Research Of Performance And Preparation Of Graphene/Epoxy High Dielectric Permittivity Polymer Composites

The advanced technology such as electrical industry and material science, has proposed much more requirements on the electric devices, and the development in these fields also put up more demands on the dielectric materials. The high dielectric constant materials played a significant role on the miniaturization and the development of the electric devices. Recently the focus of the researches has been changed into the preparation of materials with high dielectric constant, low dielectric loss, high energy storage density as well as excellent comprehensive properties. Moreover, high dielectric constant materials have become the basis for integrating more electronic components onto the PCB.One traditional way for preparing high dielectric materials is to incorporate high dielectric ceramic particles and conductive metal particles into the matrix. But it needs large amount of the fillers and the poor compatibility between the matrix and the fillers leads to a decrease in performance during processing. Additionally, with high ratio of the nano particles, the fillers will aggregate during the preparation, resulting in a poor dispersion which affects the dielectric properties and other mechanical properties.In recent years, the carbon series have arisen and attracted much attention of being a new ingredient for preparing high dielectric materials, especially the members in nano scale such as nanotube, nano graphite sheets and graphene. As for graphene, with a special two dimension structure, owns itself a characteristic of perfect electrical and thermal conductivity as well as excellent mechanical property. These advantages can be retained only in the condition that the graphene has been kept dispersed in the matrix to stay2D structure. Therefore, the dispersion and distribution of the graphene are the main points for the preparation of the composites.In this work we used graphene as the conductive fillers and poly(bisphenol a-co-epichlorohydrin) glycidyl end-capped curing with the4,4’-methylenedianiline as matrix. The graphene/epoxy composites of different ratios were prepared with the solution-mixing method. The results showed that the content of graphene cannot be increased up to3%because of the high viscosity of the epoxy and the high ratio of the graphene fillers which led to a poor dispersion of graphene in the epoxy matrix. Thus the dielectric constant of the composites was85at1000Hz and the dielectric loss was1.0. Then THF was added into the system as a solution of diluent to prepare a new series of composites with a fixed dilution ratio. The dielectric constant of the diluted composite showed a great increase which was8times higher than that of the initial ones together with much higher dielectric loss. This indicated that with the dilution, the dispersion of the graphene has been greatly improved and the contact between the fillers has also increased, which implied the formation of a much easier conductive path. With the increasing dilution concentrate, the dielectric constant soared to1000at1000Hz and then dropped rapidly while the dielectric loss showed an exactly opposite trend.In the last chapter we found the best fit of the content of graphene of3wt%and the dilution ratio of0.0200g/ml. Then we investigated the influence of curing condition with factors such as time, temperature and amount. We took a further investigation into the dielectric properties of3wt%graphene/epoxy composites with the curing time of3h,4h,5h,6h,7h and8h. It showed that the dielectric constant increased with the curing time longer than3h and could reach500after being cured for6h and remained a high level at high frequency. The dielectric constant increased with the increasing curing time and remained after6h. The DSC measurement exhibited a melting point at50℃at3h, which can be interpreted as the melting absorption peak, an exothermic peak shows up at160℃which can be explained as a reaction of epoxy and the curing agent. It was observed that the integral area decreased with the curing time which means that it was not complete in the reaction. Till8h, the integral area disappeared, indicating that the curing reaction finished. Further more, we focused on the amount of the curing agent placed an effect on the dielectric properties of the3wt%graphene/epoxy composites. The dielectric constant and loss remained at a relative low level with a less content of curing agent. With the increasing amount, the composites found its best fit of highest dielectric constant and lowest dielectric loss with the further complete of the curing procedure with the amount of30%. The DSC curves showed a Tg and an exothermic peak at220℃. The melting point appeared with the amount beyond30%indicated that the matrix had been completely cured and there was residue of the curing agent in the system.In order to take a deep understanding on the influence of the method of preparation, we adopted two methods, one is in-situ coated and the other is solution mixing. At the same content of graphene, the coated graphene@ZnPc/epoxy showed a significant improvement in dielectric constant together with the increased dielectric loss at the same time.In the last chapter we started the research from the molecule design, the fluorine-containing bisphenols and one carboxyl group in typical nucleophilic substitution reaction of poly(ether ether ketone)s containing carboxyl side group was synthesized. H1NMR and FTIR were utilized to characterize the structure, and the DSC to demonstrate its thermal properties. The polymer was dissolved in THF solution and was prepared into ternary composites using solution-mixing method. The research showed that with the addition of graft PAEK, the dielectric constant decreased compared with the composite of same content of graphene. But the mechanical properties was improved with the breaking elongation nearly doubled, which could retain the dielectric property meanwhile improve the toughness in the3D net structure of the system.