Structural Dynamics and Transport in Deep Eutectic Solvents

Deep eutectic solvents (DESs) have shown potential in many areas of electrochemical technology like solar cells and redox flow batteries. Their cheap and easy synthesis present a large design space and therefore make them a desirable alternative to toxic and/or expensive solvents currently being used commercially. However, to rationally approach the vast library of possible DESs, structure-property relationships should be developed so that properties of DESs can be predicted simply based off of the molecular structure. To elucidate this, a wide range of techniques were employed, including broadband dielectric spectroscopy, dynamic mechanical spectroscopy, differential scanning calorimetry on a series of carefully selected prototypical DESs and their derivatives. It was observed that slight changes in molecular structure of the components can have large impacts on the dynamics and physicochemical properties. For example, in choline-based DESs, changing the counteranion from chloride to bromide to iodide shifts the eutectic composition to lower ChX composition, slows down the dynamics, and decreases the dc ionic conductivity at each respective eutectic composition.