Manipulating Liquid Metals without Contact

In a landmark discovery, FLEET University of Wollongong (UOW) researchers have realized the non-contact manipulation of liquid metal.

The metals can be controlled to move in any direction, and manipulated into unique, levitated shapes such as loops and squares by using a small voltage and a magnet.

The liquid metal used is galinstan, an alloy of gallium, indium, and tin, which favors the formation of droplets due to its high surface tension.

Under the application of a small “triggering” voltage, this liquid-metal becomes a wire as the voltage causes electrochemical oxidation that lowers the surface tension of the metal.

“Because these reactions require an electrical current passing through the wire, it becomes possible to apply a force to the wire via application of a magnetic field (i.e., electromagnetic induction; the same mechanism as drives motion in an electric motor).

Thus, the wires can be manipulated to move in a controllable path and can even be suspended (against gravity) around the circumference of the applied magnetic field, assuming controlled, designed shapes.” said professor Xiaolin Wang the leader of this project.

“The non-contact manipulation of liquid metal allows us to exploit and visualize electromagnetism in new ways.”

“The ability to control streams of liquid metals in a non-contact manner also enables new strategies for shaping electronically conductive fluids for advanced manufacturing and dynamic electronic structures” said Wollongong PhD student Yahua He, the lead author of the study.

Non-contact methods of manufacturing and manipulation can minimize unwanted disturbance of objects being studied or manipulated. Previously developed non-contact technologies include object manipulation by acoustic manipulation or optical tweezers.

However, to date, free-flowing liquid streams have been particularly difficult to manipulate in a non-contact manner. Realizing highly controlled changes in directionality or complex shaping of liquids, especially without disrupting the cross-sectional shape of the stream, was the challenge for the team at UOW.

“There was an enjoyable element of discovery in this scientific process. Once the team started working on this topic, we realized that there is much more behind it,” said Wang.

“The liquid metal wires form by applying a small voltage (approximately 1 volt). However, our team found that a considerable electrical current (up to 70 mA) could be measured in the resulting wires.

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