A group of engineers at the Massachusetts Institute of Technology (MIT) have developed a new smart material that changes color when stretched or pressed. Secret messages can be encoded in it. The technology of this material, which looks like science fiction, comes from the 19th century.
It was in 1891 that Gabriel Lippmann invented a technique for creating color photographs using a mirror and a special emulsion. The image bounced off the mirror and was then printed onto the emulsion. Thanks to this invention, Lippman won the Nobel Prize in Physics in 1908.
Benjamin Miller, a researcher at MIT, took advantage of Lippman’s technique and used it in a modern holographic material. As with Lippman’s emulsion, Miller’s materials respond to light, but can be prepared in minutes rather than days.
The researchers have published their study in Nature Materials . In the article they describe how the color changing technology works. They first placed the material on aluminum sheets, as if it were the surface of a mirror, and projected images onto the sample. They then peeled it off and placed it on a black silicon mount for support. As the material was stretched, the nanoscale structures shifted and began to reflect different wavelengths, some of them invisible to our eyes.
The team claims that producing this material is perfectly feasible. Now he is investigating its properties and what potential applications it could have. Among other uses, they have seen that the material would be used to record impressions of coins, milling cutters and even fingerprints, which can be converted into compressive stress maps.
“Scaling up these materials is not trivial, because you have to control these structures at the nanoscale,” Miller explained. “Now that we’ve gotten past this hurdle, we can explore questions like can we use this material to create robotic skin that has a human-like sense of touch? And can we create touch devices for things like augmented virtual reality or medical training? It’s a big space that we’re looking at right now.”
In addition to robotics, a material like this could be used in smart textiles such as pressure-control bandages, something that would have been unthinkable with Lippman’s original emulsion.
“Lippmann’s materials wouldn’t have even made it possible to make a Speedo (a swimming trunks). Now we could make a full jersey,” added Mathias Kolle, associate professor of mechanical engineering.
“The beauty of this work is that they have developed a simple but extremely efficient way to produce large-area photonic structures, ” said Sylvia Vignolini, professor of chemistry and biomaterials at the University of Cambridge, who was not involved in the study. “This technique could be a game changer for coatings and packaging, and for wearables as well.”
Referencia: Miller, B.H., Liu, H. & Kolle, M. 2022. Scalable optical manufacture of dynamic structural colour in stretchable materials. Nature Materials. DOI: https://doi.org/10.1038/s41563-022-01318-x
