Disentanglement in polymer liquids: additive manufacturing, entanglement dynamics, and shear banding.

Tube models of entangled polymers can successfully describe many aspects of both linear and non-linear rheology of polymer melts. The tube is usually modeled by a number of constraints or entanglements Z, which in the original Doi-Edwards model were assumed to be fixed in number. Recent simulations, and potentially experiments, show that polymers can disentangle in flow. This has been predicted by Marrucci and Ianniruberto as as due to Convected Constraint Release (CCR), controlled by a parameter β. A large enough β leads to a stable constitutive relation between shear stress and shear rate. Tube models have recently been modified (by several groups) to incorporate a dynamical equation of motion for entanglements, coupled to the polymer conformation. I will discuss several recent results on the effects of disentanglement, both as controlled by the CCR parameter in models, or as measured directly in molecular dynamics simulations, including (1) the effects on additive manufacturing, (2) the behaviour under the dynamical change of flows, (3) the relation of the CCR parameter to polymer flexibility, (4) and predictions for how shear banding is more likely for smaller β (corresponding to more flexible polymers) and larger entanglement numbers Z.