Particle interactions in electrophoresis due to inertia

The inertial forces acting on two cylinders and two spheres have been calculated. The cylinders or spheres are of the same radius and zeta potential, and arbitrarily oriented in an electric field. It is found that when two particles are aligned perpendicular to the direction of the electric field, the force between them along the line of the centers is attractive. When they are along the direction of the electric field, the force between them along the line of the centers is repulsive. On a pair of arbitrarily oriented particles, the force perpendicular to the line of the centers tends to rotate the particles around the midpoint between the particle centers such that the pair is aligned normal to the applied electric field. The stable equilibrium orientation of a pair of particles and the attractive interaction forces between the particles when they are stably orientated may give rise to aggregation of particles during electrophoretic motion of a suspension.