Scientists have created a 3D-printing media that can take on different colors in different parts of a single print job. The secret lies in utilizing ultraviolet light to selectively alter the surface structure of the material as it's being dispensed.
Ordinarily, the color of the polymers extruded by 3D printers is dictated by synthetic dyes. Not only is the production of these dyes harmful to the environment, the dyes themselves may become pollutants in their own right once the printed object has been discarded.
Additionally, with a few experimental exceptions, all of the polymer filament on one spool is usually all one color. This means that if someone wants to 3D-print a single object that is different colors in different places, they need to switch back and forth between different spools.
What's more, really vivid colors – such as those seen on butterfly wings – are difficult to produce in dye form. That's because instead of pigments, butterfly wings feature nanoscale structures which reflect/scatter and absorb ambient white light in such a way that it's seen as colors such as bright red, blue or green.
Led by Assoc. Prof. Ying Diao and graduate student Sanghyun Jeon, researchers at the University of Illinois Urbana-Champaign set out to replicate that effect in a photosensitive 3D-printing ink.
The resulting gelatinous material is what's known as a "photo-cross-linkable bottlebrush block copolymer solution." It's called a bottlebrush because molecularly-speaking, it consists of densely grafted side-chain "brushes" attached to a common shared backbone.
When the ink is exposed to UV light immediately upon being extruded from the print nozzle, molecules in the tips of the brushes cross-link with one another. As the ink quickly solidifies, those linked molecules form into butterfly-wing-like nanostructures on the material's surface.
By synchronizing factors such as extrusion speed, print head motion, and UV light intensity, it's possible to tweak the process in such a way that different parts of the finished product appear as colors ranging from deep blue to orange within the visible light spectrum. The technology also allows for gradients between colors which would otherwise be impossible in 3D printing.
A paper on the research was recently published in the journal PNAS.
