Study of the transition from Fickian to Case II sorption kinetics in the system poly(ethyl methacrylate)–liquid methyl alcohol

Unidimensional transport of liquid methyl alcohol in poly(ethyl methacrylate) films at 30, 22, 10 and −5°C are presented. Kinetics of penetration, under semi-infinite conditions, are supplemented by information on the penetrant concentration profile obtained by an interferometric technique applied to the swelling polymer in situ. At 30°C, the system exhibits Fickian behavior. As the temperature is lowered, increasing deviations from Fickian kinetics are observed, with the end result of Case II kinetics at −5°C. The experimentally observed change in transport behavior is also predicted from diffusion Deborah numbers, calculated on the basis of the free volume theory of Vrentas and Duda.