Polymer-particle volume competition as a driving mechanism of elastomeric nanocomposite reinforcement from low strain to failure

Introduction of nanoparticles to elastomers can greatly enhance mechanical toughness, an effect essential for a wide range of material applications demanding mechanical robustness under load. At high strain, the primary mechanism of this enhancement is a dramatic enhancement in energy dissipation. However, the precise molecular mechanism driving this enhanced energy dissipation remains unsettled.

Here we describe simulations suggesting a potential unified picture of the origin of nanoparticulate-driven elastomer reinforcement. At low strains, we find that Poisson ratio mismatch between the elastomeric matrix and a percolated granular solid plays a central mechanistic role, causing the elastomer’s bulk modulus to contribute to the composite’s Young’s modulus. This leads to a massive internal stress balance, wherein large negative polymeric normal stresses and large positive particulate normal stresses sum to zero. This balance persists in the nonlinear response regime, pointing to a situation wherein a large normal compressive stress applied by the polymer to the filler preserves filler cohesion, enabling the emergence of a plastic nanogranular response under extensional strain. This response, in turn, provides a large dissipative addition to the mechanical response of the composite, leading to high-strain toughening. Finally, we find that this internal normal pressure balance plays a central role in mediating void nucleation and ultimate failure of the composite. Collectively, these findings suggest that nanoparticle-based elastomer reinforcement is commonly driven by polymer-particle volume competition effects from the linear regime through the initiation of failure.