Numerical calculation of free-energy barriers for entangled polymer nucleation

TL;DR

This study uses computer simulations to analyze the nucleation process in entangled polymers, revealing how molecular weight influences nucleation rates and free-energy barriers during crystallization.

Contribution

It introduces a hybrid Monte Carlo simulation approach to compute nucleation free-energy barriers in entangled polymers, highlighting the effects of molecular weight.

Findings

Critical nucleus size is independent of molecular weight.

Nucleation rate decreases as molecular weight increases.

Intramolecular growth is not a major factor in crystallization.

Abstract

The crystallisation of entangled polymers from their melt is investigated using computer simulation with a coarse-grained model. Using hybrid Monte Carlo simulations enables us to probe the behaviour of long polymer chains. We identify solid-like beads with a centrosymmetry local order parameter and compute the nucleation free-energy barrier at relatively high supercooling with adaptive-bias windowed umbrella sampling. Our results demonstrate that the critical nucleus sizes and the heights of free-energy barriers do not significantly depend on the molecular weight of the polymer; however, the nucleation rate decreases with increasing molecular weight. Moreover, an analysis of the composition of the critical nucleus suggests that intramolecular growth of the nucleated cluster does not contribute significantly to crystallisation for this system.