Viscosity of Choline Chloride-Based Deep Eutectic Solvents: Experiments and Modeling

Deep eutectic solvents (DESs) have emerged as promising “green” solvents, but their successful industrial application requires relatively low viscosity. DESs prepared from choline chloride and glycols offer such a possibility. Viscosity and density are reported for a number of DESs obtained by mixing choline chloride and a glycol (ethylene glycol, 1,2-propanediol, 1,3-propanediol, and 1,4-butanediol). The measurements were performed at 101.3 kPa, at temperatures between 293.15 and 333.15 K, and for different mole ratios of glycol and choline chloride. The viscosity was measured with a capillary viscometer, while the density was measured by means of a vibrating U-tube densimeter. The density and viscosity data have expanded relative uncertainties of 0.2 and 2.0%, respectively, with a coverage factor of 2. The viscosity of pure glycols was modeled using the extended hard-sphere (EHS) model that has its basis in kinetic theory and the molecular description of the fluid. Each DES was treated as a binary mixture, and the EHS model was used, with a mole average mixing rule, to calculate its viscosity. The measured DES viscosity data were represented with an average absolute deviation of 1.4% and a maximum deviation of 7%.