An ancient holographic trick gives a special property to the material

Researchers in the United States have found a new way to make matter change color: by stretching it. They use an ancient holographic technique for this.

See if your biceps want to grow a little bigger by looking at a band around your arm? Apply a dressing that shows if it is not too tight? A swimsuit that changes color while you swim? Such a material with chameleonic properties has come very close thanks to research at the Massachusetts Institute of Technology.

peacock feathers

Color, as a rule, is determined by paint or natural pigments. But it can also be done differently, says biotechnologist Benjamin Miller, who drew inspiration from nature in his research. “There is a phenomenon called structural color. Light reflection and therefore color is determined by the structure of the surface,” says Miller the MIT News website.

In nature, this phenomenon occurs, among other things, in peacock feathers and butterflies, but it is difficult to imitate. Indeed, the reflection is largely determined at the nanometric scale.

holographic film

Yet Miller’s group has now succeeded in making a synthetic version of this material. Earlier this week, researchers published their findings in the scientific journal Natural materials.

They started working with the holographic film, which is included in passports, among other things. This material is two-dimensional but can suggest depth. The researchers glued it to a reflective surface and then, using light, printed images on it. Nanostructures were then formed in the holographic film layer.

Lippmann process

This technology in itself is not new. Dating from the end of the 19th century, it is known as lippmann process which has the unique photographic characteristic of capturing color directly, without the use of dyes or filters.

When the print is ready, the film is again freed from the reflective material and the film can then be processed into an elastic textile. This elasticity is important: if you stretch the material or let it bounce, the nanostructure of the surface changes, and therefore also the color. This actually creates moving holograms.

Scalable

The advantage of the technology is that it is not expensive and, moreover, easily scalable.

The material is already tested in bandages. Nurses dressing with this material can tell by the color if they are applying the correct pressure. The researchers are also considering applications in robotics, for example.

Images: MIT News

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