SURFACE STRUCTURE OF CARBON BLACK AND REINFORCEMENT

From scanning tunneling micruscopy (STM) and atomic force microscopy (AFM) measurements, it was found that the lateral dimensions of the nanocrystallites systematically decrease with decreasing diameter of the primary particles. Furthermore these experiments suggest that these nanocryslallites, unregularly tilled, form the rough surface of carbon blacks. Hence, the activity of carbon black is the result of the size of the nanocrystallites and the degree of disorder on the surface. Temperature treatments of carbon black lead to a continuous increase of the lateral dimensions of the crystallites and a steady decrease in roughness. In order to quantify the surface roughness small-angle X-ray scattering (SAXS) measurements, that spanned a large scattering vector range, were evaluated by a fractal analysis. The surface fractal dimensions systematically increased with rising activity of the carbon black. Reinforcement is discussed within the scope of interaction of network chains with the carbon black surface. For this purpose, the dependency of thePayne effect on temperature, prestrain and swelling is interpreted using an adsorption mechanism of network chains on the surface of the filler particles. This mechanism requires the existence of stable and unstable bonded chains. Only the weakly bonded chains seem to be responsible for the Payne effect.