Thermal‐Rectified Gradient Porous Polymeric Film for Solar‐Thermal Regulatory Cooling

• Published in: Advanced materials (Weinheim) 2024-06, Vol.36 (26), p.e2400102-n/a
• Main Authors: Wang, Yufeng, Zhang, Xiaobo, Liu, Song, Liu, Ying, Zhou, Qisen, Zhu, Tianyi, Miao, Yue‐E, Willenbacher, Norbert, Zhang, Chao, Liu, Tianxi
• Format: Article
• Language: English
• Subjects: Concentration gradient; concentration‐gradient polymerization; Cooling; Electric fields; gradient porous film; Microspheres; passive daytime radiative cooling; Polymer films; Polymerization; Smart buildings; solar‐thermal regulation; Thermal conductivity; Thermal insulation; Thermal management; thermal rectification
• ISSN: 0935-9648; 1521-4095; 1521-4095
• DOI: 10.1002/adma.202400102

Solar‐thermal regulation concerning thermal insulation and solar modulation is pivotal for cooling textiles and smart buildings. Nevertheless, a contradiction arises in balancing the demand to prevent external heat infiltration with the efficient dissipation of excess heat from enclosed spaces. Here, a concentration‐gradient polymerization strategy is presented for fabricating a gradient porous polymeric film comprising interconnected polymeric microspheres. This method involves establishing an electric field‐driven gradient distribution of charged crosslinkers in the precursor solution, followed by subsequent polymerization and freeze‐drying processes. The resulting porous film exhibits a significant porosity gradient along its thickness, leading to exceptional unidirectional thermal insulation capabilities with a thermal rectification factor of 21%. The gradient porous film, with its thermal rectification properties, effectively reconciles the conflicting demands of diverse thermal conductivity for cooling unheated and spontaneously heated enclosed spaces. Consequently, the gradient porous film demonstrates remarkable enhancements in solar‐thermal management, achieving temperature reductions of 3.0 and 4.1 °C for unheated and spontaneously heated enclosed spaces, respectively, compared to uniform porous films. The developed gradient‐structured porous film thus holds promise for the development of thermal‐rectified materials tailored to regulate solar‐thermal conditions within enclosed environments. Highly flexible and thermally rectified gradient porous polymeric film is synthesized using a concentration‐gradient polymerization approach. This gradient porous polymeric film possesses both thermal rectification and spectral‐selective properties, making it a promising candidate as a solar‐thermal regulatory cooling material that is capable of mitigating parasitic heat and solar radiation from outdoors while on‐demand dissipating excess heat from indoors.