title: Vapor pressure of perfluoroalkylalkanes: the role of the dipole.
abstract: 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-liquid equilibria of perfluoroalkylalkanes. It is also shown that vapor-liquid 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.
authors.affiliation: Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa , 1049-001 Lisboa, Portugal.
authors.forename: Pedro
authors.initials: P
authors.lastname: Morgado
authors.forename: Gaurav
authors.initials: G
authors.lastname: Das
authors.forename: Clare
authors.initials: C
authors.lastname: McCabe
authors.forename: Eduardo J M
authors.initials: EJ
authors.lastname: Filipe