Some Controversies in the Understanding of Equilibria in Electrical Interfacial Layer

This review discusses several controversies connected to the measurements and interpretation of equilibria in the electrical interfacial layer at the solid/solution interfaces. The discussion concerns equilibria of amphoteric reactions and counterion association at the surface. The applicability of the intrinsic equilibrium constant concept for counterion association is compared to a model where associated counterions are not located fin a plane but distributed in the vicinity of central surface charged groups. Measurements indicating the adsorption of counterions in the region of the point of zero charge reveal insufficiencies of the common models based on the Gouy-Chapman theory. These results are explained in terms of the effect of the discreteness of surface charge. The differences in the double layer model and the triple layer model are discussed. Numerical simulation of interfacial layer equilibria shows that the isoelectric point can be close to the common intersection point despite the significant specific adsorption. This finding suggests that these values should be determined with high accuracy if they are used as ithe point of zero charge. It is demonstrated that mass titration method for p,z.c. determination is applicable only for pure samples. The contamination of samples by acid or base results in significant errors in p.z.c. and thus (in experimental surface charge densities. The adhesion method for determination of the isoelectric point of metallic surfaces is presented