The temperature-dependent distribution of relaxation times in glycerol: Time-domain light scattering study of acoustic and Mountain-mode behavior in the 20 MHz–3 GHz frequency range

Abstract

A time-domain light scattering study of acoustic and Mountain modes in glycerol is reported. By using light-scattering angles between 0.89° and 88.9°, a wide range of acoustic frequencies is sampled. The data also yield information about time-dependent density responses to stress and to heat (the latter is the time-dependent thermal expansion). These responses are associated with the Mountain mode and provide additional information about structural relaxation dynamics. A theoretical framework is presented which can treat these experiments as well as ultrasonics and specific heat spectroscopy. The time or frequency dependences of the elastic modulus, heat capacity, and pressure response to temperature change are all accounted for and appear to be significant. The experimental results are fit best with a distribution of relaxation times which is somewhat less asymmetric than a Cole–Davidson distribution. The width of the distribution (on a logarithmic frequency scale) does not change significantly in the 200–300 K temperature range.