Moisture unmasks camouflaged message

To reveal colorful printed patterns in all their glory — just add water

Placing a glass slide causes a thin layer of water to spread on top this blue polymer film and reveal a hidden image. Once the film dries out, the image disappears.

This is one in a series presenting news on technology and innovation, made possible with generous support from the Lemelson Foundation.

Nature’s colors can delight the eye. But these dazzling displays can also have many practical uses. For example, some animals hide themselves from predators by changing color to blend into their surroundings. This is known as camouflage. Researchers from Europe have taken inspiration from this to develop a new material. It changes color when exposed to moisture. And the researchers can decide beforehand which colors or patterns that moisture will reveal.

It all has to do with the new material’s structure.

Consider a peacock’s feathers. They’re a fairly boring brown. Yet your eye doesn’t perceive them that way. The features appear vibrant and multi-colored due to what’s known as structural color. Microscopic features on a plume’s surface can reflect or scatter light in some special way. This alters the material’s apparent color.

Waves of certain frequencies of light — colors — can sometimes interfere with, or block, each other. The result? The color seen by the observer is different from the object’s true hue. Besides peacock feathers, other examples of structural color include fish scales and certain butterfly wings.

Monali Moirangthem and Albertus Schenning are material scientists. They work in the Netherlands at the Eindhoven University of Technology. These researchers specialize in creating “smart” materials. These are ones that have been designed to exhibit unusual properties based on the conditions of their environment. (Such conditions include temperature, pressure, moisture level or the light shining on it.)

The researchers were particularly intrigued by beetles that seem to change color in response to differences in humidity. (Humidity is how much moisture is in the air.) This inspired their new artificial material with similar color-changing traits.

While other scientists have achieved this, “They were only able to change between two colors,” Schenning explains. His team didn’t want to limit its color palette to just two hues. They wanted moisture to be able to change their material from one color to any or all others.

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