Graft Density as a Design Parameter for Dynamics and Flow of Neat Poly(dimethylsiloxane) Grafted Silica Nanoparticles.

Polymer-grafted nanoparticles (PGNs) are hybrid materials that combine the processability of polymers with the functionality of nanofillers. They have applications ranging from advanced coatings, dielectrics, and biomedical systems. There is a need for a better understanding of the effect of parameters such as graft length and graft density on material properties. We investigate poly(dimethylsiloxane)-grafted silica PGNs below the entanglement molecular weight (Me) of the polymer to understand how graft density affects chain conformations, flow, and thermal response. Rheology and time–temperature superposition show high graft density PGNs behave like neat PDMS melts, while medium and low graft densities exhibit entanglement-like dynamics, including a storage modulus plateau and shear-thinning behavior. Lower grafting allows Gaussian-like chain conformations and inter/intra-particle chain overlap, inducing entanglements that jam the system. Activation energy analysis confirms a shift from free-polymer-like to nanoparticle-influenced relaxation, supported by soft glassy rheology (SGR) analysis. A minor shift in glass transition temperature occurs at high graft density due to chain stretching. These results demonstrate graft density as a key design parameter for tuning PGN flow, mechanical reinforcement, and thermal stability. SGR-derived noise temperature provides a framework to correlate topological constraints with macroscopic behavior across polymer chemistries.