Self-diffusion through a liquid–vapor interface

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Abstract
A diffusion equation containing information about the structure of the liquid–vapor interface is constructed to describe self‐diffusion in a one component, two phase fluid. Analysis of the diffusion equation in the limit of vanishing interface thickness leads to interfacial matching conditions, one of which was previously assumed ad hoc. From a study of the asymptotic long time behavior of the equation, it is found that an ordinary self‐diffusion experiment can not be expected to provide information about the interface structure. A numerical study of the diffusion equation shows that the reduced time to diffuse through the interface is independent of the ratio of the vapor and liquid densities, which is the one free parameter in the diffusion equation. An experimental test of our prediction that it takes the same time to diffuse from the liquid to the vapor as vice versa is suggested.