Viscosity of electrolyte solutions: a mode-coupling theory

Abstract

We present a versatile theoretical method for calculating the steady-state viscosity and shear relaxation function of strong electrolyte solutions. In this method, the ions are described on a primitive model level as charged Brownian spheres, and the essential ion-ion hydrodynamic interactions (HIs) are accounted for in the shear relaxation effect of the ionic atmosphere. The method combines a many-component mode-coupling theory (MCT) approach by Nägele et al (1998 J. Chem. Phys. 108 9893) with a simplified solution scheme, leading to an analytic expression for the shear relaxation contribution to the viscosity. This expression accounts for both the excluded volumes of the ions and their HIs. We show that the limiting law results for the viscosity of electrolyte mixtures by Falkenhagen and by Onsager and Fuoss are recovered at very low concentrations, and we discuss HIs corrections appearing at higher concentrations. Our numerical results for a 1:1 electrolyte reveal a strong enlargement of the viscosity caused by the HIs. The high-frequency viscosity gives the largest contribution to the total viscosity at higher concentrations.

Electrokinetic and hydrodynamic properties of charged-particles systems

“…At larger n T , the reduction of the conductivity by the relaxation mechanism becomes comparatively large to that caused by the short-time electrophoretic mechanism. As shown in [68], both the short-time and relaxation parts of Λ, and of the viscosity, are considerably affected by the HIs. At very low concentrations, the DFOF limiting law result for the conductivity is recovered by the MCT-HIs scheme.…”

“…In a series of papers, using linear response theory we have developed a unifying MCT method for calculating linear conduction-diffusion [67,68] and viscoelastic [68,69] properties of non-dilute strong electrolyte solutions. This method builds on earlier work where a general MCT for the dynamic structure factor of Brownian particle mixtures with HIs has been developed [70][71][72].…”

“…The predicted coefficients for stick hydrodynamic BC on the PM ion surfaces agree well with experimental data for the electrolyte conductivity and viscosity, for ion concentrations extending even up to two molar. To analyze the dynamic influence of ion hydration shells, [68] includes a discussion on the significance of mixed stick-slip hydrodynamic surface boundary conditions, and on the effect of solvent permeability.…”

“…A thorough description of the MCT-HIs method with numerous numerical results is contained in [67][68][69]. To illustrate the method, Figs.…”

Interference mode-locking of 2D magnetized colloids driven by dc and ac forces in periodic pinning arrays

“…Using external fields (e.g., magnetic fields and laser-optical fields [2,10]), we can track and control the movement of colloidal particles, thereby gaining an insight into the microrheological and viscoelastic properties of colloidal particles and polymer solvents as well as biological cells [11][12][13][14]. In general, external fields will cause the equilibrium system into a non-equilibrium moving state, and most studies have been devoted to the responses of simple 2D systems [9].…”