Double layer electrical conductivity as a stability criterion for concentrated colloidal suspensions

Abstract

The slightly attractive inter–particle equilibrium potential associated with electrostatically stabilized suspensions of minimum viscosity is described by the DLVO theory and commonly gauged by static ζ-potential measurements, plagued with experimental uncertainties. In this work, the electrokinetic mobility of alumina particles was measured in suspensions prepared with selected solids content and ionic strength, as well as was the electrical conductivity of each suspension and suspending liquid. Particles electrical conductivity was then calculated and related to the colloidal stability described by the DLVO theory, enabling the identification of a processing window for the stability control of concentrated suspensions. The maximum repulsive potential and distance between particles (∼46nm) corresponds to the particles maximum conductivity. When the particles conductivity is zero, the diffuse layer is fully collapsed and they stand at the minimum reversible distance (∼7nm). At the equilibrium conductivity, a potential curve is produced with a secondary attractive minimum of ∼1.5 kT at an inter–particle distance of ∼17nm, as suggested by the DLVO theory and the Equipartition of Energy theorem. The condition for accurate measurement of static ζ-potential occurs at the isoconductivity point between particles and suspending liquid.