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

P Kawak and H Bhapkar and DS Simmons, MACROMOLECULES, 57, 9466-9475 (2024).

DOI: 10.1021/acs.macromol.4c00489

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.

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