Researchers at TU Wien demonstrate that in 3D printing not only geometry, but also local material properties can be deliberately tuned. The basis is a light-curing formulation in which photochemical reactions occur only where the material is exposed to defined wavelengths and intensities. The team led by Katharina Ehrmann couples this exposure with temperature profiles, achieving spatially resolved control of crystallinity—from amorphous to semi-crystalline—within a single print run. The results were published in Nature Communications.
Technically, the approach is based on a liquid-resin chemistry whose crosslinking and molecular order can be controlled via process parameters.
“We can use different light intensities, different wavelengths, or different temperatures,” says Katharina Ehrmann. “All of this can be used to influence the properties of the 3D-printed material.
As a demonstrator, the team printed a QR code concealed by an opaque cover layer into a polymer body. Above a defined temperature threshold, the cover layer transforms, loses its crystalline character, and becomes transparent; the code becomes visible and can, depending on material parameters, be thermally “hidden” again. Another example is a warning symbol that appears only at over-temperature and thus is suitable as an indicator for cold chains. Optical characterization was carried out in the group of Andrei Pimenov at the Institute of Solid State Physics.
“Depending on the crystallinity, the material properties can also vary greatly,“ explains Michael Göschl. “Crystalline materials tend to be hard and brittle, while amorphous materials can often be soft and elastic. The optical properties can also vary, from glass-like transparency to opaque white,” says Dominik Laa. Michael Göschl and Dominik Laa are the first authors of the current publication, both of whom are researchers in Katharina Ehrmann and Jürgen Stampfl’s teams.
The work addresses a well-known limitation of additive manufacturing: the usual single-material restriction per build job. By adjusting the microstructure in situ, functional zones with different mechanical and optical properties can be produced from a single resin formulation.
“We are offering a completely new range of possibilities for 3D printing,” says Katharina Ehrmann. “Potential applications can be envisaged in many different areas, from data storage and security to biomedical applications.”
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