Nonlinear electrophoresis of dielectric and metal spheres in a nematic liquid crystal

TL;DR

This paper demonstrates that electrophoresis in nematic liquid crystals exhibits a nonlinear velocity component proportional to the square of the electric field, enabling transport of symmetric particles and offering new applications in microfluidics and displays.

Contribution

It reveals a nonlinear electrophoretic effect in nematic liquid crystals caused by orientation distortions, allowing for particle transport regardless of charge or symmetry.

Findings

Electrophoretic velocity includes a quadratic component in nematic fluids.

Symmetric particles can be transported without charge due to the nonlinear effect.

The phenomenon enables new applications in display and microfluidic technologies.

Abstract

Electrophoresis is a motion of charged dispersed particles relative to a fluid in a uniform electric field. The effect is widely used to separate macromolecules, to assemble colloidal structures, to transport particles in nano- and micro-fluidic devices and displays. Typically, the fluid is isotropic (for example, water) and the electrophoretic velocity is linearly proportional to the electric field. In linear electrophoresis, only a direct current (DC) field can drive the particles. An alternate current (AC) field is more desirable because it allows one to overcome problems such as electrolysis and absence of steady flows. Here we show that when the electrophoresis is performed in a nematic fluid, the effect becomes strongly non-linear with a velocity component that is quadratic in the applied voltage and has a direction that generally differs from the direction of linear velocity. The new phenomenon is caused by distortions of the LC orientation around the particle that break the fore-aft (or left-right) symmetry. The effect allows one to transport both charged and neutral particles, even when the particles themselves are perfectly symmetric (spherical), thus enabling new approaches in display technologies, colloidal assembly, separation, microfluidic and micromotor applications.