Szmigielski Michał
Institute of Physics, Lodz University of Technology, Łódź, Poland.
Soft Matter. 2023 Apr 12;19(15):2675-2704. doi: 10.1039/d2sm01600a.
Novel modulated nematic phases, such as twist-bend nematics, splay-bend nematics and splay nematics, are an important subject of research in the field of liquid crystals. In this article fundamental information about the discovery, structure and properties of these phases is presented. Various theoretical models of elastic properties are compared, especially the proposed formulae for the free energy density of modulated nematic phases and the conditions for their stability. The emphasis is put on the variety of material parameters and variables in the mathematical description of the structures. The elastic models are classified according to a few criteria. Flexopolarisation is indicated as a main phenomenon responsible for the formation of modulated nematic phases. The elastic models are used for analysing the deformations of the twist-bend nematic structure in external fields. Dielectric, flexoelectric, ferroelectric and magnetic effects are considered. Two types of distortions are distinguished: microscopic (connected with the deformation of the director distribution) and macroscopic (related to the change of the optic axis direction). This review can be a starting point for further studies, for example computer simulations of modulated phases and design of liquid crystalline devices.
新型调制向列相，如扭曲弯曲向列相、展曲弯曲向列相和展向列相，是液晶领域的一个重要研究课题。本文介绍了有关这些相的发现、结构和性质的基本信息。比较了弹性性质的各种理论模型，特别是调制向列相自由能密度的建议公式及其稳定性条件。重点在于结构数学描述中材料参数和变量的多样性。弹性模型根据一些标准进行分类。挠曲极化被认为是导致调制向列相形成的主要现象。弹性模型用于分析扭曲弯曲向列相结构在外部场中的变形。考虑了介电、挠曲电、铁电和磁效应。区分了两种类型的畸变：微观畸变（与指向矢分布的变形有关）和宏观畸变（与光轴方向的变化有关）。这篇综述可以作为进一步研究的起点，例如调制相的计算机模拟和液晶器件的设计。
