Chapter 8 - Glass Transition and Physical Aging of Confined Polymers Investigated by Calorimetric Techniques

Abstract

Abstract This chapter reviews the recent activity on the study of glass dynamics in polymers subjected to geometrical confinement. Special attention is dedicated to glassy dynamics in thin polymer films. Nonetheless, other kind of confinement, such as polymer nanocomposites and nanospheres, are dealt with. In this context, it is shown how calorimetric techniques contributed to significant advancement in the topic. After introducing the established phenomenology and the recent findings on the glass transition, the factors that affect the nonequilibrium glass dynamics in confinement, that is, the glass transition temperature (Tg) and the physical aging, are discussed. In light of numerous experimental evidences, it is remarked how arguments exclusively based on the alteration of the rate of spontaneous fluctuations are insufficient to catch the behavior of nonequilibrium dynamics. The role of free interfaces, not enslaved by underlying adsorbed layers, is emphasized for the comprehension of the ability of confined polymer glasses to maintain equilibrium when cooled—testified by a reduction Tg—and accelerated equilibrium recovery in the glassy state. Given the fact that these results imply that confined systems with large free interface are able to access low energy states in short-time scales, the final part of the chapter is dedicated to recent advancements toward the clarification of questions of paramount importance in glass science. In particular, the experimental evidence for the existence of the ideal glass transition is discussed.