Chinese scientists have developed a superhydrophobic coating that can be repaired by treating the surface with potassium stearate, which is often used in soap and cosmetics. This could lead to self-healing superhydrophobic surfaces in the future. 

Many superhydrophobic surfaces, often based on a biomimetic lotus leaf microstructure, have been reported in recent years for applications such as waterproof clothing and self-cleaning road signs. They contain microscopic needles that water droplets sit on and roll over to leave the surface very easily. But most are very fragile and unlike the lotus leaf in nature, unable to be repaired. Now, Zhenzhong Yang and colleagues from the Chinese Academy of Sciences, Beijing, have demonstrated a simple and cheap method of regenerating damaged needles. 

Yang made the coating using calcium hydroxide microcapsules with a porous polymethylmethacrylate-ethyl cellulose polymer shell, which are embedded in an expoxy resin on the surface. Immersing the surfaces in potassium stearate solution makes solid nano-sized needles of calcium stearate grow from the pores in the microcapsule surfaces, creating the superhydrophobicity. 

If the calcium stearate needles get scratched away, they can be fully regenerated by treating the surface again with potassium stearate solution. This can be repeated multiple times until all the calcium hydroxide in the microcapsule is exhausted, explains Yang.

'The work describes a way of making superhydrophobic surfaces more resistant to wear without reducing their effectiveness by allowing them to recover their properties once damaged; while maintaining low cost by using cheap reagents,' says Neil Shirtcliffe, an expert in superhydrophobic surfaces at Nottingham Trent University, UK. 'It is similar to the approach used by plants, which repair their surfaces in the face of damage,' he adds. 

Yang says they now plan to build on this work to make the coatings self-healing, which would enable their use in a wider range of practical applications. 

James Hodge 

Enjoy this story? Spread the word using the 'tools' menu on the left or add a comment to the Chemistry World blog.