Lightweight Polyimide Foam-Derived Carbon Foam with Anisotropic Porous Structure for Efficient Hydrophobicity and High-Temperature Thermal Insulation at 1000 °C

In this work, the fabrication of lightweight, hydrophobic, and high-temperature thermal insulative polyimide foam-derived carbon foams (PICFs) with an anisotropic pore structure was proposed. First, polyester ammonium salt (PEAS) precursor powders with different component moieties were synthesized by a copolymerization method. Then, the PEAS powders were subjected to microwave-assisted foaming, thermal imidization, and carbonization processes to prepare PICFs. The "bottom-up" directional foaming behavior and high carbon yield of polyimide foams (PIFs) constructed regular honeycomb-like pores in the vertical direction and aligned ellipsoidal strip-like pores in the horizontal direction of the PICFs. Results showed that the PICFs possessed low density (20-40 kg/m³), small pore size (128 μm), favorable mechanical properties (compressive strength of 86.01 kPa) and excellent thermal stability (<i>T</i>_5% > 800 °C). By combining micro/nano porous structures with reduced pore diameters, the PICFs exhibited excellent hydrophobicity, with a water contact angle of up to 128.8° in the vertical direction and 121.2° in the horizontal direction. The PICFs demonstrated superior thermal insulation properties at both room temperature and high temperatures, with thermal conductivity values ranging from 0.0335 to 0.1887 W/(m·K) between 25 and 1000 °C. Thus, lightweight, hydrophobic, and high-temperature thermal insulative PICFs were successfully prepared using the proposed method, which has potential applications in high-end engineering fields such as aerospace, transportation, microelectronics, and nuclear energy sectors, among others.