Density, Surface Tension, and Refractive Index of Ionic Liquids Homologue of 1-Alkyl-3-methylimidazolium Tetrafluoroborate [C_<i>n</i>mim][BF₄] (<i>n</i> = 2,3,4,5,6)

Abstract

The values of density, surface tension, and refractive index were measured for a classic series of air and water stable ionic liquids (ILs) based on tetrafluoroborate, [C n mim][BF 4 ]( n = 2,3,4,5,6)(1-alkyl-3-methylimidazolium tetrafluoroborate) in the temperature range of (298.15 to 338.15 ± 0.02) K. In terms of Glasser’s theory, the standard molar entropy and lattice energy of the ILs were calculated. Using Kabo’s method, the molar enthalpy of vaporization of the IL, Δ l g H m 0 (298 K), was estimated. According to the interstice model, the thermal expansion coefficient of ILs [C n mim][BF 4 ] ( n = 2,3,4,5,6), α, were calculated, and in comparison with experimental value, their magnitude order is in good agreement. To test this new concept of ionic parachor, [BF 4 ] − was chosen as a reference ion and its individual value of ionic parachor was determined in terms of extrathermodynamic assumption. Then, using ionic parachor of [BF 4 ] −, the ionic parachors for all corresponding imidazolium cations, [C n mim] +, were calculated and in good agreement with those obtained by Guan’s estimation, and the 17 anion ionic parachors were also obtained. In terms of ionic parachor, the surface tension and refractive index of the investigated ionic liquids were estimated, and the estimated values correlate quite well with their matching experimental values.