The film is also stretchable and bendable, offering prospective applications in wearable electronics, flexible solar cells, roll-up touchscreen displays, and electronic skin. The results are reported in Advanced Functional Materials.
“The silver nanowire is a particle, but very long and thin,” Yarin said. The nanowires measure approximately 20 μ long, so four laid end-to-end would cover the width of a human hair. But their diameter is a thousand times smaller — and considerably smaller than the wavelength of visible light, which reduces light scattering.
The team suspended the nanowire particles in water and propelled them by air via a de Laval nozzle, which has a similar geometry as a jet engine, but is just a few millimeters in width.
When the nanowires strike the surface they are being applied at supersonic speed, they fuse together, as their kinetic energy is turned to heat.
The liquid needs to be atomized so it evaporates in flight.
The ideal speed is 400 meters per second. 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.
Alexander Yarin, UIC Distinguished professor of mechanical engineering
The researchers applied the nanowires to flexible plastic films and to 3D objects. “The surface shape doesn’t matter,” Yarin said.
The transparent flexible film can be bent repetitively and stretched to seven times its original length and yet function, said Sam Yoon, the corresponding author of the research and a professor of mechanical engineering at Korea University.
Sometime this year, Yarin and Yoon and their colleagues created a transparent conducting film by electroplating a mat of tangled nanofiber with copper. According to Yoon, compared to that film, the new self-fused silver nanowire film provides better production rate and scalability.
It should be easier and cheaper to fabricate, as it’s a one-step versus a two-step process. You can do it roll-to-roll on an industrial line, continuously.
Alexander Yarin, UIC Distinguished professor of mechanical engineering
Co-authors with Yarin and Yoon are Jong-Gun Lee, Do-Yeon Kim, Jong-Hyuk Lee and Donghwan Kim of Korea University; Suman Sinha-Ray of the Indian Institute of Technology in Indore, India; and Mark T. Swihart of the State University of New York at Buffalo.
The research was supported by the National Research Foundation, GFHIM-2013M3A6B1078879, and the Industrial Strategic Technology Development Program, 10045221, funded by the Ministry of Knowledge Economy of Korea.