AbstractThe solubilities of nitrogen, oxygen, argon, methane, and carbon dioxide in thin films of crystalline oriented poly(ethylene terephthalate) in the glassy state were studied by the static sorption method. High pressure sorption isotherms were obtained for carbon dioxide. Results indicate that, above a certain film thickness, solubilities of all gasses in the crystalline oriented polymer (Mylar) are virtually identical to those in the unoriented crystalline polymer. Solubility constants are correlated with gas force constants, ϵ□k, and the heats of sorption obtained for methane and carbon dioxide are nearly the same for both the oriented and unoriented films. The sorption isotherms obtained for carbon dioxide are nonlinear but may be well described by considering dual sorption modes. One of these, ordinary dissolution, is described by Henry's law, while the other, “hole filling,” is characterized by a Langmuir expression. Solubilities of carbon dioxide in the thinnest oriented films (1 mil) are markedly higher than in the unoriented film. Analysis of the sorption data indicates that both the hole saturation constant, and the hole affinity constant, are larger in the 1‐mil oriented film. The amorphous phase appears to be different also, exhibiting a larger capacity for dissolved gas. Different thermal history, relating to the manufacture of the film, is advanced as a possible explanation for increased so
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