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Researchers are turning to 3D printing methods such as vat photopolymerisation (VPP) to overcome those challenges, thanks to its high design freedom and printing accuracy. In that method, a light is used to selectively cure and harden layers of an ink within a vat, gradually building a 3D object.
It also poses several challenges, however – CNTs affect the printability and curing properties of the ink, while simultaneously achieving high stretchability and electrical conductivity is a major hurdle.
A research team from Seoul National University of Science and Technology in Korea set out to tackle those challenges in a recent project. Led by Professor Keun Park and associate professor Soonjae Pyo, the team fabricated highly stretchable, electrically conductive CNT nanocomposites using VPP 3D printing.
“Our new CNT nanocomposites are optimised specifically for VPP-based processes, allowing fabrication of highly complex 3D structures,” Professor Park said.
The engineers first prepared polymer nanocomposite inks by adding multi-walled carbon nanotubes to resin, with concentrations from 0.1-0.9%. They agitated the mixture using ultrasonic waves to achieve uniform dispersion, before analysing the prepared inks to determine optimal printing conditions.
The team additively manufactured test specimens using the various inks, then tested their mechanical and electrical properties, as well as printing resolution. Results showed the formulation with 0.9% CNT offered the best balance of properties – it could stretch up to 223% of its original length before breaking, while still achieving a electrical conductivity of 1.64×10-3 siemens per metre, surpassing previously reported materials.
To demonstrate practical applicability, the researchers used the optimised CNT nanocomposite to create piezoresistive sensors with high sensitivity and reliable performance. They were integrated into a shoe insole, allowing the team to monitor pressure distribution at the bottom of the foot in real time, detecting different movements and postures.
“The developed smart insole device demonstrates the potential of our CNT nanocomposites for 3D printing the next generation of highly stretchable and conductive materials,” said Pyo. “We believe these materials will be indispensable for wearable health monitors, flexible electronics and smart textiles.”
The work was published in Composite Structures.
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