3D printer creates color through nanostructures
Most objects in everyday life are coloured with the help of pigments, but this has disadvantages: The colours can fade, artificial pigments are often toxic. In nature, however, there are also so-called structural colours in which the microstructure of an object produces colours. Peacock feathers are an example. They are brown pigmented, but reflect the iridescent blues and greens we see due to tiny, regularly arranged cavities in the feathers.
Nanostructures for structural staining can now be manufactured technically, and computer scientists from the Institute of Science and Technology Austria (IST Austria) and the King Abdullah University of Science and Technology (KAUST) have now developed a computer program that automatically creates 3D printing templates for nanostructures that are required to generate the colors desired by the user. Their results show the great potential of structural dyeing for industry and also open up the possibility for laymen to create their own designs. Thomas Auzinger, first author and postdoc at IST Austria, presented their the work at the computer graphics conference Siggraph 2018. IST Austria researchers are participating in five presentations at this renowned conference this year.
The changing colours of a chameleon and the shimmering blues and greens of the blue Morphof age are, among many others in nature, the result of structural colourings. Nanostructures cause interference in the light, which leads to a multitude of colors when viewed macroscopically. Structural dyeing has advantages over dyeing with pigments, but until recently the production of the necessary nanostructures was only possible using highly specialized methods. However, new methods such as direct laser writing now make it possible to print structures in the range of a few hundred nanometers. The procurement costs are comparable to those of a high-quality industrial 3D printer, which gives scientists the opportunity to experiment with structural coloration.
So far, experiments have mainly been conducted with nanostructures that occur in nature and with simple, regular nanostructural designs such as a regular arrangement of nanostructures. Thomas Auzinger and Bernd Bickel from IST Austria, together with Wolfgang Heidrich from KAUST, have now chosen a new approach that differs from previous research in several respects. Instead of reproducing the structures found in nature, they turn the question around and solve the so-called “inverse” problem: The user enters the desired color, and based on this the computer generates the nanostructure pattern that generates this color. The design tool should work completely automatically, no additional effort is required on the part of the user.
Another important difference to previous methods is that the nanostructures do not follow any particular pattern in the printing instructions and do not have a regular structure. They seem to be randomly composed, which represents a radical departure from earlier methods and brings many advantages. “When you look at the template that the computer creates, you can’t tell from the structure whether it’s a pattern for blue or red or green,” explains Auzinger. “That means the computer finds solutions that we as humans would never have found. This free-form structure is extremely powerful: it allows greater flexibility and opens up possibilities for additional colour effects”. You can also use the design tool to create directional color effects, such as a square that appears red from a certain angle and blue from another.
In addition, earlier designs based on nanostructures were often not printable. However, the new design tool guarantees that the user receives a printable template, which makes the method extremely useful for industrial use. “With the design tool, new colors and other tools can be prototyped and interesting structures can be found that can be produced industrially,” adds Auzinger. Initial tests of the design tool have already led to successful results. “I find it particularly exciting to see that computer-aided tools play an increasingly important role in production,” adds Auzinger, “and it is even more exciting to observe the expansion of the concept of computer graphics in physical and not just virtual images.