Oct 3, 2007
Nanowire coating repels water
Zinc oxide (ZnO) nanowires coated with stearic acid are record breakers when it comes to superhydrophobicity, according to French scientists. Boasting contact angles as high as 176 °, the highly water-repellent structure is ideal for keeping surfaces clean.
The surface modification is stable over a wide pH range and has been tested up to 250 °C. In addition, the film's properties remain unchanged following six months of storage under ambient illumination.
Electron microscopy shows that the film has two length scales – a common feature of hydrophobic surfaces and a property that is thought to trap large amounts of air within the structure. Measuring 3.5 µm in length and 160 nm in diameter, the wire-like ZnO structures terminate in a seemingly flat, but actually nano-roughened tip.
"The double scale roughness we observed on the top of the wires and the hydrophobicity of the adsorbed stearic acid can be compared to the double scale roughness of the lotus leaf and its accompanying low surface energy waxy coating" Chantal Badre of CNRS told nanotechweb.org. "In our case, the superhydrophobic films are prepared in a very easy way and from a very low-cost compound."
Formed by electrodeposition, the as-deposited film is dipped in an ethanol solution of stearic acid for 24 hours to activate the superhydrophobic behaviour. Simple to make and affordable, the water-repellent coating is a strong candidate for commercialization.
The group, which also includes scientists from Université Pierre et Marie Curie, Paris, is considering various applications, such as easy to clean window glass and high-performance, anti-fog spectacles, and is keen to build links with industrial partners.
The researchers presented their work in Nanotechnology.
About the author
James Tyrrell is editor of nanotechweb.org.