Electrohydrodynamic particle aggregation on an electrode driven by an alternating electric field normal to it

An approximate model for the velocity due to electrohydrodynamic flow of electrolyte in the vicinity of a dielectric sphere near an electrode is described. The model considers the interaction of a lateral electric field, caused by the presence of the sphere, with free charge produced in the diffusion layer near an electrode when alternating current is passed through it. An equation based on the model predicts that adjacent dielectric particles aggregate or separate depending on the relative magnitude of the individual ionic conductivities and the frequency of oscillation in the case of a binary electrolyte. If the anion reacts and its conductance exceeds the cation conductance, the particles repel each other; the particles aggregate if the reverse is true. The equation also predicts that separation or aggregation depends on frequency of oscillation of the current. The model accounts for observed effects of frequency and particle size found in the literature. Finally, a dimensionless group that places a constraint on the frequency at which electroneutrality remains a good assumption for calculating electrohydrodynamic flow in oscillating systems is derived.