The role of water in cholinium carboxylate ionic liquid’s aqueous solutions

• Densities and viscosities of aqueous solutions of cholinium carboxylate ionic liquids.
• 1H NMR experiments were used to probe nanoscale organization of ionic liquids in water.
• Different nanoscale organization in water for the 3 ionic liquids.

Binary systems composed of water and cholinium carboxylate ionic liquids, namely cholinium lactate ([Ch][Lac]), cholinium propanoate ([Ch][Prop]) and cholinium malonate ([Ch][Mal]) were studied from the neat ionic liquid to very diluted aqueous solutions. Densities and viscosities were measured and atypical behaviors were observed, such as the increasing density of the binary [Ch][Prop] + H2O mixtures with increasing water content. In order to get molecular level insights on the IL + H2O solvation schemes, 1H NMR studies were performed. Large deviations were obtained in the aniońs resonances when compared to those of the cation suggesting that water interacts preferentially with the anion counter-part of the ionic liquid. The increasing density of [Ch][Prop] + H2O system with increasing water content can be related to the orientation of the alkyl chains, as a result of their nanoscale organization. This behavior was confirmed through the study of the thermophysical properties of [Ch][Hex] + H2O mixtures, where this phenomenon is known to occur.

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