Linear Viscoelasticity of Dumbbells Interacting via Gaussian Soft-Core Potential

TL;DR

This study investigates the screening effect in polymer melt models using simulations of interacting dumbbells with Gaussian soft-core potential, confirming the validity of the Rouse model at high densities and analyzing deviations at low densities.

Contribution

The paper provides a simulation-based analysis of the screening effect in dumbbell models, supporting the use of the Rouse model for unentangled polymer melts.

Findings

Gaussian soft-core interaction is screened at high densities.

Relaxation moduli of interacting dumbbells resemble non-interacting ones at high densities.

Deviations occur at low densities, with broadened relaxation moduli.

Abstract

In polymer melts, the interaction between segments are considered to be screened and the ideal Gaussian chain statistics is recovered. The experimental fact that linear viscoelasticity of unentangled polymers can be well described by the Rouse model is naively considered as due to this screening effect. Although various theoretical models are based on the screening effect and the screening effect is believed to be reasonable, the screening effect cannot be fully justified on a solid theoretical basis. In this work, we study the screening effect by utilizing a simple dumbbell type model. We perform simulations for dumbbell systems in which particles interact via the Gaussian soft-core potential. We show that, if the density of dumbbells is high, the Gaussian soft-core interaction is actually screened and the static structures are well described by the ideal model without Gaussian soft-core interaction. We also show that the relaxation moduli of interacting dumbbell systems approximately coincide to those of the non-interacting dumbbell systems. In the low density systems, we observe the deviations from the ideal non-interacting systems. For example, the relaxation moduli become relatively broad. However, the relaxation moduli of such systems can be decomposed into the relaxation modes by the Gaussian soft-core interaction and the bond. The bond relaxation mode can be successfully described by a single Maxwell relaxation with effective relaxation strength and time. Our results support a naive use of the Rouse model to analyze unentangled polymer melts.