Influence of different types of SiO2 nanoparticles in polyamic acid for enhanced dielectric and mechanical performance at room temperature

In power transmission applications, there is an increasing demand for insulating materials capable of maintaining high dielectric and mechanical strength across a broad temperature range. However, achieving effective insulating properties with a single polymer is challenging. Therefore, thin films of polymer-based nanocomposites are under investigation. This study investigates the effects of three types of SiO2 nanoparticles, one as non-coated and the other two with different surface coatings, in polyamic acid (PAA) utilizing four different solvents for SiO2 dispersion within the matrix, in achieving high dielectric and mechanical strength at room temperature. High-voltage breakdown and tensile tests were performed to determine the dielectric and mechanical properties of nanocomposites, respectively. The breakdown structures were characterized using scanning electron microscopy. The characterization shows that both the nanoparticles and processing solvents have direct impact on the dielectric and mechanical performance of the samples. The combination of 3-aminopropyl triethoxysilane (APTES) surface-coated SiO2 and dimethyl sulfoxide solvent resulted in the highest performing dielectrics, with dielectric strengths of 141.15 kV/mm (alternating current, AC) and 184.60 kV/mm (direct current, DC) as well as superior mechanical properties with ultimate tensile strength of 64.34 MPa, yield strength of 43.11 MPa, and elastic modulus of 2405.05 MPa. These values represent a significant improvement of both dielectric and mechanical properties from the pure polymer by 13%-20%. The enhanced performance can be attributed to the surface functionalization of SiO2 nanoparticles with APTES that promotes molecular interactions, facilitates charge redistribution, and strengthens the interfacial adhesion when they are incorporated into PAA.