Research On Performance Of PVDF-based High Dielectric Composite Filled With BT@SSMWNT Core-shell Particles

Ceramic/polymer high-dielectric flexible composite materials possess low dielectric loss and high electrical breakdown strength.However,there are still some challenges in terms of the balance between the dielectric properties and the filler loading,and the demand for high thermal conductivity materials for the miniaturization and functional development of electronic products.In order to solve the above problems,barium titanate@super short multiwall carbon（BT@SSMWNT）core-shell filler was designed and prepared in this paper.The effect and mechanism of the filler on the dielectric properties and thermal conductivity of PVDF composites were explored.Through the design of the microstructure of the filler,the filler content reduce and a synergistic improvement in comprehensive dielectric properties and thermal conductivity is achieved.The main research contents and research results are as follows:（1）BT@SSMWNT core-shell particles with SSMWNT as the complete shell were prepared.Using it as filler,BT@SSMWNT/PVDF composite material was prepared.In the range of 10³～10⁶Hz,the composite material has good synthetical properties.When the filling amount is 60 wt%（including more than 17 wt%SSMWNT）,the dielectric constant is in range of 32～156 and the tanδis in range of0.28～1.48.The thermal conductivity of the composite material is from 0.96 to 25.43Wm^-1k^-1with the increase in the filler content.At a relatively low ceramic loading,a balance between dielectric constant and dielectric loss is achieved,and the dielectric properties and thermal conductivity are synergistically improved.The excellent overall electrical properties of the composite material are attributed to the multiple effects of the SSMWNT shell,including the application of an electric field on the BT particles to effectively improve the polarization efficiency of BT,enough interface polarization attributing from tremendous interface area,restricted charge movement reduces dielectric loss,and efficient electron heat transfer achieves high thermal conductivity（2）BT@SSMWNT core-shell particles were prepared with BT（average grain diameter 300 nm）as the core,and 300-BT@SSMWNT/PVDF composite material was prepared using it as a filler.The dielectric constant is as high as 1900,when the filling content is 60 wt%（including more than 33.8 wt%SSMWNT）at 1 KHz.When the filling content is 10 wt%,the dielectric constant of the composite is as high as 463.1,the tanδis only 1.1,and the thermal conductivity is 1.12 Wm^-1k^-1,respectively.The dielectric constant of 300-BT@SSMWNT/PVDF composite material present much higher than this of BT@SSMWNT/PVDF composite.It is due to the facts that 300-BT has a higher spontaneous polarization ability,and interface polarization increase because of the higher SSMWNT content of BT@SSMWNT core-shell particles.（3）Using the principle of charge dissipation of the"quasi-conducting zone"constructed by overlapping materials of different conductivity,a single-core double-shell core-shell filler,with BT（average grain diameter 300 nm）as the core,with SSMWNT as the intermediate layer and PANI as the outer shell layer,was prepared by in-situ polymerization.The results show that The particles has obvious core-shell structural characteristics and relatively uniform particle size which are in the range of 300～500 nm.The BT@SSMWNT@PANI/PVDF composites has a percolation threshold when the filling content is 30 wt%.The dielectric constant of the composite is as high as 1805 at 1 KHz,and the dielectric loss is only 0.42 which is much lower than that of 300-BT@SSMWNT/PVDF composite material.The excellent dielectric properties of the composite material can due to the double shell particles that make the composites achieve the microcapacitor effect,whose shell produce charge dissipation so that the low dielectric loss is achieved.