The addition of nanoscale fillers to polymer materials significantly increases their overall mechanical, electrical, and optical properties, with applications in additive manufacturing, coatings, and nano-inks. Challenges such as uniform dispersion can be addressed by covalent bonding of polymer to the nanoparticle surface, resulting in polymer-grafted nanoparticles (PGNs). One key application is in the field of preceramics for extreme environments, where the addition of ceramic nanoparticles (such as SiO2) improves the ceramic yield and flow behavior of preceramic polymers while also decreasing the volume shrinkage. But there is a need for a better understanding of the effect of design parameters such as polymer molecular weight (graft length) and number of polymer chains per surface area of the nanoparticle (graft density) on key material properties. In this study, we focus on a model PGN system to understand the effect of graft density on the structure and rheological properties both above and below the polymer entanglement molecular weight. We used a grafting-to procedure, where poly(dimethylsiloxane) chains containing reactive end-groups were covalently bound to surface-functionalized silica nanoparticles, to achieve low, medium, and high graft densities. Grafting was determined using spectroscopy and dynamic light scattering, while graft density was calculated from thermal gravimetric analysis using neat components (polymer and nanoparticles) as controls. The PGN structure was examined using electron microscopy. Finally, the flow behavior and dynamics were studied using rheology and broadband dielectric spectroscopy, respectively. This work seeks to reveal principles that describe the connections between design parameters, particle interactions, polymer interdigitation, and bulk properties.
