Credit: © 2006 ACS

It is well known that the lotus leaf displays superhydrophobic characteristics — it strongly repels water because of the combined micro- and nano-structures on its surface. Although researchers have mimicked this behaviour by packing microspheres into ordered arrays, a much rougher surface texture on the spheres is required to achieve superhydrophobicity.

Now, researchers at the Korea Advanced Institute of Science and Technology and the Chinese Academy of Sciences have decorated a monolayer of polystyrene microspheres with carbon nanotubes to create a superhydrophobic surface. Sung Oh Cho and colleagues1 deposited single- and multi-walled nanotubes on a monolayer of polystyrene spheres and treated the surface with a fluoroalkylsilane, a chemical that enhances the superhydrophobic effect. When a water droplet was placed on the surface, it remained round and showed a contact angle of 165°, which is very similar to the lotus leaf.

The researchers found that neither the bare monolayer of microspheres nor a film of nanotubes exhibit superhydrophobicity, even when their surfaces are modified with the chemical. This indicates that the effect originates from the unique combination of well-ordered spheres and the nanoscale texture of the nanotubes. Furthermore, the surface characteristics can be tuned by changing the size of the microspheres or density of nanotubes.