Physicochemical Properties of Binary Ionic Liquid-Aprotic Solvent Electrolyte Mixtures

The properties of mixtures of ionic liquids (ILs) with a variety of different aprotic solvents have been examined in detail. The ILs selected bis(trifluoromethanesulfonyl)imide (TFSI-) salts with N-methyl-N-pentylpyrrolidinium (PY15+), -piperidinium (PI15+), or -morpholinium (MO15+) cations enabled the investigation of how cation structure influences the mixture properties. This study includes the characterization of the thermal phase behavior of the mixtures and volatility of the solvents, density and excess molar volume, and transport properties (viscosity and conductivity). The mixtures with ethylene carbonate form a simple eutectic, whereas those with ethyl butyrate appear to form a new IL-solvent crystalline phase. Significant differences in the viscosity of the mixtures are found for different solvents, especially for the IL-rich concentrations. In contrast, only minor differences are noted for the conductivity with different solvents for the IL-rich concentrations. For the solvent-rich concentrations, however, substantial differences are noted in the conductivity, especially for the mixtures with acetonitrile.