Modified hollow glass microsphere in-situ reinforced polyurethane/ polydimethylsiloxane composite coating with self-cleaning and durable passive radiative cooling behaviors

Passive radiative cooling technology has been widely concerned due to its merits of energy free and zero pollution. However, most of the radiative cooling materials are highly susceptible to contamination from solid dirt and rainwater, which greatly weak their cooling effectiveness. Herein, a hydrophobic radiative cooling composite coating, composed of polyurethane/polydimethylsiloxane (PU/PDMS) and modified hollow glass microsphere (MHGM), was fabricated through in situ reinforcing and phase separation processes. By the synergistic effect of MHGM filler and the surrounded microporous PU/PDMS matrix, the PU7/PDMS3-MHGM coating possessed strong solar reflectance and thermal emittance in the atmospheric transparency window of 0.906 and 0.961, respectively, resulting in sub -ambient daytime cooling of 8.1 degrees C and nighttime cooling of 3.9 degrees C. In addition, the composite coating exhibited a higher water contact angle of 139 degrees , the dust and muddy water are unable to stain on its surface during the rinsing process, showing self-cleaning effect. More encouragingly, the composite coating still remained above 93.8 % passive radiative cooling efficiency even if after 100 cycles muddy water rinsing, certainly, such self-cleaning provides assurance for the sustainable application of radiative cooling coatings.