Original entry: Ian Burgess, Fall 2009. Edited by Lauren Hartle, Fall 2011.
DefinitionThe glass transition describes the manner in which certain materials transition between the liquid and the glass phases. The transition to a glass is marked by a solidification of the material without the addition of any long range order to the molecular packing. Unlike crystallization, there is also no discontinuous change in any thermodynamic property, and hence the transition is not, strictly speaking, a phase transition. Figure 1, taken from , illustrates the discontinuous nature of a crystalline versus the smooth glassy transition. Glass Transition Temperature, <math>T_g</math>, which varies with the material and cooling rate. It should be noted that manipulating pressure, independent of temperature, can produce a glass transition.
Polymers: In polymers above the glass transition temperature, chains have sufficient mobility to slide past each other and reconfigure under an applied stress. This mobility is substantially reduced below the glass transition. However, at temperatures above the glass transition, but below the melting point, polymers still have a finite stiffness.
Common Materials: Silica, commonly used to make windows and other commercial glass products, experiences a glass transition.
Metallic Glasses: See Metallic glasses.
 Debenedetti and F. H. Stillinger. "Supercooled liquids and the glass transition". Nature, Vol 410, 8 March 2001.
 Z. Fakhraai and J. A. Forrest, "Measuring the Surface Dynamics of Glassy Polymers" Science 319, 600 (2008).
 Kingery, W,D., Bowen, H.K., and Uhlmann, D.R., Introduction to Ceramics, 2nd Edn. (John Wiley & Sons, New York, 2006).