MIT team makes color-changing holographic film

Mention the word “hologram” and the first thing that will probably come to mind is a sci-fi fantasy like star wars or maybe Holographic Tupac. Although it may seem like futuristic technology, holograms are actually based on a photographic technique that dates back to the 19th century.

And now a team at MIT found a way to reuse this old school technique to make a cool, stretchy, color-changing holographic film that can be used in a variety of applications, from fashion to medical packaging to commercial packaging.

The ‘OG’ hologram

Related: Before color photography, there was the Lippmann process

Holography is a process that creates 3D images by “superimposing two light beams onto a physical material”. Developed in the late 1800s by French-Luxembourgish physicist Gabriel Lippman (a man of mighty mustache), the process consists of spreading an emulsion of photosensitive grains on a mirror. Exposing the plate reflects light in and out of the emulsion, causing the grains to “reconfigure their position, like many tiny mirrors, and reflect the pattern and wavelength of light from exposure”.

Although innovative, the process was by no means efficient. A single exposure could take days, and so the technique, in its oldest form, was largely abandoned

The MIT holographic film

MIT researchers studied mollusk shells and butterfly wings to develop their new holographic film.

The MIT team had studied elements of nature such as mollusc shells and butterfly wings, which appear to shimmer. The reason for iridescence can be explained by microscopic surface structures, called Bragg reflectors. These are angled and layered to reflect light; MIT compares them to tiny colored mirrors.

“Like Lippmann emulsions, current holographic materials consist of photosensitive molecules which, when exposed to incoming photons, can cross-link to form colored mirrors,” writes Jennifer Chu from the MIT news desk.

The research team experimented with exposing holographic films using nothing more than standard projectors, creating images in just minutes with vivid color reproduction that, when stretched, changed hues. The accelerated exposure time of these modern holographs may be essential to making the process viable on a large scale.

The material can even be used to send hidden messages, visible only when stretched. MIT

“As the material stretches and thins, its nanoscale structures reconfigure to reflect slightly different wavelengths, for example changing from red to blue. The team discovered that the color of the film is very sensitive to voltage. After making an entirely red film, they glued it to a silicone support of variable thickness. Where the backing was thinnest, the film remained red, while thicker sections stretched the film, causing it to turn blue,” writes Chu.

The future of holographic film

The advancements pave the way for many uses, including coatings, packaging, fashion, and other apparel. Holographic foils can even be applied in a medical setting, such as bandages. The change in material color can be used to indicate the correct amount of pressure to apply to a site when treating conditions such as venous ulcers and lymphatic disorders.

“Scaling up these materials is not trivial, because you have to control these structures at the nanoscale,” said Benjamin Miller, a graduate student in the Department of Mechanical Engineering at MIT. “Now that we’ve cleared this scaling hurdle, we can explore questions like: can we use this material to create robotic skin that has a human-like sense of touch? Are we creating touch-enabled devices for things like virtual augmented reality or medical training? That’s a big space we’re looking at now.

About Debra D. Johnson

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