A team of engineers at the University of Colorado Boulder have developed a new rubber-like film that can jump to great heights, similar to a grasshopper. Unlike traditional materials, this film can jump on its own, without any external intervention – all it needs is a little heat.

The team published their findings in the journal Science Advances, stating that this technology could one day be used to create ‘soft robots’ that can leap or lift without the need for gears or other hard components.

The material works by storing and releasing energy, much like a grasshopper’s legs, according to study co-author Timothy White.

“In nature, a lot of adaptations like a grasshopper’s leg utilize stored energy, such as an elastic instability,” remarks White. “We’re trying to create synthetic materials that emulate those natural properties.”

The novel discovery makes use of the peculiar properties of the so-called liquid crystal elastomers class of materials. These are solid and flexible polymer counterparts of liquid crystals utilized in laptops and tv screens.

In the experiment, the scientists created tiny liquid crystal elastomer wafers that were about the size of contact lenses and placed them on a heated plate. These films warped as they heated up, creating a cone that ascended until it abruptly and violently turned inside out, propelling the substance up to a height of approximately 200 times its original thickness in only 6 milliseconds.

According to study lead author Tayler Hebner, , “this presents opportunities for using polymer materials in new ways for applications like soft robotics where we often need access to these high-speed, high-force actuation mechanisms.”

Discovered by chance

The discovery of this jumping behavior was almost a serendipitous accident for Hebner, a postdoctoral researcher at the University of Oregon, and her team.

They were conducting an experiment to investigate the shape-shifting properties of various liquid crystal elastomers under varying temperatures.

McCracken, a senior research associate in White’s lab, joined the team as an observer during the experimentation.

“We were just watching the liquid crystal elastomer sit on the hot plate wondering why it wasn’t making the shape we expected. It suddenly jumped right off the testing stage onto the countertop,” Hebner adds. “We both just looked at each other kind of confused but also excited.”

Careful investigation, together with input from partners at the California Institute of Technology, allowed the researchers to determine the mechanism behind the material’s high-jumping performance.

Each of these films, according to White, is composed of three elastomer layers. He claimed that when these layers get heated, they shrink, but the upper two layers do so more quickly than the bottom layer. Due to the mismatch and the orientation of the liquid crystal molecules inside the layers, the film shrinks and takes on a conical shape. Similar to how painted vinyl siding would distort in the sun.

The film forms a cone shape, which causes tension to build within it. Eventually, the cone suddenly inverts, creating a slapping motion that propels the material upwards. Remarkably, this film can also repeatedly jump without any signs of deterioration.

“When that inversion happens, the material snaps through, and just like a kid’s popper toy, it leaps off the surface,” White adds.

However, the team’s liquid crystal elastomers are adaptable, unlike those poppers. The researchers may modify their films so that they start to hop when it becomes cold instead of hot, for instance. They may also give the films legs, causing them to leap in a certain direction.

The majority of robots definitely wouldn’t be able to move their components with this type of popping effect. However, according to White, the study demonstrates what materials of a similar kind may be able to do, including the ability to store a significant quantity of elastic energy and then release it all at once. Hebner said that the project made the lab a little more fun.

“It’s a powerful example of how the fundamental concepts we study can transform into designs that perform in complex and amazing ways,” she adds.

Source: 10.1126/sciadv.ade1320

Image Credit: Ronald Martinez/Getty Images


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