Separation of dielectric Janus particles based on polarizability-dependent induced-charge electroosmotic flow

Abstract

A new method of sorting dielectric Janus particle is proposed and studied numerically in this paper. The Janus particles are composed of two hemispheres of two different dielectric materials. When the particle is placed in a microchannel under uniform DC electric field along the channel, vortices are induced near the particle. The strengths of the four vortices are determined by the dielectric permittivity of the particle surface, the size of the particle, the external electric field and the orientation of the Janus particle in the electric field. The numerical simulation results show that the dividing line of the Janus particle will align with the channel walls in the uniform electric field. The equilibrium distance between the wall and a particle is determined by the relative polarizability ratio and the size of the Janus particle. Thus Janus particles of the same polarizability ratio and the same size will follow the same streamline; Janus particles of different polarizability ratio and different sizes will have different trajectories. Consequently, by inducing different streamlines into different branch channels, Janus particles can be separated and collected by their polarizability ratios and their sizes.