Acid‐Assisted Toughening Aramid Aerogel Monoliths with Ultralow Thermal Conductivity and Superior Tensile Toughness

Abstract Resisting extreme loading and thermal ablation encountered by aerospace devices demands for high performance engineering materials. Aerogels have achieved satisfactory thermal insulation but the intrinsic brittleness of porous skeletons fail to ensure their normal operation under severe stress fields. Herein, aramid nanofibers (ANFs) are processed into tough 3D aerogel monoliths via a multi‐scale toughening strategy, involving unidirectional freeze‐casting‐enabled microstructure orientation and acid‐assisted nanofiber cross‐linking. Scalable production of ANFs aerogels is realized through fast air‐drying without excessive energy consumption. The aligned sheets in ANFs aerogels enable extreme thermal conductivity of 15.8 mW m −1 K −1 , superinsulation from −130 to 300 °C, and durable combustion protection for 20 min. Particularly, highly aggregated nanofibers assemble into dense ANFs skeletons, endowing the tough aerogels with superior specific tensile strength (89 MPa cm 3 g −1 ), ultra‐high toughness (1.3 MJ m −3 ), and impressive fracture energy (7.36 kJ m −2 ). Such mechanical properties are highly resistant to harsh environments, including water erosion (7 days) and high temperature baking (30 days). Moreover, ANFs aerogels exhibit two to three times more energy dissipation than commercial foams against ballistic impact at 140 m s −1 . This integrated mechanical and thermal robustness may pioneer the potential application in impact‐thermal coupled safeguard for aerogel materials.