Thermodynamic Study on Phase Transition in Adsorbed Film of Fluoroalkanol at the Hexane/Water Interface. 8. Phase Transition and Miscibility in the Adsorbed Film of Fluoroalkanol Mixture

Abstract

The interfacial tension γ of the hexane solution of a mixture of 1,1,2,2-tetrahydroheptadecafluorodecanol (FC10OH) and 1,1,2,2-tetrahydrohenicosafluorododecanol (FC12OH) against water was measured as a function of the total molality m and composition of FC12OH X 2 at 298.15 K under atmospheric pressure. The γ vs m curve has one or two distinct break points depending on X 2. By plotting the γ and m values at the break points and drawing the interfacial pressure π vs mean area per adsorbed molecule A curves, it was suggested that the triple point of adsorbed film, at which the three kinds of states (gaseous, expanded, and condensed states) coexist simultaneously, exists at a middle composition. The phase diagrams of adsorption (PDA) were constructed and the excess Gibbs energy of adsorption g H,E was calculated to examine the miscibility of FC10OH and FC12OH molecules in the adsorbed film. It was found that these alcohols mix almost ideally both in the gaseous and expanded states and nonideally in the condensed state. Furthermore, the mixing of FC10OH and FC12OH in the condensed film was accompanied by a positive g H,E value. This suggests that the difference in the magnitude of mutual interaction between the same species affects appreciably the miscibility of molecules in the condensed state where the adsorbed molecules are assumed to be closely packed and arranged regularly.

Miscibility and Multilayer Formation of Fluoroalkane−α,ω-Diol Mixtures at the Air/Water Interface

“…The effect of molecular orientation on the miscibility of molecules in the adsorbed films is well understood by comparing the g H,E values with those for the mixed systems of homologous FC alcohols with normal molecular orientation. In our previous study on the miscibility of 1 H ,1 H ,2 H ,2 H -perfluorodecanol (FC 10 OH) and 1 H ,1 H ,2 H ,2 H -perfluorododecanol (FC 12 OH) at the hexane/water interface, we found that both alcohols orient almost perpendicularly and mix ideally in the gaseous and expanded states and nonideally in the condensed state even though their difference of chain length is only two . Thus, the difference in molecular orientation is probably more influential on the condensed films than on the gaseous and expanded states.…”

“…In our previous study on the miscibility of 1H,1H,2H,2H-perfluorodecanol (FC 10 OH) and 1H,1H,2H,2H-perfluorododecanol (FC 12 OH) at the hexane/water interface, we found that both alcohols orient almost perpendicularly and mix ideally in the gaseous and expanded states and nonideally in the condensed state even though their difference of chain length is only two. 10 Thus, the difference in molecular orientation is probably more influential on the condensed films than on the gaseous and expanded states. In Figure 9, the g H,E /RT vs X 2 H curve in the parallel condensed monolayer at γ ) 45 mN m -1 of the mixed FC 6 diol-FC 8 diol system is shown together with that in the normal condensed monolayer at γ ) 40 mN m -1 of the mixed FC 10 OH-FC 12 OH system.…”

“…4 In our previous study on the adsorption of a homologous FC alcohol mixture with the different chain length by only two, such as 1H,1H,2H,2H-perfluorodecanol (FC 10 OH) and 1H,1H,2H,2Hperfluorododecanol (FC 12 OH), at the hexane solution/water interface, the miscibility of both alcohols in the adsorbed film was examined by constructing the PDA and evaluating the excess Gibbs energy of adsorption g H,E . 10 It was shown that the mixing of FC 10 OH and FC 12 OH is almost ideal in the gaseous and expanded states, while it is nonideal and accompanies a positive g H,E value in the condensed state. Taking account of the experimental findings obtained by X-ray reflectivity measurements that both FC alcohols stand almost perpendicularly at the interface in the condensed film, 11,12 these results were reasonably explained by the fact that the loss of dispersion interaction between hydrophobic chains due to the chain length mismatch appreciably affects the miscibility of molecules in the condensed state.…”

“…In our previous study on the adsorption of a homologous FC alcohol mixture with the different chain length by only two, such as 1 H ,1 H ,2 H ,2 H -perfluorodecanol (FC 10 OH) and 1 H ,1 H ,2 H ,2 H -perfluorododecanol (FC 12 OH), at the hexane solution/water interface, the miscibility of both alcohols in the adsorbed film was examined by constructing the PDA and evaluating the excess Gibbs energy of adsorption g H,E . It was shown that the mixing of FC 10 OH and FC 12 OH is almost ideal in the gaseous and expanded states, while it is nonideal and accompanies a positive g H,E value in the condensed state.…”

Phase Transition and Miscibility of Binary Surfactant Mixtures in Adsorbed Film at the Air/Water Surface

“…Therefore we employed tetraethylene glycol monomethyl ether (C1E4) as the one of the analogs of C8E4. Taking into account that the phase transition causes very drastic changes in the miscibility of surfactants at the oil/water interfaces (26)(27)(28) and the discontinuous changes in the composition of the adsorbed film as well as the total surface density of the surfactants at the water/air interface (3-5), we decided to utilize the phase transition phenomena in the adsorbed film to carry out our purpose. From this point of view, DAC is most suitable because the phase transition has been reported in its adsorbed film as mentioned above.…”