Superhydrophobic bilayer coating for passive daytime radiative cooling

Area of Science:

• Materials Science
• Nanotechnology
• Sustainable Energy

Background:

• Passive radiative cooling offers an energy-free method for cooling by leveraging thermal radiation exchange with the cold universe.
• Current radiative cooling technologies require spectrum tailoring for daytime performance and improved large-scale fabrication and self-cleaning for industrial application.

Purpose of the Study:

• To develop a scalable, superhydrophobic bilayer radiative cooling coating with enhanced performance for practical applications.
• To investigate the optical and surface properties of the novel coating for effective passive cooling.

Main Methods:

• Fabrication of a bilayer coating comprising TiO2/acrylic resin paint and a SiO2/P(VdF-HFP) composite masking layer.
• Characterization of solar reflectivity, emissivity, and superhydrophobicity (water contact angle).
• Performance evaluation of the cooling effect under solar irradiance and estimation of potential energy savings for buildings.

Main Results:

• The developed coating exhibits a solar reflectivity of 94.0% and an average emissivity of 97.1%.
• The coating demonstrates superhydrophobicity with a water contact angle of 158.9°.
• The radiative cooler achieved a temperature reduction of 5.8°C below commercial white paint and 2.7°C below ambient temperature, with potential yearly energy savings of 29.0%-55.9%.

Conclusions:

• The proposed bilayer radiative cooling coating offers a scalable and effective solution for passive cooling.
• The superhydrophobic property enhances durability and self-cleaning, improving industrial applicability.
• This technology holds significant potential for reducing building energy consumption and mitigating urban heat island effects.