Effect of Surfactant on the Bridging Conformation of Associating Polymer and Suspension Rheology

Associating polymers which consist of hydrophilic long-chain molecules containing a small amount of hydrophobic groups(hydrophobes) behave as flocculants in aqueous suspensions. The effects of surfactant on the rheological behavior are studied for latex, silica, and mixed suspensions flocculated by associating polymer. Because the hydrophobes are adsorbed onto hydrophobic surfaces and water-soluble chains onto hydrophilic surfaces, two single suspensions are highly flocculated by a bridging mechanism. In latex suspensions, the surfactant molecules force to desorb the polymer chains from the particles and at the same time enhance the micellar formation between the adsorbed chains. As a result, the flow becomes shear-thickening due to the elastic forces generated in extended multichain bridges under shear fields. In silica suspensions, the additions of surfactant cause the viscosity increase which may be attributed to enhancement of micellar formation between the adsorbed chains. By mixing the silica and latex suspensions, the viscosity is substantially reduced and the flow becomes nearly Newtonian. The associating polymer in complex suspensions acts as binder between the silica and latex particles. The hetero-flocculation which leads to the formation of composite particles may be responsible for the viscosity reduction of complex suspensions.