Modeling Viscosity of Aqueous and Mixed-Solvent Electrolyte Solutions

A comprehensive model has been developed for calculating the viscosity of aqueous or mixed-solvent electrolyte systems ranging from dilute solutions to fused salts. The model incorporates a mixing rule for calculating the viscosity of solvent mixtures and a method for predicting the effect of finite electrolyte concentrations. The mixing rule represents the viscosity of multicomponent solvent mixtures using molar volumes and viscosities of pure components together with binary parameters. The effect of electrolyte concentration on viscosity is modeled by combining a long-range electrostatic term obtained from the Onsager-Fuoss theory, a contribution of individual ions, which is quantified by the JonesDole B coefficients, and a contribution of specific interactions between ions or neutral species. Formulations have been developed for the contributions of individual ions and species-species interactions to account for the effect of multiple solvents. The model accurately reproduces the viscosity of systems such as salts in water, organic or mixed water-organic solvents and aqueous acids or bases up to the pure solute limit.