Highly Efficient Outdoor Radiative Cooling Performance of Polyvinylidene Fluoride Films Enabled by Hierarchically Structured Silica Nanosphere Decorated Boron Nitride Nanosheets

Abstract

Radiative cooling technology can efficiently reflect solar radiation and emit heat into the outer space, holding considerable potential for energy conservation. However, the issues such as the surface contamination, limited durability, and opacity hinder the wide applications of radiative cooling materials. In response to these challenges, this study fabricates a polyvinylidene fluoride (PVDF) based transparent radiative cooling film by incorporating silicon dioxide nanospheres decorated boron nitride nanosheets (BNNS@SiO2) into PVDF matrix. The introduction of BNNS@SiO2 can simultaneously improve the sunlight reflectance and mid-infrared emissivity of PVDF film. The average temperature drop can reach about 7.2 °C with a maximum temperature drop of ~16.0 °C, demonstrating the excellent radiative cooling performance of the BNNS@SiO2/PVDF composite film. Additionally, the incorporation of BNNS@SiO2 imparts a rougher texture to the film surface, which enhances the hydrophobic properties and confers the self-cleaning capability for BNNS@SiO2/PVDF film. This self-cleaning feature, along with the increased mechanical strength, ensures the film outstanding stability and durability in outdoor environments. Moreover, the BNNS@SiO2/PVDF film also exhibits certain transparency, offering promising applications for outdoor settings, such as car windows and building glass.

Keywords: Radiative cooling, Boron nitride nanosheets, Transparency, Self-cleaning, Stability and durability