Entanglement on nucleation barrier of polymer crystal

TL;DR

This paper develops a theoretical model incorporating entanglement effects to better understand polymer nucleation, supported by molecular dynamics simulations showing trends opposite to classical theory.

Contribution

It introduces an entanglement free energy term into nucleation theory, addressing the unique role of entanglement in polymer crystallization.

Findings

Nucleation barriers vary with entanglement density.

Classical nucleation theory predictions are contradicted by simulations.

The new model explains previously unresolved nucleation phenomena.

Abstract

We propose a theoretical approach to quantitatively account for the role of entanglement in the nucleation of polymer melts, which is the unique feature of polymer differentiated from small molecules. By performing molecular dynamics simulations, we obtain the nucleation barriers of polymer systems with different entanglement densities, which exhibits an opposite trend compared to the prediction of the classic nucleation theory (CNT). To amend the deficiency of the CNT in polymer crystallization, we introduce the entanglement free energy to reflect the role of entanglement in polymer nucleation. Specifically, the polymer nucleation not only involves free energies of monomers inside and on the surface of a nucleus as considered in the CNT, but also affects the entanglement network around the nucleus. Our theoretical approach provides a reasonable interpretation for the unsolved nucleation phenomena of polymers in simulations and experiments.