DYNAMIC ANOMALIES AT THE GLASS-TRANSITION OF ORGANIC VAN-DER-WAALS LIQUIDS

The paper discusses the question of whether there is a characteristic temperature T(c) above the calorimetric glass transition temperature T (g). Mode-coupling theory (MCT) predicts a crossover from liquid- to s olid-like dynamics at T(c). Neutron scattering and gradient NMR experi ments have been carried out to test MCT using the molecular van der Wa als liquid ortho-terphenyl as a model system. A significant anomaly of the Debye-Waller factor and a ''decoupling'' of self-diffusion from v iscosity support the MCT predictions. A critical discussion of the rel evance of such tests and of the limitations of neutron scattering is p resented.