Novel Multilayered Structure Resin Matrix Composites With Low Dielectric Loss And High Energy Density

High dielectric constant materials with high energy density is very important for the applications of dielectric capacitors in hybrid electric vehicles,medical devices and electrical weapon systems as well as the great demand on miniaturization and package application of dielectric capacitors itselves.As a kind of high dielectric materials,the dielectric constant of conductor/polymer composites can be greatly improved when the content of conductor approaches percolation threshold owing to percolation effect,meeting the requirement of high dielectric constant for dielectric capacitors.Meanwhile,the suddenly increased dielectric loss and reduced breakdown strength are harmful to the improvement of energy density.Therefore,how to prepare a high energy density composites with high dielectric constant and low dielectric loss is a meaningful research topic.This is the goal of this thesis.Firstly,using carbon nanotube(CNT),cyanate ester(CE)and hexagonal boron nitride(h BN),three kinds of layered composites were fabricated through stacking up hexagonal boron nitride(h BN)/cyanate ester(CE)(B layer)on carbon nanotube(CNT)/CE with 0.4 wt% CNTs(C layer).According to the relative positions of B layer and C layer,layer structures are named BC,BCB and CBC,respectively.The effects of layer structure and compositions on dielectric properties,breakdown strength and energy density of composites were investigated,and also compared with those of single-layer 0.4CNT/CE composite containing 0.4wt% of CNTs.Results show that three kinds of layered composites all have significantly reduced dielectric loss,improved breakdown strength and energy density.BC and CBC structures have increased dielectric constant compared with 0.4CNT/CE,especially,for the CBC composite with 20 wt% h BN in B layer(C20BC),it's dielectric constant is as high as 323(100 Hz)and the dielectric loss is only 0.049 at 100 Hz,are 10 and 2.6×10-3 times of 0.4CNT/CE,respectively;what's more,it's breakdown strength and energy density are severally about 1.5 and 25 times of that of 0.4CNT/CE composite.The reason behind these interesting results is that on one hand,the presence of insualting B layer can block the conductive paths,thus decreasing dielectric loss and improving breakdown strength;on the other hand,the huge difference of conductivities between B layer and C layer brings about the interface polarization,which endows layer composites increased dielectric constant.Secondly,in order to maintain increased dielectric constant which comes from interface polarization,and further improve the breakdown strength as well as study the effects of layer structure on dielectric properties simultaneously,BI structure with four layers and BIB structure with five layers were prepared through spin coating B layer on one side or two sides of C20 BC structure(named I).Results show that,when the content of h BN in B layer is the same,compared to I structure,the dielectric losses of both BI and BIB are lower and the breakdown strengths are improved.However,due to the fact that the effect of blocking transportation of electrons for the presence of B layer is stronger than interface polarization,the dielectric constants of BI and BIB are not improved compared with I structure.But,we can find that the dielectric constant of BI is larger than and is 2.8 times of that of 0.4CNT/CE composite.The energy densities of both BI and BIB are 9 and 4.5 times of that of 0.4CNT/CE composite.