Volume 50

Hierarchical Designed Superhydrophobic SiO2/PVDF-HFP Nanofibrous Membrane for All-Day Radiative cooling Xin Meng, Qiang Li, Xuemei Chen

Abstract

All-day passive radiative cooling materials, which are dedicated to cool objects by reflecting solar light and dissipating heat to the cold outer space, have received extensive attention in recent years. As a common radiative cooling material, poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) has high atmospheric window infrared emittance. However, the PVDF-HFP-based radiative cooler has low reflectance of sunlight and is prone to be contaminated, which would reduce the radiative cooling performance in outdoor applications. Therefore, in order to enhance the optical property and self-cleaning capability of the PVDF-HFP membrane, we herein prepared a hierarchical superhydrophobic SiO2/PVDF-HFP nanofibrous membrane by electrospinning and electrostatic spraying technique; the radiative cooling performance of the as-prepared membrane is compared with that of the commercial PVDF-HFP membrane. The results demonstrate that the hierarchical superhydrophobic SiO2/PVDF-HFP nanofibrous membrane consists of numerous stacked nanofibers and is uniformly distributed by SiO2 particles, which enable the membrane to exhibit an average solar spectral reflectance of 97.8% and an average atmospheric window infrared emittance of 96.6% (both values are higher than those of the commercial PVDF-HFP membrane). The hierarchical SiO2/PVDF-HFP membrane achieves sub-ambient temperature up to 11.5℃ under direct sunlight and 4.1℃ at night, demonstrating superior radiative cooling performance. Moreover, the hierarchical SiO2/PVDF-HFP membrane possesses excellent self-cleaning property, remarkable flexibility, and mechanical stability, which endows the membrane with promising applications in cooling vehicles, buildings, large-scale equipment, etc.

Keywords energy-free, all-day radiative cooling, hierarchical design, nanofibers, superhydrophobic