Surface Forces Arising from Polymers and Small Ionic Additives - Yield Stress and Zeta Potential Relationship

Abstract

The effects of polymers and small ionic additives on the surface forces between metal and non-metal oxide particles in water were studied by measuring the yield stress and zeta potential of colloidal suspensions. Alumina and alumina-coated titania dispersions with adsorbed polyacrylate showed a decrease in maximum yield stress due to the formation of steric barriers. Adsorbed phosphate on alumina increased the maximum yield stress of low surface area alumina dispersions due to intermolecular hydrogen bonding between the phosphate layers. The maximum yield stress however decreased for adsorbed phosphate on high surface area zirconia dispersions due to its very rough surface morphology limiting the extent of intermolecular hydrogen bonding between adsorbed phosphate layers. Adsorbed polyethylenimine of different molecular weight on silica showed a 20-68 times increase in maximum yield stress. Forces responsible includes charged patch-bridging attraction and particle bridging via hydrogen bond depending on surface coverages. In all cases, the yield stress-DLVO force relationship is generally obeyed although for alumina and alumina-coated titania dispersions with adsorbed polyacrylate, it is true only for the positively charged region. The relative importance of these non-DLVO forces affected the values of the critical zeta potential.