Characterisation of surface activity of carbon black and its relation to polymer-filler interaction

The surface activity of commercial and experimental carbon blacks varying in particle size and primary aggregate structure was investigated with regard to surface roughness and energetic surface structure of primary particles. The energetic surface structure was described by the site energy distribution function f(Q), which was determined mainly from the gas adsorption isotherms of ethene. It was found that the surface of carbon black was energetically very heterogeneous. It consisted of at least four different adsorption sites (L Q approximate to 16 kJ center dot mol(-1); II: Q approximate to 20 kJ center dot mol(-1); III: Q approximate to 25 kJ center dot mol(-1); IV: Q approximate to 30 kJ center dot mol(-1)). The fraction of the sites I-IV depended on the production process of the carbon black grades and the particle size. For the furnace blacks, the fraction of high-energy sites decreased significantly with particle size and disappeared almost completely during graphitisation. This indicates that the reinforcing potential of carbon black is closely related to the amount of highly energetic sites that can be well quantified by the applied gas adsorption technique. The surface roughness was characterised by the surface fractal dimension, D, which was determined by two different techniques: the yardstick-method and the extended FrenkelHalsey-Hill-theory (fractal FHH-theory). It is found that the furnace blacks have an almost equal roughness with a surface fractal dimension of D-s approximate to 2.6 beyond a length scale z approximate to 6 nm. This result is shown to be in fair agreement with analytical models and computer simulations of surface growth of carbon black in a furnace reactor.