When Do Sorption-Induced Relaxations in Glassy Polymers Set In?

This study presents the kinetic sorption behavior of six different gases (CO2, C3H8, C3H6, Xe, Kr, and Ar) in films of the glassy polyimide Matrimid using a magnetic suspension balance. The dynamic mass uptake was analyzed using a model discriminating and quantifying separate contributions of Fickian diffusion and relaxations. The model provides a quantitative insight into the pressure/concentration-dependent onsets and relative magnitudes of sorption-induced relaxations. We demonstrate that any gaseven noble gasesshow non-Fickian diffusion and may induce irreversible sorption relaxations upon reaching a critical amount of volume dilation. Above this critical amount of volume dilation, kinetic sorption behavior becomes non-Fickian. For all gases studied, this critical volume dilation is unique.