Experimental methods for tracking physical aging of thin glassy polymer films by gas permeation

This paper describes methodologies that have been developed for studying the physical aging of free-standing thin polymer films and its effect on gas permeability. Both solution casting and spin coating methods were used to obtain thin polysulfone films having thicknesses in the range of 400–1000 nm. Ellipsometry has been employed to determine the thicknesses of these thin films. A thin wire frame was used to hold the thin free-standing films while heating above Tg to relax molecular orientation and to erase the ambiguous thermal history resulting from solution casting. The film underwent a significant thickness change during heating above Tg as the polymer chains relaxed. By using the method of this study, the reproducibility of gas permeability change during physical aging was demonstrated as well as the thermoreversibility of physical aging. Comparison of the results obtained by using different methods to support the thin film during heating illustrated the preference for the free-standing scheme developed in this study.