Large deformation mechanism of glassy polyethylene polymer nanocomposites: Coarse grain molecular dynamics study

The polymer nanocomposites (PNCs) have shown substantially enhanced mechanical properties compared to the conventional polymers without nano-fillers. However, the dominating deformation mechanism of PNCs and the influence of nanoparticles (NPs) on the mechanical response remain elusive, especially at large deformation. In this study, we used coarse-grained (CG) molecular dynamics (MD) model to investigate the large deformation mechanism of polyethylene (PE)-based PNCs at glassy state. Spherical NPs are modeled by the Lennard-Jones (LJ) sites placed on spherical shells and interact with PE polymer through LJ potential. We found that NP/polymer interaction strength between NP and polymer as well as NP volume fraction are the key factors that determine the mechanical properties of PE PNCs. The addition of NPs affects the mechanical behaviors of PNCs under tension and compression differently. PNCs deform affinely during compression and can be reinforced by adding NP - as long as the interaction strength of NP/polymer is higher than the polymer/polymer strength. However, PNCs are very susceptible to localized deformation upon tension as NP addition could introduce non-uniform stress distribution in the PE matrix and reduce the number of polymer/polymer entanglements. The localized deformation during tensile loading can be inhibited when the volume fraction of NPs is sufficiently large and when NP/polymer interaction strength is much higher than polymer/polymer interaction strength.