Chain retraction in highly entangled stretched polymer melts

TL;DR

This study uses computer simulations to examine how highly entangled polymer melts relax after deformation, revealing weaker chain retraction than theoretical models predict and proposing experimental tests for validation.

Contribution

It provides a detailed simulation analysis of chain retraction in entangled polymer melts, challenging existing theoretical predictions and suggesting new experimental approaches.

Findings

Chain retraction occurs immediately after deformation.

Observed contraction is weaker than GLaMM model predictions.

2D scattering function expansion aligns qualitatively with GLaMM predictions.

Abstract

We use computer simulations to study the relaxation of strongly deformed highly entangled polymer melts in the non-linear viscoelastic regime, focusing on anisotropic chain conformations after isochoric elongation. The Doi-Edwards tube model and its GLaMM extension, incorporating contour length fluctuation and convective constraint release, predict a retraction of the polymer chain extension in all directions, setting in immediately after deformation. This prediction has been challenged by experiment, simulation, and other theoretical studies, questioning the general validity of the tube concept. For very long chains we observe the initial contraction of the chain extension parallel and perpendicular to the stretching direction. However, the effect is significantly weaker than predicted by the GLaMM model. We also show that the first anisotropic term of an expansion of the 2D scattering function qualitatively agrees to predictions of the GLaMM model, providing an option for direct experimental tests.