Chapter 8 Glass Transition and Physical Aging of Confined Polymers Investigated by Calorimetric Techniques Daniele Cangialosi Centro de Fı´sica de Materiales (CSIC-UPV/EHU), San Sebastia´n, Spain Donostia International Physics Center (DIPC), San Sebastia´n, Spain 8.1 INTRODUCTION The existence of systems thermodynamically in nonequilibrium is ubiquitous in nature and is the essence of life in the universe and its time evolution [1]. Understanding the kinetics of entropy production of systems spontaneously evolving toward the most stable thermodynamic state, that is, the one with the lowest free energy, constitutes a challenge in the study of natural phenom- ena as well as those processes object of manipulation by human beings. In this sense, spontaneous transformations, that is, those based on the minimization of the free energy, can either be inhibited or catalyzed. Among the numerous examples of nonequilibrium systems, glasses are an important class, given their diffusion in nature and widespread use since the beginning of civiliza- tion. The essential requirement to form a glass is the ability of a disordered liquid to avoid, when cooled down, the thermodynamically most favorable state, that is, the ordered crystal [2–4]. Liquids exhibiting significant kinetic hindrance for the reorganization toward crystalline ordering are classified as good glass formers. Otherwise, liquids with strong tendency to crystallize can also form glasses if high cooling rates are employed and/or crystallization nuclei eliminated. Among liquids that can be easily supercooled below their melting temperature, polymers—owing to chain connectivity and, in some case, confor- mational disorder—represent an important class [5], also in view of their tech- nological relevance. However, a wide range of other materials can be obtained as glasses, for instance silicate, metallic, low molecular weight organic, chalco- genide, and colloidal glasses. During the last decades considerable effort has Handbook of Thermal Analysis and Calorimetry, Vol. 6. https://doi.org/10.1016/B978-0-444-64062-8.00013-9 © 2018 Elsevier B.V. All rights reserved. 301