The novel rubber-like material developed by University of Colorado Boulder researchers responds a bit like how grasshoppers jump by storing and releasing energy in their legs.
Graphic showing how a cone slowly builds up in an elastomer film, then inverts to launch the film high into the air over the span of less than a second. Image credit: Hebner et al., doi: 10.1126/sciadv.ade1320.
“In nature, a lot of adaptations like a grasshopper’s leg utilize stored energy, such as an elastic instability,” said University of Colorado Boulder’s Professor Timothy White.
“We’re trying to create synthetic materials that emulate those natural properties.”
In their research, Professor White and his colleagues took advantage of the unusual behavior of a class of materials called liquid crystal elastomers.
They fabricated small wafers of liquid crystal elastomers about the size of a contact lens, then set them on a hot plate.
As those films heated up, they began to warp, forming a cone that rose up until, suddenly and explosively, it flipped inside out — shooting the material up to a height of nearly 200 times its own thickness in just 6 milliseconds.
“Each of the films are made up of three layers of elastomer,” Professor White said.
“These layers shrink when they get hot, but the top two layers shrink faster than the bottom one.”
“That incongruity, combined with the orientation of the liquid crystal molecules within the layers, causes the film to contract and form a cone shape. It’s a bit like how painted vinyl sidings can warp in the Sun’s rays.”
“As the cone forms, strain builds up in the film until, all at once — snap! The cone inverts, slapping the surface and knocking the material up. The same film can also hop several times without wearing out.”
“When that inversion happens, the material snaps through, and just like a kid’s popper toy, it leaps off the surface.”
“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,” said Dr. Tayler Hebner, a researcher at the University of Colorado Boulder.
The researchers can tweak their films so that they hop when they get cold, for example, not hot.
They can also give the films legs to make them jump in a particular direction.
Most robots probably wouldn’t be able to use this kind of popping effect to make their parts move. But the team’s project shows what similar kinds of materials could be capable of — storing an impressive amount of elastic energy, then releasing it a single go.
“It’s a powerful example of how the fundamental concepts we study can transform into designs that perform in complex and amazing ways,” Dr. Hebner said.
A paper describing this research was published in the journal Science Advances.
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Tayler S. Hebner et al. 2023. Leaping liquid crystal elastomers. Science Advances 9 (3); doi: 10.1126/sciadv.ade1320
