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Display Surface Developed from Air-Water Interaction

Robin Ras (Aalto University)

Robin Ras (Aalto University)

University researchers in Finland and the U.K., and Nokia Research Center in the U.K., have developed an optical display technology based on the ability of a surface structure to repel water. The findings of the team led by physicist Robin Ras (pictured left) of Aalto University in Finland appear online this week in the journal Proceedings of the National Academy of Sciences.

Ras and colleagues devised a surface with the properties of a lotus leaf, which is superhydrophobic or extremely water-repellent. The lotus has leaves with a surface having microscopic structures that prevent water from completely wetting the leaf, leaving a thin layer of air between water and the surface.

The researchers created a similar surface with structure comprised of microposts each 10 microns in height; one micron equals one million of a meter. Grown on the microposts then were nanoscale filments, where one nanometer equals one billionth of a meter. The two size scales — micrometer and nanometer — enabled the thin layer of air to exist in two different states that correspond to each of the sizes. The team found it was easy to switch between the two states, using a nozzle to create over- or under-pressure in the water, in order to change the air layer to either state.

Ras notes that this bi-stable nature, similar to computer memory chips, creates a striking optical contrast between the states due to a change in the roughness of the interaction when air meets water. “Combined with the optical effect,” says Ras, “the surface is also a bistable reflective display.”

The display involves only the shape of the air layer, not to the surface itself. This state switching enables the creation of shapes on the surface when underwater. Take the display surface out of water, however, it emerges dry and free of writing.

Aalto graduate student and team member Tuukka Verho developed the technique to manipulate the air layer using a nozzle. The technique makes it possible switch air-layer states down to the individual pixel level, providing a high level of precision.

The following video demonstrates the display surface’s capabilities.

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