Low-Cost Preparation of High-k Expanded Graphite/Carbon Nanotube/Cyanate Ester Composites with Low Dielectric Loss and Low Percolation Threshold

Expanded graphites (EGs) or modified EGs (eEGs) were blended with multiwalled carbon nanotubes (MWCNTs) in a big weight ratio to prepare low-cost composites, coded as (EG-MWCNT)/cyanate ester (CE) or (eEG-MINCNT)/CE. The structures and properties of the composites are closely related to the loading of total conductors (f). When f <0.75 wt %, EGs are beneficial for preparing high-k composites with low dielectric loss; however, when f >= 1.05 wt %, eEGs have superior advantages. When f = 1.5 wt %, the dielectric constant and loss of (eEG-MWCNT)1.5/CE composite are about 1.6 and 0.6 times that of the (EG-MWCNT)1.5/CE composite, respectively. The origin behind these interesting results was intensively discussed. Attractively, (EG-MWCNT)/GE and (eEG-MWCNT)/GE composites have similar percolation thresholds, so the surface modification of EGs does not increase the percolation threshold; moreover, ternary composites prepared herein have much better dielectric properties than both traditional EG/CE and MWCNT/CE composites.