On the rheological modeling of associative polymers

The viscoelastic behavior of a commercial hydrophobic alkalisoluble emulsion (HASE) associative polymer in small-amplitude oscillatory, steady, and unsteady simple-shear flows is analyzed with a model that couples the upper-convected Maxwell constitutive equation with a kinetic equation that accounts for structural changes induced by the flows. A spectrum of relaxation times is considered in the prediction of rheological properties to account for the association dynamics between hydrophobic groups along the HASE backbone and physical entanglements. Viscoelastic response is similar to that of a transient network assembled through hydrophobic associations, where the kinetics of chain breakage and reformation is consistent with classical descriptions of transient network formulations. The model accounts for deviations from the Cox-Merz rule and predicts observed limiting behaviors at high strain rates in stress relaxation and inception of shear flow.