Prediction of rheometrical and complex flows of entangled linear polymers using the DCR model with chain stretch

We study the rheometrical and complex flow response of the double-convection-reptation (DCR) model with chain stretch proposed recently by Ianniruberto and Marrucci (2002) for entangled linear polymers. The single-and two-mode dierential versions of the model are used, with parameter values identied by Ianniruberto and Marrucci (2002) for a nearly monodis-perse polybutadiene solution. These authors found that the DCR model with stretch predicts well the rheometrical shear behavior of the fluid in the mod-est experimental range of deformation rates. Our calculations for the higher shear rates reached in the simulations of complex flow reveal anomalous or questionable behavior, namely shear-thickening over an intermediate range of shear rates and large chain stretch reached in fast shear flows. This behav-ior is shown to be shared by the original integro-dierential DCR theory, of which the dierential DCR model is actually a mathematical approximation. We also show that the original DCR theory with stretch predicts excessive shear-thinning at high shear rates, while its dierential approximation re-mains stable for all shear rates. Using the Backward-tracking Lagrangian particle method [Wapperom et al. (2000)], we investigate the response of the dierential DCR model in start-up flow through an axisymmetric contrac-Dedicated to Professor G. Marrucci on the occasion of his 65th birthday yAuthor to whom correspondence should be addressed; electronic mail