Surface Dynamics of Miscible Polymer Blend Nanocomposites

Diverse processes that include energy conversion, wettability, lubrication, adhesion, and surface-directed phase separation in mixtures fundamentally depend on the structure and dynamics of materials' surfaces and interfaces. We report an unusual phenomenon wherein the surface viscosity of polymer nanocomposites of polystyrene (PS), polyvinyl methyl ether (PVME), and PS-coated gold nanoparticles (PS/PVME/PS-Au) is over an order of magnitude smaller than that of the neat miscible PS/PVME blend. Our X-ray photon correlation spectroscopy studies of the surface dynamics also reveal that the polymer chains manifest dynamics associated with two separate average compositional environments: a PVME-rich region, significantly in excess of its bulk concentration, and a separate PS-rich environment, where the dynamics are approximately 2 orders of magnitude slower. The unusually rapid surface dynamics in the PS/PVME/PS-Au nanocomposite are due largely to the excess PVME chains and the polymer/brush-coated nanoparticle interactions at the free surface.