Depolarized Rayleigh–Brillouin scattering from shear waves in supercooled liquid dibutyl phthalate

Abstract

Experimental depolarized Rayleigh and Brillouin spectra of liquid and supercooled liquid dibutyl phthalate (M.P. = −35 °C) are reported over the temperature range from −116 to 70 °C. The depolarized spectra exhibit a propagating transverse wave at temperatures as high as −21.5 °C, while the Brillouin spectra exhibit a kink in the longitudinal frequency shift corresponding to the glass transition temperature at approximately −95 °C, and a maximum in the linewidth at approximately 7 °C. A single equation from the recent theory of Wang has been used to fit the experimental depolarized spectra over the entire temperature range and values of the translation rotation coupling constant δ, the orientation relaxation constant Γ, the shear wave relaxation constant η, and the elastic shear wave oscillation frequency Ω have been determined. The depolarized Rayleigh relaxation time τ is shown to obey Arrhenius type behavior with an activation energy of 6.5 kcal mol−1. η, δ, and Ω are shown to constitute an internally consistent set of parameters describing the behavior of the propagating shear wave in a viscoelastic fluid.