Highly solar reflectance and infrared transparent porous coating for non-contact heat dissipations

Passive daytime radiative cooling (PDRC) can dissipate heat to outer space with high solar reflectance ((R) over bar (solar)) and thermal emittance ((epsilon) over bar (LWIR)) in the atmospheric transmission window. However, for the non-contact heat dissipation, besides the high (R) over bar (solar), a high infrared transmittance ((tau) over bar (LWIR)) is needed to directly emit thermal radiation through the IR-transparent coating to outer space. In this work, An IR-transparent porous PE (P-PE) coating with (R) over bar (solar) = 0.96 and (tau) over bar (LWIR) = 0.88 was prepared for non-contact heat dissipations. Under the direct sunlight of 860 W m(-2), the IR-transparent coating obtained a 4 degrees C lower heater temperature than the normal PDRC coating under the same condition. In addition, the spectral reflectance of the P-PE coating after immersing in air or water changed little, which showed excellent durability for long-term outdoor applications. These results indicate the P-PE coating can be a potential IR-transparent coating for non-contact heat dissipations under direct sunlight.