limited to liquid crystals," Fukuda explains. "It can be applied to other complex materials, which can offer new insights into how structures form and change in systems."
