Nonexponential relaxations in strong and fragile glass formers

TLDR

Vitrification commonly exhibits non‑exponential, non‑thermally activated responses, previously examined with viscoelastic, dielectric, calorimetric, optical, and other techniques. The study surveys linear‑response data from about 70 covalent glass formers, ionic melts, supercooled liquids, amorphous polymers, and glassy crystals. Non‑Debye behavior broadly correlates with non‑Arrhenius relaxations, with distinct material groups showing narrow correlations; the stronger the molecular or atomic interconnectivity, the more pronounced the departure from exponential stress relaxation at a given deviation from Arrhenius behavior.

Abstract

Deviations from thermally activated and from exponential response are typical features of the vitrification phenomenon and previously have been studied using viscoelastic, dielectric, calorimetric, optical, and other techniques. Linear response data from literature on about 70 covalent glass formers, ionic melts, supercooled liquids, amorphous polymers, and glassy crystals are surveyed. Except for orientational glasses and monohydric aliphatic alcohols a distinct but broad correlation of non-Debye behavior with non-Arrhenius relaxations is found. Within the broad trend several groups of materials, distinguished by their respective molecular complexity, can be identified and are shown to exhibit narrow correlations. At a given degree of deviation from Arrhenius behavior externally imposed stresses are relaxed with a departure from exponential behavior which is stronger the more the molecular or atomic subunits of the glassforming material are interconnected with each other.