Institute of Physical Chemistry, University of Stuttgart , Pfaffenwaldring 55, 70569 Stuttgart, Germany.
Microelectronics and Nanoscience, Chalmers University of Technology , 41296 Göteborg, Sweden.
Langmuir. 2017 Jun 13;33(23):5852-5862. doi: 10.1021/acs.langmuir.7b01074. Epub 2017 May 26.
Recently, the emergence of spontaneous reflection-symmetry-broken configurations in achiral chromonic liquid crystals confined in cylindrical capillaries with homeotropic anchoring at the cylinder walls was reported, namely, the so-called twisted-escaped radial (TER) and twisted planar polar (TPP) configurations. This new example of spontaneous reflection symmetry breaking in liquid crystals was attributed to the twist elastic modulus, which is known to be unusually small in comparison to the splay and bend moduli in the case of chromonic liquid crystals. We now report the experimental observation of reflection symmetry breaking in cylindrical capillaries in the case of a classical, achiral, and nonchromonic lyotropic liquid crystal forming a nematic phase of disklike micelles orienting homeotropically at the capillary walls. We observed the same chiral TER configuration, as well as a nonplanar twisted polar (TP) configuration. The TP configuration is characterized by two half-unit so-called twist disclinations, where the director twist around the line defects drives the formation of a double helix of the disclinations along the axis of the capillary. Additionally, there is a transverse twist between the two disclination lines with the same handedness as the axial twist. Similarities with and differences from the case of chromonic liquid crystals are discussed; in particular, we examine the conditions under which spontaneous reflection symmetry breaking occurs in the nonchromonic system. It seems that the chiral TER configuration can be stabilized by the presence of point defects.
最近，在具有垂直壁向列锚定的圆柱形毛细管所限制的手性向列型色晶液晶中出现了自发反射对称破缺构型，即所谓的扭曲逃逸径向（TER）和扭曲平面极（TPP）构型。这种手性液晶中自发反射对称破缺的新例子归因于扭转弹性模量，与色晶液晶的伸展和弯曲模量相比，扭转弹性模量通常较小。我们现在报告在圆柱形毛细管中观察到手性反射对称破缺的实验，该毛细管中存在经典的、非手性的、非色晶的溶致各向同性液晶，形成垂直于壁的盘状胶束的向列相。我们观察到相同的手性 TER 构型，以及非平面扭曲极（TP）构型。TP 构型的特点是两个半单位的所谓扭曲位错，其中围绕线缺陷的指向矢扭曲导致位错沿毛细管壁的轴线形成双螺旋结构。此外，两个位错线之间存在横向扭曲，其与轴向扭曲的手性相同。讨论了与色晶液晶的相似性和差异；特别是，我们研究了在非色晶体系中自发反射对称破缺发生的条件。似乎手性 TER 构型可以通过点缺陷的存在来稳定。
