Signatures of the glass transition in a van der Waals liquid seen by neutrons and NMR

Abstract

Mode coupling theory (MCT) of the glass transition predicts the existence of a dynamic anomaly of supercooled liquids at a characteristic temperature T c well above the caloric glass transition temperature T g. A series of neutron scattering and NMR experiments on van der Waals liquids - a typical example of which is orthoterphenyl (OTP) - have been performed to test three predictions and to point out signatures of the glass transition. This contribution is meant to review our results in a concise manner: there is strong evidence for a T c according to MCT from Debye-Waller factors, from line shape studies of the dynamic structure factor and from a comparison of self-diffusion and viscosity. NMR relaxation below T c shows that there is at least one secondary process which so far is not accounted for by MCT and that the supercooled liquid becomes truely nonergodic closely above T g on a time scale of a few seconds.