Robustly Flexible,\nHighly Transparent, and Polymerization-Regulated\nPolyimide Aerogel Membranes as Efficient Thermal Insulators for Solar\nCollection

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