Ultrasound absorption near the critical point of SO2+CCl4liquid mixtures

Abstract

Ultrasonic absorption and velocity have been measured in several liquid mixtures of S${\mathrm{O}}_{2}$ + C${\mathrm{Cl}}_{4}$. Special emphasis was given to the homogeneous-solution region near the critical mixing point. Near the critical point it was found that high absorption and strong frequency dependence were characteristic of the ultrasound, unlike its behavior outside of the critical region. The frequency dependence of the absorption measurements near the critical point and along the critical isochore can be satisfactorily fit with the Kawasaki multiple-relaxation calculation by the adjustment of three fit parameters. Near the critical point the background absorption was found to be independent of frequency over the range of investigation (2 to 66 MHz). Including an adjustable single-relaxation term in the absorption fit indicated that the best fit was obtained as the amplitude of the single-relaxation term went to zero. The characteristic-frequency and amplitude parameters, taken from fits of the Kawasaki calculation to the data nearest the critical point, were scaled in reduced temperature. The characteristic-frequency data are consistent with a scaling exponent of 1.89\ifmmode\pm\else\textpm\fi{}1 if a critical temperature is chosen for the scaling that is slightly lower than the observed phase separation temperature, i.e., if the presence of a pseudospindodal curve is assumed. This is the exponent value that is predicted by the mode-mode coupling and Ising lattice-gas theories. Neither dispersion nor temperature-dependent anomalies were observed for the ultrasonic velocity.