New evidence derived from the discrimination of Henry and Langmuir modes parameters in glassy polymeric film revealed by the Freeze-Purged-Desorption method

The Freeze-Purged-Desorption (FPD) method was developed for the experimental measurement of gas permeability coefficients as a new technique using a desorption curve of gas immobilized in polymeric films. The FPD method was effectively used to evaluate four gas permeation parameters (C<INF>D</INF>, C<INF>H</INF>, D<INF>D</INF>, and D<INF>H</INF>) of glassy polymeric films (polycarbonate and polystyrene) by using CO<INF>2.</INF> The modes of the CO<INF>2</INF> gas desorption response curve (D-curve) obtained were sensitively characterized by the proportion of sorption in the Henry and Langmuir modes in the polymeric films accompanied by their own gas diffusivity. A graphical analysis of the D-curve of CO<INF>2</INF> reasonably proposed a linear relation between the desorption rate and the sorption amount of CO<INF>2,</INF> which was strongly influenced by the kind of sorption gas, film, temperature, and other factors. The desorption rate of sorbed CO<INF>2</INF> gas for the PC and PS films gave a characteristic straight line with an inflection point indicating a shift in the gas-diffusion mechanism from the complex type of the Henry and the Langmuir modes to the Langmuir mode. The characteristic D-curves obtained were graphically analyzed, and they clearly discriminated the Henry mode part and the Langmuir mode part. This discrimination process quantitatively and individually evaluated C<INF>D</INF>, C<INF>H</INF>, D<INF>D</INF>, and D<INF>H</INF>. By using the four parameters evaluated, a mathematical model to describe the D-curve was proposed, and it consistently explained the experimental D-curves. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 934–941, 2004