Multiscale dynamics in matrix-free polymer grafted nanoparticle systems

Recent work has shown that gas separation membranes constructed using only polymer grafted nanoparticles exhibit enhanced transport properties compared to the bulk. Additionally, this behavior is non-monotonic with increasing chain length (at constant grafting density). Macroscopic rheological measurements reveal a glass to liquid transition with increasing chain lengths, with the transition occurring at the point where the permeability 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 polymeric dynamics across a variety of timescales. 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 local dynamics in the polymer grafts as compared to the neat polymer. These results extend the understanding of how dynamics manifest in such systems and provide a scaffold to develop newer materials with desirable properties.