| Dielectric capacitors have the characteristics of high charge and discharge rate and low cost,and have been widely used in portable electronic computing systems,hybrid vehicles and electronic weapons.However,lower energy density hinders their practical application in high-power electronic devices.In order to obtain high energy storage density,the researches add high dielectric constant ceramic flavorings into the polymer matrix,hoping to obtain materials with high dielectric constant and high energy storage density.A large number of results show that the dielectric and energy storage performance not only depend on the intrinsic properties of the polymer matrix and filler,but also are affected by the interfacial effect,filling structure,filler size,diameter ratio,morphology effects and filler orientation effects and other factors.Compared with 0D nanoparticles,1D nanofibers are prone to polarization under the action of an external electric field,so the dielectric constant of the composite material can be improved more effectively.In addition,1D nanofibers can increase the breakdown strength of composite materials under low load,because the nanofibers arranged in the membrane can increase the path curvature during electrical tree breakdown.Compared with inorganic nanoparticle fillers,the synthesis of nanofibers is more difficult,costly,and difficult to produce on a large scale,which limits the application of polymer-based one-dimensional nanocomposites.Therefore,it is very important to find a natural nanofiber to replace synthetic nanofiber.Silicon wafer makes the outer surface of sepiolite nanofibers have a large number of silyl alcohol groups,which can improve the interface interaction between sepiolite and polar polymers,and is also beneficial to the reaction of sepiolite with different organic coupling agents.In addition,sepiolite raw materials are abundant,highly available and low cost,which ensures the continuous utilization of sepiolite.Therefore,in view of the difficulty in synthesis,high cost and difficulty in large-scale production of nanofibers,this paper proposed to use sepiolite as filler and PVDF as polymer matrix to systematically study the effect of the type of modifiers on the dielectric and energy storage properties of PVDF-based composites.The innovative achievements are as follows:(1)In view of the large surface properties between inorganic fillers and polymer matrix,resulting in uneven dispersion and poor compatibility,the sepiolite was organically modified by two siloxane aminopropyltriethoxysilane(denoted as APTES@Sep)and 1H,1H,2H,2H-perfluorodecyltriethoxysilane(PFDTES@Sep).The dielectric properties and energy storage properties of the nanocomposites loaded with different sepiolites were studied.When the filler volume fraction is 7.5%,the dielectric constant of the PFDTES@Sep/PVDF nanocomposite reaches 16.4 at 10~3Hz.The maximum discharge energy density of 7.2 J/cm~3was achieved in the2.5%-APTES@Sep/PVDF nanocomposite under the electric field of 370 kv/mm,which increases by 56%compared with that of pure PVDF.(2)In order to enhance the dielectric constants of composites,core-shell polypyrrole/sepiolite(PPy@Sep)nanofibers were prepared by in-situ polymerization method,and then introduced into PVDF matrix by solution blending method.The SEM and TEM showed that the conductive polymer poly(PPy)uniformly covered the surface of Sep,and the coating thickness was about 18 nm.The results of SEM,FITR,XRD and DSC indicated that the PPy@Sep nano-fillers were uniformly dispersed in the PVDF matrix and possessed heterogeneous nucleation effect on the crystallization of PVDF.As the content of polypyrrole sepiolite filler increases from 0 wt%to 5 wt%,the dielectric constant of the nanocomposites increases from 9 to 40 at 10~2Hz,while the dielectric loss remains low. |
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