The role of electrohydrodynamic forces in the dielectrophoretic manipulation and separation of particles

A dielectric particle suspended in a dielectric medium polarises under the influence of an electric field. If the field is non-uniform, the particle experiences a directional force and the resulting movement is referred to as dielectrophoresis. The high electric fields can also cause fluid motion, which in turn results in a viscous drag force on the particle. This paper outlines the application of dielectrophoresis to the sub-micrometre scale and discusses mechanisms responsible for fluid motion in small electrode structures. Preliminary measurements of fluid velocity in a microelectrode array are presented and are discussed in relation to theoretical models. Finally the relevance of electric field induced fluid motion to particle separation technologies is discussed.