Enhancing Dielectric and Mechanical Performance of Polyimide-based Composites with APTES-Modified SiO2 Nanofillers

Polyimide (PI) is recognized as a highly promising dielectric material for high-temperature superconductor (HTS) power transmission cables, owing to its excellent insulation properties, thermal stability, and mechanical properties. To improve its performance, this study explores PI-based nanocomposites incorporating 3-aminopropyltriethoxysilane (APTES)-functionalized SiO 2 nanoparticles to enhance dielectric and mechanical performance. Five compositions were synthesized, including pristine PI and PI with 2, 4, 6, and 8 wt.% APTES-modified SiO 2 nanofillers. The nanocomposites were fabricated by controlled thermal imidization to ensure maximum conversion from polyamic acid (PAA) to PI and strong filler-matrix adhesion. Comprehensive characterization was carried out to evaluate the dielectric and mechanical performance of the prepared nanocomposites. Scanning electron microscopy (SEM) was used to analyze the surface morphology of post-breakdown samples, while Fourier-transform infrared spectroscopy (FTIR) confirmed the successful imidization from PAA to PI. The PI/4 wt.% APTES-coated SiO 2 nanocomposite possessed a DC dielectric strength of 298.2 kV/mm at room temperature (RT) and 408.2 kV/mm at 93 K, both of which were significantly higher than those of sol-gel-derived SiO 2 composites. Incorporating APTES-modified SiO 2 resulted in improvements of ∼85.2% at RT and ∼52.4% at 93 K compared to their sol-gel SiO 2 counterparts. In addition, the PI/4 wt.% APTES-SiO 2 composite showed enhanced mechanical properties relative to pure PI. These results are attributed to the strong interaction between the silica particles and the polymer enabled by the APTES coating, which improved the material’s ability to withstand electrical field stress and reduced trapped charge buildup.