Fast relaxation in disordered systems: from a double well to a cage

Abstract

An overview of light scattering data measured in broad frequency (0.5 GHz<ν<10 THz) and temperature (10 K<T<1.2 T _g) ranges are presented for a number of glass-forming systems. The data are compared with two basic approaches: the model of asymmetric double-well potentials (ADWPs) and the mode-coupling theory. It is shown that the ADWP model provides a reasonable description of the data at low temperatures, much below the glass transition temperature T _g. It fails, however, at higher temperatures. Two possible explanations are discussed: firstly, the appearance of a new relaxation process with a near-constant-loss spectral shape and, secondly, an increase in coupling between different relaxation modes with temperature increase.

Acknowledgement

We acknowledge financial support by the National Science Foundation Polymer program under grant DMR-0080035.