Deep electrophoretic penetration and deposition of ceramic particles inside impermeable porous substrates

The electrophoretic penetration of colloidal ceramic particles into an impermeable porous graphite substrate is investigated. The substrate is immersed in a suspension containing the particles and positioned between two electrodes, An electric potential gradient between the electrodes is used to drive the ceramic particles into the pores which are closed at the far end not allowing fluid permeation. Three driving mechanisms are identified: the hydrodynamic drag force exerted on the particles due to the electroosmotic flow of the solvent inside the pores, the electrophoretic force exerted on the particles, and the stochastic Brownian force due to thermal fluctuations of the solvent molecules, While subjected to these forces, the particles may reach the walls of the pore and the short range van der Waals forces may cause their capturing and deposition onto the walls, The objectives of this paper are (a) to predict the penetration depth of a single ceramic particle moving inside an impermeable porous substrate under the effect of an electric potential gradient, (b) to derive the nondimensional parameters characterizing the motion of the ceramic particles, and (c) to gain a physical insight on the relative significance of the various mechanisms governing penetration. Qualitatively, the results are that penetration depths are governed by a favorable (if large) Peclet number and unfavorable(if large) Damkohler number. The closed pore structure of the substrate causes diminished particle penetration due to a less effective electroosmotic force, Quantitative results for the mean penetration depths and the dispersion about the mean are also provided. (C) 1996 Academic Press, Inc.