Entanglement kinetics in polymer melts are chemically specific

TL;DR

This study examines how entanglement dynamics in polymer melts depend on chemical structure, confirming universality in recovery timescales and revealing how a key parameter varies with molecular properties, aiding understanding of shear banding.

Contribution

It introduces a chemically specific analysis of entanglement kinetics, linking molecular parameters to disentanglement behavior in polymer melts.

Findings

Entanglements recover on the retraction timescale, not the reptation timescale.

The convective constraint release parameter $eta$ is independent of molecular weight.

$eta$ increases with the ratio of Kuhn length to packing length as $(b_K/p)^{1.9}$.

Abstract

We investigate the universality of entanglement kinetics in polymer melts. We compare predictions of a recently developed constitutive equation for disentanglement to molecular dynamics simulations of both united-atom polyethylene and Kremer-Grest models for polymers in shear and extensional flow. We confirm that entanglements recover on the retraction timescale, rather than the reptation timescale. We find that the convective constraint release parameter $\beta$ is independent of molecular weight, but that it increases with the ratio of Kuhn length $b_K$ to packing length $p$ as $\beta\sim (b_K/p)^\alpha$, with an exponent $\alpha=1.9$, which may suggest that disentanglement rate correlates with an increase in the tube diameter. These results may help shed light on which polymers are more likely to undergo shear banding.