Interfacial tension in binary systems containing a dense gas

An experimental system was constructed consisting of an autoclave, a device for measuring interfacial tension using the pendant-drop method, and a density-measuring device was constructed. Interfacial tension was measured at pressures up to 25 MPa and temperatures ranging from 313 to 393 K. Furthermore, the density of the coexisting phases and phase equilibria were measured. The investigated binary systems are composed of pelargonic acid or stearic acid as nonvolatile components and carbon dioxide, ethane, nitrogen, argon, helium, or hydrogen as gaseous components. The interfacial tension was found to be mainly a function of the gas content of the coexisting liquid phase. Except for helium, the interfacial tension decreases with increasing gas concentration of the liquid phase. At equal gas content in the liquid phase, carbon dioxide and ethane, having positive heat of solution, decrease the interfacial tension less than argon and nitrogen, having negative heat of solution. The influence of hydrogen on the interfacial tension does not fit in this order because of its very small size.