Transport through a slab membrane governed by a concentration-dependent diffusion coefficient: Part V. Transient-state fluxes

A study has been made of ‘adsorptive’ and ‘desorptive’ transient-permeation between initial and final steady-states. For transport governed by a constant diffusion coefficient a generalisation of the procedure proposed originally by Ziegel et al. [J. Polym. Sci. 7 (1969) 809] is given. Using results obtained in a previous study [J. Membr. Sci. 180 (2000) 133] flux-ratio curves pertaining to five functional dependencies of the differential diffusion coefficient upon concentration are presented. Standard numerical analysis techniques have been employed to derive defined integral diffusion coefficients from these curves. The integral coefficients so obtained corresponding with a flux ratio of 0.7 appear to be of particular interest. Using an extension of the Frisch procedure, it is shown that a designated area above a flux curve is equal to the relevant time-lag.