DENSITY-FLUCTUATIONS AROUND THE GLASS-TRANSITION OF LOW-MOLECULAR-WEIGHT GLASS-FORMING LIQUIDS

The Rayleigh-Brillouin spectra of ortho-terphenyl (OTP) samples with and without 'clusters' were measured in the temperature range from T(g) to T(g) + 200 K. The values of the Landau-Placzek ratio for cluster-free OTP were low, in agreement with the theoretical predictions, while for OTP with clusters much higher values were obtained. The isotropic part of the Rayleigh intensity for OTP with clusters contained an additional angular-dependent component that could be reversibly reduced after annealing the samples at temperatures > T(m). Rotational relaxation times of OTP samples with and without clusters were measured by means of depolarized Rayleigh spectroscopy. In addition to the usual rotational relaxation time, an additional fast component was found. The relaxation time of the fast process was practically constant in the entire temperature range amounting to 3 ps and the intensity decreased to zero around T0. The temperature dependence of the rotational relaxation time cannot be described by the Wohlrausch-Landel-Ferry formula over the entire relaxation time range from 4 x 10(-11) to 10 s, but only down to 10(-10) s.