Making metal loop and climb with electromagnetism

A team of researchers has figured out a way to make a stream of liquid metal move independently, looping and winding upwards, with the use of a little electricity and some magnets.

The researchers, who are based at FLEET at the University of Wollongong (UoW), found that applying a charge and a magnetic field to galinstan – an alloy of gallium, indium and tin, which is liquid at room temperature – could cause it to curve, sharply change direction, and even levitate as it drops from a nozzle.

Credit: University of Wollongong.

“The non-contact manipulation of liquid metal allows us to exploit and visualise electromagnetism in new ways,” says Professor Xiaolin Wang, a researcher at UoW.

Yahua He, a PhD student at UoW, adds that “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.”

Credit: University of Wollongong.

The researchers set up a syringe, 0.26 millimetres in diameter, which pumped out galinstan. The alloy typically has a high surface tension, meaning it tends to form individual drops rather than a continuous stream.

But a small amount of voltage – about one volt – removes this surface tension and causes the liquid metal to form a wire, with a current passing through it. According to He, the researchers achieved this with an “up-down electrode setup”: a small tub of water containing sodium and hydroxide ions, with an anode at the syringe and “liquid metal [falling] due to gravity on the cathode”.

Credit: University of Wollongong.

Wang says that with this electrochemical setup, “it becomes possible to apply a force to the wire via application of a magnetic field, ie 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.”

With the right electromagnetic induction, the researchers were able to form the stream into squares, circles and figure-eights, twisting both clockwise and anticlockwise. You can see a few in these videos.

As it falls, smoke appears to rise from the base of the experiment. He says this is hydrogen gas, formed at the cathode.

“Liquid metal seemed to work as a catalytic role,” says He. It speeds up the electrochemical reaction, causing more hydrogen to form.

Credit: University of Wollongong.

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Read more: Shape-shifting liquid metals for electronics that build themselves

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Previously, it’s been very difficult to manipulate liquid streams like this without making any physical contact with the liquid.

“The research in liquid metals was inspired by biological systems as well as science fiction, including the shape-shifting, liquid metal ‘T-1000’ robot in the James Cameron–directed film Terminator 2,” says Wang.

“This research is more than science fiction. We have conceived and realised this non-contact method for liquids, offering a new way to manipulate and shape fluids.”

According to He, “next we will try to find more manipulations [and] new phenomena as well as some practical applications with this research – such as metallic structures for advanced manufacturing.”

A paper describing the research has been published in PNAS.