Three-dimensional graphene network/phenolic resin composites towards tunable and weakly negative permittivity

Three-dimensional (3D) graphene (GR) network/phenolic resin composites with tunable and weakly negative permittivity were prepared by mechanical mixed method. Dielectric properties including permittivity, dielectric loss tangent and alternating current conductivity (sigma(ac)), were investigated in detail. When the GR content was increased from 8 to 13 vol%, a ladder-shape increase of sigma(ac) was observed, indicating a percolation phenomenon. It was found that, when the GR content exceeded 13 vol% the negative permittivity appeared attributed to the formation of 3D interconnected GR network. Moreover, the negative permittivity was easily adjusted by controlling the GR content. Compared with the metal-ceramics in our previous work, the absolute values of negative permittivity were low, which was in favor of impedance matching. For the GR content of 13 vol%, high dielectric loss above 25 over the whole frequency was also observed. Finally, the equivalent circuits were used to analyze the reason of the negative permittivity. (C) 2016 Elsevier Ltd. All rights reserved.