Gecko-Inspired Porous Dry Adhesive Patch for Attachable Radiative Cooling

Passive daytime radiative cooling (PDRC) is an energy-efficient technology that cools surfaces or spaces without consuming electrical power to combat global warming and achieve carbon neutrality. Highly scattering films based on heterogeneous composites or porous structures are commonly used for PDRC, but their utility is still limited. Here we demonstrate a new type of PDRC patch that can be attached and detached from any surface as needed. On one surface of the PDRC patch made of porous PDMS, mushroom-shaped, high-aspect-ratio micropillars mimicking geckos were formed, which exhibited an initial dry adhesion of ~3.42 N/cm² due to collective van der Waals forces. Even after 40 cycles of repeated attachment and detachment, the dry adhesion was maintained at ~2.8 N/cm². By impregnating silica nanoparticles into the pores of the porous network to form a hierarchical structure, the visible light scattering of the PDRC patch was maximized. The average solar reflectance and average infrared emittance of the resulting PDRC patch were ~87.8% and ~92.5%, respectively. In outdoor testing using a customized setup, the maximum cooling temperature of the patch during daytime was ~8.5 °C. The attachable PDRC patch developed in this study will provide a new option to selectively utilize cooling functions under various constraints.