Electrophoresis of spheroidal particles having a random distribution of zeta potential

Charge nonuniformity on colloidal particles can be a dominant factor in det ermining the bulk stability of a dispersion. However, experimental measurem ents of such nonuniformity are lacking. One straightforward technique for m easuring the charge nonuniformity on particles is "electrophoretic rotation ", and the calculations in this paper enable the interpretation of electrop horetic rotation experiments for spheroids. For systems with infinitesimal double layers, it is shown that if the charge (or zeta potential) is random ly distributed over the individual particles in a dispersion, where each pa rticle is covered with N equal-area patches, then the spheroids will on ave rage rotate with an angular velocity proportional to sigma (zeta)/rootN, wh ere sigma (zeta) is the standard deviation of zeta potential on the patches . This is true for any random distribution of zeta potential, which emphasi zes that "random" implies "nonuniform". Whereas standard translational elec trophoretic mobility gives the average zeta potential ([zeta]) on particles , the rotational electrophoretic mobility gives the standard deviation of z eta potential (sigma (zeta)).