Synergistic Effects of Carbon Nanotubes on Negative Dielectric Properties of Graphene-Phenolic Resin Composites

Carbon nanotubes-graphene-phenolic resin (CNTs-GR-PR) composites are first prepared to investigate the effects of CNTs on negative dielectric properties of GR-PR composites. The results show that microstructures are easily adjusted by the mass ratio of CNTs to GR and total carbon content, which have an impact on the negative dielectric properties of the composites. The negative permittivity from the CNT1.6-GR(5)-PR is observed with the total carbon content of 6.6 wt %, attributed to the formation of conductive pathways. Yet the permittivity of the GR(6.6)-PR still remains positive, indicating that the addition of CNTs is beneficial to the appearance of negative permittivity and shows the synergistic effect. When the total carbon content exceeds 6.6 wt %, the addition of an appropriate amount of CNTs (the mass ratio of CNTs to GR is 0.33:1 and 1:1) improves the alternating conductivity (sigma(ac)) and imaginary permittivity (epsilon), resulting from the connectivity improvement in conductive phases. As compared to the dielectric loss tangent (tan delta) from the GR(8)-PR (below 35), the tan delta of CNT4-GR(4)-PR is higher over the whole frequency and above 100 before 400 MHz, indicating the appropriate addition of CNTs enhances the dielectric loss.