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 ¯ solar ) and thermal emittance ( ε ¯ LWIR ) in the atmospheric transmission window. However, for the non-contact heat dissipation, besides the high R ¯ solar , a high infrared transmittance ( τ ¯ 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 ¯ solar = 0.96 and τ ¯ 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°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.