Segmental (α-) and Slow (SAP) Relaxation Processes: Connections with Thermodynamic Properties and Physical Aging*

In this talk we will discuss recent work in modeling and comparing two molecular level processes that are important in the relaxation of glass-forming materials: the "segmental" α- relaxation process (well-known for its association with glassy behavior) and another, slower, Arrhenius-like process, the "SAP". Both can be tracked using dielectric spectroscopy. Recent evidence indicates that the SAP drives certain stages of the physical aging process and other equilibration processes, e.g. adsorption. The SAP also appears to be connected with rheological properties, and its kinetics exhibit a compensation effect between activation energy and activation entropy. These observations motivate our interest in understanding how the SAP mechanism works and how its dynamics are connected to a material's corresponding thermodynamic properties. Using equation of state analysis and kinetic models we have recently shown strong correlations between the α- process and thermodynamic properties, e.g. free volume, thermal expansivity and close-packing. In this talk we will present results revealing thermodynamic connections to the SAP.