Pulsed field gradient (PFG) NMR has been used to probe self-diffusion of molecular and ionic species in aqueous mixtures of choline chloride (ChCl) based deep eutectic solvents (DESs), in order to elucidate the effect of water on motion and inter-molecular interactions between the different species in the mixtures, namely the Ch + cation and hydrogen bond donor (HBD). The results reveal an interesting and complex behaviour of such mixtures at a molecular level. In general, it is observed that the hydroxyl protons ( 1 H) of Ch + and the hydrogen bond donor have diffusion coefficients significantly different from those measured for their parent molecules when water is added. This indicates a clear and significant change in inter-molecular interactions. In aqueous Ethaline, the hydroxyl species of Ch + and HBD show a stronger interaction with water as water is added to the system. In the case of Glyceline, water has little effect on both hydroxyl proton diffusion of Ch + and HBD. In Reline, it is likely that water allows the formation of small amounts of ammonium hydroxide. The most surprising observation is from the self-diffusion of water, which is considerably higher that expected from a homogeneous liquid. This leads to the conclusion that Reline and Glyceline form mixtures that are inhomogeneous at a microscopic level despite the hydrophilicity of the salt and HBD. This work shows that PFG NMR is a powerful tool to elucidate both molecular dynamics and inter-molecular interactions in complex liquid mixtures, such as the aqueous DES mixtures.

Addition of water increases the DES interfacial nanostructure up to ∼40 wt%. This differs starkly from ionic liquids, where addition of small amounts of water rapidly decreases the interfacial nanostructure.

Deep eutectic solvents (DESs) have been used for the purification of oils and the extraction of active ingredients from natural products but little is known about the mechanism of the extraction process. In this study a variety of molecular solutes are dissolved in alkanes and the thermodynamics of transfer into six DESs have been quantified. It is shown that the transfer of most solutes into the DES is endothermic and driven by entropy. The largest partition coefficients were demonstrated by the liquids with the lowest surface tensions and this is thought to arise because the enthalpy of hole formation controlling the rate of solute transfer. Accordingly, it was shown that the size of the solute has an effect on the partition coefficient with smaller solutes partitioning preferably into the DES. As expected, solutes capable of strongly hydrogen bonding partitioned much better into the DES as the enthalpy of transfer was negative.

Most studies of metal electrodeposition in ionic liquids dry the electrolyte thoroughly, as water is thought to be detrimental. In some cases, water has a beneficial effect on deposit morphology.The electrodeposition of copper has been studied in 1ChCl: 2EG-water mixtures. It is shown here that the presence of water increases the apparent brightness of the deposit due to changes in the electrodeposit surface feature size, up to a water content of approximately 20 wt%. This study characterises speciation and mass transport in solution, and shows that diffusion can be controlled independently of speciation. It is shown that there is an optimal water content, which is thought to originate from formation of a bicontinuous microemulsion phase in DES-water mixtures. Additionally, the copper species remains in a predominantly ionic medium at low water content but moves to an aqueous environment when water is the main component.