GRAVITATIONAL SETTLING IN THE ELECTROPHORESIS OF SPHEROIDS WITH SMALLPOTENTIALS IN QUIESCENT FLUID

Electrophoretic motion is analyzed for non-neutrally buoyant, spheroid al particles settling in an unbounded fluid otherwise at rest. The dou ble-layer thickness is arbitrary, and the surface potential of the sph eroid is assumed to be small so that the deformation of the double-lay er is neglected. Examples are presented for spheroids when the applied electric field is perpendicular to the gravity. The electrophoretic m otions are determined for spheroids of arbitrary aspect ratios at arbi trary orientations. Depending on their orientations the gravitational drift can contribute up to 10% of the observed particle velocity in th e direction of the electric field. The gravitational contribution is m aximum when the angle between the axisymmetric axis of spheroids and t he gravity is pi/4. However, for Brownian spheroids with a uniform ori entation distribution the sedimentation effects are averaged out, thus there is no net gravitational drift in the direction of the applied e lectric field. (C) 1997 Academic Press.