Deep Eutectic Solvent with Thermo-Switchable Hydrophobicity

A deep eutectic solvent (DES) that becomes hydrophobic upon increasing the temperature is presented for the first time. The aqueous solution of this DES composed of lidocaine, an amphiphilic amine, and oleic acid forms a single transparent liquid phase at ambient temperature. A small increase in temperature triggers an abrupt phase separation while the solvent crosses the lower critical solution temperature (LCST). Considering that both ammonium and oleate ions are more soluble in water than their neutral form, the abrupt separation is induced by a decrease of the ionicity. An IR spectroscopy study established a correlation between the phase separation and the decrease of the concentration of ions. In addition, this DES has the ability to extract several dyes from water very efficiently.