Experimental and computational conductivity study of multilayer graphene in polypropylene nanocomposites†
We study the electric conductivity of compounds formed by multilayer graphene in polypropylene. Our study makes a comparative analysis between the experimental and computational results. To obtain an experimental measurement of the electronic properties, we deposited multilayer graphene (MLG) nanoparticles over a polypropylene matrix. The deposition was made over several stages, in which we added to the polymer matrix different percentages of MLG nanoparticles using the melt compounding technique, and we studied the conductivities of the nanocomposites by means of electrochemical impedance spectroscopy (EIS). The second part consists of computational calculations, in which we studied the electronic properties of a graphene sheet under a polypropylene molecule with different slabs in the monomer. In both analyses, there is a strong percolation phenomenon with a percolation threshold of around 18% of the MLG nanoparticles. Before the percolation threshold, the charge carriers are constrained in the polypropylene molecule, making the system an insulating material and creating p-type doping. After the percolation threshold, the charge carriers are constrained in the graphene, making the system a conductor material and creating n-type doping with conductivity values of around 20 S m−1. This phenomenon is a consequence of a change in the mechanism of charge transfer in the interface between the polypropylene molecule and graphene sheet. To describe the charge transfer mechanism, it is necessary to consider the quantum effect. The incorporation of the quantum effects and the percolation phenomenon make it possible for the theoretical conductivity to be close to the conductivity measured experimentally.