Ultrasound‐assisted freeze‐drying strategy to enhance nanoparticle dispersion in aerogels: A case study on polyimide/silica nanocomposite aerogel

Abstract

Thermal protection materials should possess light weight, excellent thermal insulation, flame retardant and hydrophobic properties. Aerogel are considered a promising thermal protection material due to its high porosity and low density. Among them, nano‐silica/polyimide composite aerogel has been intensively studied as they can solve the problem of fragility of nano‐silica aerogel while ensuring thermal insulation and flame retardant performance. However, the problems of nanoparticle agglomeration and the tedious preparation process remain unsolved. The ultrasound‐assisted freeze‐drying (UAFD) strategy presented in this paper avoids the tedious silica solution preparation process by hydrolyzing silica precursors to achieve good dispersion of silica. This strategy replaces the traditional approach of functionalized modification of silica nanoparticles to inhibit their agglomeration with a new method of nanoparticle dispersion by ultrasound and rapid freezing to lock the dispersed state. The UAFD strategy enables the rapid and efficient preparation of well‐dispersed nano‐silica/polyimide composite aerogels, and the hierarchical pore structure of the composite aerogels is imparted by this facile preparation strategy that cooperates with the co‐regulation capability of the tert‐butanol on the morphology of the ice template. The aerogels have substantially improved thermal insulation, flame retardant, and hydrophobic properties when compared with those prepared by conventional freeze‐drying methods.Highlights Ultrasound‐assisted freeze‐drying (UAFD) enhances nanoparticles dispersion. UAFD and tert‐butanol synergistically prepared hierarchically pore structure. Thermal protection performance of aerogels prepared by UAFD is improved.

Piperazine as a Water-Solubilizing Agent for Cross-Linking and Mechanical Enhancements in Freeze-Dried PI Aerogels

“…Significant differences in thermal insulation were demonstrated between the 5% and 3% solid content samples, with the 5% samples having higher thermal conductivity, indicating lower thermal insulation. This phenomenon can be explained by the higher porosity in samples with lower solid content, which increasing the air content within the material and results in lower density and lower thermal conductivity . Additionally, the thermal conductivity of PI aerogels varies with different molecular structures.…”

“…This phenomenon can be explained by the higher porosity in samples with lower solid content, which increasing the air content within the material and results in lower density and lower thermal conductivity. 28 Additionally, the thermal conductivity of PI aerogels varies with different molecular structures. SEM microstructural analysis showed that PI−II, which has lower thermal conductivity than PI−I, contains more pores and a complex network structure.…”

“…Recently, PI aerogel synthesis has shifted toward eco-friendly and economical methods, with many researchers adopting triethylamine and water mixtures to create PI aerogel rather than using additional solvents. To avoid potential structural problems, Xiao et al 28 used a mixture of triethylamine, tertbutanol, and water as the solvent. It promotes the formation of porous aerogels with enhanced performance by modifying the solvent crystal structure, reducing solvent use while maintaining aerogel properties.…”

Eco‐friendly production and performance evaluation of water‐resistant cellulose nanofiber bioaerogels

“…18 Additionally, treatment such as ultrasonic treatment has been employed to assist in dissolution and dispersion. 19 Further, various strategies including chemical and cationic crosslinking, coating with hydrophobic agents like silanes, reducing electrostatic repulsion through surface charge group protonation, and producing composite aerogel, have been applied to enhance the water resistant of cellulose aerogel. 7,15,[20][21][22] However, these supplementary gelation and modification procedures entail additional chemical inputs and energy consumption.…”