Can one learn about glasses from advances in granular materials?

Abstract

It is argued that the crudest view of the cooling of a glass is found if one divides its degrees of freedom into slow, configurational degrees of freedom, and fast such as vibrations and electronic excitations if appropriate. The latter can be regarded as in thermal equilibrium defining the temperature, whereas the former have a distribution which is not in equilibrium and could relax, for example, to an earlier temperature in the cooling. The crudest view of the configurational modes is to view the atoms as if they are grains in a granular material and the glass as the mode mixture where the slow try to catch up with the fast. The argument leads to the definition of three temperatures: T G the glass transition temperature for infinitely slow cooling, T g for cooling rate τ ̇ and T 0 for the temperature at which cooling starts, and their relation is T g =T 0− T 0−T G 1+μ τ ̇ (T 0−T G ) , where μ is the constant of the material.