Vapor Pressure of Perfluoroalkylalkanes: The Role of the Dipole

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• 作者：Pedro Morgado ; Gaurav Das ; Clare McCabe ; Eduardo J. M. Filipe
• 刊名：Journal of Physical Chemistry B
• 出版年：2015
• 出版时间：January 29, 2015
• 年：2015
• 卷：119
• 期：4
• 页码：1623-1632
• 全文大小：424K
• ISSN：1520-5207

文摘

The vapor pressure of four liquid perfluoroalkylalkanes (CF₃(CF₂)_n(CH₂)_mCH₃; n = 3, m = 4,5,7; n = 5, m = 5) was measured as a function of temperature between 278 and 328 K. Molar enthalpies of vaporization were calculated from the experimental data, and the results were compared with data from the literature for the corresponding alkanes and perfluoroalkanes. The heterosegmented statistical associating fluid theory was used to interpret the results at the molecular level both with and without the explicit inclusion of the dipolar nature of the molecules. Additionally, ab initio calculations were performed for all perfluoroalkylalkanes studied to determine the dipole moment to be used in the theoretical calculations. We demonstrate that the inclusion of a dipolar term is essential for describing the vapor鈥搇iquid equilibria of perfluoroalkylalkanes. It is also shown that vapor鈥搇iquid equilibria in these compounds result from a subtle balance between dipolar interactions, which decrease the vapor pressure, and the relatively weak dispersive interactions between the hydrogenated and fluorinated segments.