Influence of the Anion on the Equilibrium and Transport Properties of 1-Butyl-3-methylimidazolium Based Room Temperature Ionic Liquids

Density, surface tension, viscosity and conductivity measurements at different temperatures were carried out for a series of 1-butyl-3-methylimidazolium cation based room temperature ionic liquids (RTILs) with the anions: . The main aim of the study was to explore and understand the impact of the nature of anions on the equilibrium and transport characteristics of imidazolium based RTILs. Theoretically predicted values of surface tension and density for the investigated RTILs were found to differ from their experimentally observed values and the mismatch was greater in the case of surface tension than for the density values. The conductivity-viscosity data were analyzed in light of the fractional Walden approach for quantification of ionicity. It was found that the ionicity in the investigated RTILs follows the order [BMIM][Sal] < [BMIM][Ac] < [BMIM][MeSO4] < [BMIM][SCN] < [BMIM][BF4]. The results clearly establish that the nature of the anion affects the magnitude of both equilibrium and transport properties of imidazolium based RTILs through a complex interplay of size, charge density, shape, symmetry and ability to engage in electrostatic and non-electrostatic interactions with the imidazolium cation.