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

Abstract

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.

Metamaterial Behavior of Polymer Nanocomposites Based on Polypropylene/Multi-Walled Carbon Nanotubes Fabricated by Means of Ultrasound-Assisted Extrusion

“…Nanocomposites of iPP/graphene show σ (AC) ca. 10 −4 S/cm [20], using 30 wt % or higher of graphene. However, the fabrication of iPP/MWCNT with 10 wt % of fillers is important because a high loading of filler can reduce the mechanical properties of PP/CNT [22].…”

“…The type of electrical behavior is also dependent, in turn, on the MFI of the iPP and on the fabrication method. In a previous report [20], the dielectric constant behavior was studied as a function of the graphene content at different frequencies. It was shown that an amount of 30 wt % or 40 wt % of graphene was needed to obtain a negative dielectric constant and the crossover from negative to positive was ca.…”

“…Other preparation methods, such as the ones based on melt extrusion, typically render a poorer dispersion of carbon nanotubes compared to the one obtained by solution methods, with the consequence of the need to use larger amounts of nanoparticles to obtain acceptable or comparable properties. In this sense, Ramasamy [20] prepared polypropylene/graphene nanocomposites and observed negative values of the dielectric constant using amounts of 30%–40% of graphene. It was recently shown that the dispersion of nanoparticles in polymer matrices can be highly enhanced using ultrasound-assisted methods [21,22], thus opening the possibility of reducing the amount of nanoparticles to obtain metamaterial behavior.…”

“…To explain this effect, it has been suggested that a critical amount of conductive fillers, such as those of graphene, allow an increase in dielectric constant due to the polarization effect at the interface of polypropylene and graphene particles. However, in amounts as high as 35 wt %, which allow the percolation effect, the charge accumulation at the interface of polypropylene and graphene results in a negative dielectric constant at low frequencies [20]. Based on the negative dielectric constant of metals, Zhang et al [19] suggested a similar behavior in the case of iPP/MWCNTs NCs by studying the relationship between negative permittivity and the plasma frequency ω p .…”

MWCNT induced negative real permittivity in a copolyester of Bisphenol-A with terephthalic and isophthalic acids

“…Negative real permittivity has been observed for some polymer nanocomposites that include carbon-based nanoparticles [1]. Ramasamy et al reported, for example, that it is possible to observe a high negative real permittivity when the graphene addition reaches a critical concentration in polypropylene (PP) [3]. From this point of view, the present work was focused on producing novel polymer-based composites having negative real permittivity.…”