A Comprehensive Study of Density, Viscosity, and Electrical Conductivity of Choline Halide-Based Eutectic Solvents in H₂O

This work focused on how the addition of H₂O influences the properties of eutectic solvents with different anions and hydroxyl group numbers. Choline halides (ChCl, ChBr, and ChI) were chosen as the hydrogen bond acceptors, while ethylene glycol (EG) and glycerol (Gly) acted as the hydrogen bond donors at a 1:2 molar ratio. The density and viscosity measurements were conducted for four out of six systems, specifically those containing Br^- and I^-, across appropriate temperature and concentration ranges. Moreover, electrical conductivities were measured for all six systems. The excess molar volume and viscosity deviation were obtained and combined with those of (ChCl/EG + H₂O) and (ChCl/Gly + H₂O) for further analysis. The excess molar volume and the viscosity deviation both indicate that the contribution of H-bonding interactions is greater than packing effects, and the strengths of the H-bonding interaction are in the orders of Cl^- > Br^- > I^- and Gly > EG. Under the competition of ion concentration, viscosity, and ion interaction, the specific conductivity of the eutectic solvent solution first increases to a maximum and then decreases.