(713c) The Discovery of Novel Hydrophobic DES-Water Emulsions

We present the first experimental realization of an emulsion of a deep eutectic solvent (DES) in water. DESs are a new, innovative class of solvents presented in the literature for the first time in 2003.^[1] A DES is the combination of two or more solid components, which self-associate via hydrogen bonding and presumably Van der Waals forces forming a liquid phase upon the formation of the DES.^[2] Compared to regular solvents, DESs have the advantage that the physical properties of the solvent can be tuned through the selection of the components. Compared to ionic liquids, DESs can be prepared easily by mixing the two solid components at moderate temperatures and can be constructed from readily-available biorenewable compounds.

Until 2015 all DESs found in literature were hydrophilic, due to the high amount of hydrogen bonding groups present in the components investigated to form DESs. It was this year when a number of us reported hydrophobic DESs for the first time. These hydrophobic DESs consisted of decanoic acid and a range of quaternary ammonium salts and were used for the removal of fatty acids from water.^[3] A few months later in 2015 another publication reported the use of hydrophobic DESs for the extraction of biomolecules from an aquatic environment.^[4]

Recently, more publications regarding hydrophobic DESs were presented. One of these investigations focused on the removal of metal ions from water with a DES composed of decanoic acid and lidocaine in a 2:1, 3:1 and a 4:1 ratio,^[5] while other research focused on the capture of CO₂ with the hydrophobic DESs composed of decanoic acid and quaternary ammonium salts.

A disadvantage of many extraction processes is, however, the slow extraction due to limited interfacial area between DES and water. We show that this can be tremendously improved by employing emulsions of DES in water, stabilized by suitable surface active agents. Additionally, we investigate the fundamental properties of these novel emulsions, detailing droplet size, interfacial tension, and adsorption density.

References

[1] A. P. Abbott, G. Capper, D. L. Davies, R. K. Rasheed, and V. Tambyrajah, Chemical Communications, 2003, 70–71.

[2] M. Francisco, A. van den Bruinhorst, and M. C. Kroon, Angew. Chem. Int. Ed., 2013, 52, 3074–85.

[3] D. J. G. P. van Osch, L. F. Zubeir, A. van den Bruinhorst, M. A. A. Rocha, and M. C. Kroon, Green Chemistry, 2015, 17, 4518–4521.

[4] B. D. Ribeiro, C. Florindo, L. C. Iff, M. A. Coelho, and I. M. Marrucho, ACS Sustainable Chemistry & Engineering, 2015, 3, 2469–2477.

[5] D. J. G. P. van Osch, D. Parmentier, C. H. J. T. Dietz, A. van den Bruinhorst, R. Tuinier, and M. C. Kroon, Chemical Communications, 2016, 52, 11987–11990.