Flexible Janus Patch with Reversible Adhesion, Self-Cleaning, and Enhanced Solar Reflection for Deployable Radiative Cooling

Passive daytime radiative cooling (PDRC) provides a sustainable route to reduce energy use by reflecting solar radiation and dissipating heat into outer space without external power input. Polymer-based porous films can achieve high solar reflectance and strong mid-infrared emissivity; however, their deployment is often limited by installation challenges, poor durability, and low seasonal adaptability. To overcome these limitations, we developed a flexible and patchable PDRC platform that integrates reversible self-adhesion, self-cleaning capability, and enhanced solar reflection through a biomimetic Janus microstructure. The patch is fabricated from a monolithic silicone elastomer with bifacially engineered surfaces: the bottom side features high-aspect-ratio micropillars enabling universal dry adhesion, while the top side contains macroscale pores infiltrated with oxide nanoparticles, forming a hierarchically porous structure that maximizes solar reflection. The patch maintained a dry adhesion strength of approximately 3 N cm –2 over 40 attachment–detachment cycles and resisted surface fouling through self-cleaning. Outdoor rooftop experiments using a model house demonstrated a maximum indoor temperature reduction of 8.5 °C under direct sunlight. Together, these results highlight a versatile, reusable, and seasonally adaptive platform for durable, high-performance radiative cooling, demonstrating strong potential for real-world implementation.