Electrospun Bilayered PVDF-HFP-TiO2/Al2O3 Nanofiber Membranes for High-Performance Passive Radiative Cooling

Abstract

Passive radiative cooling is an emerging strategy for reducing heat accumulation by efficiently reflecting solar radiation and emitting thermal energy within the atmospheric transparency window (8–13 μm). In this study, we systematically compared four architectural designs for radiative cooling membranes: PVDF-HFP-TiO2, PVDF-HFP-Al2O3, a mixed PVDF-HFP-TiO2-Al2O3 composite, and bilayered PVDF-HFP-TiO2/Al2O3. The incorporation of strategically sized TiO2 (0.7–1.1 μm) and Al2O3 (50–300 nm) microspheres was found to enhance broadband solar reflectance via complementary Mie scattering, with TiO2 primarily scattering near-infrared light and Al2O3 effectively scattering visible radiation. While all of the samples exhibited high solar reflectance (~88–95%) and strong mid-infrared emissivity (~0.98), bilayered PVDF-HFP-TiO2/Al2O3 demonstrated superior cooling, achieving a temperature reduction of 12 °C compared to only 9 °C for pure Al2O3, 10 °C for the mixed composite, and 8 °C for pure TiO2. Theoretical analysis using a mid-latitude summer atmospheric model predicted a cooling power of 71.7 W/m2 and 121.7 W/m2 for the bilayered membrane during the day and at night, respectively, validating the experimental results. This structural advantage arises from the strategic segregation of optical functions into distinct layers, thus optimizing solar reflection and thermal emission while minimizing particle interference effects. The bilayered membrane exhibited excellent thermal stability, hydrophobic properties, and mechanical integrity, making it a promising candidate for energy-efficient cooling applications in buildings, textiles, and outdoor electronics.