Fractal agglomerates and electrical conductivity in carbon black polymer composites

SEM micrographs of carbon black polymer composites have been analysed in terms of their fractal geometry. Acetylene black/ethylene butylacrylate copolymer samples have a fractal dimension of about 1.8 at low filler concentrations that increases to 2.1 at high concentrations. The numerical values indicate a cross-over from diffusion limited cluster aggregation (DLCA) to reaction limited cluster aggregation (RLCA). Furnace black/EPDM composites have a fractal dimension of 1.9 at low concentrations and of 2.4 at higher filler fraction. We believe that in this case the increase in fractal dimension is only apparent and due to interpenetration. Possible connections between fractal geometry (fractal dimension and correlation length) and electrical conductivity are discussed. No clear connection could be determined.