Comparison of Rheological Behavior of Suspensions Flocculated by Polymer Bridging and Depletion

抄録

The steady shear viscosity, dynamic viscoelasticity, and creep were measured for suspensions flocculated by polymer bridging and depletion. Irrespective of flocculation mechanism, the suspensions are shear-thinning in a wide range of shear rates. However, the elastic properties are quite different. The suspension flocculated by bridging shows a plateau in the frequency-dependent curve of dynamic viscoelastic function. The floc structures with a very long relaxation time are developed over the system. On the other hand, the suspension flocculated by depletion behaves as a viscous liquid without elasticity. The flocs hardly accumulate the elastic energy. The polymer bridges transmit central and transverse forces. However, since the osmotic pressure is responsible for attractive forces in depletion flocculation, the bonds show little resistance with respect to transverse bending forces. Because of shear motion of particles, the strain energy is rapidly dissipated in suspension flocculated by depletion. The elastic properties of flocculated suspensions are determined by the vector nature of bond.