Extended thermodynamics and membrane transport (Q1118501)

We use extended irreversible thermodynamics (EIT) to describe transport phenomena in membranes. The basic assumptions of EIT are summarized and the membrane is regarded as a passive phase where diffusive and viscous flow of a binary solution may occur. It is shown that in contrast to linear irreversible thermodynamics (LIT), EIT is adequate to describe noninstantaneous transport processes across membranes. This is illustrated by showing that EIT predicts that the concentration profile inside the membrane obeys the telegraph equation instead of the usual diffusion equation. As a result we find that for dynamic osmosis the initial pressure gradient should grow as \(t^ 3\) instead of the linear dependence implied by LIT. This and other differences between LIT and EIT are pointed out and the sense in which the latter may be considered as a generalization of the former is also discussed.