Hydrophobicity-enhanced daytime radiative cooling films based on polyvinylidene fluoride-co-hexafluoropropylene and hydrophobic fumed silica

Daytime radiative cooling technology is considered a promising energy-efficient spatial cooling technology, attracting a great deal of attention. In this work, daytime radiative cooling film (DRCF) consisting of polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) and hydrophobic fumed silica (SiO2) was developed by an electrostatic spinning technology. Results showed that the hydrophobicity and spectral properties of the PVDF-HFP film could be simultaneously enhanced by adding SiO2 (SiO2 refers to hydrophobic silica without special note in this work). The water contact angle of the 6 wt% PVDF-HFP/SiO2 film could be enhanced to about 135°. The 6 wt% PVDF-HFP/SiO2 film exhibited average reflectivity of 95.7% in the solar spectrum, an average emissivity of 96.3% in the primary atmospheric window (PAW), and 97.5% in the secondary atmospheric window (SAW). It also has a maximum sub-ambient temperature drop of ∼8.10°C in Shanghai and ∼9.75°C in Qingdao, achieving average net cooling power of 101.29 W/m2 during the daytime in Qingdao. This work provides a feasible strategy with great prospects for DRCFs.