Tetrahedral symmetry in nematic liquid crystals.
Tetrahedral symmetry in nematic liquid crystals.
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DOI：
10.1103/physreve.52.702
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发表时间：
1995-07
期刊：
影响因子：
--
通讯作者：
L. Fel
中科院分区：
文献类型：
--
作者：
L. Fel
通过对称性考虑，推导出四面体向列液晶（LC）的有序参数U i j k 。与其他向列相液晶（包括单轴、双轴、立方和二十面体相）相比，U i j k 的奇数级 (= 3) 允许一级和二级从各向同性液体到四面体向列液晶的相变，并导致该向列液晶的手性 T 相中出现两种可能的螺旋结构之一。在平均场近似的框架中，发现了液晶序参数的取向部分对不同对称性液晶的极化率的贡献，并预测了从各向同性液体到非手性四面体向列液晶的二阶相变的存在。考虑了非手性 T d 相中的 Fréedericksz 转变：分叉树的特性主要取决于外部场相对于未扰动四面体相的旋转 C 3 轴和螺旋 C 4 轴的方向。讨论了螺旋T相在外场作用下的解扭和偏差。分析了四面体向列液晶中向错核心的结构。
By means of symmetry consideration the order parameter U i j k of a tetrahedral nematic liquid crystal (LC) was derived. In contrast to other nematic LC’s (including uniaxial, biaxial, cubic, and icosahedral phases) the odd rank (= 3) of U i j k permits the phase transition of both the first and second order from isotropic liquid into tetrahedral nematic LC’s and leads to the appearance of one of two possible helical structures in the chiral T phase of this nematic LC. In the framework of the mean-field approximation the contribution of the orientational part of the LC order parameter to the polarizability of LC with different symmetries was found and the existence of the second order phase transition from isotropic liquid into nonchiral tetrahedral nematic LC’s has been predicted. The Fréedericksz transition in the nonchiral T d phase was considered: the peculiarities of the bifurcation tree crucially depended on the direction of the external field with respect to the rotational C 3 and screw C 4 axes of the unperturbed tetrahedral phase. The untwisting and deviation of the helical T phase in external fields were discussed. The structure of the disclination core in a tetrahedral nematic LC was analyzed.