Abstract
Interactions between glassy polymer chains and the uniformly dispersed carbon nanotubes (CNTs) in nanocomposites were investigated with surface-grafted multiwalled CNTs dispersed in two model polymer systems, polystyrene (PS) and poly(phenylene oxide) (PPO), representing respectively brittle and ductile polymers. Although significant mechanical reinforcement in the both systems was observed, drastically different microscopic interactions, engendered from variations in the fundamental behavior of entangled chains, were noted during the nanoplastic flow of crazing or shear yielding in the nanocomposites. As revealed by a local stress analysis based on atomic force microscopy, "extensibility" of the entanglement network determines not only the mode of deformation leading to either crazing or shear yielding but also how the stretched chains interact with individual nanotubes. The results bear important implications on our understanding toward the fundamental behavior of entangled macromolecules in the glassy state. © 2008 American Chemical Society.