Physicochemical properties of deep eutectic solvents: A review

Deep eutectic solvents are a unique type of solvent with interesting physical properties, which made them comply with the green solvents criteria such as safety, non-toxicity in case of natural DESs, non-flammability, non-volatility, thermal stability, sustainability, biodegradability, and low cost. In this review, the physicochemical characteristics of deep eutectic solvents under the effect of molar ratio of HBAs/HBDs, size of anion, alkyl chain length, and molar mass on the melting point, density, viscosity, conductivity, surface tension, and refractive index have been revealed. Moreover, the polarity, pH, toxicity, biodegradability, and effect of water on the formation of DESs have been illustrated.