Uncommon Behavior of Tetra-alkyl-phosphonium 2-Cyano-pyrrolide Ionic Liquids + Glycerol and Triethanolamine Systems

We use multiple characterization methods, including viscosity, ionic conductivity, density, and surface tension measurements, to investigate the unusual transport behavior of multiple tetra-alkyl-phosphonium-2-cyano-pyrrolide ([Pnnnm][2CNPyr]) ILs in glycerol and triethanolamine solvents. Specifically, the viscosity goes through a maximum for all of the IL/glycerol and IL/triethanolamine mixtures, which cannot be explained by traditional mixing rules. Through conductivity and surface tension characterization we find substantial evidence of microstructure formation driven by the amphiphilic structure of the tetra-alkyl-phosphonium ([Pnnnm]+) cation accounting for the uncommon viscosity behavior. While micelle formation is well-known for IL+ water systems, the observation of these microstructures in nonaqueous systems is a significant discovery. The slope of the ionic conductivity as a function of IL concentration changes substantially at the critical aggregate concentration cac, at which point the ILs unde...