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 metal used is galinstan, an alloy of gallium, indium and tin, which lends itself to 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 which lowers the surface tension of the metal.
“We realised that electromagnetic induction could be used to control the liquid metal wires. 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),” said Prof Xiaolin Wang the leader of this project.
As a consequence, it was possible to manipulate the wirers in a controllable path, and could even be suspended (against gravity) around the circumference of the applied magnetic field, assuming controlled, designed shapes.
The non-contact manipulation of liquid metal will make it possible to exploit and visualise electromagnetism in new ways. The ability to control streams of liquid metals in a non-contact manner will also enable the reshaping of electronically conductive fluids for advanced manufacturing and dynamic electronic structures.
Non-contact methods of manufacturing and manipulation can minimise unwanted disturbance of objects being studied or manipulated – previously developed non-contact technologies include object manipulation by acoustic manipulation or optical tweezers.
However, the use of free-flowing liquid streams has been particularly difficult to manipulate in a non-contact manner. Realising highly-controlled changes in directionality or complex shaping of liquids, especially without disrupting the cross-sectional shape of the stream, was the challenge that the UOW research team looked to address.
Commenting Prof Xiaolin Wang said, “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.
“The team then 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.”
The UOW team’s findings are published in the January issue of Proceedings of the National Academy of Sciences of the United States of America (PNAS), the world’s premier journal for multidisciplinary research.
“By combining electromagnetic induction and fluid dynamics, we were able to manipulate the liquid metal in a controllable way, and move like soft robotics,” Professor Wang said. “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.
This non-contact manipulation is made possible by the material’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 the magnetic field. As a result, the wires could be easily manipulated in designed ways.
“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. 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,” explained co-corresponding author Prof Michael Dickey (North Carolina State University).
