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 ofβ-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 70μm,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(fc)of eCNT/CE(fc=1.6 wt%),the corresponding PVDF–eCNT1.2/CE materials have similar conductive and dielectric properties as eCNT1.2/CE composite.When f>fc,all PVDF–eCNT1.7/CE materials have much lower dielectric loss than eCNT1.7/CE,while with suitable thickness of PVDF layer(<70μm),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 5μm,its dielectric constant at 1 Hz is 1699,about ten times of that of eCNT1.7/CE,while the dielectric loss is only 2.31×10−2 times of that of the latter.The origin behind was intensively studied in terms of space charge distribution.