The new material that imitates the feathers of a bluebird

ETH researchers have developed a new component inspired by the complex structure of the plumage of the American eastern bluebird

ETH scientists have developed a new material inspired by the feathers of the eastern bluebird (Photo: Envato)

The oriental blue it is a special bird: the small singing bird hides among its very rare blue feathers, the secret to designing materials with unique characteristics. The color of the plumage, in fact, is not due to a pigment, but to the particular structure of its feathers.

Researchers at the Federal Institute of Technology in Zurich managed to replicate it, obtaining a new material which has demonstrated surprising qualities (and advantages).

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New material inspired by the feathers of the oriental bluebird

Observed under the microscope, the feathers of the eastern blue (Sialia Sialis) appear crossed by a channel network with a diameter of a few hundred nanometers, or billionths of a meter.

The rare blue color of the North American rural songbird has attracted the attention of researchers at the Laboratory of Soft and Living Materials of Federal Polytechnic of Zurich, led by the former ETH professor Eric Dufresne.

Scientists have managed to replicate the complex and fascinating structure of the feathers of the eastern blue: they have developed a new material that presents the same structural design as its feathers, and which demonstrated a surprising potential in various practical applications.

To reconstruct the plumage of the small Sialia Sialis, the researchers started from one transparent silicone rubber which has the characteristic of being able to be stretched and deformed.

They then placed the tire in one oily solution and left it to "swell" for several days in an oven at 60°C. Once the mixture cooled, they then extracted the rubber from the oil solution.

La nanostructure of the rubber, observed under the microscope, showed reticular structures similar to those that give the feathers of the eastern bluebird their characteristic blue color.

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The main difference between the new material and the Sialia Sialis feathers is in the thickness of the channels formed on its surface: the synthetic material measures 800 nanometers, while the feathers of the eastern blue are just thick 200 nanometers.

The principle behind the creation of the lattice is the phase separation, that division between the components of a mixture that occurs, for example, when they mix oil and vinegar to dress the salad.

No matter how hard you try, the two liquids tend to separate as soon as you stop vigorously shaking the emulsion: changing the temperatureHowever, it is possible to make the two components join and separate again.

This is exactly the procedure that the ETH researchers followed to mix the silicone rubber and the oily solution: the result of this very delicate process is that, inside the rubber, an entire microscopic network of channels, very similar to that of the feathers of the eastern bluebird.

As he explained Carla Fernandez Rico, the lead author of the study published in “Nature Materials”, experiments have shown that it is possible “control and select conditions such that channels are formed during phase separation".

"We managed to stop the procedure before the two phases fully merged again”, explained the researcher.

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New processing method with surprising potential

The novelty of this processing method of materials is generating a lot of interest in the physics community. “We have a simple system composed of only two ingredients, but the final structure obtained is very complex and controlled by the properties of the ingredients“, explains Fernández Rico, “we have been contacted by several groups of theorists who propose the use of physical models to understand the key principles of this new process and predict its outcome".

The potential of this special rubber created to imitate the structure of the feathers of a small blue bird is not limited to this: the new material has enormous potential in terms of technical applications and sustainable solutions.

A possible field of application is that of car's battery performance: One of the main reasons why batteries lose their charging capacity over time is that the ions (which move between the electrodes through a liquid electrolyte) end up reacting with the latter, causing physical contact between the electrodes.

A possible solution to this problem could be in replace the liquid electrolyte with solid electrolytes which guarantee good transport of ions thanks to a capillary network structure of interconnected channels. Exactly what the ETH researchers showed.

Another possible application for this material inspired by bird feathers is in moles water filters: in this case what is particularly advantageous is the surface/volume ratio, which in channel structures is enormous.

The structure of the new material, the scientists explain, allows bacteria and contaminants to be effectively removed from the water while making it travel quickly.

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Future research developments: trying with natural polymers

One of the great advantages of the new method developed in the laboratories of the ETH Zurich is that the process is completely scalable"In principle you could use a piece of rubbery plastic of any size", explains Fernandez Rico, even if then "adequately large containers and ovens would also be needed".

The new material is still far from being ready for the market: “While the gummy compound is cheap and easy to obtain, the oil phase is quite expensive. A couple of cheaper alternatives would be needed”, explains the researcher.

A solution could come from sustainable research development"Many natural polymers, such as cellulose or chitin, have a similar structure to the rubber used in our work”, says Fernández Rico, and they certainly constitute a more sustainable alternative compared to silicone rubbers derived from petroleum.

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Researchers at the Federal Institute of Technology in Zurich have developed a new material inspired by the structure of rare blue feathers (Photo: Envato)