Characteristic time and length scales in melts of Kremer-Grest bead-spring polymers with wormlike bending stiffness

TL;DR

This paper develops methods to accurately estimate key dynamic and structural parameters in Kremer-Grest polymer melts with varying stiffness, enabling precise comparisons between theory, experiment, and simulations.

Contribution

It introduces new estimation techniques for Kuhn length, entanglement length, bead friction, and Kuhn times that account for chain stiffness and entanglements.

Findings

Excellent agreement with polymer dynamics theories for monomer displacements.

Validation of methods through shear relaxation modulus in unentangled melts.

Enhanced parameter estimation for better theory-simulation-experiment comparisons.

Abstract

The Kremer-Grest (KG) model is a standard for studying generic polymer properties. Here we have equilibrated KG melts up to and beyond $200$ entanglements per chain for varying chain stiffness. We present methods for estimating the Kuhn length corrected for incompressibility effects, for estimating the entanglement length corrected for chain stiffness, for estimating bead frictions and Kuhn times taking into account entanglement effects. These are the key parameters for enabling quantitative, accurate, and parameter free comparisons between theory, experiment and simulations of KG polymer models with varying stiffness. We demonstrate this for the mean-square monomer displacements in moderately to highly entangled melts as well as for the shear relaxation modulus for unentangled melts, which are found to be in excellent agreement with the predictions from standard theories of polymer dynamics.