Effect of coating of graphite particles with polyaniline base on charge transport in epoxy-resin composites

Investigations of charge transport, in epoxy resin composites of graphite particles coated with a non-conducting polyaniline-base layer, showed that particle shape and surface structure may crucially affect the percolation behaviour of the systems. In contrast to the gradual increase in the DC conductivity of composites in the range 20-52 vol.% for pure graphite particles, due to their fragmentary nature, a steep rise of several orders of magnitude in conductivity, appeared in composites of graphite particles coated with 1.0 wt.% of polyaniline base at a particle concentration 50 vol.%. The frequency and temperature dependences indicate that, in both cases, at the maximum loading used (52 vol.%), the obtained material had ohmic conductivity. In contrast, the conductivity of epoxy composites of graphite particles, coated with 20 wt.% of polyaniline base, only slightly increased over the whole range of particle concentrations. These findings suggest that, in the case of 10 wt.% polyaniline coating, due to the irregular surface structure, a certain amount of uncoated material is present, which enables the formation of conducting contacts with ohmic conductivity in the percolation area. The 20 wt.% polyaniline coating forms a compact non-conducting layer on the surface of the graphite particles, thus preventing electrical contact.