Effect of immobilizing adsorption on mass transport through polymer films

The Freundlich isotherm used in place of the Langmuir isotherm to describe the adsorption mode in the dual sorption theory of glassy polymer-gas systems. Time-lag expressions have been derived and compared with the available corresponding results for the Langmuir case. In the case of large and moderate values of the upstream boundary activity a₀, the value of the time-lag function L^a)(l) calculated with the proposed model is close to that calculated by Paul for the Langmuir isotherm. In the case of small values of a₀, the L^a(l) values predicted by Paul and the proposed model are different and the difference increases when the value of a₀ decreases. The ability of the present model to represent systems exhibiting positive deviations from Henry's law is also described.