Longitudinal structural relaxation of highly viscous liquid: tetraethylene glycol

The sound velocities of tetraethylene glycol over the frequency range from 100 MHz to 10 GHz and in the temperature range from 243 to 313 K were measured by Brillouin scattering and high-resolution Bragg reflection methods. Velocity dispersion, which is attributed to structural relaxation, was observed for the frequencies investigated here. The relaxation curves represented by the longitudinal reduced storage modulus were well explained by a double relaxation. The relaxation strength of the fast process decreased with decreasing temperature. The fast process disappeared around 260 K. The relaxation times of the fast process obeyed the Arrhenius law, while the temperature dependence of the relaxation times of the slow process showed non-Arrhenius behavior.