Control of Rheology and Sedimentation Behavior of Colloidal Suspensions

To establish the preparation method of colloidal suspensions with low viscosity and long term stability against sedimentation, the effects of polymer and surfactant are examined for silica suspensions. The suspensions are flocculated by bridging mechanism, in which one polymer chain is simultaneously adsorbed onto two particles. Since the adsorption affinity of polymer for the silica surfaces is governed by a balance between polymer and surfactant concentrations, two bridging conformations, that is, the reversible bridging and irreversible bridging are induced. In suspensions flocculated by reversible bridging, the interparticle bonds are constantly forming, breaking, and re-forming in a quiescent state and the suspensions behaves as fluids even at very low shear rates. The sedimentation stability is evaluated through the time dependence of intensities of backscattering lights from the suspensions. The fluctuation of backscattering intensity is detected for suspensions flocculated by reversible bridging. The local motion and rearrangement of particles may be possible in the sediment. The reversible bridging is very attractive as a new technique of controlling the viscosity and sedimentation stability of flocculated suspensions.