Beetle inspires water innovation
chiara.jpg
Getting water from thin air: Chiara Neto with
Stuart Thickett (left) and Andrew Harris
Image: University of Sydney

The Namib Desert, stretching for 1600km along the Atlantic coast of south west Africa, is thought to be the oldest desert on earth, and it is certainly one of the world's most arid and inhospitable places. Near the coast, in an average year, less than 20 millimeters of rain falls on its hot red sand.

In this barren landscape, water is at a premium and the few forms of life that survive are highly adaptable - none more so than the Namib Desert Beetle or Stenocara, which has developed a unique method of harvesting water.

One of the few sources of moisture in the Namib is a fast-moving fog that comes off the Atlantic Ocean in the morning when temperatures are low. Stenocara makes use of this slim opportunity by converting the minute particles of water in the fog into beads of drinking water.

It does this via an arrangement of bumps on its wings which are hydrophilic, or water-attracting, while the surrounding part of the wing surface is water repellent. When the fog rolls in, the beetle takes up position on the crest of a sand dune. The moisture in the atmosphere condenses on the bumps, forming droplets which detach and are channelled into the beetle's mouth.

This clever trick, first explained by Oxford zoologist Andrew Parker in 2001, has prompted scientists to look for ways of creating synthetic surfaces that mimic the beetle's body technology and capture water from the atmosphere.

Until now, nobody has succeeded in making a material that can be produced on a scale large enough to be commercially viable. But a team from the University of Sydney, led by chemical engineer Andrew Harris and chemist Chiara Neto, believe they are on the brink of a breakthrough using cheap and readily available materials.

Their research, funded by the University's Institute of Sustainable Solutions, opens up a potential new way of easing Australia's long-running drought, by capturing drinking water from the humid air in coastal areas. If their ideas come to fruition, water could be collected in the early morning, when humidity is at its highest, using retracting synthetic sheets on sloping land or house roofs.

On humid days there is a surprising amount of water in the atmosphere - at 30C, up to 30 grams of water in a cubic metre of air - and to tap into it, the Sydney researchers are experimenting with two polymer films that mimic the beetle's body. When a hydrophilic layer is laid on a water-repellent base and heated, it becomes unstable and breaks up into isolated droplets. It is these droplets that draw the water from the atmosphere, like the bumps on the beetle's wing.

The technology has been used before for other applications, but never for collecting water. The team, which also includes postdoctoral researcher Stuart Thickett, is now starting to approach potential industrial collaborators for funding.

Chiara Neto says the results of laboratory tests are encouraging. "We have been able to collect a few hundred drops of water on a surface of a square centimetre or less," she said, "so we could have many billions of drops on a large polymer sheet that's exposed to the wind.

"You could potentially collect large amounts of water. We've calculated that we should be able to collect one gram of water per square centimetre per hour in Sydney, where there is typically 60 or 70 per cent humidity.

"It's not something that will ever replace dams, but it's a system that might integrate with our other methods of water collection."

Dr Neto has been in Sydney for three years. Originally from Florence, she has also studied in Germany, Italy and at the ANU. Like Associate Professor Harris, director of the University's Laboratory for Sustainable Technology, she is interested in the idea of mimicking nature to produce functional structures.

"There are some amazing engineering structures in nature," said Dr Neto, "and they all demonstrate the amazing power of evolution."

Part of her research has involved working with superhydrophobic (extremely water repellent) surfaces that mimic the way a lotus leaf repels water. "Water rolls rather than slides off a lotus leaf, taking with it any dust particles on the surface and keeping the leaf dry and clean," she explained.

These superhydrophobic surfaces could improve the efficiency of "lab on a chip" microfluidic devices that deal with minute amounts of liquid and have applications in pharmaceutics and medicine. "These are small, portable and cheap devices that could be used in developing countries to test on the spot for diseases like diabetes and malaria," she said.

On a much larger scale, she suggests, the hull of a ship coated with a superhydrophobic surface would effectively be sealed from the surrounding water by a layer of gas, allowing it to move more quickly and cutting down the fouling caused by barnacles and marine growths.


Editor's Note: Original news release can be found here.