Search

[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]

The ice-template freeze-casting strategy combining the static sol–gel and subsequent freeze-drying process is developed for the synthesis of aerogel fibers. In this process, the three-dimentional (3D) monolithic hydrogel assembled by 0D primary particles is disintegrate into 1D fibrous geometries with a precise nanostructure regulation (0D) by ice templates. [Display omitted] • A ice-template freeze-casting method is developed for the facile fabrication of aerogel fibers. • The synthesis enable a precise regulation of fibrous geometries with mesoporous structure. • The aerogel fibers have a good thermal insulation and noise reduction performance. Aerogel fibers inherit the merits of aerogel and fibrous materials, such as ultralow density, large specific surface area and high flexibility, demonstrating great potential as the next generation functional fibers. Herein, an ice-template freeze-casting strategy is developed to prepare polysilsesquioxane aerogel long fibers (PALFs) similar to natural fibers in structure. During the freeze-casting, the strong mutual interaction between solid and liquid phases in the hydrogel induces uniform nucleation and continuous growth of ice crystals in confined spaces. The three-dimensional monolithic hydrogel is gradually deconstructed into one-dimensional fibrous geometries by the growing columnar ice crystals. The obtained PALFs exhibit the polygonal cross-section with a uniform mesoporous structure. After simple physical assembly, the monolithic PALFs exhibit good thermal insulation performance (as low as 25.0 mW/(m·K) at 25 °C) and high-efficiency absorption of broadband sound waves (with a noise reduction coefficient up to 0.58). [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel lightweight and high-strength SiC/MWCNTs nanofibrous aerogel is in-situ derived from a RGO/MWCNTs aerogel. • The aerogel exhibits superior wave-absorbing properties even under thin thickness and low filling ratio. • The aerogel exhibits excellent RCS attenuation performance in C-band, X-band, and Ku-band. Developing Silicon carbide (SiC) -based materials with the characteristics of "lower filling ratio, thinner matching thickness, lighter material mass, and better microwave absorption performance" is an important focus of current research. In this work, SiC/Multi-walled carbon nanotubes (MWCNTs) nanofibrous aerogel was prepared using a selective in situ derivatization strategy with Reduced Graphene Oxide (RGO)/MWCNTs aerogels as templates. It is found that when the filling ratio is only 15 %, the minimum reflection loss of the aerogel can reach −57.36 dB. When the matching thickness is only 1.5 mm, the effective microwave absorption bandwidth can reach 3.34 GHz. Moreover, the aerogel exhibits good multi-band microwave absorption performance, significantly reducing the radar cross section (RCS) in C-band, X-band, and Ku-band. In addition, the aerogel features low density and high mechanical strength, with a density as low as 0.046 g/cm3, and specific strength and specific modulus of 4.35 kN·m/kg and 12.39 kN·m/kg, respectively. This work not only provides a new synthesis strategy for the preparation of novel silicon carbide/carbon-based materials, but also contributes to the development of light-weight, high-strength and high-performance microwave absorbing materials. [ABSTRACT FROM AUTHOR]