Nanocomposites conducting polymers

So far, the description of the electrical properties of conductive polymer nanocomposites has exploited the same formulations used for macroscopic filler composites. This may be motivated by the observation that the conductivity as a function of the nanoparticle content does not show a behavior significantly different from the one obtained with micrometric particles, both manifesting a sharp increase of the overall conductivity once a certain filling fraction is reached, a common feature of random insulator-conductor mixtures. The mainstream theory used to account for such behavior is percolation theory and identifies the insulator-to-conductor transition with the formation of a network of electrically connected conductive particles which extends through the material. However, percolation formulations require generally a sharp cutoff of the connectivity between the particles of the system to be applicable. On the other side, there is general agreement that, at least near the transition region, the main conduction mechanism between the conductive particles of the composite is quantum mechanical electron tunneling, and tunneling implies no abrupt interruption of the connectivity. This may results particularly relevant for nanocomposites, since in their case the dispersed conductive particles have at least one characteristic dimension which is in the same scale of the typical distances of tunneling. Thus, it is sensible to expect that in these materials the detailed behavior of tunneling has to be taken into account, but this in conflict with a percolation description. The main aim of this research stream is then the investigation of a tunneling-based model of conductivity in nanocomposites which does not rely on any sharp cutoff of the interactions between the filler particles to obtain the insulator-conductor transition found experimentally.