PPDA-PMDA polyimide aerogels with tailored nanostructure assembly for air filtering applications

Due to their high porosity and nanoporous morphology, aerogels have presented unique properties and thus offered a very high potential capability to be used in leading applications such as super thermal insulation and nanoparticle filtering. However, controlling the aerogels’ morphology and as a result, tailoring their properties is still a challenge. In this study, polyimide aerogels are developed through imidization of highly reactive pyromellitic dianhydride (PMDA) and p-phenylene diamine (PPDA) monomers. Unlike other monomers, the fabricated PPDA-PMDA aerogels can maintain their solid structure without any crosslinking agent content. A combination of the distinct bonding nature of the two selected monomers and the role of the 1,3,5-benzenetricarbonyl tri-chloride (BTC) chemical crosslinker provide the possibility of tailoring the aerogel morphology and cell structure. The morphology of fabricated aerogels is precisely controlled from clusters of particles to fine fibrous by altering the crosslinking agent molar fraction. Tailoring aerogels morphology results in higher filtration performance, by reduced pore size to 3.5 nm and a more than 200% increase in air permeability over the other studied polyimide aerogels. Moreover, it results in 20% reduced thermal conductivity and more than 5 times improved compression modulus over the fabricated PPDA-PMDA aerogels with similar monomers composition, but different morphology. The fabricated PPDA-PMDA aerogels present relatively lower shrinkage, as low as 5.6%, over the previously studied PPDA diamine polyimide aerogels. Due to the tailored nanostructure assembly and improved performance, this study shows the capability of PPDA-PMDA aerogels to be utilized in airborne nanoparticle filtering applications.