Light scattering and calorimetric study of the thermal diffusivity of glycerol, liquid and glass

Abstract

Light scattering experiments have been used to determine the thermal diffusivity of glycerol in a variety of situations, changing the temperature T and the wave-vector q. Depending on whether the internal relaxation time (depending on T) is very short or very long compared to the heat diffusion time (depending on q-2) we say that we are studying either a liquid or a glass. Spontaneous light scattering experiments are described first. They give essentially information concerning the dispersion of the Mountain relaxation time : the ratio of its values in the liquid and the glass. They also show that the intensity of the Rayleigh component is negligible in the glass. Forced Rayleigh scattering experiments are then related. They allow a determination of the dispersion of the Rayleigh relaxation time. Using a calorimetric technique, the dispersion of the thermal diffusivity is then found to be the inverse of that of the Rayleigh relaxation time. These results concerning relaxation times and amplitudes of the Rayleigh and Mountain components are then compared to theoretical models. It is shown that the generalized viscoelastic model gives a consistent description of acoustic, thermal and light scattering measurements in glycerol