Silica-Polymer Interface and Mechanical Reinforcement in Rubber Nanocomposites

This chapter discusses the composition and the properties of the inorganic-organic interface in silica-rubber nanocomposites that determines the strength of the interactions between the inorganic filler and the polymer and, in turn, the dynamic-mechanical behavior of the material. Many theories and experimental works are discussed, which recognized the central role of the filler-rubber interaction in defining the filler dispersion and the formation of a percolative filler network in the rubber matrix, essential to provide the reinforcing action. First the structural and surface characteristics of the silica and the silica surface modifications that determine its interaction with rubber are highlighted. Then both the interactions between filler nanoparticles (NPs) and filler-rubber interactions are examined, paying specific attention to the interface region of the rubber surrounding the filler, to the kind of covalent/van der Waals links of rubber with the silica surface, and to the gradient of polymer mobility between the more strongly interacting rubber chains localized near the surface, with a stiffer response, and the rubber further away from it. Finally the main microscopic and spectroscopic techniques, which allow to give information on the nature of silica-rubber interface, are reported showing some significant examples and discussing their capabilities and limits to support the design, control, and optimization of the inorganic-organic interface in silica-rubber nanocomposites and the improvement of their dynamic-mechanical properties.