Humidity-tolerant porous polymer coating for passive daytime radiative cooling

Dongpyo Hong, Yong Joon Lee, Ok Sung Jeon, In-Sung Lee, Se Hun Lee, Jae Yeon Won, Young Pyo Jeon, Yunju La, Seonmyeong Kim, Gun-Sik Park, Young Joon Yoo & Sang Yoon Park
Nature Communications, 15(1), 4457 (2024)
DOI : 10.1038/s41467-024-48621-6

Abstract

Coating building envelopes with a passive daytime radiative cooling (PDRC) material has attracted enormous attention as an alternative cooling technique
with minimal energy consumption and carbon footprint. Despite the exceptional performance and scalability of porous polymer coating (PPC), achieving
consistent performance over a wide range of drying environments remains a major challenge for its commercialization as a radiative cooling paint. Herein,
we demonstrate the humidity vulnerability of PPC during the drying process and propose a simple strategy to greatly mitigate the issue. Specifically, we find
that the solar reflectance of the PPC rapidly decreases with increasing humidity from 30% RH, and the PPC completely losses its PDRC ability at 45% RH and
even become a solar-heating material at higher humidity. However, by adding a small amount of polymer reinforcement to the PPC, it maintains its PDRC
performance up to 60% RH, resulting in a 950% increase in estimated areal coverage compared to PPC in the United States. This study sheds light on a
crucial consistency issue that has thus far been rarely addressed, and offers engineering guidance to handle this fundamental threat to the development of
dependable PDRC paint for industrial applications.