Understanding Structure-Property Relationships in Deep Eutectic Solvents (DESs)

Deep eutectic solvents (DESs) are an emerging class of highly tunable solvents with unique properties such as high solvent strength, wide electrochemical and thermal stability windows, nonflammability, and biodegradability/nontoxicity. These have given them potential as in many areas, including electrochemical technology applications like redox flow batteries and solar cells. However, they are held back by their relatively high viscosities and low conductivities. For this reason, it would be useful to understand how to improve these materials for target applications based off their molecular identity. Here, we use a variety of experimental techniques to study a series of choline-based DESs which are systematically varied by functional group and its position to examine the changes in local structure and dynamics and that effect on macroscopic properties. Generally, we observe that slight structural changes result in significant changes in the eutectic composition, viscosity, and dc ionic conductivity.