Polymers such as polyimide (PI) have been widely used as electrical insulators due to their high dielectric strength. PI, a well-known inert polymer, has long been used for dielectric applications as an insulation, packaging, and passivation material. It has outstanding dielectric properties, along with high mechanical strength, high flexibility, and excellent chemical resistance. In addition, it is thermally stable with a wide temperature window for operation, making it an ideal candidate as the dielectric for extreme conditions. However, using such polymers in cryogenic environments has other challenges, as they often have high coefficients of thermal expansion (CTE) and reduced flexibility, leading to high chances of damage in the materials when cooled to cryogenic temperatures. Introducing nanofillers in the form of nanoparticles or nanowires into a polymer can help improve the resulting nanocomposite’s overall CTE properties while maintaining a high dielectric strength. The resultant nanocomposites can possess new, enhanced material properties, and can potentially overcome the issues of the pure polymer dielectrics. In this research, a nanocomposite consisting of a PI host and silicon dioxide (SiO~2~) fillers was tested dielectrically at both room and cryogenic temperatures. The host polymer PI was generated from a raw material polyamide using a thermal imidization process. SiO~2~ was selected as the filler material for the final nanocomposite due to its well-known dielectric properties with a much lower CTE than the host PI. The prepared PI/SiO~2~ nanocomposite samples were inspected with a scanning electron microscope (SEM) to ensure the uniform dispersion of nanoparticles inside the host polymer. The dielectric performance of the nanocomposites was obtained using high-voltage DC dielectric breakdown testing at both room and cryogenic temperatures. The composite’s dielectric strength at room temperature exhibited a slight decrease from the pure PI’s dielectric strength of 275 kV/mm at low concentrations of SiO~2~, followed by a large drop off to about 150 kV/mm at higher concentrations. When tested at the cryogenic temperature, the nanocomposite’s dielectric strength was found to increase to 300 kV/mm and maintain this increase for all SiO~2~ concentrations. The mechanisms behind this increased dielectric strength at the cryogenic temperature and the strength drop off at high concentrations in the room temperature data can be explained through our experimental results and SEM images of broken-down samples. These findings can help expand the use of polyimide and potentially other polymers in nanocomposites for cryogenic applications. Future research will be focused on the continued improvement of the dielectric performance of these nanocomposites with increased reliability.


Enhanced Dielectric Capabilities of Polyimide/silicon Dioxide Nanocomposites in Cryogenic Applications

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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