3D-Printed Hierarchical Bilayer Metasurfaces for Simultaneous Self-Cleaning, Multispectral Protection, and Subambient Cooling

Abstract

Simultaneous self-cleaning, multispectral protection, and subambient cooling in a single coating require reconciling fundamental material conflicts: hierarchical roughness for lotus-effect wetting disrupts spectral selectivity, high-index scatterers for solar reflection impede infrared emission, and lossy networks for microwave absorption compromise optical performance. Here, we report 3D-printed hierarchical bilayer metasurfaces comprising a porous TPU-ZnO substrate and a gradient-refractive-index metasurface (TZP/MS), fabricated via vat photopolymerization with in situ slurry switching. The architecture decouples self-cleaning, multispectral protection, and subambient cooling functions through structural partitioning: the top metasurface provides hydrophobic self-cleaning (contact angle of 126.3°), broadband solar reflection (89.2% solar-weighted), and laser protection (94.2−96.8% at 532−1064 nm), while the porous underlayer enables electromagnetic (EM) absorption (−42.3 dB reflection loss, 5 GHz X-Ku bandwidth) and high infrared (IR) emissivity (97.2%) for subambient radiative cooling (9.5 °C below ambient). Critically, the self-cleaning topography sustains optical resilience: >94% reflectance recovery after particulate contamination validates autonomous performance restoration. The monolithic coating further exhibits exceptional specific strength (27,000× self-weight) and conformal flexibility. By integrating self-sustained cleanliness as an integral component of multispectral protection, this work establishes a design paradigm for durable functional coatings in demanding high-altitude environments.