ELECTROPHORETIC MOBILITY OF A SPHERE IN A SPHERICAL CAVITY

The electrophoretic behavior of a spherical particle in a spherical ca vity is analyzed theoretically, taking the effect of double layer pola rization into account. We show that for the case where the particle is positively charged and the cavity uncharged if the surface potential of particle is high, the variation of the mobility of the particle as a function of kappa a has a minimum, kappa and a being respectively th e reciprocal Debye length and particle radius. This minimum does not a ppear if the effect of double layer polarization is neglected. The var iation of the mobility as a function of kappa a has a minimum for a me dium value of lambda (= particle radius/cavity radius); it becomes neg ligible if lambda is either small or large. In the case where the part icle is uncharged and the cavity positively charged, if the surface po tential is high, the variation of mobility as a function of Ka has a m aximum; if it is low, the mobility increases monotonically with Ka. He re, the mobility is mainly determined by the drag force, rather than b y the electric force, acting on the particle as in the case where the particle is positively charged and the cavity uncharged. If both the p article and the cavity are charged, the electrophoretic behavior of th e particle can be deduced from the results of the above two cases. (C) 1998 Academic Press.