纳米SiO2/低密度聚乙烯复合材料的陷阱特性与电击穿机制

以低密度聚乙烯（LDPE）为聚合物基体，通过熔融共混的方式填充不同粒径的纳米SiO₂无机颗粒，制备纳米SiO₂/LDPE复合材料，研究提高聚乙烯电绝缘性能的纳米改性方法和机制。利用SEM表征纳米SiO₂在LDPE基体中的微观形态和分散程度，采用DSC和偏光显微镜（PLM）分析纳米SiO₂对LDPE基体结晶度和结晶形态的影响，通过热刺激电流法（TSC）分析纳米SiO₂/LDPE复合材料的陷阱密度和陷阱能级，并结合电击穿的Weibull分布研究纳米复合材料的击穿机制。研究结果表明:纳米SiO₂填充可以改变复合材料结晶度，进而增加LDPE基体本征结构缺陷和陷阱密度，同时填充纳米SiO₂颗粒可引入比LDPE基体本征陷阱更深的陷阱能级，纳米SiO₂填充颗粒引入的陷阱能级深度随着复合材料结晶度的增加而先增大后减小，填充浓度3wt%时可最有效地通过俘获载流子而抑制电击穿过程，纳米SiO₂/LDPE复合材料的击穿场强达到最高值。与60 nm SiO₂颗粒相比，30 nm SiO₂填充颗粒具有更高的比表面积，界面电极化导致更高的介电常数，更高密度的纳米界面深陷阱态对于提高电击穿场强更有效。当填充浓度为5wt%时，纳米颗粒的团聚作用导致纳米复合材料的击穿强度降低。基于电双层理论提出了电子捕捉模型和界面结构模型，合理阐释了纳米SiO₂/LDPE复合材料的微观陷阱特性及宏观电击穿机制。 

Trap characteristics and electric breakdown mechanism of SiO2/low density polyethylene nanocomposites

The silicon dioxide/low density polyethylene (SiO₂/LDPE) nanocomposites were developed by filling SiO₂ nanoparticles into LDPE matrix with melt-blending preparing method to investigate nano-modification method and correlated mechanism for insulation performance improvement of LDPE. The micro-morphology and dispersivity of SiO₂ nanofillers composite in LDPE matrix were characterized by scanning electron microscopy (SEM). The differential scanning calorimetry (DSC) and polarizing microscope (PLM) were employed to testify the effects of SiO₂ nanofillers on the crystallinity and crystal morphology of LDPE matrix. The trap energy level and density were tested by thermal stimulated current (TSC), combining the Weibull statistics of electric breakdown strength to investigate insulation breakdown performance and attributed mechanism. The nano-SiO₂ filling rate can change the crystallinity of composites, while the change will increase the intrinsic structural defects and trap density of LDPE matrix. At the same time, filling nano-SiO₂ particles can introduce deeper trap levels than the intrinsic traps of LDPE matrix. Therefore, the most efficient inhibition to electric breakdown process by trapping charge carriers with largest energy, and thus the maximum breakdown strength are obtained for 3wt% filling rate of SiO₂/LDPE nanocomposites. In comparison with 60 nm SiO₂ nanoparticles, the 30 nm SiO₂ nanoparticles with larger specific surface area filled into LDPE render higher dielectric permittivity from SiO₂-LDPE interface polarization, indicating the more efficient enhancement for electric breakdown strength by higher-density deep traps at larger-area nano-interfaces. Based on dielectric double-layer theory, the reliable models of electron capture and interface structure were put forward so as to reasonably represent the microscopic trap characteristics and macroscopic electric breakdown mechanism of SiO₂/LDPE nanocomposites.