Large-scale SiO2 particle integrated superhydrophobic thermal insulating hollow nanofiber film for daytime passive radiative cooling

Abstract

Passive daytime radiative cooling (PDRC) is a sustainable technology for cooling objects without consuming additional energy by reflecting sunlight and radiating heat to cold outer space. However, many PDRC devices proposed in recent years are complex and costly with the cooling performance degraded due to the surface contamination and heat conduction with the outdoor air, limiting their practical applications. Here, a cooling film consisting of poly (vinylidene fluoride-co-hexafluoropropylene) P(VDF-HFP) hollow nanofibers with surface adhered by SiO₂ particles is fabricated by a combination of high temperature electrospinning and spraying technology, which can achieve triple functions of PDRC, self-cleaning and thermal insulation. The P(VDF-HFP)/SiO₂ thermal insulating hollow nanofiber cooler (TIH-P(VDF-HFP)/SiO₂) has an average mid-infrared emissivity of 98.2 % (8–13 μm) and reflects 98.9 % of solar irradiance due to the vibration bonds of C−H and C−F molecular chains in P(VDF-HFP) nanofibers and the particle-nanofiber structure scattering. Besides, the TIH-P(VDF-HFP)/SiO₂ cooler exhibits the thermal conductivity of 0.019 W m⁻¹ K⁻¹ (lower than air) and a high static water contact angle (145°), which can reduce the environmental heat gain and possess self-cleaning performance, ensuring the stability and durability of the cooler. In practical applications, our cooler maintains an average temperature drop of 14 °C for the wood house model under direct sunlight even after the mud water contamination. This work provides a feasible way for fabricating thermal insulating PRDC materials and has the potential for a wide range of energy-saving and emission reduction applications.