Leaf-Inspired Porous Hydrogels with Rain-Resistant Surfaces for Reliable Hyperspectral Stealth in Jungle Environments.

Hyperspectral camouflage stealth materials can mimic the spectral reflectance of natural leaves by regulating their internal water content. However, they suffer from spectral instability under rain flushing, restricting practical applications. Achieving stable hyperspectral simulation performance remains challenging because water absorption and rain resistance are inherently contradictory. Herein, inspired by the asymmetric architecture of natural leaves, we develop a unique biomimetic leaf (abbreviated as ECMH) that integrates a rain-resistant slippery liquid-like poly(dimethylsiloxane) front surface with a green-colored porous hygroscopic hydrogel substrate by a miniemulsion polymerization process and a mechanical foaming strategy. The hydrogel substrate endows ECMH with efficient water exchange and storage capabilities, achieving excellent spectral simulation performance in the visible-near-infrared (Vis-NIR) region (with high spectral correlation coefficients exceeding 0.97 and low spectral angles below 0.19 rad when compared with 10 different natural leaves). More importantly, the front surface provides ECMH with a waterproof performance, achieving a low water sliding angle (<24°) and ensuring excellent spectral stability with slight variations (≤2.5%) in the "water absorption valleys" (i.e., spectral reflectance at 1450 and 1930 nm). This porous asymmetric biomimetic leaf achieves high-fidelity simulation across the Vis-NIR region while maintaining durability against rainfall assaults, providing a promising strategy for the development of jungle-type camouflage stealth systems.