Crazing of Nanocomposites with Polymer-Tethered Nanoparticles

TL;DR

This study uses molecular dynamics simulations to explore how polymer-tethered nanoparticles influence crazing behavior in nanocomposites, revealing effects on yield stress, extension ratio, and failure mechanisms.

Contribution

It provides new insights into how grafted chain length and nanoparticle-polymer interactions affect crazing and failure modes in polymer nanocomposites.

Findings

Grafting alters yield stress and extension ratio in nanocomposites.

Stronger nanoparticle-polymer attraction increases yield stress.

Failure mode shifts from disentanglement to bond breaking with longer grafted chains.

Abstract

The crazing behavior of polymer nanocomposites formed by blending polymer grafted nanoparticles with an entangled polymer melt is studied by molecular dynamics simulations. We focus on the three key differences in the crazing behavior of a composite relative to the pure homopolymer matrix, namely, a lower yield stress, a smaller extension ratio and a grafted chain length dependent failure stress. The yield behavior is found to be mostly controlled by the local nanoparticle-grafted polymer interfacial energy, with the grafted polymer-polymer matrix interfacial structure being of little to no relevance. Increasing the attraction between nanoparticle core and the grafted polymer inhibits void nucleation and leads to a higher yield stress. In the craze growth regime, the presence of grafted chain sections of 100 monomers alters the mechanical response of composite samples, giving rise to smaller extension ratios and higher drawing stresses than for the homopolymer matrix. The dominant failure mechanism of composite samples depends strongly on the length of the grafted chains, with disentanglement being the dominant mechanism for short chains, while bond breaking is the failure mode for chain lengths greater than 10Ne, where Ne is the entanglement length.