Researchers have discovered how to make materials that snap and reset themselves, relying only upon energy flow from their environment. The discovery may prove useful for various industries that want to source movement sustainably.

The team uncovered the physics during a mundane experiment that involved watching a gel strip dry. The researchers observed that when the long, elastic gel strip lost internal liquid due to evaporation, the strip moved. Most movements were slow but every so often, they sped up. These faster movements were snap instabilities that continued to occur as the liquid evaporated further. Additional studies revealed that the shape of the material mattered and that the strips could reset themselves to continue their movements.

Snap instabilities are one way that nature combines a spring and a latch and are increasingly used to create fast movements in small robots and other devices as well as toys like rubber poppers. Most of these snapping devices, however, need a motor or a human hand to keep moving. With this discovery, there could be various applications that won’t require batteries or motors to fuel movement.

After learning the essential physics from the drying strips, the team experimented with different shapes to find the ones most likely to react in expected ways and that would move repeatedly without any motors or hands resetting them. The team even showed that the reshaped strips could do work such as climb a set of stairs on their own.

The findings demonstrate how materials can generate powerful movement by harnessing interactions with their environment, such as through evaporation, and they are important for designing new robots, especially at small sizes where it’s difficult to have motors, batteries, or other energy sources.

For more information, contact the Army Research Laboratory Public Affairs Office at 703-693-6477.


Motion Design Magazine

This article first appeared in the April, 2021 issue of Motion Design Magazine.

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