The butterfly principle used

For their new technology, the scientists from the group of Andrew deMello, professor of biochemical engineering, drew inspiration from butterflies: The wings of Cynandra opis, a species found in tropical Africa, appear in brilliant colors. These colors are produced by extremely fine regular surface structures in the size range of the wavelength of visible light. The structures deflect light rays and thus intensify individual color components of the light or cancel out other components. The researchers led by deMello have succeeded in reproducing the surface structures of Cynandra opis and other modified structures using a nano-3D printer. In doing so, they created an easy-to-use principle for the production of so-called structural colors.

There are numerous examples of such structural colors in nature, including those due to irregular surface structures - for example, in other butterfly species. "The regular nanostructures on the wings of Cynandra opis were particularly well suited for 3D printing to recreate," explains Xiaobao Cao, a former doctoral student in deMello's group and lead author of the study. The Cynandra opis structures consist of two superimposed layers of lattice grids arranged at right angles to each other, with a lattice spacing of about half a micrometer to one micrometer.

Entire color palette

By varying this lattice spacing and the height of the lattice bars in the size range from 250 nanometers to 1.2 micrometers, the color can be varied, as the ETH researchers were able to show. They were thus able to produce all the colors of the visible spectrum using 3D printing. This includes many colors that do not occur in the natural model.

The researchers succeeded in producing the surfaces with different materials, including a transparent polymer. "This made it possible to illuminate the structure from behind to bring out the color," explains Stavros Stavrakis, a scientist in deMello's group and co-author of the study. "This is the first time we've managed to produce all the colors of the visible spectrum as structural colors in a translucent material."

Safety feature

As part of the study, the scientists produced a thumbnail image of different colored structural color pixels measuring 2 by 2 micrometers. Such thumbnail images could one day be used as a security feature on banknotes and other documents. Because the colors can be produced with transparent material, it would also be possible to manufacture color filters for nanotechnological optical measuring instruments. This fits in well with the main research activity of ETH Professor deMello's group, which develops miniaturized systems for chemical and biological experiments, so-called microfluidic systems.

Large-scale production of nanostructures is also conceivable, the researchers say. If 3D printing were used to produce a negative structure as a template, it could be used to make a large number of impressions. Thus, the principle could be suitable for the production of high-resolution color screens - for example, thin bendable screens. And finally, according to the scientists, the color pigments used today in inks for printing and painting could be replaced by such structural inks. Textured inks have several advantages over pigment inks: they are durable because they do not fade when exposed to light, and they also have a better environmental balance in most cases.

Original publication: Advances Materials – Cao et al. (2022). Replicating the Cyndra opis Butterfly’s Structural Color for Bioinspired Bidrating Color Filters

Source: chemie.de - Das Schmetterlingsprinzip genutzt

Image Source: Wikimedia: Lsadonkey - Cynandra opis bernardii male