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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]

[Display omitted] • A novel type of PI/SIO 2 composite aerogel was prepared by a confined filling strategy. • The PI/SiO 2 composite aerogels exhibit ultra-low density and super thermal insulation. • The sound insulation and mechanical properties are significantly enhanced owing to the "honeycomb-like" structure. Aerogels have enormous potential in integrated thermal insulation and noise reduction applications. According to the knowledge of the favorable mechanical and acoustic properties of honeycomb structures. We employed anisotropic "honeycomb-like" polyimide (PI) aerogels as the matrix and utilized a confined filling strategy to directionally filled continuous SiO 2 aerogels into the PI aerogel matrix. This resulted in the creation of an exceptional organic–inorganic composite aerogel (PISis) with outstanding thermal and acoustic insulation performance. The radial thermal conductivity of PISis ranged from 22.37 to 27.65 mW·m−1·K−1, and the initial decomposition temperature was approximately 524–557 °C. In the frequency range of 500–6300 Hz, the average sound transmission loss (STL) of the 18 mm thick composite material reached 30.67 ∼ 31.89 dB, and the compressive strength at 10 % strain is 0.416 MPa. The PISis exhibits a density ranging from 0.1012 to 0.1302 g/cm3. These make it an ideal lightweight, high-strength, and efficient material for thermal and acoustic insulation. [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]

• Polyimide aerogels with nano-porous structure were prepared by ambient drying. • SiO 2 nanoparticles were used as skeleton enhancers and shrinkage inhibitors. • The aerogels exhibit robust mechanical properties and efficient thermal insulation. Ambient drying of polyimide (PI) aerogel is rarely reported due to the strong cross-linking network leading to large shrinkage. In this work, the hydrophobic SiO 2 nanoparticles are used as skeleton enhancers and shrinkage inhibitors to maintain the nano-porous network structure and achieve ambient drying of PI/SiO 2 aerogels. The results show that the PI/SiO 2 aerogel prepared by ambient drying has similar thermal insulation and mechanical properties as the PI aerogel prepared by supercritical drying. The PI/SiO 2 aerogel prepared by ambient drying is low-cost and simple to operate, which is expected to realize the industrialization and wide engineering application. [ABSTRACT FROM AUTHOR]

• Phenolic resin aerogel is synthesized from linear and boron phenolic resin. • The ultralow shrinkage attributes to the strong B-O bond in boron phenolic resin. • Thermal conductivity of aerogel with a density of 0.105 g/cm3 is 0.0352 W/(m·K). • Aerogel shows excellent mechanical stability and resilience capacity. Lightweight phenolic resin aerogel with excellent thermal insulation and mechanical properties is an attractive material for thermal engineering applications. However, to synthesize such material, generally, a significant volume shrinkage would occur during the aerogel formation and the processing time is long. To conquer such issues, the lightweight phenolic resin aerogel with excellent thermal insulation and mechanical properties was synthesized by an elaborately designed process, where linear thermoplastic phenolic resin (LPR) and boron-modified thermosetting phenolic resin (BPR) were used as the raw materials. It was found that the shrinkage rate and the processing time of the phenolic resin aerogel were significantly reduced. By optimizing the synthesis process, the aerogel with a density of 0.105 g/cm3 and a thermal conductivity of 0.0352 W/(m·K) was achieved. [ABSTRACT FROM AUTHOR]

• The rGO hydrogel was prepared by a simple oxidation–reduction process. • A low-density reduced graphene oxide aerogel was obtained by the hydrogel via vacuum freeze-dried. • The 3d-rGO/epoxy resin with a three-dimensional thermally conductive skeleton was obtained by impregnation. • An ultra-high thermal conductivity of 1.79 W/m·K was obtained at the low graphene content of only 1.8 vol%. Using ascorbic acid as the reducing agent, a three-dimensional skeleton reduced graphene oxide (rGO) aerogel is prepared. The epoxy resin composites with high thermal conductivity and low filling content are successfully prepared via vacuum impregnation method combining the graphene aerogel and epoxy. The results show that the 3D-rGO/epoxy composites exhibit superior thermal conductivity to the randomly dispersed graphene epoxy composites at the same content, e.g., the 3D-rGO/epoxy composite has a thermal conductivity of 1.79 W/m*K at 1.8 vol% rGO, compared to 0.77 W/m*K for the randomly dispersed rGO/epoxy composite. The strategy of graphene/epoxy composite in this work has a broad prospect as thermal interface materials (TIMs) in the field of electronic packaging. [ABSTRACT FROM AUTHOR]

• Poor solvents were introduced into the reagent during the synthesis of PI precursor. • Submicron-scale pores are produced in aerogels owing to the poor solvents. • Aerogels in this work have low density (~91 mg cm−3) and low thermal conductivity. The sol–gel process is essentially a process of phase separation between micelles and solvent, so the influence of solvent composition on the result of phase separation will further affect the wet gel and the structure of the aerogel made by it. In this study, during the preparation of polyimide (PI) aerogels, poor solvents were introduced into the reagent during the synthesis of PI aerogel precursor, polyamic acids. The pore structure and thermal insulation performance changes of the PI aerogels caused by this behavior were studied. With the addition of poor solvent, submicron-scale pores were found inside the aerogel. In addition, the introduction of a small amount of poor solvent improved the thermal insulation performance of the prepared PI aerogel. [ABSTRACT FROM AUTHOR]