Polymer-Filler Competition-Driven Reinforcement Beyond the Payne Effect in Elastomeric Nanocomposites

Elastomeric nanocomposites are ubiquitous in automotive, aerospace, packaging, construction, and electronic materials. The nanocomposite combines the elastomer's ductility with a large tensile strength due to the nanoparticulate filler. Despite abundant research into reinforcement, there remain unresolved features of the mechanical response, e.g., low-strain softening (Payne effect) and high-strain hardening.

Our previous efforts demonstrate that low-strain reinforcement is driven by 1) a reinforced elastomer due to a reduced composite Poisson ratio, and 2) an initially jammed filler network bearing load. Subsequently, this filler network breaks, which causes the Payne effect. However, this left the origins of lingering reinforcement past ~20% strain unclear. How can non-cohesive nanoparticles bear load?

Here, we report on molecular dynamics simulations of a model nanocomposite under extensional deformation. Our results point to a competition between polymer and filler to contract to restore volume and resist contractile compression, respectively. This competition leads to a reinforced elastomer stress at large strains. These results provide novel insights into the mechanistic origins of reinforcement by nanoparticle addition, contributing to a long-standing theoretical inquiry.