Theory predicts aging process in DVDs

Polymer glasses are versatile plastics widely used in applications ranging from aircraft windshields to DVDs. Scientists at the University of Illinois have developed a theory that predicts how these materials age. The theory also explains why motions at the molecular level can have macroscopic consequences.

"Glasses, including polymer glasses, are essentially frozen liquids," said Kenneth S. Schweizer, the G. Ronald and Margaret H. Morris Professor of Materials Science at the University of Illinois. "They appear solid, but because they are frozen liquids, the molecules continually undergo small motions that lead to a time dependence of properties".

Three years ago, Schweizer and graduate student Erica Saltzman developed a theory that described the transition upon cooling of a polymeric material from a liquid to an amorphous solid or glass. The theory explained how the viscosity of a polymer glass changes dramatically over a narrow temperature range. The scientists reported that work in the July 22, 2004, issue of the Journal of Chemical Physics.

Now, in the April 20 issue of Physical Review Letters, Schweizer and postdoctoral research associate Kang Chen present a theory to describe the aging process in polymer glasses. The new theory predicts not only how polymer molecules move, but also the material properties, at a wide variety of times and temperatures.........