Molecular Mechanism of Gyroid Formation by Small Mesogenic Molecules

2023 Fiscal Year Final Research Report

• Project/Area Number: 21H01046
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 13040:Biophysics, chemical physics and soft matter physics-related
• Research Institution: University of Tsukuba
• Principal Investigator: Kazuya SAITO 筑波大学, 数理物質系, 教授 (30195979)
• Co-Investigator(Kenkyū-buntansha): 山村 泰久 筑波大学, 数理物質系, 准教授 (80303337)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: ジャイロイド / 液晶 / エントロピー / 凝集構造 / スピンモデル

Outline of Final Research Achievements

Structure analyses of the chiral cubic phase, neighboring to the gyoid phase on the phase diagram against the alkyl-chain length of rodlike mesogens, were achieved utilizing a new crystallographic algorithm. The result suggested the importance of smooth variations of molecular orientations, which is identified as a new mechanism for the structure formation of complicated superstructures consisting of rodlike molecules.
In layered liquid crystals, the details of the layer structure, such as sharpness, dominate the physical properties. For example, the details successfully explain the thermodynamic order of the phase transition between the two liquid crystalline phases, smectic A and nematic.
A headless classical Heisenberg model preferring twist, inspired by the twist in the gyroid phase, exhibits intriguing properties, such as the macroscopic degeneracy without frustration, a phase transition without long-range order in dimension two, and three-step ordering in dimension four.

Free Research Field

物性科学

Academic Significance and Societal Importance of the Research Achievements

本研究の結果は，液晶分子を棒と考えずに主要な内部構造を考慮することにより，凝集構造や物性の理解が飛躍することを示している．また，平衡状態における複雑な超構造（メゾスコピックな構造）の生成機構としては，これまでもっぱら相分離が考えられてきたが，今回の研究により相分離を伴わない機構が見出された．超構造形成や自己組織化の研究に，新しい視点をもたらした．
また，派生的に得られたスピンモデルの統計的挙動は，長距離秩序を伴わない相転移が可能であることを示すことが興味深いだけで無く，有限系の「相転移」様挙動の可能性を示しており，工学的な応用の可能性も考え得る．