Chinese researchers have made a surface that repels nearly all types of liquid. The surface could be used in a range of applications from kitchen equipment to oil pipelines, they claim.

Modified alumina nanowires (left) can repel a wide range of liquids, including crude oil (right)

Feng Zhou and colleagues at the Lanzhou Institute of Chemical Physics used electrochemistry to make a forest of aluminium oxide nanowires on the surface of a sheet of aluminium foil. Using a process called anodisation, they formed nanoscale pores on the surface, which grew and merged, leaving nanowires behind. The team then modified the nanowires with perfluorosilanes, creating a surface that repelled a variety of liquids including water, alkanes and lubrication oils, such as ionic liquids.

'Super-oleophobic [extremely oil-repelling] surfaces are in high demand to seal in lubricating oils and prevent oil creep [where oil spreads across a device away from the component it is meant to be lubricating],' explains Zhou. 'Creep may lead to lubrication failure or cause contamination of the surrounding environment. Surfaces that are non-adhesive and repellent to oils potentially have wide applications from kitchen facilities to oil transport pipelines.'

Other methods for making nanowires involve etching porous aluminium oxide membranes using acids or bases, but they are time consuming, says Zhou. His electrochemical method is simple and quick, he adds.

'This work is important because it describes an elegant method to make aluminium surfaces repel a wide range of liquids, including both water and various types of oil, which could be adopted on an industrial scale,' comments Steven Bell, an expert in super-repellent surfaces at Queen's University Belfast, UK. `As with all approaches based on nano- and micro-structured surface features, the challenge will be to combine this impressive functionality with the long term durability which is needed for many practical applications.'

Zhou agrees that applying the method industrially will not be easy. 'Unlike the success in making various super-hydrophobic materials with different synthetic strategies, examples of super-oleophobicity are very rare,' he says. 'Extending the present idea to other materials, especially engineering coatings, will be a great challenge.'

Colin Batchelor

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