Pressure effects and ultrasonic attenuation in the binary liquid mixture 3-methylpentane and nitroethane near the critical point

Abstract

Experiments are reported in which a critical mixture of 3-methylpentane plus nitroethane has been subjected to varying pressures. By varying the static pressure we have determined the dependence of the critical temperature on pressure with considerable accuracy. By sudden depressurization we have cooled the sample adiabatically leading to phase separation via spinodal decomposition; from these experiments we have determined the adiabatic thermal pressure coefficient near the critical point. By combining our data with the experimental density data of Greer and Hocken, we are able to determine the asymptotic critical behavior of the thermal-expansion coefficient and of the specific heat, consistent with two-scale-factor universality. We also obtain a value for the adiabatic coupling constant which appears in the dynamic scaling theory for the frequency dependence of the critical sound attenuation. Our thermodynamic data appear to be in good agreement with the critical ultrasonic attenuation data obtained by Ishida and Harada for 3-methylpentane plus nitroethane.