Forces between dissimilar colloidal plates for various surface conditions. II. Equilibrium adsorption effects

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Abstract
A method previously developed by the authors is used to study the effects of adsorption of ions on the electric double layer interaction between dissimilar colloidal plates immersed in 1:1 electrolyte. For adsorption models which permit the total charge on a plate to change sign, the double layer force remains finite at all plate separations, including zero. For weak adsorption of the ions on the plates the force between two dissimilar plates tends to be repulsive at small separations, looking rather like a weakened constant surface charge density model. Conversely for strong ionic adsorption the force tends to be attractive at small separations, rather as in the constant surface potential model. In this paper we discuss three adsorption models: (1) fixed primary charge density on the plates with secondary adsorption of both counter-ions and co-ions; (2) fixed primary charge density on the plates with secondary adsorption of the counter-ions only, but including the effects of a Stern layer and self-atmosphere potentials; (3) zero primary charge on both plates with equilibrium adsorption of both anions and cations from solution, the net charge density on the plates arising from differential adsorption of the ion types.

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