Surface Freezing and Molecular Miscibility of Binary Alkane–Alkane and Fluoroalkane–Alkane Liquid Mixtures

详细信息    查看全文

• 作者：Takanori Takiue ; Mayuko Shimasaki ; Miyako Tsuura ; Hiroyasu Sakamoto ; Hiroki Matsubara ; Makoto Aratono
• 刊名：Journal of Physical Chemistry B
• 出版年：2014
• 出版时间：February 13, 2014
• 年：2014
• 卷：118
• 期：6
• 页码：1519-1526
• 全文大小：418K
• ISSN：1520-5207

文摘

The surface freezing (SF) of liquid n-heptadecane (C₁₇)鈥?i>n-octadecane (C₁₈) and 1-perfluorooctyl decane (F₈H₁₀)鈥揅₁₈ mixtures were studied by surface tension and external reflection absorption FTIR (ERA-FTIR) measurements. The surface tension versus temperature curves of all pure liquids show a sharp break point at T_s corresponding to a surface liquid (SL)鈥揝F transition. The entropy of surface formation is very negative, indicating a well-ordered structure of the SF layer. The ERA-FTIR spectra in the SF state suggested that the C₁₈ molecules are densely packed in the solid state, while the packing of the hydrocarbon (HC) part of F₈H₁₀ is a little looser than the fluorocarbon (FC) part because of the difference in the cross-sectional area. In the C₁₇鈥揅₁₈ mixture, the SL鈥揝F transition was found at all bulk compositions. The estimation of the surface composition suggested that two components are miscible both in SL and SF states. The excess entropy of the surface is almost zero in both states, and thus, it was concluded that the two components are mixed almost ideally at the surface. In the case of the F₈H₁₀鈥揅₁₈ system, on the other hand, the SL layer is enriched in F₈H₁₀ with lower surface tension than C₁₈ compared to bulk liquid. The surface composition in the SF state is almost zero or unity, indicating that F₈H₁₀ and C₁₈ molecules are practically immiscible mainly due to the weak interaction between different components. Furthermore, the negative excess entropy in the SL layer suggests domain formation of F₈H₁₀ molecules at the surface.