Flame-like Glass Transitions

摘要

Glasses develop complex spatiotemporal structures within the material as they heat and cool. As the glasses' domains change from liquid to glass or vice-versa, the transition dramatically alters the mobility of the molecules and the transfer of thermal energy. The source of the complexity is caused by the interplay between the glasses' phase and its molecular mobility in a process akin to a flame, a similarity that Peter Wolynes shows is more than wordplay. Previously, Wolynes had studied glass "aging" (passive cooling) and "rejuvenation" (warming driven by external heat) using random first-order transition theory. Other researchers had used mode-coupling theory to treat dynamics in equilibrium liquids. Now Wolynes combines the two methods to create a more complete model of glass dynamics. He finds that introducing mode coupling to the model slows down aging; however, while mode coupling does not qualitatively change the results, it does change how the glass model behaves upon rejuvenation. Once glass-liquid transitions nucleate, the author says, they propagate in a manner mathematically similar to the exothermic reactions in a flame burning through a fuel source. Although experimental data are sparse for flame-like structures in glasses, Wolynes expects more evidence will come to light as researchers employ advanced imaging techniques.