Volumetric and transport properties of N-Butyl-N-methylpyrrolidinium bis(Trifluoromethanesulfonyl)imide-methanol binary mixtures

Densities, viscosities, and ionic conductivities were measured for the binary mixtures containing the ionic liquid N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide and methanol over the entire range of compositions at the temperature varying from 253.15 to 318.15 K. The densities and viscosities decrease monotonously with temperature and the content of ionic liquids (ILs). Furthermore, excess isobaric expansion coefficient has been calculated from the experimental densities. The dependence of temperature on the viscosity has been fitted to the Arrhenius law with high precision. The dependence of temperature on the ionic conductivity has also been gauged by both of the Arrhenius and Vogel-Tamman-Fulcher (VTF) equations. In fact, the shape of the curves shows that the temperature dependence of the conductivity does not follow a simple Arrhenius law, but a better fitting of experimental results is achieved using the VTF model. Additionally, the effects of ILs concentration on the viscosity and the conductivity have been examined using the Walden rule, which shows that the variation of conductivity is inversely proportional to viscosity. Excess molar volumes and viscosity deviations for all mixtures are evaluated and well fitted to the Redlich-Kister polynomial expansions. Physicochemical properties show two clearly distinguished behaviors corresponding to ILs-rich and methanol-rich regions, with distinct transport and volumetric properties. The obtained results are discussed in terms of dipolar interactions and hydrogen bonding establishment between ions of ILs and the methanol molecules.