Achieving Ultrahigh Transparency and Superior Mechanical Properties in Flexible Polyimide Nanofoams Through CO2 Foaming for Thermal Insulation

• Published in: Advanced functional materials 2024-12, Vol.34 (49), p.n/a
• Main Authors: Li, Xin'ao, Zong, Yumeng, Li, Wenjuan, Qian, Jin, Qiang, Zhe, Ye, Changhuai, Zhu, Meifang
• Format: Article
• Language: English
• Subjects: Carbon dioxide; Foaming; Insulation; Mechanical properties; nanoporous materials; Nucleation; Optical properties; Plastic foam; polymer foams; Polymers; Structural stability; super thermal insulation; supercritical CO2 foaming; Thermal conductivity; Thermal insulation; Thickness; transparent nanofoams; Windows (computer programs)
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.202409498

Transparent polymer nanofoams offer significant potential for thermal insulation, particularly for energy‐saving windows, where both transparency and low thermal conductivity are crucial. However, grand challenges remain in preparing polymer nanofoam monoliths with pore sizes smaller than 40 nm to achieve high optical transparency via minimized light scattering. Herein, the preparation of highly transparent nanofoam monoliths based on fluorinated polyimide (FPI) using CO2 foaming is reported for the first time. The high CO2 absorption capacity and robust melt strength of the FPI matrix significantly promote bubble nucleation while minimizing cell coalescence during CO2 foaming process, resulting in ultra‐small pore sizes down to sub‐10 nm. These FPI nanofoams, with a thickness of ≈0.2 mm, can exhibit high optical transmittance (>85% in the wavelength range of 500–700 nm) and low haze (≈18%), which is unprecedented for polymer foams prepared using foaming methods. Furthermore, these FPI nanofoams demonstrate superior mechanical and thermal insulation properties compared to micron‐sized FPI foams and maintain remarkable mechanical flexibility and structural stability even under harsh conditions, including extreme temperatures and water exposure. Transparent nanofoams prepared using a scalable CO2 foaming method can serve as the next‐generation thermal insulation materials, with broad potential applications in energy‐efficient buildings, and aerospace. Transparent fluorinated polyimide nanofoams are prepared using CO2 foaming method. These nanofoams exhibit high optical transmittance (>85% in the 500–700 nm wavelength range) and low haze (≈18%). Additionally, they demonstrate superior mechanical and thermal insulation properties compared to conventional micron‐sized foams, maintaining remarkable mechanical flexibility and structural stability under harsh conditions, including extreme temperatures and water exposure.