Relaxation in glassforming liquids and amorphous solids

TLDR

The authors review the dynamics of viscous liquids and glassy solids by posing key questions and summarizing current answers. They organize the review into four parts covering the high‑temperature ergodic regime, the near‑Tg nonergodic aging regime, the frozen regime with active secondary processes, and the crossover between low‑frequency vibrations and high‑frequency relaxations, including short‑time dielectric and high‑Q mechanical responses. Recent advances in short‑time dielectric response and high‑Q mechanical response at the vibrational–relaxational crossover are highlighted.

Abstract

The field of viscous liquid and glassy solid dynamics is reviewed by a process of posing the key questions that need to be answered, and then providing the best answers available to the authors and their advisors at this time. The subject is divided into four parts, three of them dealing with behavior in different domains of temperature with respect to the glass transition temperature, Tg, and a fourth dealing with “short time processes.” The first part tackles the high temperature regime T>Tg, in which the system is ergodic and the evolution of the viscous liquid toward the condition at Tg is in focus. The second part deals with the regime T∼Tg, where the system is nonergodic except for very long annealing times, hence has time-dependent properties (aging and annealing). The third part discusses behavior when the system is completely frozen with respect to the primary relaxation process but in which secondary processes, particularly those responsible for “superionic” conductivity, and dopart mobility in amorphous silicon, remain active. In the fourth part we focus on the behavior of the system at the crossover between the low frequency vibrational components of the molecular motion and its high frequency relaxational components, paying particular attention to very recent developments in the short time dielectric response and the high Q mechanical response.