Self‐Stratifying Colored Radiative Cooling Paints Through Narrow‐Band Color Preservation Scheme
Dudong Feng, April M. Witty, Fletcher I. Birnbaum, Orlando G. Rivera Gonzalez, Andrea Felicelli, Won‐June Lee, E. M. Barber, Xiulin Ruan
Abstract
Although significant energy-saving potential of passive daytime radiative cooling has led to diffusively white or reflective surfaces, achieving coloration expands their application for both aesthetic and functional purposes. However, it presents huge technical challenges in scalable processing. This work presents a novel and general self-stratifying approach for creating radiative cooling paints with various colors using selected narrow-band absorption dyes. Applied as a single coat, these paints self-assemble into an absorption-scattering dual-layer structure that efficiently displays color while minimizing light absorption. Three base colors (cyan, magenta, and yellow) are demonstrated to provide full daytime subambient cooling, achieving 93% solar reflectance and 0.94 sky window emissivity. One newly developed black paint achieves 46.3% solar reflectance and a temperature drop of up to 25 °C, outperforming commercial counterparts. A purple radiative cooling paint (mixed dyes) demonstrates the color customization potential within the CMYK space, addressing the dilemma between color and cooling for colored radiative cooling paints. The mechanical and surface properties, characterized by abrasion, adhesion, and contact angle tests, are on par with or surpassing commercial products. This unique self-stratifying mechanism enhances surface properties and provides new insights for developing high-volume loading paints and water-harvesting coatings without increasing fabrication complexity.