Experimental study of the liquid phase of SF6near its critical point

Abstract

Measurements of the long-range correlation length, the turbidity, and the susceptibility ${\left(\frac{\partial \rho }{\partial \mu }\right)}_T$ have been made as functions of temperature and distance below the gas-liquid interface, in the range $1.25\times {10}^{-6\mathrm{}}\le \frac{(T_c-T)}{T_c}\le 6.15\times {10}^{-2\mathrm{}}$. The results are found to be accurately fit by the linear parametric equation of state; however, the best single exponent ${{\gamma }^{\prime }}_L$. describing the divergence of ${\left(\frac{\partial \rho }{\partial \mu }\right)}_T$ is 1.189, which is significantly lower than the value determined in previous measurements for $T>\mathrm{}{T}_c$. A significantly better fit to the ${\left(\frac{\partial \rho }{\partial \mu }\right)}_T$ data is obtained by using a modified power law of the form $A{\mathrm{}\left|t\right|\mathrm{}}^{-\gamma }(1+D{\mathrm{}\left|t\right|\mathrm{}}^x)$, with the leading exponent fixed at 1.223, the value observed for $T>\mathrm{}{T}_c$. This is taken to indicate that corrections to pure power-law behavior are more evident for $T<\mathrm{}{T}_c$ than for $T>\mathrm{}{T}_c$. The measured values of the correlation range are compared to values determined from measurements of the reflectivity of the interfacial layer and are found to show the same temperature dependence, but to be approximately one half of the latter in magnitude. The linear parametric equation of state is tested and found to describe the variation of ${\left(\frac{\partial \rho }{\partial \mu }\right)}_T$ with temperature and height in the cell quite accurately for $T>\mathrm{}{T}_c$, but it is not capable of simultaneously accounting for all of the data both above and below $T_c$.