Micro-nano hierarchical micropattern-enhanced antifogging surface inspired by tree frogs

Fogging on glass is common but can also be dangerous when it occurs on eyeglasses, camera lenses, mirrors, and windshields of automobiles and airplanes. Inspired by the toe pads of tree frogs in nature, biomimetic structures in the form of regular arrays of micro-hexagonal prisms were fabricated. Common UV lithography, ion-beam etching, and neutral loop discharge were used to construct these arrayed microstructures. Chemical etching was then used to create various scale nanostructures to provide better wettability in the microchannel between the micro-hexagonal prisms and optical properties on the top surface of the micro-hexagonal prisms. The wettability, optical characteristics, and antifogging performance of the biomimetic antifogging gradient (BAFG) surface were tested experimentally. The BAFG surface exhibited excellent antifogging and optical properties; this stimulated the preferential formation of a water film network in the microchannel and facilitated the spreading of a stable water film on the surface. Remarkably, the transmittance of the BAFG surface reached 99% of the transmittance of the bare glass. The average transmittance for the bare glass (68.7%) under fog conditions improved to approximately 94.4% for the BAFG surface. Three stages for the condensation of vapor and the formation of the water film were described according to thermodynamic theories, which elucidate the internal mechanism. Graphical abstract