Diffusion in polymers below the glass transition temperature: Comparison of two approaches based on free volume concepts

Theories based on free-volume concepts have been developed to characterize the self and mutual diffusion coefficients of low molecular weight penetran ts in rubbery and glassy polymer-solvent systems. These theories are applic able over a wide range of temperatures and concentrations. In this paper, t wo alternative free-volume based approaches used to evaluate the solvent se lf-diffusion in glassy polymer-solvent systems are compared in terms of the ir differences and applicability.