Transient diffusion kinetics in media exhibiting axial variation of diffusion properties. Part 2.—Permeation kinetics

Abstract

Transient-state permeation of a penetrant across a slab or membrane exhibiting a gradation in diffusion properties along the diffusion axis is investigated by the methods used in the preceding analogous study of sorption kinetics. Early- and late-time transient permeation kinetics at both upstream and downstream surfaces of the membrane have been examined, in turn, in a systematic manner. It has been shown that proper analysis of data of this kind (hitherto largely unexploited in experimental practice) is potentially capable of furnishing important information about the mode and extent of the spatial variation of diffusion properties, which partly parallels and partly augments the information deducible from sorption kinetics or permeation time lags. The results of this and the preceding paper provide much of the theoretical background necessary for the practical use of transient-state analysis in a manner analogous to the method of time-lag analysis previously developed.