Dielectric properties and mechanism of composites by superposing expanded graphite/cyanate ester layer with carbon nanotube/cyanate ester layer

Electronic conductor/polymer composites with high dielectric constant have great potential in many cutting-edge fields, but they usually show high dielectric loss. Here, new composites (MWCNT/CE–5.0EG/CE) were prepared by superposing a multi-wall carbon nanotube (MWCNT)/cyanate ester (CE) composite layer with another expanded graphite (EG)/CE composite of which the loading of EGs is set as the percolation threshold (5.0 wt%) through a two-step curing procedure. No resin fault is observed at the interface between the two layers. The electrical and dielectric properties of MWCNT/CE–5.0EG/CE composites with different loadings of MWCNTs were studied. Results show that the conductivity of MWCNT/CE–5.0EG/CE composite intervenes between those of the two layers, and closes to the value of the layer with lower conductivity. Besides, when the loading of MWCNTs is 0.5 wt%, the 0.5MWCNT/CE–5.0EG/CE composite has the highest dielectric constant (up to 486 at 1 Hz) among the two-layer composites, about 4 and 1.5 times that of 0.5MWCNT/CE and 5.0EG/CE composite, respectively. Meanwhile the dielectric loss tangent of the 0.5MWCNT/CE–5.0EG/CE composite is only 1.2% or 50% of that of 0.5MWCNT/CE or 5.0EG/CE composite. The nature behind these interesting data was elucidated by investigating space charge distributions, discussing the space charge polarization and establishing equivalent circuit.