A new water repellent coating for aluminium foil could prolong the lifetime of air conditioning units, say researchers in China.

Jian Nong Wang from Tongji University, Shanghai, and Qian Feng Xu from Shanghai Jiao Tong University, have developed a superhydrophobic (very difficult to wet) silica coating that could be applied to the aluminium foil used in air conditioning units - protecting it from corrosion.

Wang and Xu prepare their coating by dipping the foil in a mixture of silica colloid particles and a polystyrene template.  The polystyrene is then removed leaving a silica network with a controlled surface roughness.

Currently, superhydrophobic coatings on aluminium are prepared as elaborate nano- or micro-structures, by various methods such as chemical etching. However, chemical etching can harm the aluminium and decrease the anti-corrosive property. 

'Beyond wettability, Wang and Xu have examined other attributes that a practical coating would likely need, such as resistance to aging in air and attack by acidic solutions,' says Chuck Extrand a specialist in hydrophobic coatings from Entegris Inc, Minnesota, US.  

'If the superhydrophobic technology is successfully used in the air-conditioning unit, the lifetime of the unit will be greatly prolonged,' says Wang. This technology 'has a bright future in many other industrial fields, such as buildings, electronic devices, and surface protection of metals or alloys used under severe conditions', he adds.

Michael Brown

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