A method to find the initial temperature range of the short-range order in the isotropic phase of nematic liquid crystals based on the electro-optical Kerr effect

摘要

It is well-known that orientational order of nematic liquid crystals (NLCs) is converted during phase transition from the long-range order (LRO) in the nematic phase to the short-range order (SRO) in the isotropic state. Finding the initial temperature range of SRO in the isotropic state can be a challenging issue because most of the physical constants disappear after this phase transition. For the first time, to resolve this issue, we introduced a new method based on the electro-optic Kerr (EOK) effect in NLC mixtures. In this method, the coherence length (xi), which was qualitatively estimated by employing the pre-transitional temperature (T*) according to the de Gennes phenomenological theory, and the refractive index (n) were correlated with the Kerr constant (B) at the same temperature in the isotropic phase. Because molecular interaction in the NLCs is one of the essential factors in the investigation of the orientational ordering, we used n and as described intra- and intermolecular interactions, respectively. In other words, n attributes to the polarization and dipole moment as an important parameter of the intramolecular interaction and xi demonstrates the intermolecular interaction and domains of SRO interaction in the isotropic phase. Finally, the initial temperature range of SRO in the isotropic phase was found from the temperature dependence with B of the normalized values of influential coefficients n and xi at the similar temperatures. Our proposed method appropriately can provide a suitable approach to distinguish the preservation of the anisotropy effect in the isotropic phase of NLCs. (C) 2018 Published by Elsevier B.V.