Optimizing Concentration of SiO₂ Nanoparticles in PAA-Based Composites for Dielectric Strength Under Cryogenic Conditions

In industries such as power transmission and cryogenics, there is a growing need for polymeric insulating materials that consistently maintain high dielectric properties across a wide temperature range. However, achieving optimal insulation performance under extreme conditions remains challenging for a single polymer system. To address this limitation, thin films of polymer-based nanocomposites are being explored. In this study, thin films of polyamic acid (PAA) with different concentrations (0,2,4,6,8 wt.%) of 3aminopropyl triethoxysilane (APTES) surface coated SiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> were fabricated. The nanoparticles were dispersed in a dimethyl sulfoxide (DMSO) solvent to ensure uniform distribution. The films were prepared using a spin coating technique, followed by a controlled curing process and subsequent peeling from the substrate. To assess their dielectric performance, high-voltage alternating current (AC) and direct current (DC) breakdown tests were conducted on nanocomposite films at a cryogenic temperature (93 K). Post-breakdown characterization of failure structures was performed using scanning electron microscopy (SEM), with elemental analysis carried out through energydispersive spectroscopy (EDS). The results indicate that the PAA nanocomposite containing 6wt. % SiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> exhibited the highest dielectric strength among all compositions. It possessed superior dielectric strength, achieving 292.79 kV /mm under AC and 373.76 kV /mm under DC conditions. This enhancement in dielectric performance is attributed to strong interfacial interactions between the APTES-functionalized SiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> nanoparticles and the PAA matrix.