Theory of relaxation in viscous liquids and glasses.

A fluid is described by a set of quasi-equilibrium structures, and a master equation gives the transitions among these structures. Any structural change is presumed to require a cooperative rearrangement involving many atoms, and this rearrangement entails a fluctuation to a high-energy transition state. The structure of the fluid varies from point to point, and the rate of this transformation depends crucially on the local structure. The resulting kinetic equation describes very well the main features of observed relation - namely, the broad distribution of relaxation times and the non-linearity (in delta-T) of relaxation following a temperature jump delta- T, where the apparent activation energy for relaxation depends on time. The kinetic equation is solved exactly, and the resulting solution is exhibited for a particular set of the parameters. The resulting relaxation function for energy relaxation goes as e(-t1/4), except at the very shortest times.