Thermodynamic study on phase transition at the water/undecyl alcohol interface

The interfacial tension of the water/undecyl alcohol (UNA) system was measured as a function of pressure at various temperatures. The interfacial tension vs pressure and temperature curves were found to have a break point. It was shown that the volume, entropy, and energy of interface formation evaluated have negative values and change discontinuously at the pressure and temperature of the break point. The equations describing the phase transition at the interface of a binary two-phase system were developed and applied to the present system. It was proved thermodynamically that the phase transition takes place at the break point. Further, it was suggested that the transition was the one between expanded and condensed states of the interface.