STRUCTURE OF PERCOLATING CARBON-BLACK FRACTAL AGGREGATES DISPERSED INA POLYMER

The structure of the clusters of primary carbon black aggregates dispe rsed in a polymer matrix is studied by small angle neutron and X-ray s cattering. 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 transitio n takes place. This result suggests a ''tip-to-tip'' sticking mechanis m which leads to more open structures than the diffusion-limited clust er-cluster aggregation model.