Superhydrophobic surface helps researchers develop optical displays from water and air (w/ Video)

June 14, 2012
Image: Aalto University

(Phys.org) -- For many years, scientists have been pursuing ways to mimic the perplexing capability of the lotus leaf to repel water. Lotus leaves hate water so much that droplets effortlessly roll off the surface, keeping it clean from dirt. Now an international team of researchers led by Aalto University have come up with an entirely new concept of writing and displaying information on surfaces using simply water. They exploit the unique way a trapped layer of air behaves on a lotus-inspired dual-structured water-repelling surface immersed under water.

To achieve the extreme of the , a surface needs to be superhydrophobic: it must have microscopic that prevent from wetting the surface completely, leaving a of air between water and the surface. When such a surface is immersed in water, a trapped air layer covers the entire surface.

The researchers lead by Dr. Robin Ras at Aalto University in Finland, University of Cambridge and Nokia Research Center Cambridge fabricated a surface with structures in two size scales: microposts that have a size of ten micrometers and tiny nanofilaments that are grown on the posts. On such a two-level surface the air layer can exist in two different shapes (wetting states) that correspond to the two size scales. The researchers found that one can easily switch between the two states locally using a nozzle to create over- or underpressure in the water, in order to change the air layer to either state.

“The minimal energy needed to switch between the states means the system is bistable, which is the essential property of memory devices, for example”, Academy Research Fellow Dr. Robin Ras points out. However, there is a feature that makes it all the more interesting: there is a striking optical contrast between the states due to a change in the roughness of the water-air interface. “Combined with the optical effect, the surface is also a bistable reflective display.”

The switching only involves a change in the shape of the air layer − nothing happens to the solid surface itself. This is demonstrated by writing shapes on the surface underwater (making use of the contrast between the states) and taking the sample out of water: the surface emerges completely dry, and no traces of the writing remain.

The method for manipulating the air layer with the was developed by Tuukka Verho, graduate student in Aalto University. He was able to show that the reversible switching can be done with precision in a pixel-by-pixel fashion.

“This result represents the first step in making non-wettable surfaces a platform for storing or even processing information”, says Academy professor Olli Ikkala. Until now, lotus-inspired surfaces have been mainly developed for applications like self-cleaning, anti-icing or flow drag reduction. This research is a landmark example how the Nature teaches materials scientists towards functional materials.

An article entitled “Reversible switching between superhydrophobic states on a hierarchically structured ” is published in PNAS, Proceedings of the National Academy of Sciences, and provides more in depth information about this project.

Explore further: Stay super-dry with Nokia's nanotechnology

More information: www.pnas.org/cgi/doi/10.1073/pnas.1204328109

Related Stories

Stay super-dry with Nokia's nanotechnology

March 7, 2012

What happens when a drop of water falls on a lotus leaf? It’s not a philosophical question, but a natural phenomenon scientists have been studying, and trying to make sense of, for hundreds of years. 

Unexpected ice-formation mechanism

January 18, 2012

(PhysOrg.com) -- Extremely hydrophobic materials cause water to roll right off objects that have been coated with them. Up to now, it was assumed that aircraft or wind turbines coated in such a way did not ice up as easily. ...

Researchers reveal Eucalypt’s nano properties

October 31, 2011

(PhysOrg.com) -- Murdoch University nano scientists have discovered that a eucalyptus plant native to south west WA has unique self-cleaning and water-repellent properties which could make it a gold mine for new nanotechnology ...

Bionic coating could help ships to economize on fuel

May 4, 2010

The hairs on the surface of water ferns could allow ships to have a 10 per cent decrease in fuel consumption. The plant has the rare ability to put on a gauzy skirt of air under water. Researchers at the University of Bonn, ...

Recommended for you

A curious quirk brings organic diode lasers one step closer

November 20, 2017

Since their invention in 1962, semiconductor diode lasers have revolutionized communications and made possible information storage and retrieval in CDs, DVDs and Blu-ray devices. These diode lasers use inorganic semiconductors ...

Carefully crafted light pulses control neuron activity

November 17, 2017

Specially tailored, ultrafast pulses of light can trigger neurons to fire and could one day help patients with light-sensitive circadian or mood problems, according to a new study in mice at the University of Illinois.

Strain-free epitaxy of germanium film on mica

November 17, 2017

Germanium, an elemental semiconductor, was the material of choice in the early history of electronic devices, before it was largely replaced by silicon. But due to its high charge carrier mobility—higher than silicon by ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.