Stuart BROWN1, Dilek YALCIN2, Shveta PANDIANCHERRI1, Tu LE3, Ibrahim ORHAN3, Kyle HEARN1, Qi HAN1, Calum DRUMMOND1, Tamar GREAVES1
1School of Science, RMIT, Melbourne, Australia
2Centre for Materials and Surface Science, La Trobe University, Melbourne, Australia
3School of Engineering, RMIT, Melbourne, Australia
The ability to synthesise large libraries of ionic liquids (ILs) is one of their greatest advantages. This enables systematic alteration of ion structure, which allows us to study structure-property trends of IL physicochemical, thermal and solvation properties, and hence to tailor ILs for applications. The influence of Coulombic, Van der Waal’s and H-bond cohesive forces, as well as Pauli repulsive forces on these properties can be better understood via the development of large libraries of ILs. Large libraries are needed due to the complexity of ILs, with ion stoichiometry, water content, ion reactivity (pKa) and ion clustering all contributing to their physicochemical properties. Here we report on the physicochemical, thermal and liquid nanostructure properties of 52 stoichiometric ion combinations from a series of 10 cations and 11 anions. Of these, 9 have not been reported before, 3 have been reported with no characterisation and 17 have undergone partial characterisation. A discussion of the importance of reproducible synthesis methods and the variance in the reported literature highlights the areas of IL characterisation for future work. The structure-property relationships consistent across ion series, including changing alkyl chain length, multiple chains on the cation and the presence of hydroxyl groups are discussed according to experimental and literature values based on the parameters discussed above. Advanced data analysis methods were applied via machine learning algorithms, random forest and k-nearest neighbour algorithms, providing a quantitative summation of individual structural moiety contributions. This study highlights the importance of the full characterisation of ILs as well as detailed reporting of their preparation for experimentation including water content and pH at 10 wt%.