Color-Changing Materials Are Elastic (And Scalable)

A team of engineers at MIT is working on a new technique for developing stretchy, color-changing, synthetic materials that are scalable and inexpensive.

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

Transcript

00:00:00 BENJAMIN MILLER: My name is Benjamin Miller. I'm a PhD candidate in the laboratory for bio-inspired photonic engineering here in Mechanical Engineering at MIT. And our group looks at how nature manipulates color and also looking at how we can take those lessons and use them to produce new materials and devices inspired by nature. Quite often in nature, color is produced not through pigments or dyes but a phenomenon known

00:00:24 as structural color. So this is how a lot of things like butterflies, bird feathers, for example, get their color. And in structural color, you have nanoscale structures that interact with light causing it to reflect certain colors. So for the past few years, my research has been looking at how can we create synthetic versions of materials like this that are also elastic? If you make them elastic, it means

00:00:44 that as you stretch or compress them, the spacing of those little nanostructures changes, in turn, changing the color of light that's reflected. So there are a lot of different ways to do this, and there's a lot of existing techniques. But a lot of them suffer from the problem they're not necessarily scalable or they're too expensive. So what we were trying to do was develop a new technique that can solve those challenges.

00:01:03 So the starting point for the technique that we use is actually using holographic recording material, sort of thing that's used for anti-counterfeiting or passports, for example. And then the manufacturing technique is actually really simple. All we do there is stick that basically to a reflective surface, so like a mirror or brushed aluminum, a steel plate. And we expose that to light from a desktop projector.

00:01:25 We make a couple of slight modifications to it. But, basically, we stick this holographic material onto a reflector, project the light onto it, and it forms these nanoscale structures within that thin holographic film. Once we've done that, we can bond that film to other materials, whether that's textiles or thin sheets of black silicone. At that point, it's essentially a structural kind of material. And then as we stretch it, again,

00:01:52 these nanoscale structures change in size, changing the color of light that's reflected. So the first application that we've been looking at is actually to develop compression bandages. So if we literally stick a thin sheet of this material onto a compression bandage then the color of that bandage is a visual indicator of how much force you're applying as you wrap it around the leg. So that means that essentially physicians can apply pressure correctly more often but also, potentially, that people could

00:02:18 just do it at home on their own, maybe take a picture with their phone just to let them know if it's done correctly.