Central Role of Filler–Polymer Interplay in Nonlinear Reinforcement of Elastomeric Nanocomposites

Abstract

Nanoparticles can greatly enhance the mechanical response of elastomeric polymers essential to a wide range of applications, yet their precise molecular mechanisms of high-strain reinforcement remain largely unresolved. In particular, long-standing questions endure over the extent to which glassy bridges or tie chains between particles are needed to facilitate reinforcement. Here we show, based on molecular dynamics simulations, that high-strain reinforcement emerges from an interplay between granular nanoparticulate compressive behavior in the normal direction and polymer incompressibility. This feedback loop, which is initiated by a mismatch in the Poisson ratios of the nanofiller and the polymer, invokes a contribution from the polymer’s bulk modulus to the elongational stress, while the tendency of the polymer to contract in the normal direction maintains a near-jammed filler state. This effect persists even once the direct filler elongational contribution becomes dissipative after the Payne effect yield, as a consequence of enduring filler normal stresses mediated by direct particle–particle contacts. These results indicate that direct particle–particle contact effects, even in the absence of potential augmenting mechanisms such as glassy polymer bridges, can drive the mechanical reinforcement effects typical of experimental systems.