Polypropylene-graphene - a nanocomposite that can be converted into a meta-material at desired frequencies

Meta material (having negative dielectric constant) characteristics were observed in polymeric nanocomposites consisting of polypropylene and graphene. By varying the concentration of graphene the frequency at which the meta material was converted into a positive dielectric material was controlled. At percolation thresholds the dielectric constant had maximum negative values at low frequencies and high positive dielectric constant values at high frequencies. The dielectric measurements reveal that low concentrations of graphene affect the relaxation behavior greatly due to the modifications in the internal field in the nanocomposites by graphene. Also at low concentrations of graphene (less than 5%) the electrical conductivity and thermal loss decreased indicating that graphene acts as trappers of mobile charges and phonons. The dielectric loss at high frequencies near the percolation threshold was also less, indicating that this nanocomposite can also be potentially used as a high dielectric constant material for micro electronics. The dielectric constants obeyed a power law and the percolation was found to be at about 35 weight percent of graphene. A model is proposed for the dielectric behavior of the polypropylene-graphene nanocomposites. We hope that by tuning the frequency of conversion of positive dielectric constant material to meta material we can create new materials that have the advantages of both meta materials and high dielectric constant materials. Also, this conducting nanocomposite is made of polypropylene which is a corrosion resistant polymer and graphene. Therefore, it is hoped that this nanocomposite will have applications in batteries where preventing corrosion is essential. This research may benefit metamaterials research and polymeric nanocomposites for batteries.