Preparation And Properties Study Of PVDF Dielectric Nanocomposites

With the rapid development of the electronic and electrical industry toward high integration,large-scale,portable and high-performance,traditional single dielectric materials have been unable to meet the modern electronic and electrical industry production requirements.Dielectric composite with low cost,easy processibility,high permittivity,low dielectric loss,high breakdown strength as well as excellent energy storage density are key to solving this problem.The conductor/polymer nanocomposite is a good choice based on the percolation theory,because it can obtain higher dielectric constant with less content of conductive filler,and its low production cost and easy processibility.Nevertheless,problems such as high dielectric loss,low breakdown strength,and low energy storage density must be solved in the process of industrial application of conductor/polymer composites.In this work,reduced graphene oxide（RGO）and hollow porous carbon sphere（HPC）were used as conductive fillers,and polyvinylidene fluoride（PVDF）was used as the matrix,designing and preparing of SiO₂@RGO/PVDF,HPC-BT/PVDF and sandwich-structured PVDF nanocomposites.The SEM,impedance and ferroelectric measurement were used to systematically study the morphology,dielectric properties and energy storage behavior of nanocomposites.The main research results are as follows:（1）GO-encapsulated SiO₂（SiO₂@GO）hybrids were prepared with electrostatic assembly method and SiO₂@RGO hybrid particles with core-shell structure were obtained after high temperature thermal reduction of SiO₂@GO.Then,SiO₂@RGO/PVDF nanocomposites were prepared with the method of spin coating,and the percolation phenomena and electrical properties of the nanocomposites were studied systematically.It is found that the special core-shell structure of SiO₂@RGO facilitates the dispersion of graphene in the polymer matrix and forms the efficient interconnection between the interface,which greatly improves the dielectric properties（dielectric constant and dielectric loss are 73 and 0.059 respectively at 1KHz）of nanocomposites at ultra-low graphene loadings（0.136 vol%）,and make the nanocomposite have low percolation threshold（0.141 vol%）.In addition,the energy density of composite is 7 times that of pure PVDF at electric field strength of 500kV/cm,and the energy storage efficiency is maintained at a relatively high value,approximately 68%.（2）The HPC spheres were prepared by the template method,and then we fabricated BT deposited in the HPC（HPC-BT）hybrid particles by sol-gel method combining with thermal treatment process.The HPC-BT/PVDF flexible dielectric nanocomposites were prepared using solution blend and spin coating method and then systematically investigated their dielectric properties and energy storage performances.The results show that the addition of HPC can indeed improve the dielectric constant of the nanocomposites,but at the same time,the dielectric loss also increases,and the addition of BT particles comes into being new interfaces,thus being down the interfacial energy between polymer and HPCs,reducing the dielectric loss（0.038）of the nanocomposite material and maintaining high permittivity（50）.At a filler content of 1 wt%,the nanocomposites exhibit breakdown strength of up to 2800 kV/cm and energy storage density of 5 J/cm³,an increase of 133%compared to pure PVDF,besides,the energy storage efficiency of nanocomposite keep a high value of 63%.（3）Trilayer-structured PVDF nanocomposites were prepared by laminating and hot-pressing.The influence of interfacial structure on the dielectric properties of the nanocomposites was systematically investigated,and the effect of filler on the breakdown strength and energy storage density of the nanocomposites was explored.The results show that the addition of PVDF with high breakdown strength could suppress the growth of the electrical branch.As a result,the breakdown strength of the nanocomposites could be as high as 3600 kV/cm and the energy storage density of nanocomposite has a high value near 10 J/cm³,an enhancement of≈386%over pure PVDF,and an increase of 108%compared with the corresponding single layer nanocomposite.At the same time,the energy storage efficiency has also been improved about 77%.