(734i) Multiscale Dynamics in Matrix-Free Polymer Grafted Nanoparticle Systems

Recent work has shown that gas separation membranes constructed using only polymer grafted nanoparticles (PGNP's) exhibit enhanced transport properties compared to the bulk. Additionally, this behavior is non-monotonic with increasing chain length (at constant grafting density) and has been verified for several polymers. Macroscopic rheological measurements reveal a glass to liquid transition with increasing chain lengths, with the transition occurring at the point where the permeability in these systems goes through a maximum. This implies a possible connection between the two behaviors although they operate at different scales. Using techniques that allow for more spatially sensitive probes, we explore the effective medium sound velocity, particle relaxation and local polymer dynamics across a variety of time and length scales. The key takeaways are i)Different sound velocity behaviors in the glass and liquid like regimes, ii)Kinetic jamming at of the particles governs long time relaxation, and iii)Faster segmental and sub-segmental dynamics in the polymer grafts as compared to the neat polymer. Relating behavior across these different time and length scales provides a complete picture of the dynamics of these systems and how they impact macroscopic properties of these materials, with special attention given to diffusion of light gases in these systems.