Sorption Kinetics at Liquid-Liquid Interfaces with the Surface-Active Component Soluble in Both Phases

A theoretical study on the sorption kinetics at liquid-liquid interfaces of surfactant component soluble in both phases is presented here. The diffusion process in bulk phases is considered as well as the presence of an interfacial potential barrier to adsorption and desorption. In the present paper, a generalization of a recent study on the sorption kinetics at a fluid interface with a surface-active component soluble in only one phase [F. Ravera et al., J. Colloid Interface Sci.156, 109 (1993)] is given. The new approach consists of writing a renormalized diffusion equation, equivalent to the kinetic sorption equation, by introducing renormalized diffusion coefficients and boundary conditions suitable for the bulk concentrations. The treatment leads to a relationship between the surface excess concentration and the time, in terms of the interfacial potential barriers of adsorption and desorption.