Study On Dielectric Property Of Modified Expanded Graphite/Epoxy Resin Composite

In recent years, with the rapid development of electronic and electrical field, thedemand for making high-k material is very urgent, it needs innovation and research. Due toits light weight, easy process, high-k polymer matrix composite which can be used as highenergy storage capacitors, electro-active materials, artificial muscles and smart skins hasbeen widely studied and applied. The conductor/polymer matrix composite can achievehigh dielectric constant when the filler content is little, but the dielectric loss also mutate inthe conductor/polymer composites when the filler content is near the percolation threshold.High dielectric loss is consumed to generate heat that should be avoided, therefore, how toreduce the dielectric loss is a hot topic in the high-k polymer matrix composite.Initially, some researcheres modified conductor with coupling agent, finding goodinterface could reduce dielectric loss; subsequently some modified conductor with coatinglayer which prevent the contaction between the conductors, so reduced leakage currentwhich will increase dielectric loss because of conductor contaction. Surface coating is aneffective method, but there are still some questions. First, if the conductor fillers are fullycovered, the interfacial polarization between conductor and resin is reduced evendisappears, the percolation threshold is high, so the amount of filler need much more thanbefore to achieve high dielectric constant; Second, the coating layer on the conductorgenerally does not have active groups, so the fillers have poor dispersibility, easy toagglomerate in the resin matrix. To solve the above problems, this paper designs a kind ofhybrid filler with controllable coating degree, and the conductor and the coating layer bothhave large number of functional groups, and then we study the influence of hybrid fillerson dielectric performance and other properties of the two-phase and three-phase composite.Expanded graphite nanoplates(EG) have high electrical conductivity, large aspectratio and large surface area, so a large number of microcapacitors are formed because ofthe layer structure; More importantly, during the manufacturing process the sheet surfacecarried the C-O-C, C-OH and C=O functional groups. Silica nanoparticles can besynthesized by St ber method, there are a large number of hydroxyl group on silica particles.In this paper, we prepare silica-coated expanded graphite hybrid fillers (ES) with acontrollable coating degree, and then the hybrids are added into epoxy resin. Afterwards,we study the effects of influence of hybrid fillers on dielectric performance and otherproperties of the two-phase and three-phase composite.First, we designed the orthogonal experiment and prepared nine kinds of ES hybridswith different areas of coating. Then the ES/EP composites were prepared. Compared withEG/EP composite, ES hybrids have a better dispersion in the resin matrix with more layerstructure. ES/EP composite has a higher dielectric constant and lower dielectric loss, thehigher Tg, mostly important, the percolation threshold remains unchanged.Second, the prepared ES were used, EG-MWCNT/EP and ES-MWCNT/EPthree-phase composite were prepared. The three-phase composite material takes advantagein obtaining high dielectric constant and low dielectric loss. The conductivity has arelationship with the dielectric properties, with the increasing degree of coating area, theconductivity of the composite drops, the dielectric constant increases and dielectric loss isreduced.