Interplay of Grafted and Adsorbed Chains at the Polymer–Particle Interface in Tuning the Mechanical Reinforcement in Polymer Nanocomposites

The polymer–particle interface consisting of grafted and adsorbed chains plays a key role in the mechanical reinforcement of polymer nanocomposites, but the synergistic effect of grafted and adsorbed chains in the interface on the mechanical properties has been less explored. In this work, we investigated the thermal and rheological behaviors of poly(methyl methacrylate) (PMMA)-grafted silica nanoparticle (GNP)-filled PMMA matrix with various graft densities, graft chain lengths, particle sizes, and particle loadings. By comparing with bare nanoparticle (NP)-filled polymer nanocomposites (PNCs), we found that the glassy modulus was reinforced more significantly by GNPs with a medium grafting density than by bare NPs or GNPs with a low grafting density. In the rubbery state, the plateau modulus is greatly enhanced by GNPs with longer grafted chains due to multiple sources of entanglements from the topological confinements imposed by both grafted and adsorbed chains at the interface. These results reveal the important role of grafted and adsorbed chains at the polymer–particle interface in tuning the mechanical reinforcement in polymer nanocomposites and also lay the groundwork for optimizing the designs of polymer nanocomposites that emphasize how interfacial engineering can be utilized to improve interfacial interactions and mechanical properties.