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Although various aerogels with electromagnetic wave (EMW) absorbing properties have been extensively explored, the development of aerogels with excellent wave absorption performance, low density, and great heat resistance has still met profound challenges. Herein, polysilazane hybrid phenolic resin aerogels (PRVS aerogels) were prepared using the vinyl addition reaction of polysilazane and cross‐linking reaction between polysilazane and phenolic resin. A SiOCN ceramic aerogel with multistage pore structure was prepared via a simple and quick freeze‐drying method and polymer‐derived ceramic (PDC) methods. The SiOCN ceramic aerogels exhibited low density (0.15–0.27 g/cm3), good heat‐shielding (thermal conductivity in the range of 0.03–0.04 W/(m·K)), and excellent wave absorption performance (i.e., RL was about –31.6 dB@16.48 GHz and EAB was 3.85 GHz when the thickness of the ceramic aerogel was 1.2 mm). Hence, the ceramic aerogel absorbing materials could meet the requirements of "wide absorption bandwidth, strong reflection loss, lightweight and thi thickness". Moreover, the mechanism of low weight, heat insulation, and wave absorption properties of the aerogels were also investigated. We believe this work is of great significance in ceramic aerogels prepared by traditional polymers, which may provide new opportunities for new ceramic aerogels with applications ranging from EMW absorption to aerospace and information technology. [ABSTRACT FROM AUTHOR]

Silicon-based ceramic aerogels obtained by the polymer pyrolysis route possess excellent thermophysical properties, but their poor mechanical properties limit their broader applicability in thermal insulation materials. Herein, SiCN(O) ceramic aerogels were prepared under the toughening effect of a crosslinker (hexamethylene diisocyanate, HDI), which maintains the structural integrity of the aerogel during the wet gel-to-aerogel conversion. The aerogel maintained a high surface area (88.6 m2 g−1) and large pore volume (0.21 cm3 g−1) after pyrolysis. Based on this, mullite-fiber-reinforced SiCN(O) aerogels composites with outstanding thermal insulation properties and better mechanical performance were synthesized via ambient pressure impregnation. Furthermore, the effect of the impregnation concentration on the mechanical and insulation properties of the composites was investigated. The results revealed that the composite prepared with a solution ratio of 95 wt.% exhibited a low density (0.11 g cm−3) and a low thermal conductivity (0.035 W m−1 K−1), indicating an ~30% enhancement in its thermal insulation performance compared to the mullite fiber; the mesoporous aerogel structures wrapped on the mullite fibers inhibited the gas thermal conduction inside the composites. [ABSTRACT FROM AUTHOR]

In this study, we investigated the tunable porous structure of SiCN(O)-derived ceramic aerogels by changing the molecular structure of the polysilazanes from linear to branched. We also studied the effect of molecular structure on the thermal insulation properties of ceramic aerogels. As the percentage of branched molecular structure in the polysilazane precursor increased, the internal microscopic pore structure of the aerogels changed from macroporous to mesoporous. The specific surface areas and pore volumes of the ceramic aerogels prepared with different precursors increased after pyrolysis at 1000 °C, ranging from 3.7 to 255.9 m2/g and 0.01–0.36 cm3/g, respectively. The corresponding thermal conductivities increased slightly as the aerogels contracted after pyrolysis. The low thermal conductivity (0.046 W/(m·K) at minimum) can be attributed to the decrease in pore size caused by adjusting the precursor structure, which limits the thermal conduction of gas in the porous aerogel materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • A facile method to fabricate well-cushioned and elastic aerogels was presented. • The mechanism of buffering capability and elasticity enhancement was elucidated. • Multifunctional intelligent transportation packaging application was demonstrated. Modern logistics applications demand intelligent packaging aerogels with excellent mechanical properties, but these materials typically do not display good resilience or dynamic cushioning. Here, we propose a facile strategy to fabricate a lamellar porous composite aerogel (CB-CNF/MXene) by the crosslinking and bidirectional freeze-drying of cellulose nanofibers (CNFs) and MXene. The obtained CB-CNF/MXene aerogel showed good resilience and dynamic cushioning capacity, could withstand up to 90 % compressive strain, bounced back to 87.1 % of its original height, and remained stable for 1000 cycles under 80 % strain. It displayed a significantly lower maximum acceleration of 27.4 g than that of expanded polyethylene (35.9 g) and expanded polystyrene (34.1 g), indicating its effective protection characteristics. CB-CNF/MXene also displayed a stable piezoresistive sensing capability of up to 4.11 kPa, demonstrating its suitability for real-time cargo monitoring. It also showed a relatively low thermal conductivity of 29.2 mW·m−1·K−1, making it suitable for cold chain transportation. [ABSTRACT FROM AUTHOR]