Electromigration of microspheres in nematic liquid crystals.

Application of an electric field to microspheres, dispersed in a nematic liquid crystal host material, causes particle translation along the direction of the average long molecular liquid crystal axis, i.e., the director. We have determined the stability regime of linear particle displacement in the parameter space of electric field amplitude and frequency for various applied electric wave forms and demonstrate a linear relationship between microsphere velocity and applied electric field amplitude. For increasing frequency the particle velocity exhibits a maximum before motion slowly vanishes. Addition of a small amount of an ionic dopant is shown to largely increase the stability region of linear microsphere motion, with particle velocities increasing until saturation is observed for increasing ion dopant concentration. It is presumed that the particle velocity is related to the surface charges adsorbed on the dispersed particles. Also the dynamics of occasionally observed two- and three-particle clusters is discussed.