Interfacial Tension of Near-Critical Cyclohexane–Methanol Mixtures

Abstract

We have measured the capillary length for the interface between the coexisting phases in the vicinity of the critical consolute temperature of mixtures of cyclohexane and methanol. The data on the capillary length ${\text{a\hspace{0.17em}=\hspace{0.17em}0.250 (T}}_c{\mathrm{\hspace{0.17em}-\hspace{0.17em}T)}}^{\text{0.44±0.02}}\mathrm{cm}$ were combined with values of the difference in density $\mathrm{\Delta \rho }$ between the coexisting phases calculated from the coexisting compositions to obtain the interfacial tension ${\mathrm{\sigma \hspace{0.17em}=\hspace{0.17em}a}}^2{\text{Δρg\hspace{0.17em}/\hspace{0.17em}2\hspace{0.17em}=\hspace{0.17em}100(1\hspace{0.17em}−\hspace{0.17em}T\hspace{0.17em}/\hspace{0.17em}T}}_c{)}^{\text{1.23\hspace{0.17em}±\hspace{0.17em}0.05}}\mathrm{erg}/{\mathrm{cm}}^2$ . Our measurements of $\sigma$ for this system combine with the only existing measurements of the effective thickness of a critical interface in a new test of theories of critical interfaces. Data include ${\text{0.09\hspace{0.17em}<\hspace{0.17em}T}}_c\text{\hspace{0.17em}−\hspace{0.17em}T\hspace{0.17em}<\hspace{0.17em}9°}\mathrm{C}$ .