Impact of a temperature-dependent stretching exponent on glass relaxation

The nonexponential relaxation behavior of glass is governed by the dimensionless stretching exponent, β, which is typically assumed to be a constant but is more accurately described as a function of temperature. Herein, relaxation calculations of glassy materials are undertaken via an iterative differential equation-based algorithm to determine when the use of a temperature-dependent (or dynamic) stretching exponent is required to capture the industrially relevant evolution of fictive temperature components, which is necessary for process engineering. Results reveal a range of liquid fragility index (m) in which a static β description is roughly equivalent to the behavior observed with a dynamic β. However, fast primary (α) relaxation modes demonstrate unique behavior in systems exhibiting excessively strong or fragile liquid behavior when a temperature-dependent stretching exponent is considered. In this special issue dedicated to the International Year of Glass, we also provide broader perspectives regarding the importance and impact of a temperature-dependent β.