Polymer permeability and time lag at high concentrations of sorbate

A recently proposed theory of polymer sorption derived from thermodynamic analysis, was used to develop general analytical expressions for permeability, time lag and steady-state profile under non-linear Types I and II sorption equilibrium observed in glassy polymer membranes and Type III equilibrium observed in rubbers. Useful subclasses of these general analytical expressions are explored in order to demonstrate their utility for characterisation.