Dynamics of Glass Relaxation at Room Temperature

Abstract

The problem of glass relaxation under ambient conditions has intrigued scientists and the general public for centuries, most notably in the legend of flowing cathedral glass windows. Here we report quantitative measurement of glass relaxation at room temperature. We find that Corning® Gorilla® Glass shows measurable and reproducible relaxation at room temperature. Remarkably, this relaxation follows a stretched exponential decay rather than simple exponential relaxation, and the value of the stretching exponent (β=3/7) follows a theoretical prediction made by Phillips for homogeneous glasses.

Thermometer Effect: Origin of the Mixed Alkali Effect in Glass Relaxation

“…1b, all glasses also show a gradual compaction in volume upon relaxation, which cannot be explained by elastic deformations since the average applied stress remains zero. Remarkably, the shape of the volume relaxation observed herein is fairly similar to that observed experimentally [7]. Further, as shown in the insets of Figs.…”

“…In contrast to the enthalpy, we find that volume features a stretching exponent β = 3/7, which corresponds to the situation in which only long-range relaxation channels are active [12]. This result agrees with experimental observations [7,17,32]. Note that previous simulations yielded a different exponent (β = 1) [1], but these glasses used in this study were not preliminary cooled to 0 K. This suggests that the presence of residual thermal excitations affects the relaxation mechanism.…”

“…However, the dramatic increase of viscosity as temperature decreases effectively prevents viscous glass relaxation at ambient temperature [5,6]. Surprisingly, recent experiments and simulations [1,7] have shown that, for certain compositions, glass can still feature some room-temperature structural and stress relaxation. This phenomenon is known as the "thermometer effect" as, in the 19 st century, thermometers made of mixed alkali lime silicate glass used to experience gradual changes of dimension over time, rendering them inaccurate [8,9].…”

“…To reveal the atomistic origin of the MAE and stretched exponential relaxation of glass, we rely here on a recently developed accelerated simulation technique, which successfully reproduced the long-term roomtemperature relaxation observed in Corning Gorilla Glass [1,7]. In that method, the glass is subjected to small, cyclic perturbations of volumetric stress, ±σ 0 .…”

“…When only long-range channels are active, by assuming an equipartitioning of the short-and long-range contributions (φ = 1/2), the model predicts β = 3/7. It should be noted that this model only applies to perfectly homogeneous glasses, that is, featuring uniformly distributed excitations, which is rarely achieved experimentally without relying on advanced industrialscale melting techniques like the fusion draw process [7]. As shown in Fig.…”