Some butterflies impress with their range of shapes and shades that change with the light. The magic happens thanks to the fact that their color diversity is accentuated by an unusual way of producing color. While the bright and dark tones are given by the pigments of their cells, the fluorescent colors or rainbow effect are made up by the structure of their wings. In fact, they do not have a single color, but when light hits millimeter scales, it reflects in different directions and turns into many colors. To the human eye, gradation changes depending on position, just as it does when looking at soap bubbles, the playable side of a DVD, or the feathers of a peacock. This is the so-called structural color, an element that is difficult to reproduce outside of nature, but which can be a new way of coloring things in the world. Among its advantages is that it is much lighter, does not absorb much heat and does not fade over the years.
Inspired by the wings of a butterfly, scientists at the University of Central Florida (USA) have developed what they say is the lightest structural ink in the world and can be produced on a large scale. In the article published in Science advancesThey explained that it is so light that it can cover a Boeing 747 with just 1.3kg of paint, instead of the 500kg normally used today.
If they were lighter, cars or planes might consume less fuel or energy. Another advantage, explained Pablo Manuel Cancelo Abad, lead author of the study, is that this ink absorbs less heat compared to regular ink, which helps keep the surface cool. “It is interesting now that there is a shift to electric cars. Save as much as possible on cooling”, he told EL PAÍS by video. In addition, due to the color fusion, it does not fade over time, so it does not need to be repainted over the years.
Common inks in their great variety, which are used in homes, machines, cars, planes, or objects, consist of pigments that absorb or reflect certain colors of light. It is a chemical phenomenon, triggered by the reflection of light on a surface – selectively integrating certain wavelengths and reflecting the rest. This new toner works in a completely different way. It is made up of two materials that do not contain pigment: aluminum and aluminum oxide. Thus, the tone perceived by human eyes depends on its shape and size on a nanometer scale, a million times smaller than a millimeter. “We grow nanoparticles made of aluminum and aluminum oxide, and depending on their sizes, they absorb certain components of light or others. Simply put, we have to control the size of these particles and with a single structure we can generate many colors,” explains the Spanish researcher who is part of the nanooptics group . from the University of Central Florida.
The researcher from the laboratory showed a small tube containing transparent colored acetone and a thin layer of foil containing the structural dye. By moving it quickly, all the liquid takes on color. With this mixture, you can make a spray or mix it up with some resin and then transfer it to the surface. To reproduce the butterfly’s painting, the scientists used these pigments. “We mix the powder that has a color with the fennel oil. We make a kind of paste and with the help of a brush we paint it as if it were an oil painting. The oil evaporates and the solid residue remains. That’s how it works,” the expert details.
Sensilo Abad stresses that the technology behind the nanostructures uses standard machinery, which is already in place in the semiconductor, electronics or aerospace industry, so it can be easily replicated on a large scale. “It’s not a laboratory idea or a proof-of-concept, but rather a technology that can be applied,” he adds.
The limitation, he stresses, is the cost of production, but that will slow as high volume is reached. While it wouldn’t be the best choice for home wall paint, it’s definitely worth it for applications where the added benefits balance the cost. This is the case of electric vehicles, as well as air transport or even space, which requires endurance of extreme conditions. Aluminum melts around 600 degrees Fahrenheit. If you use commercial color, you lose it quickly.
Sensilo Abad confirms that the project is in the process of being sold for a patent and that companies from various industries have shown interest, such as the automotive, air, steel or cosmetic industries. However, this technology can also be applied to perform functional coatings, which go beyond aesthetic painting.
The researcher claims that his team, led by Professor Debashis Chanda, has created temperature and humidity sensors. That is, a type of coating changes color in response to chemical components, which can be used to aid in medical treatments. Let’s imagine a sensor that changes color in response to glucose concentrations, for a person with diabetes. In the case of children or patients with communication difficulties, it would be very useful to develop a lipstick that changes color according to the glucose concentration in saliva. Thus, that person’s caregiver can tell them they have to take insulin or whatever they need,” he concludes.
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