Effect of the size and affinity for water of excluded ions on interparticle forces

The influence of non-adsorbed (excluded), indifferent electrolyte cations (Li+, Na+, K+ and Cs+ and tetralkylammonium cations; alkyl=methyl, ethyl, propyl, butyl) on the viscosity of silica and alumina slurries was studied. Silica and alumina slurries were studied at and below the pH of the isoelectric point where the indifferent electrolyte cations would not be expected to adsorb significantly on the surface. Slurries prepared with ions with the highest affinity for water (such as lithium) always exhibited the highest viscosity. It appears that a lyotropic sequence effect for excluded ions exists and is correlated to the hydration of ions and surfaces. Direct spectroscopic measurements are needed to test this assumption.