In the future, smart clothing could monitor our posture, communicate with smartphones and manage our body temperature. But first, scientists need to find a way to effectively print complex, flexible and durable circuits on a variety of fabrics. Now, researchers are reporting ACS Applied Materials and Interfaces developed a conductive 3D printing ink made from droplets of liquid metal coated with alginate, a polymer derived from algae.
Conventional electronics are rigid and unable to withstand the twisting and pulling motions that pass through clothing during normal daily activities. Due to their liquid nature and excellent conductivity, gallium-based liquid metals (LMs) are promising materials for flexible electronics. However, LMs do not stick well to fabric, and due to their large surface tension they tend to ball up during 3D printing instead of forming a continuous circuit. Yong Hee and his colleagues wanted to develop a new type of conductive ink that could be 3D printed directly onto fabrics in intricate patterns.
To make their ink, the researchers combined LM and alginate. Shaking the solution and removing excess liquid resulted in LM microdroplets coated with an alginate microgel shell. The ink was too thick until it was squeezed through a nozzle for 3D printing, which broke the hydrogen bonds in the microgel and made it more liquid. Once the ink reaches the surface of the fabric, the hydrogen bonds are reformed, allowing the printed pattern to retain its shape. Team 3D printed the new ink on a variety of surfaces including paper, polyester fabric, non-woven fabric and acrylic-based tape. Although the printed patterns were not initially conductive, the researchers activated them by stretching, pressing, or freezing, which broke the dried alginate network to attach to the LM microdroplets.
After activation, the printed circuit had excellent electrical conductivity and strain sensing properties. Furthermore, applying a small voltage across the ends of the circuit causes it to heat up even in very cold temperatures. To demonstrate the ink’s capabilities, the team 3D printed a range of electronics onto commercial fabrics. On a T-shirt, he printed a near-field communication tag that directed a smartphone held nearby to open a Web site. Other sensors printed on the clothing monitored the movement of the elbow or knee joint. And a circuit powered by a small battery heated the printed pattern to above 120 F in less than a minute. LM-alginate inks can be recycled by soaking the fabric in a weak sodium hydroxide solution, recovering the fresh liquid metal for new applications.
one volt. Fabrication of Printed High-Performance Thin-Film Transistors
Pengcheng Wu et al, Liquid metal microgels for three-dimensional printing of smart electronic fabrics, ACS Applied Materials and Interfaces (2022). DOI: 10.1021/acsami.1c22975
Provided by American Chemical Society
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