New technique prints silver nanowires that stretch and flex

Researchers have developed a new technique that enables circuits to be printed on flexible, stretchable substrates using silver nanowires.

The advance from a group at North Carolina State University (NC State) is said to make it possible to integrate the material into an array of electronic devices.

Silver nanowires are flexible, stretchable and conductive. Consequently, they have attracted interest for use in prosthetic devices and wearable sensors but challenges exist.

Silver nanoparticles can be used to print circuits, but the nanoparticles produce circuits that are more brittle and less conductive than silver nanowires. Conventional techniques for printing circuits don’t work well with silver nanowires as the nanowires can clog the printing nozzles.

“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,” said 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 20μm long, the resulting circuits have the desired conductivity, flexibility and stretchability,” said 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,” said 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.”

According to NC State, the size of the printing area is limited only by the size of the printer, meaning the technique could be scaled up.

The researchers are said to have used the new technique to create prototypes that make use of the silver nanowire circuits, including a glove with an internal heater and a wearable electrode for use in electrocardiography. NC State has filed a provisional patent on the technique.

“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 said.

The paper, “Electrohydrodynamic Printing of Silver Nanowires for Flexible and Stretchable Electronics,” is published in the journal Nanoscale.

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