(33j) Contrasting Reinforcement Mechanisms in Elastomeric Nanocomposites

The addition of granular nanoparticles to an elastomeric matrix reinforces their mechanical response significantly, allowing their utilization in myriad integral industries. Despite a century of inquiry into the microscopic mechanisms involved in this nanoparticulate reinforcement, a consensus remains lacking. Two such prominent reinforcement mechanisms are the glassy bridge reinforcement model, whereby dynamically frozen polymer segments nearby filler particles connect dispersed filler particles, and the direct contact model, which posits that direct filler-filler contacts reinforce the elastomer.

To decipher the relative roles of these hypothesized mechanisms, we utilize molecular dynamics stretching simulations. We stretch a model filled elastomer, i.e., nanoparticle clusters dispersed in an elastomer matrix, to 200% extension and analyze resulting atomic stresses. Our findings demonstrate that 1) reinforcement is due to a preferred Poisson ratio mismatch between filler and polymer, 2) filler-filler contacts mediate reinforcement at high strains, 3) glassy bridges are not necessary for reinforcement, and 4) spatially resolved stresses can differentiate between various mechanisms of reinforcement.

*This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Award Number DE-SC0022329.