Segmental dynamics in matrix-free polymer grafted nanoparticles

Polymer grafted nanoparticle based composite materials display a rich spectrum of complex chain and nanoparticle dynamics. Specifically, composite materials constructed using only polymer grafted nanoparticles display several dynamic anomalies–spanning a large range of time and length scales. We focus on the segmental and local dynamics of polymer chains using spatial and temporally sensitive probes with the view of identifying the primary dynamic driving force for penetrant transport in polymers. The composite materials used in the study exhibit enhanced light gas diffusivities highly dependent on the graft chain length and the grafting density, providing a chemically homogenous platform for identification of the relevant dynamics. We find that the segmental motions are highly accelerated in the composites; these speeded up dynamics appear to correlate with the diffusivities observed for these materials, in contrast to localized side group dynamics which are less affected by grafting and do not seem to affect transport. In fact, side group motion is invariant in the presence of high pressures of CO₂ further supporting this assertion.