In order to investigate the effect of pressure on the adsorption at interfaces, the interfacial tension was measured as a function of pressure and composition for the systems of water and dilute solutions of 1-octadecanol in cyclohexane, benzene, and their equimolar mixture. The interfacial density of 1-octadecanol and the volume of interface formation were evaluated from the experimental data. Under atmospheric pressure, cyclohexane exhibits a significant adsorption of 1-octadecanol and a rapid decrease in the volume of interface formation, giving rise to the phase transition from the expanded to the condensed state in the adsorbed film, while benzene and equimolar mixture display only a small decrease in the thermodynamic quantities on the 1-octadecanol adsorption. Under high pressure, however, all the systems studied cause the phase transition. The effects of pressure and solvent on the phase transition of the adsorbed film were revealed on the basis of the thermodynamic quantities.
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