De Luca Gino, Rey Alejandro D
Department of Chemical Engineering, McGill University, 3610 University Street, Montreal, Quebec H3A 2B2, Canada.
J Chem Phys. 2007 Sep 14;127(10):104902. doi: 10.1063/1.2775451.
The textures exhibited by nematic liquid crystals confined to cylindrical capillaries under homeotropic anchoring have been studied for nearly thirty years. One of the reasons behind this maintained interest is that the processing of many high-performance fibers including carbon fibers and spider silks involves these textures. Three of these textures, the planar radial with line defect, the planar polar with two line defects (PPLD), and the escape radial (ER), are relatively well understood. A third one, the escape radial with point defects presents, however, some unresolved issues and recent studies have questioned the real nature and dimensionality of the defects involved in this texture. It seems that the defects are not in the form of points but rather in the form of closed lines or rings. This paper presents a detailed study on the connection between point and ring defects in a cylindrical cavity using three-dimensional simulations based on the continuum Landau-de Gennes theory. The results show that true point defects cannot exist in cylindrical cavities and that the merging of two ringlike defects may lead to two qualitatively different stable textures, namely, the ER and PPLD textures. The various results are in qualitative agreement with recent molecular dynamic studies and with theoretical predictions based on experimental observations. The predictions provide new insights on the structural connections between synthetic and biological superfibers.
近三十年来，人们一直在研究垂直排列的向列型液晶在圆柱形毛细管中呈现的织构。持续关注这一现象的原因之一是，包括碳纤维和蜘蛛丝在内的许多高性能纤维的加工过程都涉及到这些织构。其中三种织构，即具有线缺陷的平面径向织构、具有两个线缺陷的平面极性织构（PPLD）和逃逸径向织构（ER），人们相对比较了解。然而，第三种织构，即具有点缺陷的逃逸径向织构，存在一些尚未解决的问题，最近的研究对这种织构中涉及的缺陷的真实性质和维度提出了质疑。似乎这些缺陷不是点状的，而是封闭线或环的形式。本文基于连续介质朗道 - 德热纳理论，通过三维模拟对圆柱形腔体内点缺陷和环形缺陷之间的联系进行了详细研究。结果表明，圆柱形腔体内不可能存在真正的点缺陷，两个环形缺陷的合并可能导致两种性质不同的稳定织构，即ER织构和PPLD织构。各种结果与最近的分子动力学研究以及基于实验观察的理论预测在定性上是一致的。这些预测为合成超纤维和生物超纤维之间的结构联系提供了新的见解。
