Synthesis of micro/nano multi-scale polyimide aerogels via confinement-controlled freeze-casting.

[Display omitted] • A method is developed for the regulation of secondary unstable dendrites during ice crystal growth. • The flexible polyimide (PI) aerogels possesses a micro/nano multi-scale porous skeleton. • The PI aerogels are characterized by ultra-low density and exceptional thermal insulation. The freeze-casting is widely utilized as a tool for regulating micro-scale pore structures in the fabrication of flexible polyimide (PI) aerogels for applications in adsorption, filtration, and fire-retardant. Herein, a confinement-controlled freeze-casting method is developed to fabricate PI aerogels with excellent thermal insulation properties by designing multi-scale structural adaptability. In a confinement-controlled system, the enhanced solid/solid and solid/liquid interface interactions in the solution dispersion system induce dendritic evolution of ice crystals. Under the directional freezing, grown dendritic ice crystals squeeze the loaded particles to form polyamic acid salt (PAAs) cryogels. Followed by template removal and thermal imidization, PI aerogels with a micro/nano-scale slit-like porous structure were obtained. The PI aerogels are characterized by ultra-low density (as low as 9.82 mg/cm3) and exceptional thermal insulation performance (25.0 mW/(m·K) at 25 °C). [ABSTRACT FROM AUTHOR]