Engineers at the University of Colorado Boulder (CU Boulder) have developed a first-of-its-kind material that deforms and then propels itself into the air when heated. Researchers say this material could be used to help soft robots jump or lift objects.
Researcher Tayler Hebner, who earned her PhD in chemical and biological engineering from CU Boulder in 2022, and her colleagues are exploring different ways a material known as liquid crystal elastomer behaves when exposed to heat. These materials are a solid and elastic version of liquid crystals used in screens such as those in laptops or TVs, and they could even be utilized in windshields to protect pilots from temporary blindness caused by laser pointers.
Hebner stated: “We were just observing the liquid crystal elastomer sitting on a heating plate and wondered why it wasn’t forming the expected shape. It suddenly appeared right from the testing phase on the tabletop.”
Further investigation with colleagues from the California Institute of Technology revealed that the cause of the jumping behavior is due to a film the size of a contact lens, consisting of three layers. When heated, the top two layers contract faster than the bottom layer, causing it to form a cone shape. Ultimately, due to accumulated tension, the inverted cone strikes the surface it is being heated on and leaps into the air. In experiments, researchers found that in just 6 milliseconds, the film could increase its thickness by 200 times.
Researchers compare the functionality of the material to how grasshoppers store energy in their legs before jumping.
Co-author of the study, Timothy White, a professor of chemical and biological engineering at CU Boulder, remarked: “When the inversion occurs, the material punctures through and resembles a child’s popper toy, jumping off the surface. In this regard, research conducted at Harvard University in 2020, where the design of the popper toy inspired an actuator that could one day assist soft robots in traversing rugged terrain.”
Researchers compare the action of the film to how grasshoppers achieve impressive jumps and believe it could also play a role in the development of soft robots—machines that operate without metal or other hard materials like the fast-walking machines that use light and magnetic fields. White stated: “In nature, many adaptations, such as grasshopper legs using stored energy, involve elastic instability. We are trying to create synthetic materials that mimic those natural properties.”
As part of exploring the structure of the films being utilized, the research team discovered that the material could also be made to jump by cooling it instead of heating it. They also mentioned that by adding legs to the film, the material could control its direction. While the team acknowledges that the material may not become the primary source of movement in soft robots, they feel this discovery contributes to the knowledge of how to improve the operation of these advanced machines, showcasing the potential for storing and releasing energy under certain conditions.
