(709d) Molecular Modeling of Polymer Nanocomposites

Polymer nanocomposites, whereby small particles with at least one dimension less than 100 nm are dispersed in a polymer matrix, are a promising new class of materials with properties that depend sensitively on the size, shape, surface functionality, and dispersion state of the particles. In some cases, maintaining uniform dispersion of the particles is crucial to their utility, while in others controlling their arrangement relative to each other is important. Polymer nanocomposites are promising materials because a small amount of the particles can have a substantial impact on the resulting properties due to the large surface-to-volume ratio of the particles.  In this talk, I will describe our recent efforts at simulating various properties of polymer nanocomposites. In particular, I will describe how grafted nanoparticles can be used to control nonlinear mechanical properties, including the strain hardening modulus. Strain hardening is a phenomenon commonly observed in polymer glasses, whereby the stress increases when deformation continues beyond the yield point. Originally thought to be a manifestation of entanglement effects, it has recently been shown that strain hardening is due to alignment of the chains and their increasing resistance to plastic flow. We have shown that grafting polymer chains to the surface of nanoparticles leads to an enhancement of strain hardening due to the inability of the grafted chains to align with the deformation.