STRUCTURE OF PERCOLATING CARBON-BLACK FRACTAL AGGREGATES DISPERSED IN A POLYMER

The structure of the clusters of primary carbon black aggregates dispersed in a polymer matrix is studied by small angle neutron and X-ray scattering. The fractal dimension is found to decrease continuously for increasing concentration Phi of carbon black from D = 1.75 at Phi = 0, corresponding to the value for the isolated primary aggregates, to 1.5 in the considered concentration range where a percolation transition takes place. This result suggests a ''tip-to-tip'' sticking mechanism which leads to more open structures than the diffusion-limited cluster-cluster aggregation model.