Search

The thermophysical properties of three lipidic ionic liquids, 1-oleyl-3-methylimidazolium bistriflimide, 1-elaidyl-3-methylimidazolium bistriflimide, and 1-linoleyl-3-methyl-imidazolium bistriflimide are measured at 1 bar as a function of temperature over the range of 273 K to 353 K and correlated to appropriate models. Each of these compounds is a variation on 1-C18-3-methylimidazolium bistriflimide, where the C18 chain contains one or more unsaturations, incorporated into the structure to lower the melting point. Derived properties such as molar volume and volume expansivity are also calculated. The data are compared with literature values for shorter chain 1-n-alkyl-3-methylimidazolium bistriflimide salts. The longer chains impart lower densities and higher viscosities relative to their shorter chain homologues. Although the subtle structural differences between the three compounds result in significant differences in melting points, there is less of an effect on the liquid phase thermophysical properties.

A series of novel lipid-inspired ionic liquids have been synthesized employing the thiol-ene "click" reaction in a single-step process. The thermal properties were determined by differential scanning calorimetry (DSC) and showed observable trends between the C16, C18, and C20 analogues. The minimum melting points for each equivalent chain length series occur at sequential odd sulfur positions, 3, 5, and 7 for the C16, C18, and C20 series, respectively. The magnitude of melting point depression relative to the saturated homologue is observed to have a strong dependence on the position of the sulfur in the side chain. Additionally, the sulfur position corresponding to the lowest melting point for a homologous series shifts further down the chain as the chain length is increased, indicating that the maximum effect takes place near the center of the ion and not the center of the thiaalkyl chain. This synthesis provides tunability and improved thermal stability for 1-methyl-3-thiaalkylimidazolium bistriflimides and insight into structure-property relationships of lipidic ionic liquids.

Ionic liquids of cations bearing two lipid-like aliphatic tails are shown to have values of T(m) that can be very low, and that can be tuned up or down by the addition, deletion, or combination of dipolar modules and side-chain double bonds.