The Thermodynamic Significance of Order Parameters During Glass Relaxation

The thermodynamic state of a glass is often described in terms of a number of order parameters, each of which evolves toward its equilibrium value during glass relaxation. The problem comes in identifying these order parameters and determining their physical significance. The authors argue that the order parameters in a glass can be defined in terms of a set of configurational temperatures, each corresponding to a particular mode of energy storage. The evolution of glass properties can then be calculated using a coupled set of rate equations describing the relaxation of the configurational temperatures toward their equilibrium values, viz., the reservoir temperature. The authors illustrate the concept of configurational temperatures by considering the free energy of mixing in alkali borate and silicate glasses.