Temperature Effect on the Adsorption of Fluorooctanols at the Hexane/Water Interface

The interfacial tensions of the hexane solution of fluorooctanols (1,1,2,2-tetrahydrotridecafluorooctanol, TFC8OH, and 1,1-dihydropentadecafluorooctanol, DFC8OH) against water were measured as a function of temperature and molality under atmospheric pressure. By drawing the interfacial pressure π vs mean area per adsorbed molecule A curves, it was concluded that the adsorbed film of TFC8OH exhibits a first-order phase transition between the gaseous and expanded states and that of DFC8OH shows the two types of phase transitions from the gaseous to the expanded state and from the expanded to the condensed one at the hexane/water interface. The comparison of the π vs A curve between TFC8OH and DFC8OH shows that the intermolecular interaction is enhanced by the substitution of fluorine for hydrogen on the β-carbon of TFC8OH. Furthermore, the difference in the transition pressure between DFC8OH and TFC10OH (1,1,2,2-tetrahydroheptadecafluorodecanol) is explained by the differences in London dispersion force bet...