Thermodynamic Study of Choline Chloride-Based Deep Eutectic Solvents with Water and Methanol

To study the effects of type and content of cosolvent as well as temperature on the properties of two well-known deep eutectic solvents (DESs), i.e., ChCl/EG (choline chloride + ethylene glycol at a molar ratio of 1:2) and ChCl/Gly (choline chloride and glycerol at a molar ratio of 1:2), the density and viscosity of the mixtures of ChCl/EG or ChCl/Gly with methanol (MeOH) and water (H₂O) over the whole compositional range at temperatures from 288.15 to 323.15 K as well as the molar enthalpy of mixing for the mixtures of ChCl/EG or ChCl/Gly + MeOH were experimentally measured. The excess molar volume, viscosity deviation, and excess molar Gibbs energy of activation were further calculated to study the effects of temperature, types of cosolvent and DES, and their contents on the nonideal behavior of these pseudobinary systems. The molar enthalpy of mixing measured in this work was further compared with those with H₂O as the cosolvent reported in the literature. It shows that the mixing of these two DESs with MeOH is exothermic, which is opposite compared to those mixed with H₂O. Additionally, the nonrandom two-liquid model and Gibbs-Helmholtz equation were combined to represent the experimental results of the enthalpy of mixing.