Properties of binary mixtures of a novel natural deep eutectic solvent (glycolic acid + xylitol) and water at several temperatures

The density, viscosity, and conductivity of the binary mixture composed of (glycolic acid + xylitol)(3:1) NaDES and water were measured at atmospheric pressure and different temperatures T  = (303.15 K, 313.15 K, 323.15 K, 333.15 K, 343.15 K). The density and viscosity values decrease with increasing temperature, while the conductivity values increase over the entire concentration range. The binary system's excess molar volumes (V E ) and viscosity deviations (Δη) were calculated and fitted by the fourth-order Kister equation based on the experimental data. With the increase of the water mole fraction, the conductivity values of the system first increase gradually and then decrease dramatically, and the conductivity reaches the highest when the water mole fraction is 0.9548. In addition, the structures of the binary system were characterized by infrared spectra and optimized by quantum chemical simulation. At the molecular level, the amounts and types of hydrogen bonds in the binary system increase by adding water. It is speculated that hydrogen bonding may affect the excess properties of the system.