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Water-Based Hydrophobic Paints for Daytime Radiative Cooling
Abdulrahman K Aljwirah1,2,3, Xiaojie Liu1,2,4, Orlando Rivera Gonzalez1,2
1School of Mechanical Engineering, Purdue University, West Lafayette, Indiana 47907, United States.
ACS Applied Materials & Interfaces
|May 21, 2025
Summary
New water-based radiative cooling paints using barium sulfate, calcium carbonate, and hexagonal boron nitride offer effective daytime cooling. These eco-friendly, low-volatile organic compound (VOC) paints provide a scalable solution for reducing energy costs and mitigating climate change.
Area of Science:
- Materials Science
- Nanotechnology
- Environmental Science
Background:
- Radiative cooling paints offer a scalable method for daytime cooling but often contain harmful volatile organic compounds (VOCs).
- Addressing VOCs is crucial for the widespread adoption of radiative cooling paint technology.
Purpose of the Study:
- To develop and present environmentally friendly, water-based, and hydrophobic radiative cooling paints.
- To demonstrate subambient cooling performance and low VOC content in novel paint formulations.
Main Methods:
- Formulation of single-layer, metal-free radiative cooling paints using BaSO4, CaCO3, and hBN.
- Characterization of paint properties including solar reflectance, sky window emissivity, water contact angle, and VOC content.
Main Results:
- Paints achieved daytime subambient cooling of 2.7 °C (BaSO4), 2.6 °C (CaCO3), and 2.5 °C (hBN).
- High solar reflectance (93.7–96.1%) and strong sky window emissivity (0.825–0.932) were observed.
- Low VOC content (18–30 g/L) and high water contact angles (118–139.9°) confirmed hydrophobic and eco-friendly properties.
Conclusions:
- The developed ultrawhite radiative cooling paints are metal-free, water-based, hydrophobic, and low-VOC.
- These paints present a viable, eco-friendly alternative for passive cooling, potentially reducing energy consumption and combating climate change.
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