One of the interesting developments was a discovery that a broken symmetry of the particle can result in a nonlinear electrophoresis, with a quadratic dependence of the velocity on the field. Clearly, the AC driving mechanism should somehow break the classic linear Smoluchowski relationship between the velocity of particles v and the electric field E . There is a growing interest in finding mechanisms for particle manipulation that uses an alternating current (AC) electric field, as with the latter, it is much easier to produce steady flows and to avoid undesirable electrochemical reactions. The most known technique is electrophoresis in which charged particles are moved by an applied direct current (DC) electric field. Historically, however, the most popular driving agent of particle motion has been the electric field. Control over the particles can be achieved in a variety of ways, including the design of self-propelled particles. Drug delivery, macromolecule separation, display of information and colloidal assembly are just a few examples of potential applications. 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.Ĭontrolled manipulation and motion of small particles has become a topic of great interest over the past decade. 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 effect exists only in an LC and disappears when the material is melted into an isotropic fluid. This perpendicular component of velocity is proportional to the square of the field. The most interesting is the second type of nonlinear electrophoresis that causes the sphere to move perpendicularly to the applied field. 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. Electrophoresis in the nematic LC shows two types of nonlinearity in the velocity versus field dependence. The electric field causes no distortions of the LC director far away from the sphere. 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. We describe electrophoresis of spherical dielectric particles in a uniformly aligned nematic medium with a negative dielectric anisotropy.
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