Molecular design of a filler-polymer interface to control elastomer reinforcement

Automobiles are an integral part of today’s society. Tires are a key component of the automotive supply chain, and as the only part of the vehicle that touches the road, tires contribute significantly to vehicle safety and fuel efficiency. Silica (SiO₂) nanofillers improve the processability of rubber and the fuel economy of a car compared to traditional carbon black (CB), playing a critical role in the development of environmentally “green” tires. However, to fully realize the performance potential of SiO₂-filled rubber, the much weaker reinforcement compared to CB-filled rubber must be addressed. It is generally agreed that “bound rubber (BR)” (i.e., polymer chains that are physically (for CB) or chemically (for SiO₂) adsorbed onto the filler surface) plays a critical role in rubber reinforcement. Here, we present an integrated experimental and computational study of the BR in SiO₂-filled polybutadiene (PB) rubbers. A simplified SiO₂-filled PB system with silane coupling agents but without polymer crosslinking and filler network structures is used. Neutron scattering combined with isotope labeling and molecular dynamics simulations are performed to reveal the structures and dynamics of BR on the SiO₂ surface. The results are further compared with our previous results on CB fillers to derive rich and complex physics and material design insights into the filler-polymer interface required for the development of tougher and more abrasion-resistant reinforced synthetic rubbers.