Figure 4

Depth of the dimples and photos of the fabricated superhydrophilic patterns. (a) Etching time and etched dimple depth for each etching voltage to obtain a dimple with CA lower than 20°. (b) Round superhydrophilic dimple array that was fabricated using the twice etching method; inset in (b) shows 20 μL droplets pinned by the dimple on the vertical substrate, diameters of the dimples are 4.0 mm. (c) Flower-like water trapped in the etched superhydrophilic dimple. Superhydrophilic patterns fabricated on (d) magnesium substrate and (e) titanium substrate using the twice etching method. Insets in (c–e) are CA images of superhydrophobic areas fabricated on aluminum, magnesium and titanium surfaces, respectively. For clear observation, the deionized water used for the demonstrations in (b-e) was dyed red or blue using food colouring.