Influence of nano-SiO2 dispersion on the direct current dielectric properties of SiO2/LDPE nanocomposite

The dielectric properties of SiO2/low-density polyethylene (LDPE) composites are closely related to the dispersion of nano-SiO2 in LDPE matrix. In order to study the mechanism of tensile treatment on the dispersion of nano-silica particles in the LDPE matrix at room temperature, a hydrophobic nano-SiO2 with a particle size of 7 nm was selected to be fused and blended with LDPE to prepare SiO2/LDPE nanocomposites. The prepared nanocomposites were stretched three times, and the dispersion of nanoparticles and the crystallinity of the composites were characterized by SEM and DSC, the trap energy levels and trap densities of the composites were analyzed by thermally stimulated galvanometry (TSC). The effects of stretching on the dispersion of nanoparticles and the resulting changes in direct current dielectric properties were investigated by experimentally testing the space charge, electrical conductivity, and direct current breakdown strength of the nanocomposites. The results show that stretching at room temperature helps the dispersion of nanoparticles and reduce the agglomeration size of nanoSiO2 particles from about 200 nm to about 100 nm. However, stretching will destroy the crystal structure of LDPE and deteriorate its properties; The DC dielectric properties of LDPE can be improved by introducing deep trap levels by doping nano-SiO2.The space charge accumulation of the stretched SiO2/LDPE is suppressed, and the mechanism of conducting current is changed. By fitting the conductance current data, it is found that the conductance of the stretched SiO2/LDPE is dominated by ion hopping conductance, and its hopping distance is reduced to about 1.98 nm. Compared with LDPE, the DC breakdown field strength of SiO2/LDPE is improved by about 43%, The main reason for the decrease of the breakdown strength of SiO2/LDPE after stretching at room temperature is the structural defects of the LDPE matrix caused by the stretching process. © 2023 Beijing University of Aeronautics and Astronautics (BUAA). All rights reserved.