(670a) Chemical Heterogeneity in Interfacial Layers of Polymer Nanocomposites

It is well-known that particle-polymer interactions strongly control the binding and conformations of adsorbed chains on particles. Interfacial layers around nanoparticles consisting of adsorbed and free matrix chains have been extensively studied to reveal their rheological contribution to the behavior of nanocomposites. In recent works, we reported that poly(methyl methacrylate) adsorbed nanoparticles dispersed in poly(ethylene oxide) displayed thermal stiffening response above the glass transition temperatures of both polymers. This was explained by the confinement and dynamic coupling phenomenon in dynamically asymmetric and miscible polymer blend with a large glass transition temperature difference. In this talk, I will present how chemical heterogeneity of interfacial layers around the well-dispersed nanoparticles governs the microscopic mechanical properties in various polymer nanocomposites. Low glass-transition temperature composites consisting of poly(vinyl acetate) coated silica nanoparticles in poly(ethylene oxide) and poly(methyl acrylate) matrices; and of poly(methyl methacrylate) silica nanoparticles in poly(methyl acrylate) matrix are examined using rheology and X-ray photon correlation spectroscopy. We demonstrate that miscibility between adsorbed and matrix chains in interfacial layers lead to the observed unusual reinforcement. Our results also suggest that packing of chains in the interfacial regions contribute to the reinforcement in polymer nanocomposites. These results reveal the impact of dynamic and chemical heterogeneities in interfacial layers, which can be utilized to design shape changing and mechanically adaptive polymer composites.