Highly compressible and anisotropic polyimide aerogels containing aramid nanofibers

High performance and low density polyimide aerogels have promoted significant interest in the fields of thermal barriers, sensors, mechanical cushioning and so on. However, most of reported polyimide (PI) aerogels suffer from unsatisfied compressibility, flexibility and elasticity. Herein, a series of compressible and elastic aerogels with highly tunable three dimensional architectures were fabricated by integrating the strong and rough aramid nanofiber (ANF) with PI via a facile bidirectional freeze-drying technique. Effects of processing conditions, including the slope angle of freeze-drying, solid concentration and ANF weight fraction, on the micromorphology of resultant aerogels have been systematically studied. With a controlled ratio of the PI and ANF, the PI/ANF composite aerogel demonstrates a highly aligned and wave-shaped anisotropic porous structure, and consequently shows a combination of excellent compressibility, elasticity and fatigue resistance even for up to 500 cycles. Moreover, the PI/ANF composite aerogel exhibits a good compressibility in liquid nitrogen, high thermal stability and ultra-low thermal conductivity, indicating its great potential in some harsh circumstances.