New nanocomposite materials made of an insulating matrix and conducting fillers: Processing and properties

The work described in this paper deals with the preparation and the charact erization of an homogeneous composite material composed of electrically con ductive fillers dispersed in a thermoplastic insulating matrix. These fille rs were chosen to have either a spherical shape or a high aspect ratio. pro cessing of these conductive polypyrrole particles, which were obtained eith er through a classical polymerization of pyrrole in the presence of stabili zer, or polymerization onto the surface of cellulose monocrystals is detail ed. The relationship of filler content in the composite to electrical and m echanical properties was investigated. In order to characterize the connect ivity of the fillers in the matrix. electrical measurements were performed and these results have been compared with the predictions of the statistica l percolation theory. Further analysis was undertaken by considering the in fluence of the network of rigid particles on the viscoelastic properties of the composites. These results were compared with two models; first, with a mechanical percolation approach which was based on strong interactions bet ween fillers, and second, with a mean field model, which in no way accounte d for interactions between fillers. In recent developments, it has been sho wn that these materials used as coating on various substrate could be good sensors, allowing to determine some specific features of the substrate defo rmation.