Rods in a lyotropic chromonic liquid crystal: emergence of chirality, symmetry-breaking alignment, and caged angular diffusion
Rods in a lyotropic chromonic liquid crystal: emergence of chirality, symmetry-breaking alignment, and caged angular diffusion
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DOI：
10.1039/d1sm01209f
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发表时间：
2021-12-01
期刊：
影响因子：
3.4
通讯作者：
Yodh, A. G.
中科院分区：
文献类型：
--
作者：
Ettinger, Sophie;Dietrich, Clarissa F.;Yodh, A. G.
在溶致发色液晶中，液晶指向矢的扭曲变形比展曲或弯曲变形消耗的能量少得多。这一特点导致了新的镜像对称破缺导演配置时，液晶LC被限制的界面或包含悬浮颗粒。例如，在对齐的LCLC π相中的球形胶体诱导手性指向矢扰动（“扭曲的尾部”）。由于其长轴和均匀远场指向矢之间的纵横比（α）和平均取向角（θ），定向LCLC中棒状颗粒的不对称性提供了更丰富的可能性。在这里，我们报告的董事配置，平衡取向，和角扩散的棒状粒子与平面锚定悬浮在一个对齐的液晶LC。视频显微镜显示，违反直觉，三分之二的杆有一个角度的平衡取向（θ不等于0），随着α的增加而减少，而只有三分之一的杆对齐（θ = 0）。偏振光学视频显微镜和Landau-de Gennes数值模拟表明，成角度的和对齐的杆伴随着不同的手性指向矢配置。倾斜杆具有平行于其长轴且大致平行于衬底壁的纵向镜平面（LMP）。对齐的棒具有横向和纵向镜像平面（TLMP），其中横向镜像平面垂直于棒的长轴。有效地，LCLC的小扭转弹性常数促进手性指向矢配置，其修改杆沿沿着远场指向矢取向的自然趋势。附加的扩散实验证实，杆有角度地限制与强度，取决于α。
In lyotropic chromonic liquid crystals (LCLCs), twist distortion of the nematic director costs much less energy than splay or bend distortion. This feature leads to novel mirror-symmetry breaking director configurations when the LCLCs are confined by interfaces or contain suspended particles. Spherical colloids in an aligned LCLC nematic phase, for example, induce chiral director perturbations ("twisted tails"). The asymmetry of rod-like particles in an aligned LCLC offer a richer set of possibilities due to their aspect ratio (alpha) and mean orientation angle (theta) between their long axis and the uniform far-field director. Here we report on the director configuration, equilibrium orientation, and angular diffusion of rod-like particles with planar anchoring suspended in an aligned LCLC. Video microscopy reveals, counterintuitively, that two-thirds of the rods have an angled equilibrium orientation (theta not equal 0) that decreases with increasing alpha, while only one-third of the rods are aligned (theta = 0). Polarized optical video-microscopy and Landau-de Gennes numerical modeling demonstrate that the angled and aligned rods are accompanied by distinct chiral director configurations. Angled rods have a longitudinal mirror plane (LMP) parallel to their long axis and approximately parallel to the substrate walls. Aligned rods have a transverse and longitudinal mirror plane (TLMP), where the transverse mirror plane is perpendicular to the rod's long axis. Effectively, the small twist elastic constant of LCLCs promotes chiral director configurations that modify the natural tendency of rods to orient along the far-field director. Additional diffusion experiments confirm that rods are angularly confined with strength that depends on alpha.