A new technique for printable and flexible circuits comes from a team of researchers at North Carolina State University. The technique allows researchers to print circuits onto flexible and stretchable substrates with silver nanowires.
These images show two printed silver nanowire patterns: a horseshoe (top) and Peano curve (bottom) design, with high resolution. The printing technique was used to make a prototype glove containing an internal heater. The bottom shows infrared images of the wearable heater going through an on-off cycle. (Source: Yong Zhu)
Silver nanowires have interested researchers for years. They have many potential applications, from prosthetic devices to wearables. The nanowires have significant flexibility, stretchability and conductive properties. While there is a lot of potential for the nanowires, they have not been used in the past because actually producing them has been a challenge.
The nanoparticles used to produce circuits are much more brittle and less conductive than silver nanowires. Conventional techniques for printing circuits don’t work with silver nanoparticles because the nanowires often clog printing nozzles. This is a challenge that the researchers attempted to solve.
"Our approach uses electrohydrodynamic printing, which relies on electrostatic force to eject the ink from the nozzle and draw it to the appropriate site on the substrate," says Jingyan Dong, co-corresponding author of a paper on the work and an associate professor in NC State's Edward P. Fitts Department of Industrial & Systems Engineering. "This approach allows us to use a very wide nozzle - which prevents clogging - while retaining very fine printing resolution."
"And because our 'ink' consists of a solvent containing silver nanowires that are typically more than 20 micrometers long, the resulting circuits have the desired conductivity, flexibility and stretchability," says Yong Zhu, a professor of mechanical engineering at NC State and co-corresponding author of the paper.
"In addition, the solvent we use is both nontoxic and water-soluble," says Zheng Cui, a Ph.D. student at NC State and lead author of the paper. "Once the circuit is printed, the solvent can simply be washed off."
The size of the printing area is limited. This means that the technique could be used for even bigger projects if the printer is scaled up.
This new technique has been used for prototypes using silver nanowire circuits. Some of these prototypes are a glove with an internal heater and a wearable electrode for electrocardiography.
"Given the technique's efficiency, direct writing capability, and scalability, we're optimistic that this can be used to advance the development of flexible, stretchable electronics using silver nanowires - making these devices practical from a manufacturing perspective," Zhu says.
The paper on this research was published in Nanoscale.
