The origin of mechanical enhancement in polymer nanoparticle composites with ultra-high nanoparticle loading

TL;DR

This study uses molecular dynamics simulations to investigate the mechanical enhancement in polymer nanoparticle composites with ultra-high nanoparticle loading, revealing that polymer bridging is the key factor behind improved properties.

Contribution

It provides a molecular-level understanding of the origin of mechanical enhancement in highly loaded PNCs, emphasizing the role of polymer bridging effects.

Findings

Modulus increases at low polymer fill fractions.

Polymer bridging is identified as the primary source of enhancement.

Nanoparticle rearrangement influences mechanical properties.

Abstract

Polymer nanoparticle composites (PNC) with ultra high loading of nanoparticles (> 50%) have been shown to exhibit markedly improved strength, stiffness, and toughness simultaneously compared to the neat systems of their components. Recent experimental studies on the effect of polymer fill fraction in these highly loaded PNCs reveal that even at low polymer fill fractions, hardness and modulus increase significantly. In this work, we aim to understand the origin of these performance enhancements by examining the dynamics of both polymer and nanoparticles (NP) under tensile deformation. We perform molecular dynamics (MD) simulations of coarse-grained, glassy polymer in random-close-packed nanoparticle packings with a varying polymer fill fraction. We characterize the mechanical properties of the PNC systems, compare the NP rearrangement behavior, and study the polymer segmental and chain-level dynamics during deformation below the polymer glass transition. Our simulation results confirm the experimentally-observed increase in modulus at low polymer fill fractions, and we provide evidence that the source of mechanical enhancement is the polymer bridging effect.