Superhydrophobic polytetrafluoroethylene/polyvinylidene fluoride coating for passive daytime radiative refrigeration

Abstract

Passive daytime radiation refrigeration (PDRR) is a new type of refrigeration that requires no extra energy consumption and also cools objects by reflecting radiant heat from sunlight and mid-infrared wavelengths. However, the properties of ordinary radiative refrigerative (RR) materials are degraded by surface dust accumulation during use. In this work, superhydrophobic radiative refrigerative (SRR) polytetrafluoroethylene/polyvinylidene fluoride (PTFE/PVDF) coating was prepared by one-step spraying method with PTFE as white pigment, PVDF as binder, and N, N-dimethylacetamide (DMAC) as solvent. The PTFE/PVDF coating (containing 20 wt% of PTFE) exhibits synergistic effect with high water contact angle (CA, 153.7°), low water sliding angle (SA, 7.7°), high solar reflectivity (SR, 93.7%), and high infrared emissivity (IE, 93.3%). Under a clear sky and direct sunlight, the coating achieves a RR temperatures of 5.8 °C (shielding convection heat) and 5.3 °C (without shielding convection heat) respectively under two measurement conditions. In addition, the coating exhibits excellent self-cleaning properties that can automatically remove dust accumulated on the surface with the assistance of rainfall, thus maintaining its RR performance for a long time. More importantly, the mechanical robust self-cleaning function also provides excellent corrosion resistance and anti-UV aging ability. The PTFE/PVDF SRR coating developed in this work is simple to fabricate, can be applied over a large area, and has good durability, which is conducive to promoting the practicalization of RR coatings.