Peng Chenhui, Lavrentovich Oleg D
Department of Physics and Materials Science, The University of Memphis, Memphis, TN 38152, USA.
Department of Physics and Chemical Physics Interdisciplinary Program, Advanced Materials and Liquid Crystal Institute, Kent State University, Kent, OH 44242, USA.
Micromachines (Basel). 2019 Jan 10;10(1):45. doi: 10.3390/mi10010045.
Phenomena of electrically driven fluid flows, known as electro-osmosis, and particle transport in a liquid electrolyte, known as electrophoresis, collectively form a subject of electrokinetics. Electrokinetics shows a great potential in microscopic manipulation of matter for various scientific and technological applications. Electrokinetics is usually studied for isotropic electrolytes. Recently it has been demonstrated that replacement of an isotropic electrolyte with an anisotropic, or liquid crystal (LC), electrolyte, brings about entirely new mechanisms of spatial charge formation and electrokinetic effects. This review presents the main features of liquid crystal-enabled electrokinetics (LCEK) rooted in the field-assisted separation of electric charges at deformations of the director that describes local molecular orientation of the LC. Since the electric field separates the charges and then drives the charges, the resulting electro-osmotic and electrophoretic velocities grow as the square of the applied electric field. We describe a number of related phenomena, such as alternating current (AC) LC-enabled electrophoresis of colloidal solid particles and fluid droplets in uniform and spatially-patterned LCs, swarming of colloids guided by photoactivated surface patterns, control of LCEK polarity through the material properties of the LC electrolyte, LCEK-assisted mixing at microscale, separation and sorting of small particles. LC-enabled electrokinetics brings a new dimension to our ability to manipulate dynamics of matter at small scales and holds a major promise for future technologies of microfluidics, pumping, mixing, sensing, and diagnostics.
电驱动流体流动现象，即电渗，以及液体电解质中的粒子输运，即电泳，共同构成了电动学的研究主题。电动学在各种科学技术应用中的微观物质操纵方面显示出巨大潜力。电动学通常针对各向同性电解质进行研究。最近已经证明，用各向异性电解质或液晶（LC）电解质替代各向同性电解质，会带来全新的空间电荷形成机制和电动效应。本综述介绍了基于液晶的电动学（LCEK）的主要特征，其根源在于在描述液晶局部分子取向的指向矢变形时电场辅助的电荷分离。由于电场分离电荷然后驱动电荷，因此产生的电渗速度和电泳速度随外加电场的平方而增加。我们描述了一些相关现象，例如在均匀和空间图案化的液晶中胶体固体颗粒和液滴的交流电（AC）液晶电泳、由光活化表面图案引导的胶体聚集、通过液晶电解质的材料特性控制LCEK极性、微尺度下LCEK辅助混合、小颗粒的分离和分选。基于液晶的电动学为我们在小尺度上操纵物质动力学的能力带来了新的维度，并为微流体、泵送、混合、传感和诊断等未来技术带来了重大希望。
