Nanostructure and polymer solvation in ionic liquids and deep eutectic solvents

Ionic Liquids (ILs) and Deep Eutectic Solvents (DESs) are solvents of great interest due to the spontaneous nanostructure that they exhibit, as a result of interactions between the ionic components in the case of ILs and interactions between ionic and molecular components in DESs. By modifying the base ionic and molecular components, the nanostructure and resulting physicochemical properties, can be “tuned”. This has made them attractive systems for use as solvation media. This thesis applies a combination of experimental and theoretical techniques to elucidate the nanostructure of a range of IL mixtures and DESs, and how physicochemical properties such as solvation, viscosity and melting temperature depression arise from this. The IL propylammonium nitrate (PAN) was primarily studied with and without dissolved halide salts to develop the understanding of the interplay between nanostructure and solvation, using small angle neutron scattering (SANS) and quantum mechanical molecular dynamics (QM/MD) simulations. The addition of halide salts was found to reduce the ability of poly(ethylene oxide) (PEO) to solvate in the IL, highlighted by a decrease in radius of gyration determined by SANS experiments. Further investigation applying QM/MD revealed the reduction in solvation of PEO in the IL mixtures was a result of the halide anions having a greater ionic interaction with the propylammonium cation, effectively displacing the polymer. QM/MD methods were also applied to three choline chloride based DESs, using urea, ethylene glycol, or glycerol as hydrogen bond donors (HBD) to develop the understanding of how physicochemical properties such as viscosity and melting temperature depression arise from their nanostructure. The origins of these effects were found to be subtle, resulting from a combination of HBD acidity, functional group type, functional group propensity, HBD shape, and HBD orientation. The ability for the HBD to more effectively intercalate the ionic components of the DES was found to be directly proportional to the melting temperature depression observed in the eutectic. The density of hydrogen bonds in each DES was also found to be directly proportional to the viscosity of the system. Solvation of PEO in these systems was also studied, and it was shown that the HBD type directly affected how the polymer solvates. The combined theoretical and experimental approach used in this thesis constitutes a comprehensive investigation of these solvent systems and provides deeper understanding then either could produce on their own. This thesis has developed the understanding of the relationship between property and nanostructure that will assist the development and application of ILs and DES as designer solvents.