Drifts in penetrant partial molar volumes in glassy polymers due to physical aging

Sorption and dilation measurements on three different glassy polymer materials are reported to characterize the presence of unrelaxed volume and how it is affected by physical aging. Substantial changes in the sorption and dilation due to physical aging were observed for 25.4 μm thick films of Matrimid® and Lexan®, but not significantly for Ultem®. Such effects are more pronounced when the partial molar volume is considered, since the more aged samples showed less sorptive capacity yet more swelling as compared to their unaged counterparts. Experimentally observed trends in the partial molar volume due to physical aging are qualitatively consistent with trends expected based on the idealized dual mode sorption and dilation models. On the other hand, quantitative discrepancies between expected and observed dilation behaviors reveal some limitations associated with the conventional simple interpretation of the model parameters.