A diffusion-based approach to mixed adsorption kinetics

A new theoretical approach has been developed which allows mixed kinetics of non-ionic surfactants to be studied in the unitary framework of an extended diffusion-controlled problem. This treatment not only allows one to consider a large class of surface models, but also provides a better understanding of the relation existing between the presence of a potential barrier and the diffusion-controlled adsorption. In particular it is shown that the assumption of the presence of adsorption barriers does not depend on the local equilibrium hypothesis. In fact the theoretical treatment takes into account the possibility that mixed kinetics also occur in the absence of potential barriers. By this treatment a general equation is obtained which allows the adsorption as a function of time to be evaluated by numerical or analyical procedures for a given particular surface model.