value D=1.89. In the case of transmission electronic microscopy
observations, the fractal dimension of the infiite cluster was
determined to be constant, having the average value of D~l.80.
This result highlights the selfsimilarity of the conducting
network above the percolation threshold at the different length
scales corresponding to the electronic and optical microscopic
observations. The part of the bonds responsable for the electrical
conductivity is called the backbone since a large fraction of the
electrical path is located on dead-end branches or isolated
clusters which carry zero current. Representations of the
backbones have been deduced from the binary micrographs and
their fractal dimensions Da have been calculated.The values of
Da increases slightly as the volume fraction of PPy increases,
(see tig.2) suggesting that the backbone becomes more irregular,
while the theory’ predicts a constant value Da= 1.6.