FRACTAL ANALYSIS OF THE PERCOLATION NETWORK IN EPOXY-POLYPYRROLE COMPOSITES

The macroscopic de conductivity and structure of epoxy-polypyrrole com posites are studied as a function of the polypyrrole amount and interp reted with percolation concepts. The fractal dimension D of the infini te cluster is found to increase substantially from 1.25 to 1.88 with t he conducting filler concentration. An original representation of the conducting backbone is obtained using image analysis techniques and su ggests a finitely ramified structure. The Minkowski dimension of the b ackbone is determined to be an excellent approximation of the fractal dimension D-B and it is seen to increase as the polypyrrole concentrat ion increases while the fractal dimension of the elastic backbone is f ound to keep the constant value D-E = 1.13. These results are compared to scaling percolation theory.