Molecular Orientation and Multilayer Formation in the Adsorbed Film of 1H,1H,10H,10H-Perfluorodecane-1,10-diol at the Hexane/Water Interface; Temperature Effect on the Adsorption of Fluoroalkane-diol

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• 作者：Takanori Takiue ; Tsubasa Fukuda ; Daiki Murakami ; Hideaki Inomata ; Hiroyasu Sakamoto ; Hiroki Matsubara ; Makoto Aratono
• 刊名：Journal of Physical Chemistry C
• 出版年：2008
• 出版时间：April 3, 2008
• 年：2008
• 卷：112
• 期：13
• 页码：5078 - 5084
• 全文大小：147K
• 年卷期：v.112,no.13(April 3, 2008)
• ISSN：1932-7455

文摘

The adsorption of 1H,1H,10H,10H-perfluorodecane-1,10-diol (FC₁₀diol) at the hexane/water interface wasinvestigated by the measurement of temperature dependence of interfacial tension and the thermodynamicdata analysis in order to know the effect of two hydroxyl groups at both ends of the hydrophobic chain andthe rigidity of the hydrophobic chain on the adsorption of fluorocarbon alcohol at the interface. The curvesof interfacial tension versus temperature and concentration show break points corresponding to the phasetransitions in the adsorbed FC₁₀diol film. The interfacial pressure versus mean area per adsorbed moleculecurve shows three kinds of states connected by two discontinuous changes. The area value after the firstphase transition is very close to the calculated cross-sectional area of the FC₁₀diol molecule along its majoraxis, and thus the FC₁₀diol molecules form a condensed monolayer with molecular orientation parallel to theinterface. Another noticeable point is that the value after the second phase transition point decreases furthermoreto 0.12 nm², which is much smaller than the cross-sectional area of the fluorocarbon chain, 0.28 nm², withincreasing interfacial pressure. This suggests that FC₁₀diol molecules pile spontaneously and successivelyform a multilayer above the second phase transition. Furthermore, the partial molar entropy and energy changeof adsorption in the expanded and condensed states were evaluated and compared to those of 1H,1H,2H,2H-perfluorodecanol (TFC₁₀OH), which orients almost perpendicular to the interface. In addition to the contactof two hydroxyl groups with hexane in the bulk solution, the results are explained by the dependence ofpartial molar entropy and energy at the interface on the following factors resulting from the parallel orientationof FC₁₀diol at the interface; (a) hydrogen bonding of two hydroxyl groups with water molecules, (b) hydrogenbonding between two hydroxyl groups facing each other, and (c) the fluorocarbon chain-water contact. Theadsorbed FC₁₀diol film is stabilized by factors a and b, which overwhelm the energetic disadvantage causedby factor c. Furthermore, the entropy change of adsorption s in the multilayer is compared to the s_calcalculated on the assumption that the condensed monolayer piles to form the multilayer. It was suggestedthat FC₁₀diol molecules are not so densely packed in the multilayer compared to the first condensed monolayerand therefore the multilayer is not simply formed by the piling of condensed monolayers.