Study On Preparation And Dielectric Properties Of BaTiO₃@CNTs/PVDF Composite

The rapid development of electronic science and technology,has driven the greater demand and higher requirements for electronic equipment,energy storage facilities,microelectronic capacitors and other fields which closely related to daily life.The material should not only have excellent dielectric properties,but also good mechanical properties.However,the traditional high dielectric materials can not meet these two requirements at the same time.In order to overcome the disadvantages of traditional high dielectric composite materials,barium titanate(BT)was introduced between polyvinylidene fluoride(PVDF)and carbon nanotubes(CNTs)by surface coating.In this paper,BT@CNTs core-shell filler was prepared by three different methods,and the dielectric properties of the composite were investigated.(1)Using the mixed acid to modify the original CNTs,introducing carboxyl groups on the surface,and aminated the BT obtained by sol-gel method through silane coupling agent.The modified BT was adsorbed on the carboxyl CNTs surface by electrostatic interaction force.The morphological characteristics and surface electrical properties of the coated filler were characterized by SEM,TEM and Zata potential.Finally,the cross-sectional SEM and dielectric properties of the BT@CNTs/PVDF composite were explored.The results show that BT particles are successfully coated on the surface of CNTs,but BT particles are partially agglomerated.At room temperature of 1 kHz,the filling amount of CNTs is 5 wt%,the dielectric constant of the composite is 48.25,and the dielectric loss is 0.236,when the BT@CNTs content of BT is 5 wt%and CNTs is 5 wt%,the dielectric constant of the composites can be effectively reduced to 0.036.This shows that BT@CNTs as a filler can effectively reduce the dielectric loss of composite materials.With the increase of the BT content in the coating filler,the dielectric constant of the composite material shows a decreasing trend.This is because the dielectric constant of the BT ceramic powder is lower than that of the conductive particles CNTs.The intrinsic influence of BT will reduce the dielectric constant.(2)Also use mixed acid to modify the original CNTs to produce defects on the surface,and then combine the sol-gel method and the impregnation sintering method to prepare BT@CNTs,which are used as high-dielectric fillers to prepare BT@CNTs/PVDF composites.The results show that the particle size distribution of BT particles coated on the surface of CNTs is between 20-30 nm,and the percolation threshold of the composite material prepared from the coated filler has been improved.The percolation threshold of the CNTs/PVDF system is 4.07%increased to 4.39%.At room temperature of 1 kHz,when the filling amount of the encapsulated filler BT@CNTs is 25 wt%,the dielectric constant of the BT@CNTs/PVDF composite is 25.21,and the dielectric loss is 0.034.(3)Use HNO₃to modify the original CNTs to produce defects on the surface,and then prepare BT@CNTs by hydrothermal method,which is used as a high-dielectric filler to prepare BT@CNTs/PVDF composite materials.The results show that the optimal hydrothermal temperature for preparing BT@CNTs filler by hydrothermal method is 220?,and the optimal hydrothermal time is 2 h.The BT coating on the surface of CNTs is continuous and uniform.The percolation threshold of the composite material prepared from the coated filler has been greatly improved,from 4.07%of the CNTs/PVDF system to 7.99%.At room temperature of 1 kHz,when the filling amount of BT@CNTs is 35 wt%,the dielectric constant of the composite is 53.96,which is 4.89 times that of pure PVDF,and the dielectric loss is 0.054.