Order parameter of dual-frequency nematic liquid crystals measured over a wide range of thicknesses

Basic physical properties of liquid crystals strongly depend on the orientational order parameter. Given a fundamental importance of this parameter, it was measured for a variety of liquid crystals by means of various experimental techniques. At the same time, the reported results were limited to a relatively narrow range of thicknesses of the studied liquid crystal cells (typically, within a 1–20 µm interval). This paper presents the values of the orientational order parameter of dual-frequency nematic liquid crystals measured over a wide range of thicknesses (from 5 to 200 µm). The non-monotonous dependence of the order parameter S on the cell thickness obtained for relatively thin layers (S for thicker (60–200 µm) liquid crystal samples. The obtained results are important for the development of emerging, non-display, applications of liquid crystals utilising thick cells and fast switching materials such as dual-frequency nematics. In particular, they provide a basis for understanding recently discovered two regimes of electro-optical switching of thin and thick layers of dual-frequency nematics (Crystals, 9(6), pp. 314, 2019).

液晶的基本物理性质强烈依赖于取向序参数（orientational order parameter）。鉴于该参数的核心重要性，学界已通过多种实验技术对多种液晶的该参数开展了测量。然而，已报道的研究结果仅局限于较窄的液晶盒厚度区间（通常为1~20 µm）。
本文报道了双频向列相液晶（dual-frequency nematic liquid crystals）的取向序参数数值，其测量覆盖了5~200 µm的宽厚度范围。针对较薄液晶层测得的序参数S随盒厚度变化的非单调依赖关系，与厚层（60~200 µm）液晶样品的结果存在显著差异。
本研究结果对于开发基于厚盒与快开关材料（如双频向列相液晶）的新兴非显示类液晶应用具有重要价值。具体而言，这些结果为理解近年发现的双频向列相液晶薄层与厚层的两种电光开关机制提供了理论依据（Crystals, 9(6), pp. 314, 2019）。