Importance of Quench Conditions on the Subsequent Physical Aging Rate of Glassy Polymer Films

For over a decade, research from the gas permeation community has observed faster physical aging rates with decreasing thickness of free-standing films, termed “accelerated aging”. These deviations in the aging rate from bulk behavior occur at film thicknesses of several micrometers, the largest “confinement” length scale ever reported. Here we systematically address various possible causes of this phenomenon from differences in molecular structure, quench depth below T g, experimental technique, sample preparation, and stresses on the film. We demonstrate that the physical aging of the material is strongly dependent on conditions during the formation of the glassy state. Although supported films do not display any film thickness dependence to their aging rate at this large length scale, films quenched in a free-standing state exhibit a strong thickness dependence. We suggest differing quench conditions may impose unintended stresses trapping the glassy films into different states (potential energy minima), dictating the subsequent physical aging rate.