Nanoscale Stress Distribution in Silica-Nanoparticle-Filled Rubber as Observed by Transmission Electron Microscopy: Implications for Tire Application

Nanoparticle-filled rubber under tensile deformation was observed in situ by transmission electron microscopy (TEM), and the spatial distributions of the local maximum and minimum principal strains (εmax and εmin) under tensile deformation were determined experimentally for the first time. The local εmax showed that deformation behavior depends heavily on the local structures and their spatial arrangements. Additionally, greatly deformed rubbery regions were found to appear along a network consisting of silica aggregates (silica-aggregate network). The distribution of the local εmin revealed the reorganization mechanisms of the internal hierarchical structures. The finite element method (FEM) was then applied to a series of TEM images under tensile deformation to simulate the structural changes, principal strains, and von Mises stress. The simulated morphology and εmax were in excellent agreement with the experimentally obtained morphology and strain. The distribution of the simulated von Mises stress, obtainable only from the FEM based on the experimental results, revealed that large stress propagates along the silica-aggregate network parallel to the tensile direction, suggesting that the silica-aggregate network may be primarily responsible for providing mechanical strength to the nanoparticle-filled rubber under deformation. Since the stress concentrates along the silica-aggregate networks, cavities appeared along these “stress pathways.” The present study would pave the way to understanding the microscopic factors determining the macroscopic mechanical properties of rubber nanocomposites mainly used for automobile tires and seismic isolation rubber.