UOW’s Xiaolin Wang in his laboratory. Photo: University of Wollongong.
UOW’s Xiaolin Wang in his laboratory. Photo: University of Wollongong.

In a landmark discovery, researchers at the University of Wollongong (UOW) in Australia have realized the non-contact manipulation of liquid metal. Using just a small voltage and a magnet, they can move the metal in any direction and manipulate it to form unique, levitated shapes such as loops and squares.

The liquid metal is galinstan, an alloy of gallium, indium and tin, which favours 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 a result of the voltage causing electrochemical oxidation that lowers the metal’s surface tension.

“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 (ie, electromagnetic induction, the same mechanism as drives motion in an electric motor),” explained Xiaolin Wang from UOW. Wang is a node leader and theme leader at the ARC Centre of Excellence for Future Low-Energy Electronics Technologies (FLEET), and led the research team from UOW’s Institute for Superconducting and Electronic Materials within the Australian Institute for Innovative Materials.

The galinstan wires can be manipulated to move in a controlled path, and can even be suspended (against gravity) around the circumference of the applied magnetic field, assuming controlled, designed shapes.

“The non-contact manipulation of liquid metal allows us to exploit and visualize electromagnetism in new ways,” said Yahua He, a PhD student at UOW and lead author of a paper on this work in the Proceedings of the National Academy of Sciences. “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”

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

To date, however, 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 realised 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 70mA) could be measured in the resulting wires.

“There was a creative leap at this point, as the team realised that electromagnetic induction could be used to control the liquid metal wires in a non-contact manner. This was the key to finally successfully solving the challenge, thereby developing a new strategy for shaping fluids in a non-contact manner. By combining electromagnetic induction and fluid dynamics, we were able to manipulate the liquid metal in a controllable way, and move like soft robotics.

“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. [But] 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.”

The non-contact manipulation is made possible by galinstan’s unique fluid dynamic and metallic properties. As soft, current-carrying conductors, the wires present minimal resistance to manipulation via Lorentz force under a controlling magnetic field, allowing them to be easily manipulated in designed ways.

This very low resistance to movement allows unusually fine control of resulting shapes. “Usually, liquid streams break up into droplets. For example, streams of water coming from a faucet or hose start out as a cylinder, but quickly break up into droplets,” said co-corresponding author Michael Dickey at North Carolina State University. “However, the liquid metal wire has a string-like property, similar to waving ribbons in the air. That property allowed us to manipulate the liquid metal stream into continuous loops and other shapes.”

This story is adapted from material from FLEET, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.