Superhydrophobic photonic-phononic FEP composites for daytime radiative cooling

[Geoengineering News]

https://www.sciencedirect.com/science/article/abs/pii/S0925346725006421

Authors

Wenlong Zhou, Sujing Lin, Ningyuan Xie, Shengxing Wang, Xiaohan Ma, Mai Liu, Ruina Ma, Shijie Li, Yongzhe Fan

27 June 2025

https://doi.org/10.1016/j.optmat.2025.117282

Highlights

•We propose a superhydrophobic radiative cooling coating with a simple preparation process.

•FEP and (K-Al2O3,K-TiO2) have complementary radiative properties in the atmospheric window with an average emissivity of 0.981.

•The combination of Al2O3 and TiO2 particles with synergistic effect is expected to achieve full-spectrum reflectance in the solar radiation band, with an average reflectivity of 0.981.

•A temperature drop of 10.3 °C is achieved under direct outdoor sunlight.

•Building micro-nano structures on the surface, water contact angle reaches 162.8°.

•The optical and superhydrophobic properties of the material are highly stable.

ABSTRACT

Passive Daytime Radiative Cooling (PDRC) is a new type of cooling that does not require additional energy consumption and cools objects by reflecting radiative heat from sunlight and mid-infrared wavelengths. In this study, we prepared PDRC materials by embedding TiO2 and Al2O3 particles into FEP and using a spray-combined phase separation method. The synergistic effect of the formed surface micro-nano-structures, combined with the molecular vibration of FEP, the relatively low band gap and high refractive index in the near-infrared wavelengths of TiO2, and the phonon polarisation resonance of Al2O3, carry out a multiple composite of complementary properties to further improve the optical properties of the PDRC coatings. The PDRC coating has high average reflectance (0.984) in the solar spectral band (0.3-2.5 μm) and high average emissivity (0.981) in the atmospheric window band (8-13 μm). In addition, the PDRC coating has good hydrophobicity with a water contact angle (WAC) of 162.8°. Under direct sunlight conditions, the PDRC material showed a good temperature drop (10.9 °C) compared to ambient temperature and radiative cooling power (98.7 W/m2). The prepared coatings maintained superhydrophobicity and excellent cooling properties when immersed in solutions with different pH and UV radiation. The PDRC coatings developed in this work are simple to fabricate, can be applied over large areas, and have good durability, which is conducive to the promotion of the practical use of RC coatings.

Source: ScienceDirect