Surface tension for octafluorocyclobutane, n-butane and their mixtures from 233 K to 254 K, and vapour pressure, excess Gibbs function and excess volume for the mixture at 233 K
Fluid Phase Equilibria, 2 (3):
199 - 213 (1978)DOI: 10.1016/0378-3812(78)80009-0
Abstract
The surface tensions of octafluorocyclobutane (234 to 267 K), n-butane (238 to 273 K) and of their mixtures (232 to 254 K) have been measured by differential capillary rise; there is a slight minimum in the isotherms near x(c-C4F8) ≈ 0.8 but no maximum. The total vapour pressure and density of the liquid mixture were measured at the triple point temperature of c-C4F8, 233 K. The mixture displays marked positive azeotropy. The excess Gibbs function and excess volume are both large and positive but the deviation from ideality is insufficient for liquid—liquid immiscibility whose absence was confirmed by visual observation at temperatures down to the solid—liquid phase boundary. All the foregoing are consistent with theoretical expectations based upon the dominant effect of an interaction energy between the unlike components which is smaller than that predicted by the Berthelot geometric mean rule. No inferences can be drawn as to the role of chain flexibility.