Researchers at the Massachusetts Institute of Technology (MIT) have devised a new method for producing images with a set of unique color-changing properties, which they say combine 21st century holography with 19th century photographic technology.
MIT scientists were recently able to print large-format images of flower bouquets on a flexible material that converts the colors and wavelengths of light that are reflected once stretched. As a result of this unique photo printing technology, photos appear to change shades from warmer to cooler colors as the unique, flexible film is stretched.
Similar effects were successfully achieved with detailed images of objects that included coins, berries, and even a human fingerprint. MIT now says they have created the first fully scalable technology that allows large printed materials to be produced that have “structural colour,” which are defined as color properties determined by the microstructure of the material itself, as opposed to pigmentation or pigments.
According to Ben Miller, Ph.D. Candidate in the Bioinspired Photonic Engineering Laboratory in the Department of Mechanical Engineering at MIT, the scalability of the materials produced by his research team requires the ability to control structures at the nanoscale. Success in doing so will allow such materials to be used in a wide range of potential applications, which may include robotic skins with tactile capabilities similar to human skin, and other advanced touch sensing technologies or devices with applications in augmented reality.
“It’s a huge space we’re looking at right now,” Miller said in a statement.
Also of interest is that this new photo printing technology resulted from a combination of modern hologram technology and a 19th-century photographic technology, invented by a former recipient of the Nobel Prize in Physics.
Miller recently said the idea for this unique material goes back in part to its origins on a visit to the MIT Museum, where he visited the facility’s current exhibition on holography.
Miller said he was struck by how holography mimics the ways in which nature produces structural color.
“I realized that what they do in holography is kind of the same thing,” Miller said. Following on, Miller began reading about Gabriel Lippmann’s studies of the phenomenon known as interference in the nineteenth century, an effect that arises from the superposition of two separate systems of waves. Lippmann went on to receive the 1908 Nobel Prize in Physics for his innovative use of the phenomenon of interference to create color photography, an achievement he still remembers well. Lippmann, through a rather complex process, was able to create structural color images of objects by exposing an emulsion made of tiny photosensitive grains which, when exposed to light, could be reconfigured according to the wavelengths of light they were exposed to.
In a similar way, modern holography relies on particles that interact with photons in ways that form color effects capable of producing unique images that have three-dimensional properties. Based on Lippmann’s early photographic experiments, Miller now wondered whether modern hologram technology might not have similar applications, albeit without the same painstaking effort that Lippmann’s experiments required in the nineteenth century. Specifically, Miller decided to see if images with structural coloration similar to that of Lippmann’s could be produced in a large-scale format.
Enter Matthias Kohli, an associate professor of mechanical engineering at MIT who specializes in biology-inspired optics, optoelectronics, and materials science. Kolle is currently the head of the MIT Laboratory of Biologically Inspired Photonic Engineering, which studies ways in which the natural coloring properties of different types of materials can be reproduced in the laboratory.
Cole explained in an email to Abstraction. Intuitive examples are soap bubbles or oil films in a rain puddle.
As Kolle notes, color in such natural states is a result of the way light waves from different surfaces close together (such as the inner and outer surfaces of a soap bubble in the example given above) interfere in construction or deconstruction methods. Kolle likens this to the way that getting up across the surface of the lake by two different boats results in higher waves in one case, while the other results in shorter waves.
“The distance between these different surfaces on which the light waves are reflected determines the color,” Cooley says. “So the layer of oil on a pond of water has different colors because its thickness varies; the soap bubble is of different colors because the thickness of its wall varies.”
As Kolle explains, this effect can be greatly amplified in some cases, such as those involving multiple surfaces. This played a major role in the materials that Miller, Cole, and MIT researchers were able to produce.
“In the materials that Ben Miller produced in my collection, we use the same effect,” Cooley said. Abstraction. “[W]Create several “surfaces” in the material that the light can reflect on and adjust the distance between them to get specific colors. If it’s done in a stretchable material, we can modify the distance between the reflective surfaces just by crushing or stretching the material and that changes its color.”
Cooley and the research team at the Massachusetts Institute of Technology used a conventional projector to send images that include flower bouquets — not unlike those used by Lippmann in his original experiments — onto a transparent film with 3D properties attached to aluminum foil. In just minutes, the team succeeded in producing large and highly detailed images. A process that would have taken days under Lippmann.
One of the most interesting aspects of the latest research involves the way its structural properties change at the nanoscale level as the material is stretched. As these small structures are reshaped, the wavelengths of light they reflect vary. This is partly due to the sensitivity of the material to stress, the application of which causes a number of changes in color and other effects.
The team also discovered that the unique material could have applications in projecting hidden images. By tilting the film at an angle, the material’s nanostructural properties reflect light in unique ways, which included the reflection of infrared light from images created from exposure to red light. This means that by stretching the material, any “secret” invisible images that normally only reflect light at infrared wavelengths will be revealed, now marked in red.
Kolle notes that this unique property of the materials his team produced “can encode messages” along with other potentially useful applications.
The MIT team hopes to explore ways such materials can be used in a wide range of applications, which may include color-changing bandages that can provide simple visual indicators of pressure changes when treating various disorders.
On the part of Kolle, the usefulness of materials like this is already evident, and insofar as it exceeds the capabilities of its nineteenth-century predecessors.
“3D materials are very good nowadays,” said Cooley. extractionAnd it only takes a few minutes or even seconds to form a structure in them when exposed to light.
Elsewhere, Cooley summed things up more candidly — and with humor — in a recent MIT press release announcing the new discoveries.
“Liebmann’s materials wouldn’t even have allowed him to produce a Speedo,” Cooley said.
He added, “Now, we can make whole clothes.”
The MIT team’s paper, “Scalable Optical Fabrication of Dynamic Structural Color in Stretchable Materials,” was published in the journal nature materialsand can be found online.
This article has been updated to include additional quotes shared by Professor Matthias Kohli with a briefing on the MIT team’s research.
Micah Hanks is the editor-in-chief and co-founder of The Debrief. Follow his work on micahhanks.com and on Twitter: Tweet embed.
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