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.
The interfacial tensions of the water-decyl alcohol (DEA), -undecyl alcohol (UNA), and -dodecyl alcohol (DOA) systems were measured as a function of temperature and pnssure. The thermodynamic quantitie of interface formation were evaluated from the experimental results; the entropy, volume, and energy were found to have negative values and change discontinuwly at the break point on the interfacial tension vs temperature and pressure curves. These results were discussed in terms of the orientation of alcohol molecules at the interface caused by the interaction between alcohol and water molecules. Further, it was suggested that the phase transition takes place between the expanded and condensed states at the interface.
IntroductionThe adsorption of alcohols at oil-water interfaces has been studied with continuous interest.'-" We have investigated the adsorbed films of long-chain alcohols at oil-water interfaces by measuring the interfacial tension as a function of temperature, pressure, and concentration and by analyzing the results to obtain the thermodynamic quantities such as the interfacial densities of the alcohols and the entropy, volume, and energy changes associated with a d s~r p t i o n '~-~~ based on the thermodynamics of interface~;'~ the state of their adsorbed films is found to be appreciably dependent on the thermodynamic variables, the hydrocarbon chain length of the alcohols, and the kinds of oils. These results and our previous works on the interface formation of water-organic compound systemsIb18 have aroused much interest to study the interface formation of water-long-chain alcohol systems in the absence of oil.In this study, we choose decyl alcohol (DEA), undecyl alcohol (UNA), and dodecyl alcohol (DOA) because they are liquid at room temperature and their structures are simple. The interfacial tension between the water-rich and alcohol-rich phases was measured as a function of temperature for the DEA, UNA, and DOA systems and also of pressure for the DEA and UNA systems.
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