Structural Relaxation Rate and Aging in Amorphous Solids

Abstract

The structural relaxation in amorphous materials is discussed within the Tool-Narayanaswamy-Moynihan model (TNM), the Kovacs-Aklonis- Hutchinson-Ramos model (KAHR), and the entropy-based Adam-Gibbs- Scherer-Hodge model (AGSH). These three phenomenological models are most frequently used for the description of experimental structural relaxation data by a suitable set of parameters obtained by curve fitting. The parameter sets reported in the literature for 250 different amorphous material compositions are analyzed on the basis of the isothermal relaxation rate R depending on the nonexponentiality parameter fi and the nonlinearity contribution, defined for the TNM, KAHR, and AGSH models as a = -(dln z/dTf)i. The R10 calculated at 10 K below Tg represents a scale for the structural relaxation rate. It describes the structural relaxation kinetics in very different amorphous materials such as organic polymers, epoxy resins, sugars, hydrated starch, simple organic molecules, oxide glasses, chalcogenide glasses, halide glasses, metallic glasses, volcanic glasses, and tektite. This approach can be used for the kinetic comparison of structural relaxation behavior in different amorphous materials as well as in the assessment of the aging treatment and composition design for their future applications.