(640h) Interfacial Effects and the Anomalous Swelling Behavior of Supported Polymer Thin Films in Supercritical Carbon Dioxide

Well-documented studies on the dynamic properties of polymers at surfaces and interfaces have shown that constrained thin films behave quite differently from bulk coatings. Surfaces undoubtedly dominate the behavior of materials with a small characteristic length as a result of their high surface-to-volume ratio and the importance of surface effects on the thickness dependence of the glass transition temperature of thin films as well as the importance of mobility in the vicinity of surfaces and interfaces in understanding properties such as adhesion and friction have been extensively studied over the past decade, and although relevant as scientific issues per se, they could also have relevant technological implications in the future. Moreover, recent experimental results suggest that there is an interesting anomaly in the sorption behavior of thin polymeric films brought in contact with supercritical fluids; Indeed, a non-monotonous trend in swelling has been observed crossing the critical pressure of the fluid for temperatures close to the critical temperature. However, while there is consistency among different studies about the experimental evidence of such phenomena, the picture that emerges is not yet clear and not much has been done so far to develop theoretical models. In this work we review existing theories and present a new interpretation, focused on the interactions between the supercritical phase dissolved in the polymeric matrix and the polymer substrate, suggesting that the very effect that can be use to explain Gibbs Excess Adsorption on hard surfaces could also be responsible of such phenomena.