Rheological and thermodynamic properties of deep eutectic solvents

Deep eutectic solvents (DES) and Natural deep eutectic solvents in particular (NADES), are seen as the most promising green alternatives to environmental detrimental solvents,, but also to ionic liquids. Moreover, because of its peculiar compositions, NADES can also provide an array of different properties that can be the basis for novel processes. However, such development requires the establishment of a strong knowledge basis on the systems’ fundamental properties. In this view, we have developed and characterized NADES based on choline chloride and betaine combined with natural occurring sugars, such as glucose, xylose and sucrose. For each system, the component molar ratios that provide the lowest eutectic points were determined and were further characterized in terms of their rheological and thermodynamic properties. The rheological properties are highly dependent of the nature of the components. Nevertheless, in general, the results obtained have shown that these systems are highly viscous, withtypical viscosities higher than 1000Pa.s at 20°C and have Newtonian behavior. The viscosity decreases significantly with both temperature and water content and for temperatures higher than 60°C, the systems with 5 wt%  water, the viscosity is typically lower than 1Pa.s. Differential scanning calorimetry (DSC) characterization has shown thatfor the presence of water in the system up to 5 wt.% does not compromise the single phase behavior of the NADES.

The results obtained demonstrate that the NADES properties can be finely tunned by careful selection of its constituents. The knowledge of this properties will be  essential for the development of future sustainable industrial processes.