A new type of “ink” enables 3D printing of electrochemically switchable conducting polymers using a light-based process. Researchers at the universities of Heidelberg and Stuttgart have succeeded in making so-called redox polymers usable for additive manufacturing using digital light processing.
The resulting complex two- and three-dimensional structures can be manipulated electrochemically to change their color. This opens new perspectives for the production of 3D printed optoelectronic devices. The research work was carried out as part of the graduate school “Mixed Ionic-Electronic Transport: From Fundamentals to Applications”, which is supported by both universities.
Digital light processing (DLP) is a light-based 3D printing process in which a light-sensitive “ink” is built up layer by layer to form a three-dimensional object through selective irradiation with UV light. Compared to other additive manufacturing processes, DLP enables complex structures to be manufactured quickly. “Although the technology is already being used successfully in dentistry, for example, DLP printing of conductive polymers for applications in optoelectronics has so far been a challenge,” explains Prof. Dr. Eva Blasco. The researcher and her team at the Institute for Molecular Systems Engineering and Applied Materials at Heidelberg University are researching unique functional materials for 3D printing. The project was carried out in close collaboration with Prof. Dr. Sabine Ludwigs and her group at the Institute of Polymer Chemistry at the University of Stuttgart, who are experts in the conduction of polymers and electrochemical switching.
The two research teams developed a new methacrylate-based “ink” that carries redox-active carbazole groups. These redox units allow such materials to donate or accept electrons in their polymer chains, making them electrically conductive and able to change color depending on their oxidation or reduction state. In their current work, the researchers were able to use this photoconductive ink formulation to produce structures that can be manipulated electrochemically even after printing and whose properties remain switchable. “This research was made possible through close, interdisciplinary collaboration in our laboratories in Heidelberg and Stuttgart,” emphasize Christian Delavier and Svenja Bechtold, who are both working on their dissertations as part of the graduate school.
This carbazole-containing ink formulation was used to directly additively produce two-dimensional pixel arrays and checkerboard patterns as well as a multilayered three-dimensional pyramid. Originally almost transparent, these complex structures initially took on a light green color through electrochemical stimulation, then became dark green and finally practically black. “This process is completely reversible and, depending on the structure, can be controlled down to the pixel level. The control in the third dimension, i.e. in relation to the height of the architectures, is particularly exciting,” adds Sabine Ludwigs. According to Prof. Blasco and Prof. Ludwigs, the combination of high-resolution, light-based 3D printing with redox polymers opens up new possibilities for the additive manufacturing of pixel displays or actuators for soft robot applications where the volume can be switched electrochemically.
The German Research Foundation supports the graduate school “Mixed Ionic-Electronic Transport” (GRK 2948) at the universities of Heidelberg and Stuttgart. The results of their current research appear in the journal “Advanced Functional Materials”.