Density, Viscosity, and Refractive Index of a Choline Chloride plus D-(-)-Fructose Deep Eutectic Solvent plus Water Mixture at Different Temperatures: An Experimental Study and Thermodynamic Modeling

In the present study, first, the deep eutectic solvent (DES) of choline chloride + D-(-)-fructose was prepared using the heating method. Then, its physical properties including density, viscosity, and refractive index were experimentally measured at temperatures in the range of 283.15-343.15 K and a full composition range of DES at atmospheric pressure (83.09 kPa). The values of these three properties decrease with an increase in temperature, while the mole fraction has a nonlinear effect on these properties. For the density and refractive index, an increase in the mole fraction of DES to 0.3 causes a sharp increase in these physical properties, while from 0.3 to 1, this increase occurs slowly. For viscosity, increasing the mole fraction of DES has little effect at first, but at high mole fractions of DES, a sharp increase in viscosity occurs. In addition, the sharp change in the viscosity of DES depends on the temperature so that at low temperatures, this phenomenon occurs faster. So, adding water to DES will tailor the viscosity of the mixture to facilitate its applications. A polynomial equation was used to describe the density and refractive index as a function of temperature and mole fraction. Experimental viscosity was fitted to the Vogel-Tammann-Fulcher (VTF) equation. Using the measured data, in sequence, the values of excess molar volume (VmEx), viscosity deviation (Delta eta), and refractive index deviation (Delta nD) were calculated. The Redlich-Kister polynomial equation, finally, was used to correlate the values of VmEx, Delta eta, and Delta nD.