Molecular Dynamics Simulation of Entangled Melts at High Rates: Identifying Entanglement Lockup Mechanism Leading to True Strain Hardening

In the present work, molecular dynamics simulations are carried out based on

the bead-spring model to indicate how the entanglement lockup manifests in

the late stage of fast Rouse-Weissnberg number (WiR>>1) uniaxial melt

stretching of entangled polymer melts. At high strains, distinct features show

up to reveal the emergence of an increasingly tightened entanglement

network. Chain tension can build up, peaking at the middle of the chain, to a

level for chain scission, through accumulated interchain interactions, as if

there is a tug-of-war ongoing for each load-bearing chain. Thanks to the

interchain uncrossability, network junctions form by the pairing of two or

more hairpins. It is hypothesized that the interchain entanglement at

junctions can lockup through prevailing twist-like interchain couplings as long

as WiR > 9. In this limit, a significant fraction of chains act like cyclic chains to

form a network held by interchain uncrossability, and appreciable chain

tension emerges.