Physicochemical Properties of [C₆mim][PF₆] and [C₆mim][(C₂F₅)₃PF₃] Ionic Liquids

Abstract

The density, viscosity, conductivity, and heat capacity of 1-hexyl-3-methylimidazolium hexafluorophosphate ([C6mim][PF6]) and 1-hexyl-3-methylimidazolium tris(perfluoroalkyl)trifluorophosphate ([C6mim][(C2F5)3PF3]) were measured in the (293.15 to 343.15) K range. According to these experimental and estimated results, the coefficients of thermal expansion and conductivity apparently increase from [C6mim][PF6] to [C6mim][(C2F5)3PF3], while the crystal energy, the temperature dependence of the heat capacity, and viscosity greatly decrease from [C6mim][PF6] to [C6mim][(C2F5)3PF3] in the examined temperature range. These comparisons were combined to assess the effect of the replacement of three F atoms of the hexafluorophosphate anion by three hydrophobic C2F5-groups on the physicochemical properties of [C6mim][PF6] and [C6mim][(C2F5)3PF3].