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Zapping Tiny Metal Drops With Sound Creates Wires for Soft Electronics
Zapping liquid metal droplets with ultrasound offers a new way to make wiring for stretchy, bendy electronics.
The technique, described in the Nov. 11 Science, adds a new approach to the toolbox for researchers developing circuitry for medical sensors that attach to the skin, wearable electronics and other applications where rigid circuit electronics are less than ideal (SN: 6/1/18).
The researchers began by drawing on sheets of stretchy plastic with lines of microscopic droplets made of an alloy of gallium and indium. The metal alloy is liquid at temperatures above about 16° Celsius.
Though the liquid metal is electrically conductive, the droplets quickly oxidize. That process covers each of them with a thin insulating layer. The layers carry static charges that push the drops apart, making them useless for connecting the LEDs, microchips and other components in electronic circuitry.
By hitting the microspheres with high-frequency sound waves, the researchers caused the microscopic balls to shed even smaller, nanoscopic balls of liquid metal. The tiny spheres bridge the gaps between the larger ones, and that close contact allows electrons to tunnel through the oxide layers so that the droplets can carry electricity.
When the plastic that the drops are printed on is stretched or bent, the larger balls of metal can deform, while the smaller ones act like rigid particles that shift around to maintain contact.
The researchers demonstrated their conductors by connecting electronics into a stretchy pattern of LEDs displaying the initials of the Dynamic Materials Design Laboratory, where the work was done. The team also built a sensor with the conductors that can monitor blood through a person's skin (SN: 2/17/18).
[...] Majidi isn't convinced that the ultrasound approach is a game changer for flexible circuits. But he says that it's high time the subject is appearing in a leading journal like Science. "I'm personally really excited to see the field overall, and this particular type of material architecture, is now gaining this visibility."
W. Lee et al. Universal assembly of liquid metal particles in polymers enables elastic printed circuit board [science.org]. Science. Vol. 378, November 11, 2022, p. 637. doi: 10.1126/science.ade1813 [doi.org].
