NEAR-CONTACT ELECTROPHORETIC PARTICLE MOTION

The near-contact axisymmetric electrophoretic motion of a pair of sphe rical particles with thin electric double layers and differing surface zeta-potentials is analysed for low Reynolds numbers and moderate sur face potentials. Near-contact electrophoretic motion of a spherical pa rticle normal to a planar conducting boundary is analysed under the sa me assumptions. Pairwise motion is computed by considering touching pa rticles in point contact; relative motion is described by a perturbati on about the touching state using lubrication theory. Analytical formu lae are derived for two particles of disparate sizes, and for the moti on of a single particle towards a boundary; numerical calculations are performed for all size ratios. The results have a universal form with respect to the particle zeta-potentials. All results indicate that th e electrophoresis is a much more efficient mechanism of near-contact m otion than is buoyancy. An explanation for this finding is given in te rms of the electro-osmotic slip velocity on the particle surfaces that facilitates fluid removal from between approaching surfaces.