Effect of induced-charge double layer on dielectrophoretic motion of particles

In ionic solutions, the double layer formation due to induced surface charges is seen to effect particle motion in AC electric fields as opposed to the fixed charge electrophoresis case wherein the double layer causes no net motion in an AC field. A method to numerically evaluate the effects of the induced-charge double layer on the dielectrophoretic motion of particles is developed in this paper. The technique involves a matched asymptotic expansion of the electric field near the particle surface, where the double layer is formed, and is written as a jump condition for the electric potential when the thickness of the double layer is small compared to the size of the particle. The developed jump condition is amenable to numerical evaluation and has been implemented in the finite element scheme. While the classical dielectrophoretic analysis ignores the effect of the electric double layers formed in ionic solutions, our results reveal their effect to be generally non-negligible and important for accurate modeling of the behavior of small particles in electric fields at frequencies up to MHz ranges.