The Curious Case of Hydrophobic Deep Eutectic Solvents: A Story on the Discovery, Design, and Applications

Hydrophobic deep eutectic solvents (DESs) are a new generation of water immiscible solvents that have been presented in the literature for the first time in 2015. These solvents have been used for many applications. Here, an overview is given regarding hydrophobic DESs with their physicochemical properties, applications, and the challenges and limitations that the field currently is experiencing. First, a general introduction and an introduction to hydrophobic DESs are presented to explain more about DESs, their origin, and hydrophobic ones. Here, also, an overview of all the hydrophobic DESs presented in the literature is given. After the introduction, physicochemical properties such as density, viscosity, melting point, degradation temperature, volatilities, and solvatochromic properties are discussed. It is continued with the discussion of 21 different applications of hydrophobic DESs. In general, applications related to liquid–liquid extractions, liquid–liquid microextractions, formation of two and three phase systems, removal of components from leaves, gas–liquid extractions, formation of hydrogels, membrane formation, centrifugal partition chromatography, formation of a ferrofluid, coating, photoluminescence, and dye-sensitized solar cells, and catalysis have been investigated. Finally, challenges and limitations of hydrophobic DESs are discussed.