Luffa-Sponge-Structured Silica/Polyimide Composite Aerogels with Integrated Ultra-Strong Mechanics, Superhydrophobicity, and Exceptional Flame Retardancy

Traditional silica aerogels suffer from inherent brittleness and insufficient mechanical properties, which severely restrict their large-scale applications in high-end thermal insulation and flame retardancy. Aiming at low-cost industrialization, we employ cost-effective sodium silicate as the silicon source and hexamethyldisilazane (HMDZ) as the hydrophobic modifier and innovatively introduce polyimide (PI) nanofibers to construct SiO2/PI composite aerogels. A unique luffa-sponge “seed (dispersed phase)–vein (connecting phase)” topological structure is realized. The interwoven PI nanofibers form a continuous and tough 3D network, which immobilizes SiO2 particles, restrains slippage and agglomeration, and transfers stress through strong interfacial interactions, thereby fundamentally overcoming the brittleness of silica aerogels. The optimized composite aerogel shows a thermal conductivity as low as 26.20 mW/(m·K) and a compressive strength of 21.62 MPa at 70% strain. Meanwhile, it exhibits superhydrophobicity with a water contact angle of 151° and remarkable self-extinguishing behavior. This work provides a low-cost strategy to integrate topology design and multifunctionality, realizing the combination of ultra-low thermal conductivity, high mechanical robustness, superhydrophobicity, and excellent flame retardancy in one aerogel. The as-prepared composite shows great potential in thermal insulation, flame retardancy, aerospace, and new energy applications.