KINETIC-EQUATIONS FOR TRANSFER-CONTROLLED ADSORPTION-KINETICS

Kinetic equations are presented for the adsorption of a surfactant fro m a liquid bulk phase to a liquid/liquid or air/liquid interface, for a situation where diffusion equilibrium between bulk and subsurface is established, and consequently the transfer of surfactant from the sub surface to the surface is the rate-determining step in the adsorption process. These equations are obtained in away very similar to that by which the Butler-Volmer equations are obtained in electrode kinetics, where also the reaction rate is the rate-determining step. Essential f or both is that the standard free energy of the activated complex is s plit into a chemical part and a part which depends on the external for ce field (surface pressure for adsorption, electrical potential for tr ansfer controlled electrochemical reactions), This part of the standar d free energy of the activated complex is a fraction of the force-held -dependent part of the adsorption standard free energy, This reasoning leads f.i. to the Langmuir kinetic equation for the adsorption proces s, This Langmuir kinetic equation is extended for regular solution beh avior and, for the case of an indifferent electrolyte, added to the su rfactant system. These equations are in agreement with previous experi mental observations, except for the regular system where experimental data are still lacking. (C) 1995 Academic Press, Inc.