Static and dynamic properties of large polymer melts in equilibrium

TL;DR

This study investigates the static and dynamic properties of large semiflexible polymer melts, confirming theoretical predictions and providing detailed insights into their behavior using molecular dynamics simulations.

Contribution

It offers a comprehensive analysis of equilibrium properties of semiflexible polymer melts, validating theoretical models and linking entanglement length to mechanical properties.

Findings

Mean square internal distance matches ideal chain predictions.

Reptation and Rouse theories accurately describe monomer and chain motion.

Entanglement length predicts plateau modulus consistent with stress measurements.

Abstract

We present a detailed study of the static and dynamic behavior of long semiflexible polymer chains in a melt. Starting from previously obtained fully equilibrated high molecular weight polymer melts [{\it Zhang et al.} ACS Macro Lett. 3, 198 (2014)] we investigate their static and dynamic scaling behavior as predicted by theory. We find that for semiflexible chains in a melt, results of the mean square internal distance, the probability distributions of the end-to-end distance, and the chain structure factor are well described by theoretical predictions for ideal chains. We examine the motion of monomers and chains by molecular dynamics simulations using the ESPResSo++ package. The scaling predictions of the mean squared displacement of inner monomers, center of mass, and relations between them based on the Rouse and the reptation theory are verified, and related characteristic relaxation times are determined. Finally we give evidence that the entanglement length $N_{e,PPA}$ as determined by a primitive path analysis (PPA) predicts a plateau modulus, $G_N^0=\frac{4}{5}(\rho k_BT/N_e)$, consistent with stresses obtained from the Green-Kubo relation. These comprehensively characterized equilibrium structures, which offer a good compromise between flexibility, small $N_e$, computational efficiency, and small deviations from ideality provide ideal starting states for future non-equilibrium studies.