The sorption isotherms and transport coefficients for CO
2 in poly (vinyl acetate) (
Tg=31°C) film were measured by gravimetric and volumetric sorption methods, and permeation method. Solubility data observed at 45°C from the three methods gave concordant linear sorption isotherms and seemed to obey Henry's law only. Nonlinear isotherms observed at 25 and 15°C were successfully interpreted in terms of the dual-sorption transport model. The two diffusion coefficients,
DeI and
DeE, were obtained using the short-time method and the long-time method for the model of Fickian diffusion, together with the equilibrium solubility (
Ce) from the volumetric sorption measurement. The experimental sorption rate curves are initially agreed with the calculated curves using
DeI and the Fickian sorption rate equation, but when the sorption equilibrium is approaching, the curves are in accord with the calculated curves using
DeE. The experimental permeation rate curves initially deviate from the calculated curves using
Da and the Fickian permeation rate equation. These observations suggest that some relaxation process is superimposed on the diffusion process. The non-Fickian transport data of both the sorption and permeation were successfully correlated with a model that superimposes diffusion of the Fickian model upon the time-dependent diffusion model. The relaxation phenomena were also observed in PVAc/Ar system at 25°C to 45°C from permeation experiment.
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