Identifying the Thermal Barriers of Glass Aging via Isoconversional Analysis

We employ isoconversional analysis to gain insights on aging time-dependent thermal barriers in glasses evolving toward equilibrium. This is applied to glasses of different natures, including small molecules and polymers. Our analysis indicates that as relaxation proceeds, equilibration kinetics involves increasingly larger activation barriers. The latter equals that of the α-relaxation at the final stage of aging. In contrast, the relatively low thermal barriers at the initial and intermediate stages of aging indicate that mechanisms different from the α-relaxation mediate aging in these conditions. We discuss the nature of these mechanisms in the light of the complexity of glass aging.