Thin lamellar films with enhanced mechanical properties for durable radiative cooling

Passive daytime radiative cooling is a promising path to tackle energy, environment and security issues originated from global warming. However, the contradiction between desired high solar reflectivity and necessary applicable performance is a major limitation at this stage. Herein, we demonstrate a "Solvent exchange-Reprotonation" processing strategy to fabricate a lamellar structure integrating aramid nanofibers with core-shell TiO2-coated Mica microplatelets for enhanced strength and durability without compromising optical performance. Such approach enables a slow but complete two-step protonation transition and the formation of three-dimensional dendritic networks with strong fibrillar joints, where overloaded scatterers are stably grasped and anchored in alignment, thereby resulting in a high strength of similar to 112 MPa as well as excellent environmental durability including ultraviolet aging, high temperature, scratches, etc. Notably, the strong backward scattering excited by multiple core-shell and shell-air interfaces guarantees a balanced reflectivity (similar to 92%) and thickness (similar to 25 mu m), which is further revealed by outdoor tests where attainable subambient temperature drops are similar to 3.35 degree celsius for daytime and similar to 6.11 degree celsius for nighttime. Consequently, both the cooling capacity and comprehensive outdoor-services performance, greatly push radiative cooling towards real-world applications.