The origin of the electric and dielectric behavior of expanded graphite-carbon nanotube/cyanate ester composites with very high dielectric constant and low dielectric loss

High performance expanded graphite (EG)-multiwalled carbon nanotube (MWCNT)/cyanate ester (CE) composites with very high dielectric constant, low dielectric loss and low percolation threshold were developed. In order to understand the electric and dielectric behavior of EG-MWCNT/CE composites, EG/CE and MWCNT/CE binary composites were also prepared for comparison. Results show that the ternary composites have greatly different electric and dielectric properties from the binary composites. The percolation threshold of the EG-MWCNT/CE composite is much lower than that of either the EG/CE or MWCNT/CE composite. With the same content of conductive fillers, the EG-MWCNT/CE composite shows a much higher dielectric constant than EG/CE and MWCNT/CE composites. In addition, to obtain the same dielectric constant, the dielectric loss of the EG-MWCNT/CE composite is lower than that of either binary composite. The difference is attributed to the synergistic effect between EG and MWCNT. The addition of EG not only improves the dispersion of MWCNTs in the resin matrix, but also helps to form conductive networks. An equivalent circuit model is proposed.