Brillouin Scattering: Viscoelastic Measurements in Liquids

The theory of Rayleigh scattering from density fluctuations is applied to data taken in glycerol and n-butanol over wide temperature ranges. It is shown that Brillouin scattering is useful in evaluating the viscoelastic parameters of a liquid when all corrections are properly applied. The position, half-width, and intensity of the Brillouin lines as well as the total intensity are the main features of the spectrum used. The definition of the Landau-Placzek ratio was generalized to be applicable to relaxing liquids and glasses and its behavior was studied over a 200°C temperature range in glycerol. The hypersonic data indicate that at high temperatures (∼70°C) in glycerol the distribution of relaxation times is narrower than that ultrasonically found at lower temperatures (∼−10°C). This result is in agreement with the concept that the origin of the distribution is related to cooperative behavior which is less pronounced at higher temperatures.