EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Tread rubber requires wet-grip performance and low-rolling resistance for low fuel consumption. To modify the mechanical properties of the rubber suitable for the tread, dispersion of silica nanoparticles in the rubber is effective. It is believed that the silica nanoparticles connect with the rubber by forming covalent bonds via the silane coupling agent (SCA) and that the amount of the covalent bonds between silica and the rubber should affect the mechanical properties of the rubber. However, the spatial distribution of the bonds between the silica fillers and the rubber has not been visualized experimentally.
In this work, we studied a styrene-butadiene rubber (SBR) composite filled with silica fillers to visualize the spatial distribution of the covalent bonds between the silica and rubber via SCA. Si L2,3-edge spectra were investigated by electron energy-loss spectroscopy using scanning transmission electron microscopy to analyze the chemical bonds and to visualize its spatial heterogeneity. The Si L2,3 spectra were obtained from the silica-filled SBRs containing (a) 0 and (b) 17 vol % SCA. The spectral profiles obtained from the edge of the silica fillers in the SBR with SCA were different from those without SCA. Such difference reflects the presence of the covalent bond via SCA at the surface of the silica fillers. Real-space maps of the chemical bonds were constructed by MLLS fitting method using the reference spectra of the silica and the SCA. The chemical maps of the silica-filled SBRs showed the spatial heterogeneous distribution of the SCA molecule, which corresponds to the chemical bond distribution between silica and rubber. This analytical technique can clarify the origin of the mechanical properties of the silica-filled rubber and can be applied for the evaluation of the rubber products.