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A low-density, high-specific surface area, high-strength and large-sized carbon aerogel preparation process is a key technology in the industrial application of aerogel science. In recent years, ingenious nanostructure design, along with salt templates, drying optimization and other strategies have been applied by numerous scientists. As a result, the specific surface area of carbon aerogel has significantly increased and the density reduced. However, the preparation of high-strength and large-sized intact carbon aerogel at low cost is still a challenge due to the limitations of thermal treatment equipment and drying process. In this study, we propose an improved preparation method of ambient pressure solvothermal polymerization and auxiliary ambient pressure drying by the principle of acid–base two-step catalysis using resorcinol and furfural as raw materials. Resultantly, the condensation and cross-linking reaction process is stabilized by the ambient pressure solvothermal polymerization, which effectively reinforces the interfacial bonding between primary particles and forms a high-strength skeleton. The breaking strength of the aerogels reach up to 9.74 MPa. The auxiliary ambient pressure drying can greatly reduce the drying shrinkage and density of the aerogel and solve the problems of drying deformation and cracking of large-sized carbon aerogel. The drying shrinkage and density of the obtained carbon aerogels are reduced to 3.22% and 0.203 g/cm3, respectively, and the specific surface area reaches 675.057 m2/g. Moreover, the large-sized sample (70 mm (d) × 25 mm (h)) can also be prepared by this method since the strength of skeleton can resist the capillary force of pore structure, and the nanoporous architecture can be perfectly retained. Therefore, this study provides a new preparation scheme for the industrial large-scale production and application of carbon aerogel. [ABSTRACT FROM AUTHOR]

[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]