Multiscale equilibration of highly entangled isotropic model polymer melts

TL;DR

This paper introduces a multiscale computational method for efficiently preparing equilibrated, highly entangled polymer melts, enabling detailed simulations across multiple length scales with high accuracy.

Contribution

A novel multiscale approach combining lattice Monte Carlo, theoretical modeling, and force-capped simulations to generate equilibrated polymer melts across all relevant length scales.

Findings

Successfully generated large-scale equilibrated polymer melts with high entanglement density.

Achieved chain statistics in agreement with literature across all length scales.

Demonstrated the method's efficiency and accuracy for complex polymer systems.

Abstract

We present a computationally efficient multiscale method for preparing equilibrated, isotropic long chain model polymer melts. As an application we generate Kremer-Grest melts of $1000$ chains with $200$ entanglements and $25000$-$2000$ beads per chain, which cover the experimentally relevant bending rigidities up to and beyond the limit of the isotropic-nematic transition. In the first step, we employ Monte Carlo simulations of a lattice model to equilibrate the large-scale chain structure above the tube scale while ensuring a spatially homogeneous density distribution. We then use theoretical insight from a constrained mode tube model to introduce the bead degrees of freedom together with random walk conformational statistics all the way down to the Kuhn scale of the chains. This is followed by a sequence of simulations with carefully parameterized force-capped bead-spring models, which slowly introduce the local bead packing while reproducing the larger scale chain statistics of the target Kremer-Grest system at all levels of force-capping. Finally we can switch to the full Kremer-Grest model without perturbing the structure. The resulting chain statistics is in excellent agreement with literature results on all length scales accessible in brute-force simulations of shorter chains.