Dynamics of Polymer-Mediated Nanoparticle Network in Polystyrene-Grafted Silica Nanoparticle Melts

Polymer-grafted nanoparticles (GNPs) have vastly different physical properties than the same polymer on its own, due to the formation of numerous “layers” as the polymer is grafted onto the nanoparticle (NP) surface. For spherical GNP melts without a polymer matrix, previous research has shown that there is an inner “dry” brush zone with highly stretched polymer chain segments, and a “wet” brush zone consisting of chains interpenetrating with others and following Gaussian statistics. However, an understanding of the dynamics of a network-like NP microstructure via polymer–mediated bridges between neighboring NPs is still lacking. To gain insight into this, well-defined GNPs composed of SiO₂ NPs grafted with polystyrene (PS) chains of different chain length and grafting density were prepared by surface-initiated atom transfer radical polymerization. The in-situ structure and dynamics of the NP network were investigated using X-ray photon correlation spectroscopy above the glass transition temperature of bulk PS. In addition, quasi-elastic neutron scattering measurements were used to selectively study the dynamics of the polymer bridges. The comparison between the dynamics of the NP network and the dynamics of the polymer bridges has not been studied to date and represents a major advancement for the study of GNPs. These experimental results are further correlated with the GNP melt’s thermal and mechanical properties to reveal the structure-dynamics-properties relationship.