Brillouin scattering from liquid n-alkanes

Abstract

The hypersonic phonon velocity and absorption of the n-alkanes C₁₂H₂₆ to C₃₆H₇₄ have been obtained from Brillouin scattering measurements over a 20°C to 140°C temperature range. A master equation relating hypersonic phonon velocity to relative free volume, V_s ∝v_f ^-1/3, is found for the above range of molecular weights and temperatures. The variation of the phonon velocity and absorption over the frequency range 250 MHz to 5 GHz suggests that there may be a common relaxation mechanism in this n-alkane series with a relaxation time of order 10^-11 s. Estimates of the high frequency volume viscosity and its temperature dependence have been made.