Stress Relaxation in Entangled Polymer Melts

TL;DR

This paper uses extensive simulations to analyze stress relaxation in entangled polymer melts, testing tube models and confirming the Likhtman-McLeish theory with specific adjustments, advancing understanding of polymer dynamics.

Contribution

It provides a detailed simulation-based validation of tube models for stress relaxation, including parameter-free tests and specific modifications to existing theories.

Findings

Excellent agreement with Likhtman-McLeish theory using double reptation approximation.

Identification of the role of high-frequency modes in contour length fluctuations.

Validation of the primitive path analysis for entanglement length.

Abstract

We present an extensive set of simulation results for the stress relaxation in equilibrium and step-strained bead-spring polymer melts. The data allow us to explore the chain dynamics and the shear relaxation modulus, $G(t)$, into the plateau regime for chains with $Z=40$ entanglements and into the terminal relaxation regime for $Z=10$. Using the known (Rouse) mobility of unentangled chains and the melt entanglement length determined via the primitive path analysis of the microscopic topological state of our systems, we have performed parameter -free tests of several different tube models. We find excellent agreement for the Likhtman-McLeish theory using the double reptation approximation for constraint release, if we remove the contribution of high-frequency modes to contour length fluctuations of the primitive chain.