Diffusion across an Interface

Ideal diffusion in the sense of Fick's law in a heterogeneous system composed of two liquids is discussed by means of a three-region model where the two bulk liquid regions adjoin a third region which characterizes the liquid-liquid interface. When diffusional resistance terms are defined in the usual manner, three classes of interfacial diffusion may be conveniently described by our model. It is found that extraordinary resistance to diffusion at the interface gives rise to perturbations in the observed concentration profile of the bulk regions; these perturbations diminish with time and disappear in the limit of vanishing resistance.