Preparation Of Acceptor-doped Filler/Polyimide Composites And Dielectric Properties

Synthesizing high-performance polymeric dielectrics is essential for the development of electrical insulation and aerospace,among others,but achieving both dielectric constant and breakdown strength in polymeric dielectrics is still a challenge.In this work,Si_1-0.75xAl_xO₂（x=0.5,1,1.5,2 mol%）（SA（x mol%））acceptor-doped fillers were prepared by ball-milling and sintering methods and introduced into pyrene-type polyimide（PI）to synthesize polymeric composite dielectrics containing different contents（0.25,0.5,0.75,1,1.25,1.5 vol%）.The hole traps in the filler were used to achieve the regulation of carrier transport in the composite media,and the improvement mechanism of the polymer-based composite media by the acceptor filler was analyzed in depth.By controlling the concentration of hole traps and the volume fraction of the filler,the electrical behavior of polymer-based composite media is examined,and a strategy is proposed for the preparation of polymer-based composite media that can simultaneously improve the dielectric constant,reduce the dielectric loss,and high breakdown strength.Characterization tests revealed that Al³⁺was successfully substituted for Si⁴⁺in Si O₂by high-temperature sintering,and the concentration of hole traps in Si O₂ was regulated by controlling the doping amount of Al³⁺in Si O₂.XRD results showed that Al³⁺successfully occupied the position of Si⁴⁺in the subjected main doped filler.It was further confirmed using XPS that a large number of oxygen vacancies are formed when Al³⁺is substituted for Si⁴⁺,and when 1.5 mol%of Al³⁺is doped in Si O₂,the oxygen vacancy content increases by 148.2%compared to Si O₂ oxygen vacancies and by 90.61%compared to SA（0.5 mol%）oxygen vacancies.SEM results show that the acceptor-doped filler is uniformly dispersed in the pyrene-type PI matrix with no obvious agglomeration.Meanwhile,the SAXS test also showed that the acceptor-doped filler can improve the mass fractal and reduce the surface fractal of the polymer medium,effectively improving the dispersion of the filler in the polymer matrix.The performance test results showed that the dielectric constant and breakdown strength of the composite medium increased continuously with the increase of the concentration of hole traps in the filler at the same volume fraction.Among them,when the volume fraction of the acceptor-doped filler is controlled to 1.25 vol%,the concentration of Al³⁺introduced in Si O₂ increases from 0.5 mol%to 1.5 mol%,and the dielectric constant and breakdown strength E_b of the composite medium at 1 Hz increase from 3.33 and 480.7 k V/mm to 3.60 and 581.5 k V/mm,respectively,and the loss angle tangent at 1 Hz decreases from 0.005 to 0.003,and the corona resistance life decreases from 26.82 to 25.27 hours,which is nearly 40%higher than that of pure PI and pure Si O₂/PI composite media.This demonstrates that a small number of hole traps in the composite media can significantly increase the dielectric constant while effectively trapping carriers and reducing dielectric losses.The dielectric constant,dielectric loss,and breakdown field strength E_b of the polymer composite media increase with increasing volume fraction for the same concentration of cavity defects contained in the filler.Among them,when Al³⁺introduced into Si O₂ was controlled at 1.5 mol%,the volume fraction of filler introduced in the polymer matrix increased from 0.25 vol%to 1.25 vol%,and the dielectric constant and breakdown field strength E_b of the composite media increased by 6%and 10.67%,respectively,and the corona resistance life was improved by 17%.In particular,the breakdown field strength E_b of 1.25 vol%SA（1.5 mol%）/PI composite media was 98.4%higher than that of pure PI and 27.4%higher than that of Si O₂/PI composite film.The synergistic enhancement mechanisms of filler volume fraction and hole trap concentration on the dielectric and breakdown properties of polymer-based dielectrics were systematically investigated,and a short-time breakdown and charge transport model was constructed to elucidate the key role played by the regulation of the volume fraction of the acceptor-doped filler in achieving the synergistic optimization of the dielectric properties and insulation performance of polymer-based composite dielectrics,which provides a new strategy for the synthesis of high-performance polymers.