Anisotropic sliding of multiple-level biomimetic rice-leaf surfaces on aluminium substrates

The realisation of special anisotropic sliding behaviour of liquids on metal substrates is very important for applications in fluidic control and water directional transportation. Proposed is a method combining lithography assisted electrochemical etching, anodic oxidation and fluoridation to construct the three-level microstructures (macro/micro/nano) of rice leaves on aluminium. Similar to the natural rice leaf, the prepared surface was endowed with multiple-level microstructures and exhibits superhydrophobicity. The measurements show the biomimetic rice-leaf surface has different anisotropic sliding behaviour with water droplets of different volumes. The perpendicular and parallel sliding angles (SAs) of a 4 l water droplet were 6.8 degrees and 2.7 degrees, respectively, the anisotropy was 4.1 degrees, which is comparable to that of a natural rice leaf. A mathematical model is presented to explain the mutational significant anisotropy of SAs (10.2 degrees) when the water droplet was only 2 l. This method is simple and economical, and is believed can be used for the fabrication of large-area biomimetic rice-leaf surfaces on metal.