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[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]

• Pore structure is key parameter influencing its properties. • The agglomeration of SiO 2 aerogels modified is significantly improved. • The best way is modified by cation, non-ionic and inorganic surfactant. • The strength and thermal conductivity of the sample are 17.16 MPa and 0.1889 W/(m∙K) SiO 2 aerogel and cement-based cementing materials mixed prone to fragmentation, agglomeration, flying and floating, resulting in SiO 2 aerogel in cement-based cementing materials can not be evenly distributed. In addition, the mixture of hydrophobic SiO 2 aerogel and cement-based cementing materials has low adhesion and poor compatibility. In this study, the SiO 2 aerogels were modified in different ways for improved compatibility with inorganic cementing materials. The results show that the SiO 2 aerogel slurry (A4) modified by cation, non-ionic and inorganic surfactant had superior dispersibility in inorganic cementing materials. When the content of A4 was 30 wt%, the dry density, thermal conductivity and compressive strength of the sample were 1136.4 kg/m3, 0.1889 W/(m∙K), and 17.16 MPa, respectively. [ABSTRACT FROM AUTHOR]

• Pressureless sintering with cold/hot isostatic pressing is employed. • Thermal conductivity reached 620 W/mK, which is 57 % higher than that of pure copper. • Hot isostatic pressing is employed to eliminate the closed holes and gaps between diamond and copper. • Open pores in copper skeleton closed post high-temperature pressureless sintering. Diamond/copper composites exhibit excellent thermophysical properties and demonstrate wide potential for heat dissipation applications. However, due to high hardness, it's difficult to process complex shape parts. To overcome the challenge, this study proposes the isostatic pressure technique. A pressureless sintering combined with cold and hot isostatic pressing is employed to prepare shaped diamond/copper composites with thermal conductivity reaching 620 W/mK, which is 57 % higher than that of pure copper. Cold isostatic pressing is used to enhance the density of the skeleton, followed by pressureless sintering to change the pore structure from open hole to closed hole. Finally, hot isostatic pressing is employed to eliminate the closed holes, thus improving the comprehensive performance of the composite. [ABSTRACT FROM AUTHOR]