Researchers from the FAMU-FSU College of Engineering have developed a parameter set for 3D printing graphene-based structures with optimized conductive qualities.
After a series of test runs, the team found that while factors like print pressure and nozzle diameter affected the composite’s properties, at specific speeds, its particles could be aligned vertically. Using these parameters as a guide, the scientists produced a material with enhanced strength and conductivity, potentially making it ideal for use within military applications such as 3D printing heat sinks or shielding.
“We found that a wide-range of matrix filler combinations allow for versatility in the properties of the printed material,” said lead author Professor Subramanian Ramakrishnan. “By fine tuning the way they are processed, we can suggest guidelines that maximize the effectiveness and performance of the composites.”
Conductive matrix-filler composites
Composites are so widely-used within 3D printing, and there are so many matrix-filler combinations available, that users can often tailor them to meet the specific needs of their application. Likewise, graphene nanoplatelets (GNPs) are potentially well-suited to this role, due to their optimal thermal and electrical properties, and ideal aspect ratio for the job.
Epoxy resins, meanwhile, are known for their flexibility and ease of processing, which could make them perfect for combining with GNPs to form thermal interface materials. However, the properties of such composites would depend on factors such as the rheology of the inks used to create them and their concentration, areas that aren’t yet fully understood.
Previous studies have shown that using Direct Ink Writing (DIW) to 3D print GNP-loaded materials, induces a shear force on their filler, causing their particles to align with the orientation of the print. How exactly this occurs and its impact on conductivity remains somewhat of a mystery, hence the team sought to quantify the exact mechanics of the process.
“Our aim is to 3D print lightweight conductive composites and to study the effect of printing conditions on particle orientation and final composite performance,” explained Ramakrishnan. “The combination of epoxy resins and graphene nano-platelets is of interest in several applications for the U.S. Air Force.”
Identifying the optimized set-up
In order to fabricate optimal graphene structures, the team developed a novel ink, in which they included concentrations of GNPs that varied from 7% up to 18%. The custom material was then loaded into an nScrypt 3Dn-300 system, and deposited using different speeds and pressures to generate the widest possible dataset.
Once the composites had been printed and cured into specimens, their electrical resistance was measured using X-ray and microscopy processes. Interestingly, results showed that the inks with GNP levels higher than 13% exhibited increased shear thinning, yielding samples with enhanced strength and conductivity.
Similarly, the scientists found that increasing the print speed from 5 mm/s to 40mm/s caused more shear, and led the material’s particles to converge in the print’s direction. In fact, the effect was so profound, that compared to GNP-infused injection molded parts, the team’s samples were up to 619 s/cm more conductive.
Overall, the researchers believe that their parameter set represents a cost-effective method of controlling particle orientation that could yield novel polymeric nanocomposites. What’s more, given that U.S. Air Force Research Laboratory scientists contributed to the study, the materials could also find end-use military applications such as corrosion-resistant coatings or even shielding.
Unlocking graphene’s potential
Graphene’s inherent electrical transmitting properties make it ideal for 3D printing electronic devices, and a number of researchers have investigated its potential in this area.
Scientists from the University of Nottingham made a breakthrough in additive manufactured electronics in November 2020, when they fabricated graphene into multiple layers. The novel process yielded materials that could be used as a basis for fabricating enhanced additive semiconductors.
U.S. researchers on the other hand, have opted to utilize Optomec’s Aerosol Jet Printing (AJP) technology to fabricate electrosensing food testing sensors. Using a graphene-based ink, the team were able to 3D print interdigitated electrodes onto a polymer base, forming devices that could be used in food processing facilities.
Elsewhere, a team based at the University of Southern California (USC) have utilized the strength of graphene to 3D print a set of novel self-sensing armor. Although the scientists have only conducted tests with a LEGO figurine so far, they believe that in future, it could be deployed within military applications.
The researchers’ findings are detailed in their paper titled “Printability and performance of 3D conductive graphite structures.” The research was co-authored by Roneisha Haney, Phong Tran, Edward B.Trigg, Hilmar Koerner, Tarik Dickens and Subramanian Ramakrishnan.
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Featured image shows a 3D printed cone of graphene-based material that the FAMU-FSU team used for masks in their lab. Photo via FAMU-FSU.
