Research On Dielectric Properties Of Polyetherimide Composites Based On Interfacial Interaction Controlling

In recent years,with the development of wind power generation and microelectronic systems,polymer dielectric materials have received extensive attention due to their flexibility,high breakdown strength,and excellent charge-discharge efficiency.However,due to the weak polarization ability and low dielectric constant of the polymer,the improvement of the energy storage density of the dielectric material is greatly limited.Ceramic fillers with high dielectric constant,such as Barium titanate（BT）,Silicon carbide（SiC）,Barium strontium titanate（BST）,etc.or conductive fillers with high electrical conductivity,such as Carbon nanotubes（CNTs）,Graphene nanoplatelets（GNPs）,Carbon nanofibers（CNFs）,etc.,are widely used dielectric filler to prepare dielectric polymer composites.However,due to their high surface energy and the different properties between filler and polymer matrix,a large number of interface defects can be introduced,which will greatly reduce the breakdown strength of composites.It is difficult for dielectric polymer composite to realize the practical application as dielectric capacitors.Therefore,it is of great significance to prepare composites with high dielectric constant and low dielectric loss by interfacial modification of fillers.Silicon carbide whisker（SiCw）is a kind of semiconductor filler with high thermal conductivity,which has received extensive attention as reinforcement for high temperature resistant dielectric materials.In this paper,the surface of SiCw was modified by different methods,and modified SiCw was introduced into the high temperature-resistant polyetherimide（PEI）matrix.The interactions between different interface layers3-aminopropyltriethoxysilane（AMEO）,polyurea（PUA）,aromatic polythiourea（ArPTU）and PEI matrix were investigated,and the effects of interfacial interaction on the dielectric properties of the composites at room temperature and high temperature were explored.The study found that compared with PUA and ArPTU,the modification of AMEO is more excellent in improving the high-temperature dielectric properties of the composites.Then a composite material with high energy storage density was prepared by surface modification of wide-bandgap nano-zirconia（ZrO₂）by AMEO,and the mechanism of AMEO interface layer under high temperature and high electric field was explored.The main results in this paper are as follows:（1）SiCw is easy to agglomerate in the PEI matrix,and the interfacial compatibility between the SiCw and PEI is poor.To solve this problem,SiCw-AMEO fillers were prepared by surface modification firstly,and then introduced them into PEI matrix to prepare SiCw-AMEO/PEI dielectric composites by solution compounding.Structural characterization proves that there are hydrogen bondings between SiCw-AMEO and PEI matrix,and morphological characterization shows that SiCw-AMEO can be uniformly dispersed in the PEI matrix,at the same time,SiCw-AMEO and PEI have good compatibility.The dielectric properties test found that the presence of the AMEO interfacial layer reduces the strong interfacial polarization between SiCw and PEI,resulting in a lower dielectric constant of SiCw-AMEO/PEI than SiCw/PEI.The uniform dispersion and good interfacial adhesion between SiCw-AMEO and PEI suppress the dielectric loss of the composite.When the content of SiCw-AMEO is 15 wt%,the dielectric constant and dielectric loss of the composite at 25℃are 16.2 and 0.031,respectively.Meanwhile,AMEO can form deep traps and capture the carriers at the interface.In the range of 25-150℃,SiCw-AMEO/PEI exhibits better high-temperature dielectric properties than SiCw/PEI.（2）Aiming at the problem that the interfacial modification of AMEO reduces the dielectric constant of the composites,polymer shells PUA and ArPTU with different dipole moment were prepared on the SiCw surface by in-situ polymerization,and corresponding SiCw-PUA/PEI and SiCw-ArPTU/PEI composites were prepared.Structural characterization proved that PUA/ArPTU can have strong hydrogen bonding with PEI.The morphological characterization found that SiCw-PUA/SiCw-ArPTU and PEI have good interfacial adhesion.The dielectric properties test found that the high dipolar groups of PUA/ArPTU can make them produce dual interface polarization with SiCw and PEI,respectively.At the same filler content,the dielectric constants of SiCw-PUA/PEI and SiCw-ArPTU/PEI composites are higher than those of SiCw/PEI.In addition,the urea group of PUA and the thiourea group of ArPTU have high dipole moments and can act as electron traps,which can reduce the number of conduction carriers,resulting in lower dielectric losses.However,under high temperature conditions,the high temperature dielectric properties of composites could be deteriorated due to the occurrence of secondary reactions.It is found that ArPTU with higher dipole moment can generate stronger interfacial polarization and deeper traps to capture carriers,which promotes the further improvement of the dielectric properties.When the content of SiCw-ArPTU is 15 wt%,the dielectric constant of SiCw-ArPTU/PEI composite reaches 19.6,the dielectric loss is reduced to 0.017.（3）It is difficult for the SiCw with a narrow band gap to maintain the excellent insulating properties of the composites at high temperature and high field,and the agglomeration of the filler will cause electric field distortion and greatly reduce the breakdown strength of the composites.To solve this problem,ZrO₂-AMEO filler was prepared by surface modification of wide band gap nano-ZrO₂,and corresponding ZrO₂-AMEO/PEI composite was prepared.The dielectric properties test shows that AMEO could form strong interaction on the filler surface and increase the molecular interphase polarizability,which promotes the improvement of the dielectric properties of the nanocomposite.In addition,AMEO and the wide-bandgap ZrO₂ nanoparticles can synergistically form deeper traps to capture carriers at high temperature and high electric field,significantly reducing the leakage current density at room temperature and high temperature.When the content of ZrO₂-AMEO filler is 3 vol%,the dielectric constant of ZrO₂-AMEO/PEI composite is 7.3,the dielectric loss is 0.004,and the energy storage densities at 25℃and 100℃reach 6.41 J/cm³ and 3.41 J/cm³,respectively.