A nonlinear elastic model for shear thickening of suspensions flocculated by reversible bridging

The flow of suspensions flocculated by reversible bridging of polymer with weak affinity for the particle surface is Newtonian in the limit, of zero s hear rate, shear-thickening at moderate shear rates, and plastic implies th e polymer bridges are constantly forming and breaking in a quiescent state. The stress after cessation of steady shear exponentially relaxes at long t imes. The relaxation time is not affected, by the sheer rate. The strain-de pendent curve of storage modulus at a constant frequency shows a rapid incr ease when the strain is increased above a critical level. The critical stra in is independent of frequency. Therefore, the shear thickening may be prim arily attributed to the elastic effect of extended bridges. Since the polym er coils are forced to desorb at some degree of extension, the suspensions become nearly plastic at high shear rates. The intrinsic mechanism of sheer -thickening flow far suspensions flocculated by reversible polymer bridging is the nonlinear elasticity due to entropy effect of extended bridges and forced desorption due to hydrodynamic effect. By combination of the nonline ar elasticity and single relaxation time, a rheological model is derived to quantitatively express the shear-thickening flow. The model prediction and experimental results are in good agreement.