A Nonlinear Elastic Model for Shear Thickening of Suspensions Flocculated by Reversible Bridging

Abstract

The flow of suspensions flocculated by reversible bridging of polymer with weak affinity for the particle surface is Newtonian in the limit of zero shear rate, shear-thickening at moderate shear rates, and plastic with a constant stress independent of shear rate in high shear fields. The Newtonian flow implies that the polymer bridges are constantly forming and breaking in a quiescent state. The stress after cessation of steady shear exponentially relaxes at long times. The relaxation time is not affected by the shear rate. The strain-dependent curve of storage modulus at a constant frequency shows a rapid increase when the strain is increased above a critical level. The critical strain is independent of frequency. Therefore, the shear thickening may be primarily attributed to the elastic effect of extended bridges. Since the polymer coils are forced to desorb at some degree of extension, the suspensions become nearly plastic at high shear rates. The intrinsic mechanism of shear-thickening flow for suspen...