Waterborne acrylic/CaCO3 composite coatings for eco-friendly passive radiative cooling with hydrophobic easy-cleaning

초록

Passive daytime radiative cooling (PDRC) has emerged as a promising energy-free cooling strategy; however, many high-performance coatings rely on organic solvents and suffer from durability and contamination issues under outdoor conditions. In this study, we develop an eco-friendly waterborne acrylic/CaCO3 composite coating that simultaneously achieves efficient radiative cooling and hydrophobic easy-cleaning. Micro-sized CaCO3 particles induce strong solar reflectance through Mie scattering, while the acrylic binder provides high mid-infrared emittance via intrinsic molecular vibrations. The optimized film with 70 vol% CaCO3(PA–C70) exhibits a solar reflectance of 95.24% in the 0.3–2.5 µm range and an average emittance of ~ 90% within the 8–13 µm atmospheric window. After PFOTS-based surface treatment, the reflectance and emittance further increase to 97.95% and 93.3%, respectively, along with enhanced hydrophobicity (water contact angle of 119°). Outdoor measurements demonstrate stable cooling performance with a maximum sub-ambient temperature reduction of 9.3 °C. In addition, the coating shows effective removal of dust and liquid contaminants, confirming its easy-cleaning capability. These results highlight the potential of waterborne composite coatings as sustainable, scalable, and practical solutions for real-world radiative cooling applications.

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