Brillouin scattering study of glass-forming propylene glycol

The elastic properties of propylene glycol (PG) were studied by Brillouin scattering between 100 K and 442 K using a high-resolution Fabry–Perot interferometer. The acoustic phonon velocity, phonon damping, and relaxation time were measured as functions of temperature. At high temperatures, the temperature dependence of the relaxation time obeyed the Arrhenius law, τ = τ0 exp (ΔE/kBT). We obtained ΔE = 0.27 eV and τ0 = 6.40 × 10−16 s. The dynamical properties between racemic PG and chiral isomer (S)-PG were compared and small differences, which were within the experimental uncertainty, were observed. These differences were attributed to the molecular interaction, which played an important role in relaxation. Neither material displayed an elastic anomaly at its melting point.