The interfacial tensions (γ) of the hexane solutions of 1H, 1H-perfluorononanol (FDFC9OH) and its ω-hydrogenated analogue 1H, 1H, 9H-perfluorononanol (HDFC9OH) against water were measured as a function of temperature and concentration under atmospheric pressure in order to know the effect of ω-dipoles on the adsorption behavior of fluorononanols. The interfacial pressure (π) versus mean area per adsorbed molecule (A) curves consist of two discontinuous changes among three different states: the gaseous, expanded, and condensed states. The A values at given π in the gaseous and expanded states are larger for HDFC9OH than for FDFC9OH. The changes in partial molar entropy (s1 -H - s1O) and energy (u1 -H - u1O) of adsorption were evaluated. Their values are negative, and therefore, the alcohols have a smaller entropy and energy at the interface than in the bulk solution. Furthermore, the u 1-H - u1O value is more negative for HDFC9OH than for FDFC9OH in the expanded state and also in the condensed film just above the expanded-condensed phase transition point. This seems to be due to the following: (1) HDFC9OH may tilt from interface normal for ω-dipoles to interact effectively with water molecules in the interfacial region and to reduce their own repulsive interaction between neighbors arranging parallel in the adsorbed film. This leads to a lower u1-H value for HDFC9OH than for FDFC9OH. (2) The contact of ω-dipoles with hexane molecules in the bulk solution is energetically unfavorable, and thus, the u1O value of HDFC9OH is expected to be larger than that of FDFC9OH.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
- Materials Chemistry