High-performance non-contact radiative cooling enabled by solar reflectance and infrared transparent porous poly (4-methyl-pentene) film

Traditional passive radiative cooling materials typically exhibit high solar reflectance and mid-infrared emissivity, delivering excellent cooling performance when in direct contact with the surface of an object. However, when the surface of an object is not in contact with radiative cooling materials, the heat emitted by the object first passes through the air with a lower thermal conductivity and is then transferred to radiative cooling materials. Subsequently, the radiative cooling materials transmit the thermal radiation to outer space. This process significantly increases the thermal resistance of the radiative system, thereby impeding the dissipation of heat from the object. To enhance the performance of non-contact radiative cooling, radiative cooling materials must possess high solar reflectance and mid-infrared transmittance. While blocking solar radiation, they should enable the thermal radiation emitted by the object to pass directly through the infrared-transparent material. In this study, we prepared porous poly(4-methyl-pentene) (P-TPX) films with a solar reflectance of 88.6% and an infrared transmittance of 88.11%, aiming to achieve efficient non-contact radiative cooling. Under identical conditions, the P-TPX film, which is transparent to infrared radiation, exhibited superior cooling performance compared to the Poly(vinylidene fluoride-co-hexafluoropropene) porous (P-P(VdF-HFP)) film, which has higher infrared emissivity. The temperature difference between the two films reached up to 4.5 °C, indicating that the infrared-transparent P-TPX film can achieve efficient non-contact radiative cooling.