Forget dyes and pigments, researchers from the Institute of Science and Technology Austria (IST Austria) and the King Abdullah University of Science and Technology (KAUST) have developed a new way to create colour effects using a computational design tool and 3D printing. The novel process uses the design tool to automatically generate 3D printable nanostructures which create defined colours when light is shone through them.
Though many of the things we encounter on a daily basis are coloured by pigments, many natural organisms and objects are given their colour from structural coloration—a phenomenon where the object’s microstructure causes the appearance of different hues. The research team highlights peacock feathers as a prime example of structural coloration, saying that while the feathers appear to be brightly coloured in blues and greens, the feather itself is actually pigmented brown and it is the long hollows within the feathers which reflect the bright colours.
Seeking to recreate this natural occurrence, the IST Austria and KAUST researchers realized they could leverage new technologies, such as 3D printing to fabricate nanostructures that mimic structural coloration microstructures. Most impressively, the joint research team has developed a computational design tool that automatically generates 3D printable templates for nanostructures which correspond to a pre-defined colour.
The innovative research could have a significant impact on a range of industries, as structural colouration poses a number of advantages over pigment-based colouring. For instance, it does not fade, it creates the possibility to produce more colour effects and it doesn’t pose any toxic risks, as many pigments do.
“The design tool can be used to prototype new colours and other tools, as well as to find interesting structures that could be produced industrially,” commented Auzinger.
In their work, the researchers credit the feasibility of their structural colouration achievement to the increased accessibility of fabrication technologies such as direct laser writing. The technology, they say, costs as much as a high quality industrial 3D printer and enables printing at the scale of hundreds of nanometers—think several hundred times thinner than a single human hair. This technology has drastically opened the possibilities of structural coloration experiments.
Notably, the research effort has gone beyond what previous scientists have explored, which has been limited primarily to recreating nature-inspired or simple nanostructural designs. The new approach, spearheaded by Thomas Auzinger and Bernd Bickel from IST Austria and Wolfgang Heidrich of KAUST, is based on an inverse design task in which the user inputs the colour they want to create and the computer generates a nanostructure pattern that produces the colour effects when exposed to light.
Another aspect of the research which differs from previous approaches has to do with the fact that the computer tool generates randomly composed patterns instead of a particular pattern. Auzinger explains:
“When looking at the template produced by the computer I cannot tell by the structure alone, if I see a pattern for blue or red or green. But that means the computer is finding solutions that we, as humans, could not. This free-form structure is extremely powerful: it allows for greater flexibility and opens up possibilities for additional colouring effects.” (For example, the design tool can create a square pattern that, when printed, displays directional colouring. In other words, it will be red from one angle and blue from another.)
Crucially, the design tool also ensures that whatever pattern it comes up with can be reproduced physically using the aforementioned printing process. The automation of the design tool, which requires “no extra effort on the part of the user,” also makes structural coloration experiments and applications more accessible to non-experts.
“It’s amazing to see something composed entirely of clear materials appear coloured, simply because of structures invisible to the human eye,” said IST Austria professor Bickel “We’re eager to experiment with additional materials, to expand the range of effects we can achieve.”
“It’s particularly exciting to witness the growing role of computational tools in fabrication,” added Auzinger, who will be presenting the project at SIGGRAPH 2018. “And even more exciting to see the expansion of ‘computer graphics’ to encompass physical as well as virtual images.”