Effects of Material Preparation in Polyimide/SiO 2 Nanocomposites for Low-Temperature Dielectric Applications

Introducing nanomaterial fillers into a host polymer can significantly change its properties and affect its behaviors. The resulting nanocomposites have the potential to possess new, often enhanced characteristics, making them uniquely qualified for a broader spectrum of new applications. This research investigates the effects of material preparation on nanocomposites using polyimide (PI) as the host polymer and silicon dioxide (SiO2) nanoparticles as the filler. The fabrication and characterization of the PI/SiO2 nanocomposites were explored based on samples produced from two different approaches—a direct mixing process using as-purchased SiO2 nanoparticles and a sol-gel process that relied on chemical reactions to produce SiO2 inside a solvent. The prepared samples and the distribution of the SiO2 nanoparticles in the nanocomposites were characterized with profilometry and scanning electron microscopy (SEM). The characterization showed that the directly mixed samples contained visible nanoparticle agglomerates while the sol-gel films had the nanoparticles uniformly distributed inside the host polymer. The DC dielectric breakdown testing revealed that the sol-gel films outperformed the directly mixed samples at both room (300 K) and cryogenic (164 K) temperatures. When the temperature is cooled down to 92 K, the sol-gel samples demonstrated higher dielectric strengths than pure PI films. Our investigation shows that high-quality PI/SiO2 nanocomposites, especially when prepared through the sol-gel process, are promising candidates as dielectrics that can be used in a variety of cryogenic applications.