Preparation And Dielectric Properties Of Multilayer Nanocomposites Based On Poly(Aryl Ether Sulfone)

With the widespread popularity of advanced electronic products and electronic power energy systems,people's demand for electrical energy storage devices such as capacitors is increasing.As one of the storage and transportation systems,dielectric capacitor materials have a wide range of applications in smart grids,electric vehicles,high-energy weapons,electronic equipment and communications due to their extremely high power density and environmental protection.Compared with ceramic dielectric materials,polymer-based dielectric materials have the advantages of high breakdown strength,low dielectric loss,high power density and easy processing,and are suitable for practical applications.Unfortunately,as the core material of capacitors,high-performance polymer dielectric materials still have poor thermal stability and cannot adapt to working problems in high-temperature environments,resulting in a sharp drop in charge and discharge efficiency and energy storage density at high temperatures;In addition,the composite material has the problem of dielectric mismatch caused by the interface between the nanoparticle and the polymer,which causes the dielectric loss of the material and the increase of the leakage current density,and there is also the contradiction that the dielectric constant and the breakdown strength cannot be both at the same time.The existence of these problems hinders the application of polymer dielectric composites in electronic power systems.In this thesis,cross-linkable polyaryl ether sulfone with good thermal stability was designed and synthesized as the polymer matrix,and the surface-modified barium titanate,titanium dioxide and boron nitride nanosheets were selected as the fillers for each layer.Three layers of thin films are superimposed through the scraping process,and the interface-enhanced"sandwich structure"polymer-based nanocomposite film material is obtained after heat treatment.The mechanical properties,dielectric properties and energy storage properties of single-layer and three-layer polymer film materials at room temperature and high temperature are systematically studied.The main research contents are as follows:1?First,a high-temperature resistant poly(aryl ether sulfone)polymer matrix with propylene side groups was designed and synthesized,and the surface of barium titanate titanium dioxide and boron nitride nanoparticles was modified.The single-layer BN-BCB@DPAES?BT-BN-BCB@DPAES?TiO₂-BCB@DPAE,BN-BCB/BT-BCB/BN-BCB@DPAES?BN-BCB/TiO₂-BCB/BN-BCB@DPAES three-layer polymer nanocomposites.After heat treatment,a cross-linked composite material with nanoparticles as cross-linking sites is obtained,in which the interlayer polymer molecular segments in the three-layer composite film exhibit hand-in-hand cross-linking behavior.It can effectively weaken interface problems.The composite film obtained with the sandwich structure has excellent thermal stability and mechanical properties.2?Sandwich structure composites show good dielectric stability and excellent energy storage performance at high temperatures.At 150?and 500 MV/m,the dielectric loss of BN-BCB/BT-BCB/BN-BCB@DPAES is only about 0.006,the discharge energy density is 4.64 J/cm³,and the charging and discharging efficiency is above 85%,including the greatly improved breakdown field strength(556 MV/m),greatly reduced leakage current density.In order to avoid the crystal transformation of barium titanate nanoparticles at high temperatures and further increase the energy storage density of the system,we chose modified titanium dioxide nanoparticles(TiO₂-BCB)as the filler for the intermediate layer.Under the same amount of filler,the dielectric constant of the BN-BCB/TiO₂-BCB/BN-BCB@DPAES sandwich structure composite film reaches 6.1,and the loss remains at about 0.007.At the same time,the discharge energy density reaches 5.0 J/cm³(500 MV/m,?>80%)at 150?,and the breakdown strength of 555 MV/m is also better than single-layer composite film materials.The finite element simulation results show that the formation of a cross-linked transition layer between the layers of the multilayer nanocomposite through the entanglement of polymer molecular segments can effectively block the growth path of the electrical tree and greatly increase the breakdown strength of the material.In summary,the interface-enhanced sandwich structure poly(aryl ether sulfone)-based nanocomposite film material has excellent energy storage density and ultra-high charge and discharge efficiency at 150?,and meets the application requirements of long-term use at high temperatures.This work proves a way to improve energy storage performance by designing interlayer polymer molecular segments entangled to form a cross-linked network in the multilayer nanocomposite structure,it provides new ideas for the design of high-performance dielectric polymer nanocomposites.