Evolution of Nanofiller Microdynamics During Stress Relaxation Revealed by X-ray Photon Correlation Spectroscopy*

In a highly loaded, silica-filled, crosslinked model rubber closely mimicking commercial materials, the filler network structure and dynamics of the silica filler particles change when the silica surface is modified with silane coupling agents. Reduction in size scales characteristic of the structure are quantified using ultra-small-angle X-ray scattering (USAXS) measurements and the filler particle microdynamics after step strain probed with X-ray photon correlation spectroscopy (XPCS). The evolution of filler particle dynamics depends on the chemical functionality at the silica surface and observing these differences suggests a way of thinking about the origins of hysteresis in reinforced rubbers. These microscopic filler dynamics are correlated with the macroscopic stress relaxation of the materials. The combination of static and dynamic X-ray scattering techniques with rheological measurements is a promising approach for elucidating the microscopic mechanisms of rubber reinforcement.