Controllable Preparation And Dielectric Properties Of Graphene/Barium Titanate/Polymer-based Composites

In order to meet the diverse needs of dielectric materials in various fields,researchers have focused more on polymer-based dielectric materials.How to control the internal structure of the composite system through the dispersion of fillers in the matrix,obtain the ideal dielectric constant and ensure the lower dielectric loss is an urgent problem.At present,there is a lack of effective and feasible theoretical basis and technical guidance.In this paper,polymers with different structural characteristics are selected as matrix,nano-carbon materials and ceramic materials are introduced as fillers,and different composite structure designs are adopted to explore the mechanism of action between filler and matrix in different composite systems.The structure-activity relationship between structure and dielectric properties of polymer-based dielectric materials is established to provide theoretical basis and design guidance for the research and development of polymer dielectric composites.In a composite system based on thermosetting resin,using carbon materials of different dimensions,namely two-dimensional few-layer graphene(GNP).zero-dimensional spherical carbon black(CB),and three-dimensional layer stacked nano-graphite(nanoG),composite with epoxy resin(EP)was performed.The study found that two-dimensional GNP has better dispersion in epoxy,and with different GNP contents.EP/GNP system has high activation energy.GNP with lamellar structure strongly interact with epoxy resin,hindering the formation of crosslinked reticular structures,which favors the orientation of polar groups.The interfacial polarization is enhanced.When the content of GNP increased from 0.5 wt.%to 1.0 wt.%,EP/GNP system appears percolation phenomenon.Thus,the mechanism of two-dimensional graphene materials in dielectric composites of thermosetting matrix is revealed.By introducting of nano-sized ceramic particles barium titanate(BT)to the EP/GNP system and studying the dielectric properties EP/BT/GNP ternary systems,find there is some synergy between GNP and BT.It is Not only beneficial to the increase of dielectric constant but also effectively hinders the increase of dielectric loss.Poly(vinylidene fluoride)(PVDF)composites filled with graphene(GNP)and barium titanate(BT)were prepared by solution method and hot pressing method.By changing the amount of filler,it was found that when the content of GNP was 0.2 wt.%,the microcapacitor structure would be formed in the matrix.When the content of GNP was 0.8 wt.%,the parallel microcapacitors overlapped each other to form a conductive path,and percolation phenomenon appeared in the system.By analyzing the influence of graphene and barium titanate on the dielectric properties of the composites,the synergistic effect of interface polarization effect and microcapacitor effect in improving the dielectric properties of the composite system was revealed,and the mechanism of controlling the dielectric properties by the design of conductive layer dielectric layer structure was revealed.In this paper,we try to use the microcapacitor structure in the single-layer composite film to prepare the layered structure film with microcapacitor structure by hot pressing method.PVDF/GNP is the upper and lower conductive layer,and PVDF/BT is the dielectric layer in the middle layer.By changing the thickness of different layers and the content of GNP and BT in each layer,a series of three-layer films were prepared.Although the theory of interface polarization and micro capacitance can not explain the dielectric properties of thin films.However,when the frequency is 10～105 Hz,the dielectric loss influence loss of each layer is less than 0.05,and there is no obvious fluctuation.It shows that the layer structure design is conducive to reduce the dielectric loss of the composite system and keep relatively stable,which has a positive effect on improving the dielectric properties.Based on the structure design of conductive layer dielectric layer,the miscible PS and PVDF were used as matrix resins and GNP and BT as fillers.The blend system of composite fillers was prepared by blending method,and the microcontrolled phase structure was formed.The selective distribution of GNP and BT in PS/PVDF matrix was found.The conductive filler GNP is selected to be distributed in PS phase,while the dielectric filler BT is selected to be distributed in PVDF phase.Due to the selective distribution of fillers,when the matrix is cocontinuous,the fillers can also be continuously distributed in the matrix,resulting in(PS/GNP)(PVDF/BT)system.The dielectric constant of the system is higher than that of other blends,and the dielectric constant of the matrix is increased by three times.When the frequency is greater than 105 Hz,the maximum dielectric loss is about 0.09.The results show that the breakdown strength of the filler selective composite system is higher than that of other blends,and the shape parameter β of the breakdown field strength increases,and the reliability of the material is improved.For the blend system with co-continuous matrix and pre-selective distribution of fillers,conductive filler forms conductive layer,and dielectric filler forms dielectric layer.Therefore,the dielectric constant of the system can be predicted by using the mixed dielectric model.The theoretical prediction value of the dielectric constant is in good agreement with the measured value.