New flexible displays inspired by animal skins can change color, convey information, and send veiled messages

Researchers at the University of Illinois Urbana-Champaign have made significant progress in developing flexible displays inspired by the adaptive skins of animals like chameleons and octopuses. These displays have the capability to change color, convey information, and even transmit encoded messages through infrared radiation. The engineering team, led by Professor Sameh Tawfick from the mechanical science and engineering department, has created capillary-controlled robotic flapping fins to construct switchable optical and infrared light multipixel displays. Remarkably, these displays are 1,000 times more energy efficient than traditional light-emitting devices.

The study explores the use of bendable fins and fluids that can switch between straight and bent positions, as well as hot and cold states, by manipulating the volume and temperature of small fluid-filled pixels. By altering the volume of fluids within the pixels, the researchers can control the flipping direction of the flaps, similar to the movement of old-fashioned flip clocks. Additionally, adjusting the temperature enables communication between the pixels using infrared energy. The research findings have been published in the journal Science Advances.

Professor Tawfick’s interest in the field of elasto-capillarity, which focuses on the interaction between elastic and capillary forces, began during his time as a graduate student. His investigations initially revolved around the fundamental science of hair wetting but have since evolved to encompass soft robotic displays at the University of Illinois.

To illustrate elasto-capillarity with a relatable example, Professor Tawfick explains how our hair behaves in the shower. When wet, our hair clings together and bends or forms bundles due to the application of capillary forces. These forces are subsequently released as the hair dries out.

A video of a single-fin arrangement

Within the laboratory setting, the research team successfully developed small pixel boxes measuring a few millimeters in size. These pixels incorporate flexible polymer fins that undergo bending when filled or emptied of fluid through a network of miniature pumps. By arranging the pixels into arrays, information can be conveyed through the resulting display, as explained by Tawfick.

Importantly, the design is not restricted to cubic pixel boxes alone. The fins can be arranged in various configurations, allowing for the creation of different images, even on curved surfaces. The level of control is highly precise, enabling complex motions such as mimicking the unfolding of a flower blossom.

An additional noteworthy feature of these new displays is their ability to transmit two simultaneous signals. One signal is visible to the human eye, while the other can only be detected using an infrared camera.

A schematic of the mechanism displaying simultaneous optical and infrared signals of the words “OK” and “NO.” In the graphic, cold pixels are indicated by a blue color and hot pixels are indicated by a pink color. Credit: Sameh Tawfick.

Tawfick highlighted an intriguing aspect of the new displays, stating, “By controlling the temperature of individual droplets, we can display messages that are only visible using an infrared device, or we can simultaneously transmit two different messages.” However, he also acknowledged certain limitations associated with these displays.

During the development process, the research team encountered difficulties due to the unavailability of commercially accessible miniature pumps required to regulate the fluids within the pixels. Additionally, the entire device’s functionality relies on its horizontal orientation and is significantly compromised when rotated by 90 degrees. This limitation proves disadvantageous for applications such as billboards and public signage.

Nevertheless, Tawfick provided an optimistic outlook, explaining that when the size of liquid droplets is reduced sufficiently, they become insensitive to gravity, similar to how a raindrop sticks to a window without falling. The team discovered that by utilizing fluid droplets five times smaller, the influence of gravity can be mitigated, paving the way for improved performance and expanded applications of the technology.

A video of a four-fin arrangement

The research team expressed their intention to focus on addressing the influence of gravity on droplets in their future applications, leveraging their understanding of this scientific aspect.

Tawfick conveyed his enthusiasm for the future of this technology, as it introduces a novel concept to the vast market of large reflective displays. He emphasized that they have successfully created a new generation of displays that boast several advantages: they consume minimal energy, can be scaled up, and are even flexible enough to be seamlessly integrated onto curved surfaces. This versatility opens up exciting possibilities for the technology’s trajectory and potential applications.

Source: University of Illinois at Urbana-Champaign

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