Original entry: Ian Burgess, Fall 2009
The glass transition is a phase transition that occurs in certain materials 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 volume. For many materials, glass transitions are observed only when the liquids are supercooled, as more adiabatic cooling results instead in the transition to a crystalline solid.
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 lost below the glass transition. However, at temperatures above the glass transition, but below the melting point, polymers still have a finite stiffness.
1. Z. Fakhraai and J. A. Forrest, "Measuring the Surface Dynamics of Glassy Polymers" Science 319, 600 (2008).
2. Kingery, W,D., Bowen, H.K., and Uhlmann, D.R., Introduction to Ceramics, 2nd Edn. (John Wiley & Sons, New York, 2006).