Surface tension and 0.1 MPa densities of imidazolium-, pyridinium-, pyrrolidinium-, and piperidinium-based tris(pentafluoroethyl)trifluorophosphate ionic liquids

Experimental data over the temperature range from 263 to 363 K are presented on the air–liquid interfacial tension and 0.1 MPa densities for four ionic liquids with the tris(pentafluoroethyl)trifluorophosphate (FAP) anion and with the 1-(2-methoxyethyl)-1-methylpyrrolidinium, 1-(2-methoxyethyl)-1-methylpiperidinium, N-(3-hydroxypropyl)pyridinium, and 1-(2-hydroxyethyl)-3-methylimidazolium cations. The surface tension data were obtained by the Wilhelmy plate method with an estimated combined expanded uncertainty at 0.95 confidence level of ±0.2 mN m−1. The reported density data were obtained using a single-sinker buoyancy method with an estimated expanded combined uncertainty at 0.95 confidence level ±0.8 kg m−3 (4.6 × 10−4ϱ). The Krűss K100MK2 tensiometer was used to determine the surface tension and buoyancy forces. A value of 224.79 cm3 mol−1 follows for the FAP anion contribution to the ionic liquids molar volume at 298.15 K and 0.1 MPa from the group contribution analysis of the density data. In contrast to the common organic liquids, the studied ionic liquids show a negative value of the temperature derivative of the isochoric thermal volume expansion coefficient in the studied temperature interval.