Brillouin light scattering from transverse and longitudinal acoustic waves in glycerol

Abstract

Brillouin light scattering experiments from transverse acoustic (TA) and longitudinal acoustic (LA) waves in glycerol have been performed in the temperature range between 170 and $229\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, including both the supercooled and the glassy state of the system. The intensity of light scattered by TA modes is about four orders of magnitude lower than that scattered by LA modes, giving an exceptionally low ratio of the photoelastic constants ${P}_{44}∕{P}_{12}\ensuremath{\approx}0.01$. The analysis of the frequency positions of Brillouin doublets gives a linear temperature behavior of both transverse and longitudinal elastic moduli for temperatures higher than that of the glass transition ${T}_{g}=187\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, a bend at ${T}_{g}$ and a less pronounced variation below ${T}_{g}$. A linear relation is also found between shear and longitudinal moduli of glycerol with angular coefficient close to 3, suggesting a Cauchy-like relation to hold around ${T}_{g}$.