New Parametric Model for Estimating the Viscosity of Choline Chloride-Based Deep Eutectic Solvents and Their Aqueous Mixtures

Deep eutectic solvents (DESs) derived from choline chloride (ChCl) have attracted significant interest as environmentally friendly alternatives to traditional solvents. However, their wider industrial application is often limited by high viscosity, which is strongly affected by temperature, water content, and the composition of hydrogen-bond donors (HBD). In this study, a new parametric correlation is presented for estimating the viscosity of aqueous ChCl-based DESs over broad composition and temperature ranges. The model combines the Arrhenius viscosity framework with the Grunberg–Nissan mixing rule, explicitly incorporating the effects of hydration and the HBA:HBD molar ratio through a four-parameter formulation. A comprehensive database of 1228 experimental viscosity measurements from various literature sources for eight chemically diverse aqueous ChCl-based DES systems, including monoethanolamine, ethylene glycol, glycerol, phenol, m-cresol, o-cresol, 1,2-propanediol, and 1,3-propanediol, was used for model development. The proposed correlation accurately reproduces experimental viscosities, achieving coefficients of determination between 0.990 and 1.000, with average absolute relative deviations ranging from 6.68% to 10.56%. Unlike existing models that require extensive, system-specific experimental matrices, this model effectively captures the substantial viscosity reduction due to hydration, the temperature dependence of viscous flow, and the influence of HBA:HBD stoichiometry utilizing only four global parameters per DES family based on molar composition.