News in Science

Rose petals inspire nano-raspberry surfaces

Wet or dry Scientists have developed a new material that can be painted onto surfaces to keep them wet or dry, and which never needs cleaning.

The new nanostructure coating, reported in the journal Chemistry of Materials, could reduce condensation in aircraft cabins, keep walls and roofs dry in buildings, or be used for some medical tests in remote areas without the need for high tech laboratories.

"We call them raspberry particles because they're composed of spherical nanoparticles, held together in raspberry shaped structures," says study lead author Dr Andrew Telford of the University of Sydney.

"Raspberry particle films can be described as sticky tape for water droplets. They can trap tiny drops, preventing them from rolling off surfaces, even upside down."

Telford and colleagues based their idea on the structure of water repellent surface layers found on some rose petals, which cause water droplets to bead up into balls.

Customised molecules

According to Telford, the raspberry particles can be made out of different molecules to achieve specific properties.

The material used in the study was polystyrene, however Telford says using fluorinated polymers would give the raspberries water repellent surfaces, while using molecules containing a charge would allow them to soak up water.

"So you can keep the same nanostructure by using these raspberry particles, just tweak the molecules they're made of in a very simple way, and you could go from one extreme to the other," he says.

"This means we will be able to design surfaces that do whatever you need them to do. We could design a surface that stays dry forever, never needs cleaning, can repel bacteria and even prevent mould and fungi growth."

"This could be used on quick-dry walls and roofs and would also help to cool down houses through evaporation."

Medical applications

Raspberry particles could also have applications in the rapid processing of simple medical tests, and those requiring very high turnover rates, without the need for expensive equipment.

"There's this new idea of doing work with liquids without the need of a vessel, because you're just working on freestanding droplets," says Telford.

"That may have implications for making medical tests very cheap and easy to do."

Telford says the raspberry particles are easy to manufacture in large quantities, using simple techniques similar to making paint.

As to the question of how long before you'll be able paint your house with raspberry particles?

"That's a good question," says Telford, "We would like to understand how to control of this material, and find the right molecules to make a surface that always stays dry or always stays wet.

"Those two extremes have the highest potential in terms of commercial viability."