Liquid Crystal Institute and Chemical Physics Interdisciplinary Program, Kent State University, Kent, OH 44242, USA.
Philos Trans A Math Phys Eng Sci. 2013 Mar 4;371(1988):20120255. doi: 10.1098/rsta.2012.0255. Print 2013 Apr 13.
We describe electrophoresis of spherical dielectric particles in a uniformly aligned nematic medium with a negative dielectric anisotropy. A spherical particle that orients the liquid crystal (LC) perpendicularly to its surface moves under the application of a uniform direct current or alternating current electric field. The electric field causes no distortions of the LC director far away from the sphere. Electrophoresis in the nematic LC shows two types of nonlinearity in the velocity versus field dependence. The velocity component parallel to the applied electric field grows linearly with the field, but when the field is high enough, it also shows a cubic dependence. The most interesting is the second type of nonlinear electrophoresis that causes the sphere to move perpendicularly to the applied field. This perpendicular component of velocity is proportional to the square of the field. The effect exists only in an LC and disappears when the material is melted into an isotropic fluid. The quadratic effect is caused by the dipolar symmetry of director distortions around the sphere and is classified as an LC-enabled electrophoresis (LCEEP). The nonlinear electrophoretic mobility of particles in LCEEP offers a rich variety of control parameters to design three-dimensional trajectories of particles for microfluidic and optofluidic applications.
我们描述了在具有负介电各向异性的均匀排列向列相介质中球形介电粒子的电泳。当一个垂直于表面排列液晶的球形粒子在直流或交流电场的作用下运动时，电场不会导致液晶指向矢在远离球体的地方发生变形。在向列相液晶中的电泳在速度与场的关系中表现出两种类型的非线性。平行于外加电场的速度分量随电场线性增长，但当电场足够高时，它也表现出三次方的依赖关系。最有趣的是第二种非线性电泳，它导致球体垂直于外加电场运动。这个垂直速度分量与场的平方成正比。这种效应只存在于液晶中，当材料融化成各向同性流体时，这种效应就会消失。二次效应是由球体周围的指向矢扭曲的偶极对称引起的，被归类为液晶增强电泳（LCEEP）。LCEEP 中粒子的非线性电泳迁移率为设计微流控和光流控应用中粒子的三维轨迹提供了丰富的控制参数。
