DILATANT FLOW OF FLOCCULATED SUSPENSIONS

The polymer coil whose size is comparable in solution to particle diameter makes a flexible bridge between two particles. The steady-shear viscosity and dynamic viscoelasticity were measured for suspensions flocculated by the bridging mechanism. When both the particle and polymer concentrations are increased beyond some critical levels, the suspensions show unique flow profiles consisting of Newtonian viscosity in the limit of zero shear rate, dilatant flow at moderate shear rates, and pseudoplastic flow at high shear rates. The existence of Newtonian viscosity indicates that polymer bridges are constantly forming, breaking, and re-forming in a quiescent state. Therefore, the adsorption-desorption process is considered to be reversible. When the shear rate is increased, the polymer coils are rapidly extended and the restoring forces cause an increase in resistance to flow. Although the dilatant flow is primarily attributed to the extension of bridge, the network structure of unbounded flocs is essential. The combination effect of extension of flexible bridges between particles and formation of network structure is discussed on the basis of the percolation theory.