(Left) photograph of a large-scale silver nanowire-coated flexible film; (right) silver nanowire particles viewed under a microscope. Images: S.K. Yoon, Korea University.A new, ultrathin film that is both transparent and highly conductive to electric current can be produced by a cheap and simple method devised by an international team of nanomaterials researchers from the University of Illinois at Chicago (UIC) and Korea University.
The film is also bendable and stretchable, offering potential applications in roll-up touchscreen displays, wearable electronics, flexible solar cells and electronic skin. The film is reported in a paper in Advanced Functional Materials.
The new film is made of fused silver nanowires, and is produced by spraying the nanowire particles through a tiny jet nozzle at supersonic speed. The resultant film possesses nearly the electrical conductivity of silver plate and the transparency of glass, says senior author Alexander Yarin, professor of mechanical engineering at UIC.
"The silver nanowire is a particle, but very long and thin," Yarin said. The nanowire is around 20µm long, so four laid end-to-end would span the width of a human hair. But their diameter is a thousand times smaller – and significantly smaller than the wavelength of visible light, which minimizes light scattering.
To produce the film, the researchers suspend these nanowire particles in water and then propel them by air through a de Laval nozzle, which has the same geometry as a jet engine but is only a few millimeters in diameter. "The liquid needs to be atomized so it evaporates in flight," Yarin explained. When the nanowires strike a surface at this supersonic speed, they fuse together, as their kinetic energy is converted into heat.
"The ideal speed is 400 meters per second," Yarin said. "If the energy is too high, say 600 meters per second, it cuts the wires. If too low, as at 200 meters per second, there's not enough heat to fuse the wires."
The researchers applied the nanowires to flexible plastic films and to three-dimensional objects. "The surface shape doesn't matter," Yarin said.
The transparent flexible film can be bent repeatedly and stretched to seven times its original length and still work, said Sam Yoon, corresponding author of the study and a professor of mechanical engineering at Korea University.
Earlier this year, Yarin, Yoon and their colleagues produced a transparent conducting film by electroplating a mat of tangled nanofiber with copper. Compared to that film, this self-fused silver nanowire film offers better scalability and production rate, Yoon said.
"It should be easier and cheaper to fabricate, as it's a one-step versus a two-step process," said Yarin. "You can do it roll-to-roll on an industrial line, continuously."
This story is adapted from material from the University of Illinois at Chicago, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.