Volumetric Properties of Binary and Ternary Mixtures of Choline Chloride-Based Deep Eutectic Solvent with Water at Several Temperatures

Abstract Densities were measured for a series of choline chloride-based deep eutectic solvents (DESs) mixed with water over the entire composition range at several temperatures. The investigated systems include DESs formed with acids, polyols, and thiourea, as well as ternary DESs containing mixed hydrogen bond donors. From the experimental density data, excess molar volumes (VmE) were calculated and correlated using the Redlich–Kister polynomial equation. The excess molar volumes are strongly dependent on composition, temperature, and they deviate significantly from ideality. For all the systems positive VmE values were found, indicating the presence of strong specific interactions and effective molecular packing following mixing. Variations in H-bonding and structural effects related to the nature and stoichiometry of the hydrogen bond donors are reflected in differences in the magnitude and position of VmE extrema. These findings provide reliable volumetric data and contribute to a better understanding of intermolecular interactions in DES–water mixtures.