Free-volume theories for self-diffusion in polymer–solvent systems. I. Conceptual differences in theories

Conceptual differences in two recent versions of the free-volume theory for self-diffusion in polymer–solvent systems are identified and discussed. The validity of the assumptions of these two theories is tested using experimental data. In all cases, the experimental evidence favors the Vrentas–Duda free-volume theory over the Paul version of this theory.