Microscopic Deformation of Filler Particles in Rubber under Uniaxial Deformation

Structural studies of filled polymer networks under periodic deformation are of great importance to the industries concerned with rubber. The degree of reinforcement provided by the filler depends on a number of variables: the size of the polymer-filler interface, the size of primary particles, the size and shape of filler clusters. In the tyre industry it is necessary to optimize mechanical properties such as low rolling resistance, good wet grip and long lifetime. There have been studies of unfilled polymer networks and filler model-systems (block copolymers), but because their complexity, industrial rubber samples have escaped investigations. We performed SAXS, USAXS and SANS measurements on carbon black filled natural rubber (poly-isoprene) under uniaxial deformation at ESRF ID-02 and Forschungszentrum Jülich KWS-2. The scattering patterns of the studied filler particles show power-law decay over many decades in scattering vector q. At the scale of primary particles we detected surface fractal behavior and for the characteristic size of the primary particles we calculated lengths of the order of 10 nm. X-ray scattering was used for time resolved experiments (about 10 frames per second) and neutron scattering was used to distinguish between scattering from the studied fillers and the additives (especially zinc oxide) used in industrial materials.