Blending ionic liquids: how physico-chemical properties change

Ionic liquids offer the opportunity of tailoring their properties by changing the chemical structure of the cation and anion. Blending of two or more liquids adds a further dimension to this "chemical space". Here we present the results of a study of three binary and one ternary mixture of the ionic liquids formed by the N-butyl-N-methylpyrrolidinium cation with bis(trifluoromethanesulfonyl)imide, bis(pentafluoroethanesulfonyl) imide and (trifluoromethanesulfonyl)(nonafluorobutanesulfonyl) imide. We have collected viscosity and NMR-based data on ion-ion correlations (NOE) and diffusion (DOSY). We also attempt to establish a quantitative correlation between mixture and the corresponding pure liquid properties. We find that the binary mixture containing the two very different anions has an intriguing and somewhat anomalous behaviour.