Senyuk Bohdan, Adufu Richmond E, Smalyukh Ivan I
Department of Physics, University of Colorado, Boulder, Colorado 80309, United States.
Department of Electrical, Computer and Energy Engineering, University of Colorado, Boulder, Colorado 80309, United States.
Langmuir. 2022 Jan 18;38(2):689-697. doi: 10.1021/acs.langmuir.1c02546. Epub 2022 Jan 6.
Colloidal particles in liquid crystals tend to induce topological defects and distortions of the molecular alignment within the surrounding anisotropic host medium, which results in elasticity-mediated interactions not accessible to their counterparts within isotropic fluid hosts. Such particle-induced coronae of perturbed nematic order are highly responsive to external electric fields, even when the uniformly aligned host medium away from particles exhibits no response to fields below the realignment threshold. Here we harness the nonreciprocal nature of these facile electric responses to demonstrate colloidal locomotion. Oscillations of the electric field prompt repetitive deformations of the corona of dipolar elastic distortions around the colloidal inclusions, which upon appropriately designed electric driving synchronize the displacement directions. We observe the colloid-hedgehog dipole accompanied by an umbilical defect in the tilt directionality field (-field), along with the texture of elastic distortions that evolves with a change in the applied voltage. The temporal out-of-equilibrium evolution of the director and -field distortions around particles when the voltage is turned on and off is not invariant upon reversal of time, prompting lateral translations and interactions that markedly differ from those accessible to these colloids under equilibrium conditions. Our findings may lead to both technological and fundamental science applications of nematic colloids as both model reconfigurable colloidal systems and as mesostructured materials with predesigned temporal evolution of structure and composition.
液晶中的胶体粒子往往会在周围各向异性主体介质中诱导拓扑缺陷并使分子排列发生畸变，这导致了弹性介导的相互作用，而这种相互作用在各向同性流体主体中的同类粒子间是不存在的。即使远离粒子的均匀排列主体介质在低于重新排列阈值的电场下没有响应，这种由粒子诱导的扭曲向列相序的电晕对外部电场也具有高度响应性。在此，我们利用这些简单电响应的非互易性质来演示胶体运动。电场的振荡促使胶体包裹体周围偶极弹性畸变电晕发生重复变形，在经过适当设计的电驱动下，这些变形使位移方向同步。我们观察到胶体刺猬偶极伴随着倾斜方向性场（θ场）中的脐点缺陷，以及随着外加电压变化而演变的弹性畸变纹理。当电压开启和关闭时，粒子周围指向矢和θ场畸变的非平衡时间演化在时间反转时并非不变，从而导致横向平移和相互作用，这与这些胶体在平衡条件下的情况明显不同。我们的发现可能会带来向列相胶体在技术和基础科学方面的应用，既作为可重构胶体系统的模型，也作为具有预先设计的结构和组成时间演化的介观结构材料。
