Study On The Preparation Of High Dielectric Constant Barium Titanate/Polyvinylidene Fluoride Composites And Their Structural Properties Based On The New Technology

With the rapid development of the electronic and electrical industry,the traditional ceramic dielectric materials are difficult to meet the new requirements of the electronic and electrical industry due to the disadvantages of the high loss,difficult processing and friability.The polymer based dielectric composites have the advantages of the low loss,low cost,easy processing and good mechanical properties,which can effectively make up for the deficiency of ceramic dielectric materials.So polymer based dielectric composites play an increasingly important role in the microelectronics industry and have the broad application prospects in the fields of the small electronic packaging,electrical insulation,flexible sensors and other fields.The barium titanate（BT）has a high dielectric constant,the polyvinylidene Fluoride（PVDF）is an excellent dielectric polymer matrix with good flexibility,low density,low impedance,high energy storage density and easy processing.Therefore,the BT/PVDF dielectric composites have been widely studied and applied.At present,BT/PVDF composites dielectric constant is often increased by adding a high amount of BT.There are some problems such as poor compatibility between the filler and matrix,big brittleness and high dielectric loss and so on existing for this kind of composite.In this paper a new processing has innovatively been explored to prepare the BT/PVDF dielectric composites which is named solution blending-vacuum hot press molding technology.Moreover,on the basis of this process,the core-shell structure BT@SiO₂ nano-filler with adjustable thickness of silicon dioxide coating has been further prepared,and the interface properties of the BT@SiO₂ nano-filler and PVDF has been systematically studied and improved to obtain BT@SiO₂/PVDF dielectric composites with excellent performance.Further,a small amount of nanoscale conductive carbon black was introduced into BT@SiO₂/PVDF dielectric composite prepared by using BT@SiO₂ nano-filler coated with a certain thickness of silicon dioxide,the microcapacitor is constructed in the composites prepared.Therefore,BT@SiO₂/PVDF/C dielectric composite with high dielectric constant were prepared successfully.The detailed contents are as follows:（1）BT filler dispersion in DMF and PVDF dissolution in DMF were made firstly,and then the ball mill is used for ball-milling to ensure the uniform mixing of the BT filler and PVDF matrix in DMF.the film is formed by heating and solvent evaporating,and then it was further molded by using vacuum hot press to obtain BT/PVDF dielectric composite.The morphology,dielectric property and breakdown property of the composite have been characterized by using the scanning electron microscope（SEM）,impedance analyzer（PIA）and dielectric strength tester（BDS）.The results shown that the composite prepared by the traditional solution blending method is loose and porous,and the solution blending-vacuum hot press molding technology can effectively enhance the interface bond between the matrix and filler,the material is more compact,and the internal defects are relatively less.By changing the ratio of the filler and matrix,the BT/PVDF dielectric composites with dielectric constant of 10～21 at frequency of100 Hz can be prepared,and the characteristic breakdown strength is decreased from 113kV/mm to 62.7 kV/mm with the loading of filler increased.（2）The modified St（?）ber method is used to prepare BT@SiO₂ nano-filler.Appropriate molecular weight of PVP is selected and the dosage is adjusted,the stirring,centrifugal and other process parameters are optimized,BT particles were successfully coated with a layer of SiO₂ with controllable thickness which has good insulating property.The prepared BT@SiO₂nano filler were studied by SEM,EDS,laser particle size analyzer,Fourier transform infrared spectrometer（FTIR）,thermogravimetric analyzer（TGA）,X-Ray Diffraction（XRD）.The results shown that the core-shell structure is obtained,the shell thickness for the prepared BT@SiO₂ nano filler is controllable,the surface of core-shell particle contains a large number of hydroxyl groups.The dynamic contact angle tester（DCAT）was used to verify that the introduction of SiO₂ layer could enhance the interface affinity between the filler and the matrix.The BT@SiO₂/PVDF dielectric composites were also prepared by solution blending-vacuum hot press molding technology.The morphology,dielectric properties and breakdown properties of the composites have been systematically studied by SEM,PIA and BDS.The results shown that BT@SiO₂ has good dispersion in the PVDF matrix.When the mass ratio of the filler to matrix is 3:10,compared with BT/PVDF composites,the dielectric constant of prepared BT@SiO₂/PVDF composite at a frequency of 100Hz has been increased from 14 to 24,and the characteristic breakdown strength has been increased from 70.3 kV/mm to 113 kV/mm.（3）BT@SiO₂/PVDF/C dielectric composites were further prepared.The BT@SiO₂ nano filler with shell thickness about 46 nm was selected,the mass ratio of the filler and matrix was controlled at 3:10.And a small amount of nano conductive carbon black（NCCB）was dispersed in DMF using ultrasonic cell crushing apparatus,then NCCB dispersion,BT@SiO₂ dispersion and PVDF solution were mixed through ball mill.Then BT@SiO₂/PVDF/C dielectric composites were prepared using vacuum hot press molding.The morphology,dielectric properties and breakdown properties of the composites have been systematically studied by SEM,PIA and BDS.The results shown that carbon black can increase the interface interaction of composites markedly.And due to the microcapacitor effect,the dielectric constant of the prepared BT@SiO₂/PVDF/C dielectric composite increases to 45～183 at a frequency of 100Hz,which is significantly improved compared with the BT@SiO₂/PVDF composites,and its characteristic breakdown strength does not significantly decrease.