Featuring controlled by flexible fins and more flexible liquid drip,

CHAMPAIGN, Ill. — Flexible screens that can change color, convey information, and even send hidden messages via infrared radiation are now possible, thanks to new research from the University of Illinois Urbana-Champaign. Engineers inspired by morphing the skin of animals such as chameleons and octopuses have developed capillary-controlled robotic wing fins to create interchangeable optical and infrared light multipixel displays that are 1,000 times more energy efficient than light-emitting devices.

The new study led by professor of science and mechanical engineering Sameh Tawfick demonstrates how fins and bendable fluids can simultaneously switch between straight or bent and hot and cold by controlling the volume and temperature of tiny fluid-filled pixels. Varying the volume of liquid in the pixels can change the direction of the flip flaps – similar to old-fashioned flip clocks – and varying the temperature allows the pixels to communicate via infrared energy.

The research findings are published in a journal Science Advances.

Tawfick’s interest in the interaction of elastic forces and capillaries – or elasto-capillarity – began as a graduate student, spanning the fundamentals of hair wetting and leading to his research in soft robotic displays in Illinois.

“An everyday example of elasto-capillarity is what happens to our hair when we shower,” says Tawfick. “When our hair is wet, it sticks together and bends or knots when capillary forces are applied and released when it dries.”

In the lab, the team built tiny boxes, or pixels, a few millimeters in size, which contain fins made of a flexible polymer that bend as the pixels are filled with liquid and drained using a system of tiny pumps. Pixels can have one or more fins and be arranged into an array that forms a display to convey information, said Tawfick.

Click here to see a single fin assembly video

Click here to see a video of the four-fin assembly

“We’re also not limited to cubic pixel grids,” says Tawfick. “The fins can be arranged in a variety of orientations to create different images, even along curved surfaces. The controls are precise enough to produce complex movements, such as simulating the blooming of a flower.”

The study reports that another feature of the new display is the ability to send two signals simultaneously – one that can be seen with the human eye and one that can only be seen with an infrared camera.

“Because we can control the temperature of these individual droplets, we can display messages that can only be seen using infrared devices,” says Tawfick, “Or we can send two different messages at the same time.”

However, there are some limitations to the new display, says Tawfick.

While building the new device, the team discovered that the tiny pump needed to control the pixel fluid was not commercially available, and the entire device was gravity sensitive – meaning it only worked when it was in a horizontal position.

“Once we rotated the screen 90 degrees, performance degraded greatly, which was a detriment to applications such as billboards and other signs that were intended for the public,” said Tawfick. “The good news is, we know that when liquid droplets get small enough, they become insensitive to gravity, much like when you see a raindrop sticking to your window and not falling. We have found that if we use liquid droplets that are five times smaller, gravity no longer matters.”

The team said that because the science behind the effect of gravity on droplets is well understood, it will provide a focal point for the next application of the new technology.

Tawfick says he’s excited to see where this technology goes because it brings fresh ideas to large market spaces with large reflective displays. “We have developed a new type of display that requires minimal energy, is scalable, and is even flexible enough to be placed on curved surfaces.”

Illinois researchers Jonghyun Ha, Yun Seong Kim, Chengzhang Li, Jonghyun Hwang, Sze Chai Leung and Ryan Siu also participated in the study.

The Air Force Office of Scientific Research and the National Science Foundation supported the research.

Editors note:

To contact Sameh Tawfick, call (217) 244-6303; e-mail (e-mail protected).

The paper “A capillarity-controlled polymorphic display and texture integrated system” available online. DOI: 10.1126/sciadv.adh1321