Molecular design of a filler-polymer interface in silica-filled rubbers

Silica (SiO₂) nanofillers improve the processability of rubbers (i.e., less energy required) and a car’s fuel economy compared to traditional carbon black (CB), playing a critical role in creating environmentally "green" tires. However, to achieve the performance potential of SiO₂-filled rubbers at full capacity, the much weaker reinforcement effect compared to CB-filled rubbers should be resolved. There is general agreement that "bound rubber" (i.e., polymer chains that are physically adsorbed on the filler surface) plays a critical role in rubber reinforcement. In the case of SiO₂-filled rubbers, the filler-polymer interface is more complicated than CB-filled rubbers due to the inclusion of a silane coupling agent which strengthens the poor chemical interaction between SiO₂ and rubber. In addition, it is expected that the chemisorption at random sites along a single polymer chain rather than the physisorption of a polymer chain is dominant on the SiO₂ surface. Using simplified SiO₂-filled polybutadiene in conjunction with neutron scattering/spectroscopy techniques, we reveal the structures and dynamics of bound rubber on the SiO₂ surface. The results will be further compared with our previous results on CB fillers, deriving rich and complex physics and material design insight into the filler-polymer interface necessary for automobile tires.