Experimental evidence and theoretical analysis of physical aging in thin and thick amorphous glassy polymer films

Through time-dependent gas transport properties, we have investigated the p hysical aging process of amorphous glassy polymer films made from a polynor bornene. By combining the concepts of free volume and the kinetic theory of glass stabilization, it was found that the time dependence of the gas perm eability could be rationalized through the thickness dependence of the glas s transition temperature. A mathematical relationship was developed that di rectly relates polymer physical aging (tracked by the gas permeability deca y) and sample thickness. It was confirmed by permeation measurements with n itrogen and helium that the aging process is accelerated for thin glassy po lymer films (about 8000 Angstrom). The theoretical results show that accele rated aging for thin films compared to thick films can be qualitatively pre dicted, based on the decrease in the glass transition temperature when the film thickness decreases. (C) 1999 John Wiley & Sons, Inc.