Jeong Joonwoo, Kang Louis, Davidson Zoey S, Collings Peter J, Lubensky Tom C, Yodh A G
Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104; and
Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104; and.
Proc Natl Acad Sci U S A. 2015 Apr 14;112(15):E1837-44. doi: 10.1073/pnas.1423220112. Epub 2015 Mar 30.
We study chiral symmetry-broken configurations of nematic liquid crystals (LCs) confined to cylindrical capillaries with homeotropic anchoring on the cylinder walls (i.e., perpendicular surface alignment). Interestingly, achiral nematic LCs with comparatively small twist elastic moduli relieve bend and splay deformations by introducing twist deformations. In the resulting twisted and escaped radial (TER) configuration, LC directors are parallel to the cylindrical axis near the center, but to attain radial orientation near the capillary wall, they escape along the radius through bend and twist distortions. Chiral symmetry-breaking experiments in polymer-coated capillaries are carried out using Sunset Yellow FCF, a lyotropic chromonic LC with a small twist elastic constant. Its director configurations are investigated by polarized optical microscopy and explained theoretically with numerical calculations. A rich phenomenology of defects also arises from the degenerate bend/twist deformations of the TER configuration, including a nonsingular domain wall separating domains of opposite twist handedness but the same escape direction and singular point defects (hedgehogs) separating domains of opposite escape direction. We show the energetic preference for singular defects separating domains of opposite twist handedness compared with those of the same handedness, and we report remarkable chiral configurations with a double helix of disclination lines along the cylindrical axis. These findings show archetypally how simple boundary conditions and elastic anisotropy of confined materials lead to multiple symmetry breaking and how these broken symmetries combine to create a variety of defects.
我们研究了向列型液晶（LCs）的手性对称破缺构型，这些液晶被限制在圆柱状毛细管中，在管壁上具有垂直取向锚定（即垂直表面排列）。有趣的是，具有相对较小扭曲弹性模量的非手性向列型液晶通过引入扭曲变形来缓解弯曲和展曲变形。在由此产生的扭曲逃逸径向（TER）构型中，液晶指向矢在中心附近与圆柱轴平行，但为了在毛细管壁附近达到径向取向，它们通过弯曲和扭曲畸变沿半径方向逃逸。在聚合物涂层毛细管中使用日落黄FCF进行手性对称破缺实验，日落黄FCF是一种具有小扭曲弹性常数的溶致变色液晶。通过偏振光学显微镜研究其指向矢构型，并通过数值计算进行理论解释。TER构型的简并弯曲/扭曲变形还产生了丰富的缺陷现象学，包括一个非奇异畴壁，它分隔具有相反扭曲手性但相同逃逸方向的畴，以及奇异点缺陷（刺猬），它分隔具有相反逃逸方向的畴。我们展示了与具有相同手性的奇异缺陷相比，具有相反扭曲手性的奇异缺陷在能量上的偏好，并且我们报道了沿着圆柱轴具有双螺旋位错线的显著手性构型。这些发现典型地展示了受限材料的简单边界条件和弹性各向异性如何导致多重对称性破缺，以及这些破缺的对称性如何结合产生各种缺陷。
