A new smart paint blends art and science – Advanced Science News

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in brand new A study published in Advanced scienceNortheastern University researchers led by Daniel Wilson combined science and art when they created a natural pigment-based coating that responds to sunlight.

“We can develop new optical materials and control mechanisms from scratch, but we can learn a lot from the materials and methods employed in biology,” Wilson said. “We’re excited to build on the ability to change colors to create cephalopod-inspired color formulas that are durable and flexible.”

The chemistry behind the color change

The colors used in conventional paint are stable, which means that they do not easily participate in chemical reactions, they provide a long-lasting and permanent color. Color change only really occurs when the color fades due to wear and tear.

But some pigments such as xanthommatin can change their color to a completely different color under the influence of different stimuli. Light, electricity and chemical species. In nature, such colors help some creatures Camera from hunters And send visual signals.

“Xanthommatin and other pigments broadly classified as ommochromes are formed by the metabolism of the amino acid tryptophan,” said research scientist Cassandra Martin, first author of the study. “These pigments control the appearance of cephalopods [such as squids and octopuses]Also some crabs and insects.

The ability to change the color of xanthommatin is based on a chemical reaction, which accepts electrons and what chemists call “reduced” or loses them and becomes “oxidized”. “The visible color of xanthommatin is controlled by the oxidation state of the molecule: the oxidized form is yellow, and the reduced form is red,” explained Martin.

In an earlier study, Wilson found that this color change in xanthommatin was caused by exposure to sunlight. Using this simple catalyst, the researchers manipulated xanthommatin into the membrane, making the pigment responsive to light.

Formula

The team incorporated titanium dioxide into the formula to complete the coating, the white color used in all commercial paints. “Titanium dioxide offers what we call high hiding power, which means that the coating completely covers the underlying color,” Martin said.

Here, however, titanium dioxide has an important role in the xanthommatin color changing mechanism, which serves as a source of electrons that reduces xanthommatin and accelerates the color change. “Also, titanium dioxide is a semiconductor. […]That is, it facilitates electron transport and mobility,” Martin added. In this context, this indicates a more efficient color change, which is powered by an external light source – in this case sunlight.

The team incorporated these functional ingredients into polyurethane, which acts as a glue that holds the ingredients together and helps them stick to the surface after the paint dries.

All lights on color

Composition in hand, scientists tested the new coating’s ability to transform light. They found that the color change only occurred in the presence of titanium dioxide, and surprisingly, formulations with smaller and more concentrated titanium dioxide particles showed more significant and faster color changes.

In 12 minutes, the most concentrated small particles reached 85% of the total color change, while the composition with large particles took 27 minutes. The secret? Smaller particles have a higher surface-to-volume ratio than larger ones, providing greater surface area for light collection and xanthommatin reduction compared to membranes of comparable size with larger particles.

One characteristic of light-responsive colors is their ability to return to their original color when the light source is removed. The team found that they successfully achieved the first yellow color when all their coatings stopped irradiating. Moreover, the colors changed between red and yellow ten more times without problems, which shows the high stability of the color changer.

Digging deeper into the mechanism, scientists found that out of the entire solar spectrum, only ultraviolet radiation triggers a transition from yellow to red, while visible and infrared rays remain unaffected by the color of the coating.

Ultraviolet rays are more powerful and therefore more effective at removing electrons from titanium dioxide to reduce xanthommatin. This discovery opens up new possibilities for the dynamic arts, where UV light can be directly used as a power source for color transfer.

A mixture of art and science

In a proof-of-concept “exhibition” designed to demonstrate the potential of their paint, the team painted and covered parts with adhesive tape to create an image of a husky dog.

When exposed to sunlight, the uncovered areas turn red while the masked areas are yellow. After removing the light source, the red area gradually returned to its original color, causing the image to disappear. A similar strategy was used to create the cover image for this article.

Furthering their artistic exploration, the team realized that xanthommatin could be combined with stable pigments to contribute to the palette of their color-changing formulas. They mixed xanthommatin with the blue dye extracted from lapis lazuli to produce various shades of green with the oxidized xanthommatin (yellow plus blue) turning purple (minus xanthommatin plus blue).

“We are excited to see how xanthommatin and titanium dioxide can be integrated into standard coating processes and consumer products because our color-changing pigments respond to ambient sunlight,” said Wilson.

“For example, formulas like ours can be used to create surfaces that change color depending on the weather – think exterior colors that change the color of a house or building throughout the day, or show different colors in sunny and cloudy conditions – or to create dynamic or adaptive patterns that adapt to the environment A controlled temporary work of art,” he concluded.

With this development, the future holds the promise of ever-increasing color change Combining art with practicality.

Reference: Cassandra L. Martin et al., Color-changing dyes activated by a combination of photo-responsive bio-inspired dyes and semiconductorsAdvanced Science (2023) doi: doi.org/10.1002/advs.202302652



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