Preparation And Performance Regulation Of High Dielectric Constant And Low Dielectric Loss Polymer Nanocomposites

Traditional dielectric materials have gradually failed to meet the demand for electronic devices in the fast-growing electronics industry due to their low dielectric constant,high dielectric loss,and low energy storage density.They usually require electronic devices to be small,integrated,flexible and high performance.The problems in the current two types of high dielectric polymer composites are:Conductive nanoparticle/polymer composites still have problems such as high dielectric loss,low percolation threshold,and extremely poor breakdown strength;Ceramic nanoparticle/polymer composites also have problems such as 'excessive filler concentration,poor filler compatibility,and poor mechanical properties of the composite.These problems have severely limited their applications in dielectric materials.In this thesis,with the preparation of different high-dielectric hybrid fillers as the theme,a variety of hybrid fillers with various structures are designed and synthesized.Then,by modifying the surface of the filler,hybrid fillers with different special surface structures are prepared.Finally,by adjusting the interfacial interaction between the filler and the polymer matrix,the dielectric properties of the composite are improved from different dimensions.At the same time,some applications have been explored.This is of great significance for solving many problems of current dielectric materials.The main research contents and results of this thesis are as follows:(1)A core-shell-structured hybrid is synthesized by coating strontium titanate(STO)shell onto the multiwalled carbon nanotubes(MWCNTs)via sol-gel processing.The amount of STO nanoparticles coated on the surface of MWCNTs can be controlled by adjusting the amount of surfactant.The composites prepared by compounding with epoxy resin can achieve a dielectric constant of 283 at 1 kHz and a dielectric loss of only 0.07 in an extremely low filler loading amount(11 wt%).When the filler content is 5 wt%,the composite exhibits highest energy density.STO as a barrier layer effectively suppresses the dielectric loss of the composites,and its high dielectric properties can also have a gain effect on the dielectric constant of the composites.(2)Barium titanate nanoparticles were attached to the surface of MWCNTs(B@CNTs)by the sol-gel method,and then hyperbranched polyamide was coated on the surface of B@CNTs by in-situ polymerization to obtain HB-Pa/BT composite-coated MWCNTs(H-B@CNTs).After the hybrid powders were compounded with epoxy resin(EP),nanocomposites with high dielectric properties were prepared.In this system,the addition of barium titanate nanoparticles can significantly increase the dielectric constant of the composite.Meanwhile,hyperbranched polyamides also play an important role in improving the dielectric properties and breakdown strength of H-B@CNTs/EP composite.First,hyperbranched polyamide can effectively prevent the barium titanate from falling off the surface of MWCNTs.Secondly,hyperbranched polyamide can effectively improve the dispersibility of B@CNTs in polymer matrix.Finally,hyperbranched polyamides can prevent MWCNTs from overlapping to form a conductive network and suppress the generation of local leakage current,thereby effectively improving the breakdown strength of conductive filler/polymer composites.(3)One-dimensional ceramic calcium copper titanate nanowires(CCTO NWs)were synthesized by a two-step hydrothermal method.After introducing amino groups on the surface of the NWs using a silane coupling agent,a hyperbranched polyamide-coated CCTO NWs(HB-Pa@CCTO NWs)was prepared by in situ polymerization.The nanocomposites filled with HB-Pa@CCTO NWs presented higher dielectric constant than those filled with CCTO NWs alone.Moreover,the dielectric loss of these composites remained at low values(tan ?<0.05)in the entire frequency range.As polymer shells were formed by in situ polymerization on the surface of CCTO NWs,in which special organic molecules bonded on the surface of CCTO NWs can effectively enhance the interactions between NWs and EP matrix,thereby resulting in a higher interface polarization,better dispersion of NWs,and lower interface defects in the epoxy resins matrix.Moreover,HB-Pa@CCTO NWs simultaneously enhanced the breakdown strength,energy density,and mechanical properties of epoxy resins.(4)Based on the successful synthesis of CCTO NWs by hydrothermal method,Sr2+ doped calcium copper titanate nanowires(SCCTO NWs)were synthesized by introducing strontium.The composite prepared after compounding with silicone rubber exhibits extremely low dielectric loss,and has a stable dielectric constant and dielectric loss over a wide frequency range.This is mainly due to the introduction of Sr2+ to make the NWs have a more regular surface morphology,thereby reducing the internal defects and voids in the composites.In addition,Sr2+ doping makes the composites have a larger grain boundary resistance,which will effectively reduce the dielectric loss.In the end,the dielectric properties of composites are greatly improved.In addition,Sr2+ doped composites also have high thermal stability,tensile strength,breakdown strength,and energy density.(5)In this work,CCTO NWs were introduced into silicone rubber to successfully prepare a push-type triboelectric nanogenerator(TENG).Without the need for complex surface treatment,the introduction of high dielectric constant NWs significantly enhanced the dielectric constant and surface charge potential of silicone rubber films.TENG can output a maximum voltage of 350 V,a current density of 0.375 ?A/cm2 and a power density of 40.7 ?W/cm2 at a very low filler concentration(5 wt%),and it can light up to 100 white LEDs.In addition,TENG also has excellent stability and durability,which can be assembled into human motion sensor devices for human energy collection,and can also be used as a self-powered system to charge commercial capacitors.