From temporary tattoos that track your blood alcohol level, to a paper skin that responds to stimuli much like the real thing, to energy-generating rubber sheets, it's no stretch to realize that flexible electronics will be a big part of technology going forward. Adding yet another option this field is an advancement out of the University of Illinois Chicago (UIC) and Korea University – a clear, flexible film made by mini jet engines that could find a home in roll-up phone displays and other bendy electronics.
To create the film, UIC researchers suspended silver nanowires in water and then blasted them out with air through what's known as a de Laval nozzle. The nozzle, which features an hourglass-shaped pinch along its length, is the same as that used in rockets and jet engines (and a few years ago one was used to shoot a ping pong ball out at Mach 1.2) but in this case, it only measured a few millimeters across.
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Though small, the nozzle is mighty indeed, blasting the nanowires out at supersonic speeds which causes the water to evaporate in flight and the particles to fuse when they strike the surface at which they're directed thanks to the heat generated by friction.
A researcher holds a large-scale version of the transparent film on the left, while the right side shows the silver nanoparticles under magnification
"The ideal speed is 400 meters per second (894 mph)," said Alexander Yarin, UIC professor of mechanical engineering and senior author on a paper describing the method. "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 particles themselves are only 20 microns wide – which means that if they were lined up end-to-end, they'd reach the width of a human hair – but their diameter is a thousand times smaller. This makes them tinier even than the wavelength of visible light, which reduces the amount of light that scatters when it passes through them and makes the film as transparent as glass – yet able to efficiently conduct electricity.
The film can be laid down on three-dimensional objects or a simple plastic sheet, with the process able to spray out a 100-square-centimeter area in about 30 seconds. The film can also be stretched to seven times its original length while still functioning and it can be bent repeatedly without degrading.
The research has been published in the journal Advanced Functional Materials.View gallery - 2 images