Article
Article
Glass transition
Article By:
Grest, Gary S. Exxon Research and Engineering Company, Annandale, New Jersey.
Last reviewed:January 2020
DOI:https://doi.org/10.1036/1097-8542.290850
The transition which occurs when a liquid is cooled to an amorphous or glassy solid. This can occur only if the cooling rate is fast enough to prevent crystallization which would otherwise occur if time had been sufficient for the sample to reach true equilibrium at each temperature. Since the crystal is invariably the thermodynamically stable low-temperature phase, the glass transition corresponds to a transition from a high-temperature liquid into a nonequilibrium metastable low-temperature solid. Experimentally, this transition occurs at a temperature Tg where the shear viscosity becomes immeasurably large, greater than 1 × 1015 poises (1 × 1014 pascal-seconds). Changes in the heat capacity and coefficient of thermal expansion are also generally observed near Tg. See also: Amorphous solid; Crystal structure; Viscosity
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