Researchers at the FAMU-FSU School of Engineering have developed a set of parameters for 3D printing graphene structures with optimized electrical conductivity. 

After a series of test runs, the team found that although factors such as printing pressure and nozzle diameter affect the properties of the composite material, the particles can be arranged vertically at a certain speed. Using these parameters as a guide, scientists have produced a material with enhanced strength and conductivity, which may make it ideal for military applications such as 3D printed heat sinks or shields.

"We found that a wide range of matrix filler combinations allow the versatility of printed materials," said lead author Professor Subramanian Ramakrishnan. "By fine-tuning their processing methods, we can come up with guidelines to maximize the effectiveness and performance of composite materials."

Composite materials are so widely used in 3D printing, and there are so many matrix-filler combinations available, users can usually customize them to meet the specific needs of their applications. Similarly, graphene nanosheets (GNP) may be very suitable for this role because they have the best thermal and electrical properties, as well as an ideal working aspect ratio.  

At the same time, epoxy resins are known for their flexibility and ease of processing, which makes them very suitable for combining with GNP to form thermal interface materials. However, the properties of such composite materials will depend on factors such as the rheology and concentration of the inks used to make them, fields that are not yet fully understood. 

Previous studies have shown that the use of direct ink writing (DIW) to 3D print GNP-supported materials will generate shear on the filler, causing the particles to align with the printing direction. How exactly this happened and its effect on conductivity is still a mystery, so the team tried to quantify the exact mechanism of the process. 

"Our goal is to 3D print lightweight conductive composites and study the effects of printing conditions on particle orientation and final composite properties," Ramakrishnan explained. "The combination of epoxy resin and graphene nanosheets is interesting in several applications in the US Air Force."

In order to make the best graphene structure, the team developed a new type of ink, which contains GNP concentrations ranging from 7% to 18%. The customized materials are then loaded into the nScrypt 3Dn-300 system and deposited using different speeds and pressures to generate the widest possible data set. 

Once the composite materials are printed and cured into samples, their electrical resistance is measured using X-ray and microscopy techniques. Interestingly, the results indicate that inks with GNP levels above 13% exhibit increased shear thinning, resulting in samples with enhanced strength and conductivity. 

Similarly, the scientists found that increasing the printing speed from 5 mm/sec to 40 mm/sec would cause greater shear and cause the particles of the material to converge in the printing direction. In fact, this effect is so profound that compared to injection molded parts injected with GNP, the team’s samples have a conductivity of up to 619 s/cm. 

In general, the researchers believe that their parameter set represents a cost-effective way to control the orientation of particles that can produce new polymer nanocomposites. More importantly, given the contributions of scientists from the US Air Force Research Laboratory to this research, these materials can also find end-use military applications, such as corrosion-resistant coatings and even shielding. 

Unleash the potential of graphene  

Graphene's inherent electrical transmission properties make it an ideal choice for 3D printing electronic devices, and many researchers have studied its potential in this field. 

Scientists at the University of Nottingham made a breakthrough in additive manufacturing of electronic products in November 2020. They made graphene into multiple layers. The materials produced by this new process can be used as the basis for the manufacture of enhanced additive semiconductors. 

On the other hand, American researchers chose to use Optomec's Aerosol Jet Printing (AJP) technology to manufacture electrical induction food detection sensors. Using graphene-based inks, the team was able to 3D print cross electrodes on polymer substrates, forming devices that can be used in food processing facilities.

Elsewhere, a team at the University of Southern California (USC) used the strength of graphene to 3D print a novel set of self-inducing armor. Although scientists have only tested the Lego figurine so far, they believe that it can be deployed in military applications in the future. 

The researchers' findings are detailed in their paper entitled "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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The featured image shows the 3D printed cones of graphene-based materials used by the FAMU-FSU team to make masks in their laboratory. The photo is from FAMU-FSU.

Paul is a graduate of history and journalism and is keen to find exclusive news about the latest technology news.

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