Strain hardening in bidisperse polymer glasses: Separating the roles of chain orientation and interchain entanglement

TL;DR

This study uses simulations to disentangle the effects of chain orientation and entanglement on strain hardening in glassy polymers, revealing that chain orientation is locally determined and entanglements have an indirect role.

Contribution

It demonstrates that chain orientation and strain hardening are primarily governed by local interactions, with entanglements playing a minimal direct role in the strain range studied.

Findings

Chain orientation is consistent across monodisperse and bidisperse systems.

Stress in mixtures equals the weighted average of monodisperse stresses.

Entanglements have at most an indirect effect on strain hardening.

Abstract

The effects of entanglement and chain orientation on strain hardening in glassy polymers are separated by examining mixtures of chains with different lengths. Simulations show that the orientation of a molecule of a given chain length is the same in monodisperse systems and bidisperse mixtures, even when entangled and unentangled chains are mixed. In addition, the stress in mixtures is equal to the weighted average of the stresses in monodisperse systems. These results indicate that chains contribute independently to strain hardening, that chain orientation is determined by local interactions with the surrounding glass, and that entanglements play at most an indirect role in strain hardening in the range of strains typically studied. We discuss these results in the context of recent microscopic theories.