Influence of counterion type and diffusion on the primary electroviscous effect

A review of our latest results on the primary electroviscous effect is presented here. The aim is to incorporate several electrokinetic topics (electrophoretic mobility, zeta potential, primary electroviscous coefficient, counterion diffusion, etc.) into the discussion. In this way, a deeper knowledge of some phenomena involved in electrokinetics can be achieved by relating ideas and contributions from different scopes. First, some previous results are revised and commented. Then, several interesting findings regarding counterion diffusion and type are reported, including theoretical predictions and experimental data when possible. Colloidal suspensions of polystyrene latex have been used as the experimental system, which has been characterized electrokinetically, making electrophoresis, size and viscosity measurements. Zeta potential has been obtained by different conversion theories and used for the theoretical calculations of the primary electroviscous effect using Boothʹs and Watterson–Whiteʹs theories. A good agreement is generally obtained between experiment and theory. Reduction of counterion diffusion has been considered as a possible explanation for the theoretical underestimation of the primary electroviscous effect. It has been shown that the inclusion of the real diffusion coefficients of the ionic species present in the double layer, instead of the ones at infinite dilution, improves the agreement. In order to study the influence of the type of electrolyte ions composing the double layer, four electrolytes have been used. Electrophoretic mobility against electrolyte concentration has been measured and zeta potentials have been calculated. Then, viscosity measurements have been carried out to find the primary electroviscous effect, which displays, within the concentration range studied, similar values for the different electrolytes.