The light scattering relaxation function of glass-forming molecules: a general probabilistic approach

Depolarized photon correlation spectra of two fragile glass-forming epoxy molecules of different molecular weights are reported. The correlation function of the simplest molecule shows stretched-exponential behaviour, while deviations from this form have been observed for the larger molecule, suggesting the presence of a second, long-time power law. The relaxation dynamics is suitably described for both systems in terms of a probabilistic approach based on the tool of the limit theorems of probability theory. On the basis of this theory, the presence of the long-time power law can be related to the existence of intermolecular interactions, while the stretched-exponential behaviour of simple molecules can be obtained in the case of negligible long-range interactions.