Effect of water on amine-based deep eutectic solvents (choline chloride + monoethanolamine): Structure and physicochemical properties

Water, can not only regulate the thermodynamic properties of deep eutectic solvent (DES), but also affect its supramolecular structure. Therefore, it is necessary and meaningful to study the effect of water on DES. In this work, amine functionalized DES (choline chloride + monoethanolamine) was successfully prepared, and the densities and viscosities of DES + H2O were measured from 293.15 K to 323.15 K. The effects of DES composition, water content and temperature on the excess molar volume, partial molar volume, apparent molar volume, limiting molar volume, coefficient of thermal expansion, viscosity deviation and activation energy for viscous flow were investigated. The hydration and structural changes of DES were analyzed. Additionally, the Redlich-Kister equation was used to correlate the excess properties of DES + H2O. Finally, a three-stage theory of effect of water on DES, namely the pure DES stage, the destruction stage and the thorough destruction stage, was proposed. Conclusively, it can be seen that an appropriate amount of water is very helpful to improve the properties of DES, otherwise the structural advantages of DES will be lost. It is hoped that this study will lay a foundation for the application of DES.