Directional transport of water droplets on superhydrophobic aluminium alloy surface

The directional transport of water droplets has great potential applications in biochemical analysis. An aluminium (Al) alloy surface with a contact angle (CA) of 154° and a sliding angle of about 3.5° was prepared by the electrochemical etching method, which is eco-friendly and economic. An arc path line with a radius of 50 mm and a width of 400 μm was created on the superhydrophobic surface by means of lithography. CAs of water droplets on the lines exhibit anisotropy and 50 μl water droplets could slide exactly along the created line when the substrate was tilted to about 7°. The anisotropic wettability and mechanism of water droplets transport on the surface was investigated. The surface still has great water transport capability after 8 months, indicating that the water transport property of the patterned surface is stable and persistent. This method combines electrochemical etching and lithography; it is universal and economical, and could be used to build patterns on various substrates to realise the directional transport of water droplets.