Ultralow interfacial tension in the vicinity of the upper critical solution temperature of the mixture of water and isobutyric acid

The ultralow interfacial tension of the binary liquid mixture of water and isobutyric acid has been measured as a function of temperature under atmospheric pressure in the vicinity of the upper critical solution temperature. It has been observed that the interfacial tension decreases monotonously as the temperature increases and is reduced to zero at the critical solution temperature. The results have been analyzed on the basis of the thermodynamics of interfaces. It has been found that the formation of interface is accompanied by increases in entropy and energy, which vanish at the critical solution temperature. This behavior has been considered in terms of the partial molar thermodynamic quantities of components. The brief discussion of the critical exponent has been also given for the present system.