Fabrication of polyimide aerogels for thermal insulation by modulating cation-π interactions and chain rigidity

Recently, PI aerogels have demonstrated immense potential for applications across various fields due to their outstanding properties, however, the trade-off between strength and toughness has hindered broader use. To overcome this challenge, we have achieved a synergistic enhancement of pore structure and framework by adjusting molecular chain rigidity and cation-π crosslinking density, leading to significant improvement in strength and toughness of PI aerogels. The results reveal that the cation-π bonds help the pore structure transition from a lamellar stacking arrangement to a web-like pore structure, accompanied by a significant reduction in pore size. Peculiarly, as the flexibility of molecular chains increases, the web-like pore structure shifts from disordered cylindrical arrays to regular hexagonal prism arrangement. Moreover, the varied chain rigidity also endows the cation-π bonds with different binding energy. Hence, PI aerogel based on BTDA exhibits the highest mechanical enhancement due to the synergistic effects of more ordered pore structure and much strong cation-π interactions, with its specific strength, specific modulus, and toughness increasing by 154.5%, 251.8%, and 164.3%, respectively. Additionally, it also demonstrates an ultralow density (0.0489 g/cm 3 ) and outstanding thermal insulation performance (0.0427 W/m·K). This presents a novel strategy for fabricating low-density, high-strength-toughness, and low thermal conductivity PI aerogels, which is beneficial for further applications of PI aerogels.