Tuning the physicochemical properties of protic-aprotic ionic liquids upon reciprocal binary mixing

Abstract

The alterations in properties of protic/aprotic (2-hydroxyethylammonium formate)/ 1-butyl-3-methylimidazolium methyl sulfate) ionic liquids (ILs), based on reciprocal binary mixing concept ([A][B][X][Y]) have been investigated by studying the density, speed of sound, and viscosity of mixtures as a function of temperature. The volume of mixing, isentropic compressibility, excess molar isentropic compressibilities and activation energy of viscous flow have been derived, which indicate a very high level of non-ideality in the mixtures desired to take advantage of improved solvent properties. FTIR spectral analysis and solvatochromic parameters (normalized Reichardt’s parameter, dipolarity/polarizibility, hydrogen bond donor and acceptor coefficients) determined through the solvatochromic probes have been utilized to examine the hydrogen bonding and ion-ion interactions prevailing in the studied systems. Although significant alterations in hydrogen bonding and ion-ion interactions are observed, dispersion type interactions dominate over chemical interactions as indicated by a high positive deviations in the volumes of mixing.