Theoretical and experimental studies of water interaction in acetate based ionic liquids

Water interactions in 1-ethyl-3-methylimidazolium acetate ([emim][CH3COO]) were studied utilizing classical and ab initio simulation methods. The self-diffusivities for water and the ionic liquid (IL) were studied experimentally using pulse field gradient NMR spectroscopy and correlated with computational results. Water forms hydrogen bonding networks with the ionic liquid, and depending on the concentration of water, there are profound effects on the self-diffusivities of the various species. Both simulation and experiments show that the self-diffusivities for species in the water-[emim][CH3COO] system exhibit minima at 40-50 mol% water. Water interaction with the [CH3COO](-) anion predominates over the water-water and water-cation interactions at most water concentrations. Simulations further indicate that decreasing water-[CH3COO](-) interaction will increase the IL and water self-diffusivities. Self-diffusivities in the water-IL systems are dependent upon the cation in a complex way. Water interactions with [P-4444][CH3COO] are reduced compared to [emim][CH3COO]. The [P-4444](+) cation is bulkier than the [emim](+) cation and has a smaller self-diffusivity, but when water was introduced to [P-4444] [CH3COO], the water-[CH3COO](-) hydrogen bonding network in the [P-4444][CH3COO] was much smaller than the one observed in [emim][CH3COO].