Electrophoretic mobility of a particle covered with an ion-penetrable membrane

The electrophoretic behavior of a planar particle covered by an ion-penetra ble membrane, which simulates a biological entity, is investigated. We show that, in general, a point charge model will overestimate the electrophoret ic mobility of a particle and the deviation increases with the increase in the concentration of fixed charge and with the decrease in the thickness of membrane layer. As in the case of a point charge model, the present model also predicts a local maximum in the absolute mobility as the thickness of membrane layer varies. If the sizes of counterions of various valences are the same, then the lower the valence of counterions, the larger the mobilit y, and the larger the counterions, the greater the mobility. The latter is consistent with the experimental observations in the literature. For the le vel of the concentration of fixed charge examined, the effect of colons on the mobility is negligible.