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Near-contact electrophoretic particle motion

Published online by Cambridge University Press:  26 April 2006

Michael Loewenberg  and
Robert H. Davis
Michael Loewenberg
Affiliation:
Department of Chemical Engineering, University of Colorado, Boulder, CO 80309-0424, USA Present address: Department of Chemical Engineering, Yale University, New Haven, Connecticut, CT 06520-2159, USA.
Robert H. Davis
Affiliation:
Department of Chemical Engineering, University of Colorado, Boulder, CO 80309-0424, USA
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Abstract

The near-contact axisymmetric electrophoretic motion of a pair of spherical particles with thin electric double layers and differing surface zeta-potentials is analysed for low Reynolds numbers and moderate surface potentials. Near-contact electrophoretic motion of a spherical particle normal to a planar conducting boundary is analysed under the same assumptions. Pairwise motion is computed by considering touching particles in point contact; relative motion is described by a perturbation about the touching state using lubrication theory. Analytical formulae are derived for two particles of disparate sizes, and for the motion 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 the electrophoresis is a much more efficient mechanism of near-contact motion than is buoyancy. An explanation for this finding is given in terms of the electro-osmotic slip velocity on the particle surfaces that facilitates fluid removal from between approaching surfaces.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 288 , 10 April 1995 , pp. 103 - 122
Copyright
© 1995 Cambridge University Press

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