Shear Banding in Entangled Polymer Melts: Dependence on the Effectiveness of Flow-Induced Constraint Release

The Doi-Edwards tube theory of polymer dynamics predicts an unstable constitutive curve for all entangled polymer liquids, which is a signature of shear banding, in which a homogeneous fluid separates into layers with different shear rates under flow. However, experiments indicate that banding occurs only in certain polymers and only for large entanglement numbers Z. The incorporation of convective constraint release (CCR) of entanglements into tube models can eliminate the constitutive instability for less-entangled polymers, depending on the rate of entanglement removal. This rate is proportional to the CCR parameter β, which has recently been shown to increase with the stiffness of the polymer chain [1]. We use a recent extension of the Rolie-Poly tube model that incorporates CCR as well as the kinetics of entanglements [2] to predict which combinations of entanglement number Z and CCR rate parameter β lead to shear banding. We compare these predictions to non-equilibrium MD simulations of semiflexible bead-spring polymers of varying flexibility and find surprisingly close agreement with the predictions of the model.

[1] Dolata, Cunha, O’Connor, Hopkins, and Olmsted, ACS Macro Letters 13, 896 (2024).

[2] Dolata and Olmsted, J. Rheology 67, 269 (2023).