Determination of Viscosity, Ionic Conductivity, and Diffusion Coefficients in Some Binary Systems: Ionic Liquids + Molecular Solvents

Abstract

Experimental data for viscosities, diffusion coefficients of ferrocene, and conductivities were obtained for three ionic liquid mixtures: 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF 4 ), N -methyl- N -butylpyrrolidinium bis(trifluoromethylsulfonyl)imide (bmpyNTf 2 ), and N -methyl- N -hexylpyrrolidinium bis(trifluoromethylsulfonyl)imide (hmpyNTf 2 ) + dimethylformamide (DMF) or + 3-picoline as cosolvents, in the range of temperature T = (295.2 to 325.2) K. At a given temperature, the viscosity decreases exponentially with the mole fraction of the added cosolvent, and the variation of the diffusion coefficient agrees with the Stokes−Einstein law. Concerning the conductivity, addition of the polar solvent dimethylformamide produces an increase much greater than the addition of 3-picoline. The viscosity, diffusion coefficient, and conductivity follow the Arrhenius model in the explored temperature range. Consequently, moderate heating and addition of a cosolvent are two good means for obtaining conditions well adapted to electrosynthetic applications in ionic liquids.