Effect of Equilibration on Primitive Path Analyses of Entangled Polymers

TL;DR

This study investigates how different equilibration methods influence entanglement density measurements in polymer systems, revealing that local chain stretching significantly affects N_e and that equilibration impacts are less critical for craze extension ratios.

Contribution

It demonstrates that local chain stretching from poor equilibration inflates entanglement density measurements and clarifies the effects of equilibration on polymer structure analysis.

Findings

Equilibration methods can cause a two to threefold difference in N_e values.

Local chain stretching increases apparent entanglement density.

Quenching into a glass state has minimal impact on N_e.

Abstract

We use recently developed primitive path analysis (PPA) methods to study the effect of equilibration on entanglement density in model polymeric systems. Values of N_e for two commonly used equilibration methods differ by a factor of two or three even though the methods produce similar large-scale chain statistics. We find that local chain stretching in poorly equilibrated samples increases entanglement density. The evolution of N_e with time shows that many entanglements are lost through fast processes such as chain retraction as the local stretching relaxes. Quenching a melt state into a glass has little effect on N_e. Equilibration-dependent differences in short-scale structure affect the craze extension ratio much less than expected from the differences in PPA values of N_e.