Viscosities of electrolyte solutions

Abstract

The effect of solute–solvent interactions on the viscosity of dilute electrolyte solutions is considered in terms of the solute contribution to the activation free energy, enthalpy or entropy, for viscous flow. Two classes of electrolyte are considered, those involving inorganic ions and those involving larger organic ions such as the tetraalkylammonium salts. The solute contributions to the activation free energies for viscous flow Δμ 2 θ‡ for inorganic electrolytes vary systematically with the charge and radius of the ion in a way that is consistent with a primarily electrostatic effect, increasing linearly with the ionic charge and with the inverse of the ionic radius. In contrast, the Δμ 2 θ‡ values for the tetraalkylammonium halides increase linearly with the cationic volume. For both types of electrolytes, Δμ 2 θ‡ in organic solvents is relatively insensitive to the solvent, while the values for aqueous systems are markedly different from those in the organic solvents.