NEUTRON AND LIGHT-SCATTERING STUDY OF RELAXATION DYNAMICS IN A GLASS-FORMING FRAGILE MOLECULAR LIQUID

We present experimental results on the structural relaxation dynamics of a fragile molecular glass, propylene carbonate, from quasielastic neutron and inelastic light scattering investigations of the supercooled liquid. The data show the power law and the scaled dynamics predicted in recent mode-coupling theories for the glass transition. As expected, the critical behaviour occurs at a temperature much higher than the calorimetric glass transition temperature. The relaxation is found to be considerably stretched despite the high probe frequencies (GHz) and there is no indication of any crossover to exponential decay. This is in contrast to the single relaxation time behaviour expected at short relaxation times/high frequencies in phase-space models and also contrary to the reported general behaviour of simple glass-formers. Comparing with data of ionic glass-formers of similar fragility we conclude that there is no simple relation between nonexponentiality of the relaxation decay and degree of fragility as has been suggested.