THE ELECTROSTATIC INTERACTION FORCE BETWEEN A CHARGE-REGULATED PARTICLE AND A RIGID SURFACE

The electrostatic interaction force between a charge-regulated particl e covered by an ion-penetrable charged membrane and a rigid charged su rface immersed in a mixed (a:b) + (c:b) electrolyte solution is analyz ed. The membrane contains both acidic and basic functional groups, and a general form for each is assumed which allows multiple proton trans fer among functional groups. The rigid surface is negatively charged, and the net charges carried by the particle is also negative. We show that if the separation distance between the particle and the surface i s greater than a critical value, the multivalent cations present in th e liquid phase have the effect of reducing the repulsion force between the particle and the surface. The reverse is true if the separation d istance is smaller than the critical value. For a constant total numbe r of functional groups in the membrane phase, if the membrane is suffi ciently thin, the variation of repulsion force as a function of separa tion distance exhibits a maximum. (C) 1996 Academic Press, Inc.