Brillouin scattering study on glass-forming ethanol

Brillouin spectra of glass-forming ethanol have been investigated over a wide temperature range from the liquid to the glassy phase. From the temperature dependence of the sound velocity and the damping factor, it was found that the velocity dispersion was negligible in the high-temperature range above 300 K where the relaxation frequency of the α process passes through the Brillouin frequency window, which may suggest a weak coupling between the dominant Debye-type α process and the density fluctuation modes. Instead, the coupling between the β process and the acoustic wave seemed to be dominant in the liquid phase. A fast relaxation process had to be incorporated into the memory function of the phenomenological viscoelastic theory to reproduce the full spectral line shape over the whole temperature range. Considering the temperature dependence of derived relaxation parameters, the fast process seems to be of vibrational origin.