Depolarized light scattering study of glycerol

Abstract.

We have obtained depolarized (anisotropic) light scattering spectra of the glass forming material glycerol in a wide temperature (160 to 430 K) and frequency (0.4 GHz to 48 THz) range and compared them with light scattering and dielectric spectroscopic data from the literature. The excess wing, which is usually discussed concerning dielectric data, is strongly pronounced in light scattering of glycerol. The temperature evolution of the wing, together with that of the fast relaxation spectrum, leads to a susceptibility minimum that persists in the spectra down to Tg ≈185 K and flattens with decreasing the temperature below ~290 K. The α-peak in light scattering is significantly wider and weaker in amplitude than in the dielectric loss spectra, and thus cannot be interpolated by the asymptotic laws of the mode coupling theory (MCT). However, similar trends were reported in the literature for solutions of MCT models for rotational dynamics. Furthermore we can identify in both the light scattering and the dielectric data two distinct regimes of temperature evolution with a blurred crossover in the range of 300–320 K. The high-temperature regime is characterized by a nearly temperature independent shape of the α-peak and of the susceptibility minimum, and a nearly temperature independent strength of the fast dynamics. In contrast, at low temperatures the excess wing emerges and the relaxation strength of the fast dynamics changes strongly with the temperature.