Fabrication and origin of asymmetric polyvinylidene fluoride-carbon nanotube/cyanate ester materials with high dielectric constant and low dielectric loss through building double-layered structure

High dielectric loss has been the biggest sticky problem for high-k conductor/polymer composites. Herein, a new asymmetric material consisting of one layer of beta-phase poly(vinylidene fluoride) (PVDF) and another layer of carboxylated carbon nanotube (eCNT)/cyanate ester (CE) composite was fabricated, coded as PVDFx-eCNTq/CE, where x is the thickness of PVDF layer ranging from 3 to 70 mu m, q is the loading of eCNTs (f), taking values of 1.2 and 1.7 wt%. The influences of f and x values on dielectric properties and breakdown strengths of PVDF-eCNT/CE materials were systematically studied. When f is smaller than the percolation threshold (f(c)) of eCNT/CE (f(c) = 1.6 wt%), the corresponding PVDF-eCNT1.2/CE materials have similar conductive and dielectric properties as eCNT1.2/CE composite. When f > f(c), all PVDF-eCNT1.7/CE materials have much lower dielectric loss than eCNT1.7/CE, while with suitable thickness of PVDF layer (<70 mu m), PVDF-eCNT/CE materials have significantly improved dielectric constants and breakdown strengths. For the PVDF-eCNT1.7/CE material of which the thickness of PVDF layer is 5 mu m, its dielectric constant at 1 Hz is 1699, about ten times of that of eCNT1.7/CE, while the dielectric loss is only 2.31 x 10(-2) times of that of the latter. The origin behind was intensively studied in terms of space charge distribution.