Effect of adsorption affinity of polymers on the viscosity behavior of suspensions

The viscosity behavior of suspensions flocculated by bridging was examined as a function of adsorption affinity of polymers for the particle surface. The polymer chains having strong affinity form fragile bridges between particles as a result of irreversible adsorption. Because the flocs are broken down on the application of shear fields, the flow is shear-thinning. The decrease in the adsorption affinity by the addition of small amounts of surfactant causes the reversible adsorption. The suspensions flocculated by reversible bridging are Newtonian at low shear rates because the polymer bridges are forming and breaking in a quiescent state. When the coil size is comparable to the particle diameter, the suspensions show shear-thickening flow in high shear fields. The shear thickening is induced by the elastic effects of extended bridges. The flow profiles of suspensions flocculated by polymer bridging are controlled by changing the adsorption affinity of polymers. (C) 1998 Academic Press