Low percolation threshold in flexible graphene/acrylic polyurethane composites with tunable negative permittivity

Graphene (GR)/acrylic polyurethane (APU) composites with low percolation threshold and tunable negative permittivity were prepared by coating and pressing method. The microstructures and dielectric properties including alternating current conductivity (σac), reactance (Z″) and permittivity (ɛ′ and ɛ″) were investigated in detail. A percolation phenomenon from σac was observed when the GR content was increased from 0.9 to 6 vol%, and the percolation threshold was 1.8 vol%. The percolation threshold was obviously lower than those from the reported carbon/silicon nitride, carbon nanotube/phenolic resin and GR/phenolic resin composites, which was possibly attributed to the well dispersion and unique microstructure of GR in APU. Moreover, the negative permittivity was obtained from the much lower GR content (only 3 vol%) than the previously reported composites. In addition, compared with other composites with negative permittivity, the dielectric loss (ɛ″) from the GR/APU composites was obviously reduced.