Elongational flow response of compressible polymer melts

The molecular-level flow response of macromolecules underlies their rheological behavior and affects their processing. The correlation between molecular characteristics, such as polymer rigidity and compressibility, and their macroscopic rheological response remains an open question. With coarse-grained molecular dynamics simulations, the current study explores the effects of polymer rigidity and compressibility on their flow response for both linear and ring polymers. We find that, as for incompressible polymers, the chains extend along the flow direction for both architectures. In contrast to incompressible polymers, the systems undergo a flow-induced transition at high flow rates, in which the viscosity and density increase dramatically, independent of chain length. In ring polymers, at high flow rates, topological links or knots give rise to a large increase in extensional viscosity before the onset of the flow-induced transition.