Defining deep eutectic solvents

When it comes to choosing a solvent for a particular application, researchers and industries have a number of options available to them. One relatively new and growing class of materials is deep eutectic solvents (DESs) – a type of ionic fluid formed from a mixture of at least two substances — which exhibits a melting point that is significantly lower than those of its constituent parts.   

DESs are highly versatile with a wide range of applications, some of which are shared with conventional ionic liquids (room temperature molten salts). Both DESs and conventional ionic liquids are low in volatility, non-flammable, and possess a high ionic strength. Both are tunable and are effective in many conditions, making them an attractive option for solubilizing chemicals, metals, and enzymes. However, DESs stand apart from conventional ionic liquids in that they offer increased ease of preparation and components that are relatively inexpensive.

When it comes to green technologies, some of DESs’ potential uses include: biomass processing, protein stabilization, precious metals recovery, and electrical energy storage, to name a few. Moreover, many DES components can also be derived from bio-based sources.

The first DES system was only reported in 2003, and there is currently no widely accepted criterion to identify whether a particular mixture is a DES. In a paper recently published in the journal Physical Chemistry Chemical Physics, members of Tufts School of Engineering’s Green Energy and Novel Electrolytes Lab (GENELab) introduced a quantitative metric based on molar excess Gibbs energy and proposed a threshold value for it to define a true deep eutectic system. Ultimately, “accurate measurement of the eutectic point temperature and composition is critical for concluding that any mixture be categorized as a DES,” the team wrote.

The paper was authored by PhD candidate Bricker Like, undergraduate alum Christina Uhlenbrock, E22, and GENELab principal investigator Matthew Panzer, Dean of Research for Tufts School of Engineering and professor in the Department of Chemical and Biological Engineering. A seed grant from the Tufts Data Intensive Studies Center supported the research. The data-driven, theoretical project was a fresh venture for the team, which more typically conducts its solution-processed materials research through experimental investigations.

Panzer and fellow researchers in the GENELab seek to understand how solution-processed materials – including ionic liquid- and DES-based gel electrolytes – can be developed and incorporated into novel electrochemical devices. Their work is driven by the global need for safer, cleaner, and more sustainable energy solutions. Like, the first author of the paper on DESs, is a graduate researcher in the lab and a second-year PhD student in chemical engineering. Uhlenbrock graduated from Tufts in 2022 with a BS in chemical engineering and is now pursuing a PhD in chemical engineering at the University of Michigan.

“This particular work represents so much of what makes Tufts unique – collaboration between undergraduate and graduate students, willingness to try new methods and new ideas, and cross-university support,” says Panzer. “It all came together to result in the first time a quantitative metric has been proposed in the literature to define a DES.”

Learn more about the research and about the GENELab.