Soliton-induced liquid crystal enabled electrophoresis

TL;DR

This paper introduces a novel AC electrophoresis mechanism in nematic liquid crystals where symmetry breaking occurs only above a threshold field, enabling controlled particle transport via director perturbations called directrons.

Contribution

It presents a new electrophoresis mechanism driven by liquid crystal director reorientation, allowing particle movement without pre-existing asymmetry and controlled by field frequency.

Findings

Threshold-dependent symmetry breaking induces particle motion.

Director perturbations form topologically trivial solitary waves.

Particle transport is controllable via field frequency.

Abstract

Manipulation of particles by a uniform electric field, known as electrophoresis, is used in a wide array of applications. Of especial interest is electrophoresis driven by an alternating current (AC) as it eliminates electrode blocking and produces a steady motion. The known mechanisms of AC electrophoresis require that either the particle or the surrounding medium are asymmetric. This asymmetry is usually assured before the field is applied, as in the case of Janus spheres. We report on a new mechanism of AC electrophoresis, in which the symmetry is broken only when the field exceeds some threshold. The new mechanism is rooted in the nature of electrophoretic medium, which is an orientationally ordered nematic liquid crystal. Below the threshold, the director field of molecular orientation around a spherical particle is of a quadrupolar symmetry. Above the threshold, the director forms a polar self confined perturbation around the inclusion that oscillates with the frequency of the applied field and propels the sphere. The director perturbations are topologically trivial and represent particle like solitary waves, called "director bullets" or "directrons". The direction of electrophoretic transport can be controlled by the frequency of the field. The AC directron induced liquid crystal enabled electrophoresis can be used to transport microscopic cargo when other modes of electrophoresis such as induced charge electrophoresis are forbidden.