Free volume theory of diffusion: Method of predicting activation energies of diffusion for gases in elastomers

• Published in: Journal of applied polymer science 1981-02, Vol.26 (2), p.629-641
• Main Authors: Kosiyanon, Rochana, McGregor, Ralph
• Format: Article
• Language: English
• ISSN: 0021-8995; 1097-4628
• DOI: 10.1002/app.1981.070260222

It is well established that diffusion and relaxation processes in polymers above Tg are closely related in that they are both governed by the polymer segmental motions, which are believed to be determined by the free volume present in the system. The diffusion coefficients of gases in elastomers can be accounted for by the WLF equation using the “universal values” of constants A and B. The parameter K = BD/Bη of Frisch and Rogers is used as a correction factor. An analysis has been made of the diffusion of five gases in nine elastomers, from data found in the literature. K and log Dg are shown to vary with the penetrant but not with the polymer. Therefore, once the values of K and log Dg of gases are determined, their diffusion coefficients in any elastomers of known Tg at a variety of temperatures can be estimated. From the Arrhenius and the WLF relationships, an equation is derived to predict the activation energy of diffusion directly from the temperature of diffusion, the glass transition temperature of the amorphous polymer, the predetermined value of K, and the universal constants A and B. In the systems studied, the predictions agree on the average to within 11–17% of the values calculated from the experimental data.