Chemical and Dynamic Heterogeneities in Interfaces for Adaptive 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 contribution to the overall thermal and mechanical behavior of nanocomposites. Using miscible polymers of different chemistries as adsorbed and matrix layers in composites, the interfacial layer dynamics, hence the mechanical properties can be modulated unusually. We recently showed that when glass transition temperature difference between adsorbed and matrix polymers were large and polymer-polymer interactions were neutral, they reversibly stiffened with temperature. In this talk, I will present the extent of chemical heterogeneity of interfacial layers in adsorbed and polymer-grafted nanoparticles and discuss the role of interfacial layer mixing and chain conformation on the mechanical properties. Low glass-transition temperature composites with different matrix polymers [poly(vinyl acetate), poly(methyl acrylate) and poly(ethylene oxide)] will be discussed with particles of different surface chemistry; and polymers with different architectures. Interfacial layer design strategies in polymer nanocomposites will be outlined. These dynamic and chemical heterogeneities in interfacial layers can be used to design mechanically adaptive polymer nanocomposites.