A model for the nonlinear rheology of associating polymers

Theories for transient networks formed by associating telechelic polymers require that the kinetics of chain detachment and reattachment processes are somehow specified. We propose here very simple choices for such kinetics, that are nevertheless based on plausible molecular mechanisms. Specific evolution equations are then formulated for the populations of both elastically-active chains and chains temporarily detached from the network. By using typical closure approximations, the rheological model is finally elaborated into a set of ordinary differential equations. For steady shear flows, these nonlinear equations predict shear thickening at moderate shear rates followed by shear thinning at higher shear rates, in agreement with observations. In the limit of slow flows, analytical expressions for the viscosity and the relaxation times are also obtained. (C) 2000 Elsevier Science B.V. All rights reserved.