Functional Superhydrophobic PDMS Composite Films for Passive Radiative Cooling

As cooling energy demand keeps rising, passive daytime radiative cooling (PDRC) is emerging as a strong alternative to conventional air-conditioning. It is imperative to ensure that the functionality of radiative cooling polymer films encompasses self-cleaning properties and UV durability to facilitate their extensive and long-term practical applications in outdoor settings subjected to prolonged sun exposure. Functional antiultraviolet radiative cooling films with the superhydrophobic characteristics of “rose petal effect” and “lotus effect” by regulating the mass of K2Ti6O13 (PT) fibers and SiO2 particles are prepared and studied in this work. The film of the lotus effect (LP film) displayed a maximum water contact angle (WCA) of 161° and a water sliding angle (WSA) of 6.3°, while the film of the rose petal effect (RP film) exhibited a similar WCA of 155° and an extremely large WSA exceeding 180°. The reflectivities of the RP film and LP film at 0.4–0.9 μm are 93.2 and 96.1%, respectively, while their corresponding emissivity values in the band of 8–13 μm are measured as 99.48 and 99.53%. Compared to the uncoated Al sheet, the RP film and LP film demonstrate a maximum temperature reduction of up to 11.9 and 12 °C, respectively, at an outdoor test. The most advantageous aspect is that the solar reflectance of the RP/LP film remained virtually unaltered even after undergoing 600 h of continuous UV exposure, demonstrating its exceptional ability to absorb high-energy UV photons and convert them into less harmful heat. This work provides a complete approach to boosting the outdoor performance of polymer-based PDRC materials by adding self-cleaning and UV durability.