Fig. 1. Schematic illustration and fabrication process of a snake scale-like surface via the IBLA method. (a) The photographs of the West African Gaboon Viper (Bitis rhinoceros). (b) Photographic image of the dorsal skin of a living individual of Bitis rhinoceros after sprinkling with water. Figure reproduced with permission from ref.¹⁰, Copyright 2014, PLOS Publishing. (c) SEM image of the hierarchical structures of the dorsal scale surfaces of Bitis rhinoceros. Figure reproduced with permission from ref.¹⁰, Copyright 2014, PLOS Publishing. (d) Schematic illustration of the manufacture of snake scale-like artificial surface by IBLA technique. (e−g) SEM images of the as-prepared sample surfaces at different magnifications.

Fig. 2. Micro/nanostructures, and wetting behavior of the superhydrophobic surfaces with different hierarchical structures by different steps of the laser processing. (a) SEM images of the hierarchical structures of the snake scale-like array by one step laser processing; the inset shows that the CA of the water droplet is 73°. (b, c) SEM images of (a) at different magnified scales. (d) SEM images of the hierarchical structures of the snake scale-like array by two steps laser processing; the inset shows that the CA of the water droplet is 133°. (e, f) SEM images corresponding to (d) at different magnified scales. (g) SEM images of the hierarchical structures of the snake scale-like array by three steps laser processing; the inset shows that the CA of the water droplet is 159°. (h, i) SEM images corresponding to (g) at different magnified scales. (j) Time-dependence of CAs for the hierarchical surfaces by different steps laser processing exposed to air. (k) Superhydrophilicity of the complete three-level hierarchical surfaces in 30 h. (l) Wetting results (CAs and SAs) on the surface corresponding to opposite directions, respectively.

Fig. 3. Directional water transport property and water repellency of the superhydrophobic surface. (a) Time sequences of snapshots of a water droplet rolling on the as-prepared surface along the positive and negative directions. See Movies S2 and S3. (b) Time sequences of snapshots of water stream flowing through the as-prepared surface along the positive and negative directions. See Movies S4 and S5. The as-prepared surfaces in (a) and (b) are tilted 30°.

Fig. 4. Mechanism of directional water transport. (a) Schematic illustration of the molecule/atom interaction mechanism. (b) The intrinsic contact angle on snake scale. (c) The apparent contact angle on snake scale. (d) Schematic illustration of liquid flow in the positive direction of snake scale-like structures. (e) Schematic illustration of liquid flow in the negative direction of snake scale-like structures.

Fig. 5. Simulated regimes of the droplet sliding on the snake scale-like surface along the positive and negative directions. (a,b) Local magnification of the simulation structures. (c, e, g) Time sequences of simulations of a water droplet rolling on the as-prepared surface along the positive direction. See Movie S6, Supplementary information. (d, f,h) Time sequences of simulations of water droplet rolling on the as-prepared surface along the negative direction. See Movie S7, Supplementary information.

Fig. 6. Application of the surface as a “ship skin” for controllable navigational direction. (a) The simulated model and the real object of the ship, and the schematic illustration of the water circulation system. (b, c) Time sequences of snapshots of an armoured ship moving under the continuous water flow along the positive and negative directions of the as-prepared surface. See Movie S8, Supplementary information.