3-D Conductive Structures Built with Liquid Metal

Michael Dickey (North Carolina State University)

Engineers at North Carolina State University in Raleigh developed techniques to build three-dimensional objects with electrical conductivity from liquid metal at room temperature. A team from the lab of chemical engineering professor Michael Dickey published its findings online last week in the journal Advanced Materials.

The NC State researchers devised a series of methods using a liquid metal alloy of gallium and indium. When the alloy is exposed to the oxygen in the air, the outside surface solidifies, developing a skin that enables the alloy to retain its shape in spite of gravity and surface tension. Most other liquids will spread out on a plane or combine into a single liquid drop.

In their paper, Dickey and colleagues reported on a proof-of-concept study that describes methods for forming wires by extruding the liquid metal from a syringe. The oxide skin reaches from the syringe needle to the deposit surface and, as long as the gallium-indium alloy flows from syringe, a wire forms. Applying a vacuum to the syringe stops the flow and severs the wire.

Another technique stacks droplets, where the short bursts of pressure on the alloy form round objects. The oxide surface lets the droplet retain its shape, without merging into other drops, yet still connect to other the droplets physically and with the ability to conduct a current. Still another method creates wires by intruding the alloy into a coil-shaped polymer microchannel mold, then dissolving the mold, leaving only the wire.

The NC State researchers built simple electronic devices, demonstrating the process to form the objects and their ability to conduct electricity. In a demonstration of flexible electronics, the team embedded the wires extruded from the syringe in a flexible polymer, and connected the wires to small, surface-mounted LED bulbs. The current flowed through the wires illuminating the bulbs, even when the polymer surface with the embedded wires was being bent.

The following video from Dickey’s lab demonstrates some of these processes.

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