Electrophoresis of an axisymmetric particle along its axis of revolution perpendicular to two parallel plane walls
Journal
Microfluidics and Nanofluidics
Journal Volume
9
Journal Issue
4-5
Pages
623-634
Date Issued
2010
Author(s)
Abstract
The axisymmetric electrophoretic motion of a dielectric particle of revolution situated at an arbitrary position in a slit microchannel is studied theoretically at the quasisteady state. The applied electric field is uniform, along the axis of symmetry of the particle, and perpendicular to the two plane walls of the slit. The electric double layer at the particle surface is assumed to be thin relative to the particle size and to the particle-wall gap widths. A method of distribution of a set of spherical singularities along the axis of symmetry within a prolate particle or on the fundamental plane within an oblate particle is used to find the general solutions for the electric potential distribution and fluid velocity field. The apparent slip condition on the particle surface is satisfied by applying a boundary collocation technique to these general solutions. Numerical results for the electrophoretic velocity of a prolate or oblate spheroid along its axis of revolution and perpendicular to two plane walls are obtained with good convergence behavior for various cases. The effect of the confining walls is to reduce the velocity of the particle, irrespective of its aspect ratio or the relative particle-wall separation distances. For fixed separation parameters, the normalized velocity of the spheroid decreases with a decrease in its axial-to-radial aspect ratio, and the boundary effect on electrophoresis of an oblate spheroid can be very significant. When a spheroid with a specified aspect ratio is located near a first plane wall, the approach of a second wall far from the particle can first increase the electrophoretic mobility to a maximum, then reduce this mobility when the second wall is close to the particle, and finally lead to a minimum mobility when it reaches to the same distance from the particle as the first wall. For a given separation between the two plane walls relative to the axial size of the spheroid, the electrophoretic mobility has a maximum when the spheroid is located midway between the walls and decreases as it approaches either of the walls.
SDGs
Type
journal article