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arXiv 1303.6239cond-mat.softastro-ph.COcond-mat.mtrl-sci
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自组装溶致变色液晶中各向同性-非晶相变过程中缺陷和类晶的形态发生

Morphogenesis of defects and tactoids during isotropic-nematic phase transition in self-assembled lyotropic chromonic liquid crystals

Young-Ki Kim, Sergij V. Shiyanovskii, Oleg D. Lavrentovich

摘要:

本文研究了溶致变色液晶(LCLC)中液晶(N)和各向同性(I)之间一级相变中的原子核结构和拓扑缺陷。LCLC由各种长度的自组装分子聚集体形成,并显示出宽的两相区域。这些缺陷的出现是两种机制的结果。1)表面各向异性机制,由于在封闭的I-N界面处的指向矢的优先(切向)取向,赋予每个N核(类核)拓扑缺陷,以及2)Kibble机制,当不同取向的N类核彼此合并时形成缺陷。相变的不同情形涉及具有指向矢场的非平凡拓扑的正(N-in-I)和负(I-in-N)类触体以及多个连接的类触体中类触体配置。闭合的I-N界面限制了一个类星体,它有一定数量的尖点;尖点两侧的界面边缘形成一个不同于π的角度。每个尖点的N边包含一个点缺陷-boojum。尖点的数目表示当绕着触面的闭合边界旋转时,指向矢垂直于I-N界面的次数。我们推导出守恒定律,连接的尖点c的数量的拓扑强度m的缺陷在N部分的简单连接和多重连接tactoids。我们演示了如何弹性各向异性的N相的结果在非圆形形状的向错的核心。一个广义的Wulff结构是用来推导的I和N tactoids的形状作为I-N界面张力各向异性的函数在冻结的指向矢场的各种拓扑电荷m。类晶面和拓扑缺陷的复杂形状和结构表明了表面各向异性在液晶相变形态发生中的重要作用。

英文摘要:

We explore the structure of nuclei and topological defects in the first-order phase transition between the nematic (N) and isotropic (I) phases in lyotropic chromonic liquid crystals (LCLCs). The LCLCs are formed by self-assembled molecular aggregates of various lengths and show a broad biphasic region. The defects emerge as a result of two mechanisms. 1) Surface anisotropy mechanism that endows each N nucleus (tactoid) with topological defects thanks to preferential (tangential) orientation of the director at the closed I-N interface, and 2) Kibble mechanism with defects forming when differently oriented N tactoids merge with each other. Different scenarios of phase transition involve positive (N-in-I) and negative (I-in-N) tactoids with non-trivial topology of the director field and also multiply connected tactoids-in-tactoids configurations. The closed I-N interface limiting a tactoid shows a certain number of cusps; the lips of the interface on the opposite sides of the cusp make an angle different from pi. The N side of each cusp contains a point defect-boojum. The number of cusps shows how many times the director becomes perpendicular to the I-N interface when one circumnavigates the closed boundary of the tactoid. We derive conservation laws that connect the number of cusps c to the topological strength m of defects in the N part of the simply-connected and multiply-connected tactoids. We demonstrate how the elastic anisotropy of the N phase results in non-circular shape of the disclination cores. A generalized Wulff construction is used to derive the shape of I and N tactoids as the function of I-N interfacial tension anisotropy in the frozen director field of various topological charges m. The complex shapes and structures of tactoids and topological defects demonstrate an important role of surface anisotropy in morphogenesis of phase transitions in liquid crystals.

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