(181aw) Structure and Dynamics in Matrix Free Polymer Grafted Nanoparticle Based Systems

Recent work has shown that materials comprised only of nanoparticles densely grafted with polymer chains (GNPs) possess unusual properties. Their gas permeability shows nonmonotonic behavior with increasing polymer chain length, with peak permeabilities of 8-20 times relative to the neat polymer are observed, depending on the probe diffusant. This behavior has been observed for a variety of graft polymers, core sizes and grafting densities thus indicating a potentially universal behavior for such composites. Using a combination of X-Ray Photon Correlation Spectroscopy, Brillouin Light Scattering and Inelastic X-Ray Scattering we can probe the collective dynamics of these systems and show that these systems undergo a transition from a soft glass to a liquid with increasing polymer chain length at a constant grafting density. In fact, this transition is reflected in the static structure of the system where a hard sphere order parameter based on the first peak of the structure factor shows a similar melting transition as seen from the dynamics studies as well as suppression of long-range density fluctuations for shorter chains. This transition manifests itself in a host of anomalies in the fast relaxations (ps – ns) of the tethered polymer chain due to distortions of the polymer corona in the jammed colloidal system, thus providing a scaffold for constructing materials with controllable dynamics at different length and time scales.