Facile equilibration of well-entangled semiflexible bead-spring polymer melts

TL;DR

This paper introduces an improved equilibration method for semiflexible polymer melts that combines double-bridging with core-softened potentials, significantly speeding up simulations and enabling analysis of stiffer chains.

Contribution

The authors develop a hybrid simulation approach that overcomes energy barriers in equilibrating semiflexible polymer melts, extending the applicability of the DBH method to stiffer chains.

Findings

Method reduces equilibration time by several times compared to standard DBH.

Enables equilibration of melts with chain lengths up to 40 times the entanglement length.

Provides new expressions for Kuhn length and entanglement length dependent on chain stiffness.

Abstract

The widely used double-bridging hybrid (DBH) method for equilibrating simulated entangled polymer melts [R. Auhl et al., J. Chem. Phys. v. 119, p. 12718, 2003] loses its effectiveness as chain stiffness increases into the semiflexible regime because the energy barriers associated with double-bridging Monte Carlo moves become prohibitively high. Here we overcome this issue by combining DBH with the use of core-softened pair potentials. This reduces the energy barriers substantially, allowing us to equilibrate melts with $N \simeq 40 N_e$ and chain stiffnesses all the way up to the isotropic-nematic transition using simulations of no more than 100 million timesteps. For semiflexible chains, our method is several times faster than standard DBH; we exploit this speedup to develop improved expressions for Kremer-Grest melts' chain-stiffness-dependent Kuhn length $\ell_K$ and entanglement length $N_e$.