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New Materials That Move In Response to Light

Scientists from Tufts University School of Engineering have designed new materials that move in unique ways when exposed to light. These magnetic elastomeric composites could one day lead to a wide variety of designs that perform all sorts of different movements. This technology could be used in everything from solar arrays to tiny engines, and create a whole new field for solar power.

The research team was inspired by nature, where there are plenty of examples showing how light can compel movement and change. For this experiment, the light actuated materials were based on the principle of the Curie temperature. The Curie temperature is the temperature above which specific materials can change their magnetic properties. Scientists can turn the magnetism of a material on and off by heating or cooling it accordingly.

To mimic this behavior, scientists took biopolymers and elastomers and doped them with ferromagnetic CrO2, which heats up when exposed to sunlight or lasers. This causes the materials to temporarily lose their magnetic properties until they’ve once again cooled down.

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“We could combine these simple movements into more complex motion, like crawling, walking, or swimming. And these movements can be triggered and controlled wirelessly, using light.”

Fiorenzo Omenetto, Ph.D., corresponding author of the study and the Frank C. Doble Professor of Engineering in the School of Engineering at Tufts
Photo Credit: SilkLab, Tufts University

Researchers showed of some of these more complicated moves by specially constructing soft grippers capable of capturing and releasing objects based on their exposure to light. Because of the materials used, the scientists can control minute movements in the material, allowing them to bend either towards or away from the light source.

Scientists constructed a basic Curie engine in order to show the sheer versatility of these materials. Light actuated film was first shaped into a ring; the ring was then placed on a needle post near a permanent magnet. A laser was focused on a specific spot on the ring, causing it to locally demagnetize the spot. The unbalanced net force of the ring causes it to turn. Turning rotates the demagnetized spot away, allowing it to regain its magnetization. Meanwhile a new spot on the ring is demagnetized by the light. This continuous magnetization and demagnetization causes the ring to continuously rotate.

Further research is needed to fully understand the properties of these materials, but this is a significant step forward in harnessing the properties of solar power.

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