Robustly Flexible, Highly Transparent, and Polymerization-Regulated Polyimide Aerogel Membranes as Efficient Thermal Insulators for Solar Collection

Efficient thermal insulators that can maintain their efficacy at extreme temperatures are in pressing demand, particularly in fields such as energy saving, aerospace, and sophisticated equipment. Herein, a novel and facile polymerization-regulated optimal strategy is adapted to realize the comprehensive performance of polyimide (PI) aerogel membranes with mechanical robustness, high flexibility, hydrophobicity, light transmittance, and efficient thermal insulation. Benefiting from the hydrolysis of monomers and chemical imidization reaction process verified by a thermo-chemo-mechanically coupled theoretical model, the viscosity of precursors, shrinkage rate, and microstructure of aerogels are precisely controlled, leading to a low thermal conductivity range of 0.023-0.044 W/(m·K). The fabricated PI aerogel membranes, which undergo a remarkable transformation from their initial brittle and opaque nature to a state of high flexibility and transparency, exhibit a 3.0 times increase in tensile strength (4.6 MPa) and a 8.4 times improvement in elongation at break (20.6%) over previous studies while demonstrating an exceptional light transmittance of 92.5% across a wide spectral range from 500 to 2500 nm. Additionally, the PI aerogel membranes possess superior mechanical properties and a wide temperature resistance range extending from -196 to 300 °C. These flexible PI aerogel membranes can be effectively adjusted to meet the practical application of a circular ring solar thermal collector, which displayed a high solar heat collection temperature of 135 °C at a thickness of 0.5 mm. The coordination between the thermophysical properties and mechanical properties of the PI aerogel membranes in this work holds great promise for application requirements of thermal insulators in optical elements under harsh environments.