Equilibration of High Molecular-Weight Polymer Melts: A Hierarchical Strategy

TL;DR

This paper presents a hierarchical backmapping strategy to efficiently generate equilibrated high molecular-weight polymer melts with microscopic detail, using sequential coarse-graining and local relaxation steps, scalable to very long chains.

Contribution

A novel hierarchical backmapping method that combines coarse-grained Monte Carlo and molecular dynamics to efficiently equilibrate high molecular-weight polymer melts.

Findings

Successfully equilibrated systems with up to 1000 chains of 2000 monomers.

The method's efficiency is independent of molecular weight, depending only on system size.

Confirmed robustness through structural and conformational property analysis.

Abstract

A strategy is developed for generating equilibrated high molecular-weight polymer melts described with microscopic detail by sequentially backmapping coarse-grained (CG) configurations. The microscopic test model is generic but retains features like hard excluded volume interactions and realistic melt densities. The microscopic representation is mapped onto a model of soft spheres with fluctuating size, where each sphere represents a microscopic subchain with $N_{\rm b}$ monomers. By varying $N_{\rm b}$ a hierarchy of CG representations at different resolutions is obtained. Within this hierarchy, CG configurations equilibrated with Monte Carlo at low resolution are sequentially fine-grained into CG melts described with higher resolution. A Molecular Dynamics scheme is employed to slowly introduce the microscopic details into the latter. All backmapping steps involve only local polymer relaxation thus the computational efficiency of the scheme is independent of molecular weight, being just proportional to system size. To demonstrate the robustness of the approach, microscopic configurations containing up to $n=1000$ chains with polymerization degrees $N=2000$ are generated and equilibration is confirmed by monitoring key structural and conformational properties. The extension to much longer chains or branched polymers is straightforward.