On the non-exponential versus non-Arrhenius behaviour of the structural relaxation in glass-forming liquids

The various routes by which a liquid may form a glass have recently been related to the structural properties of the glass, at one extreme represented by network glasses of strong covalent bondings and at the other by typical non-network systems of weak van der Waals or Coulomb bonding types. The authors examine the success of such an approach by comparing data on structural relaxations in glass-forming liquids chosen to cover a wide range of behaviour from non-network ionic and molecular systems to a network forming oxide glass. They also include data of a glass-forming polymeric system. While there seems to be a strong correlation between increasing fragility (i.e. decreasing temperature and resistance in the medium-range order) and increasing departure from Arrhenius behaviour of the relaxation time, there is no simple relation between the degree of fragility and non-exponentiality as has been suggested.