New research that will be published in Physical Review Letters could be used to power the muscles of robots in the future. For the first time, scientists have shown that liquid metal can be made to pulse using electric currents in a controlled way.
A team of scientists led by Xiaolin Wang at the University of Wollongong in Australia have demonstrated that they can make droplets of gallium beat like miniature hearts. Gallium is a metal that is normally a soft, solid at room temperature that can be cut with a knife. At around 30 degrees Celsius, gallium becomes a liquid. It can be used to make mirrors but surprisingly, can also be found in the human body. It is present in very small amounts in the body because there are traces of it in water.
The team heated up the gallium so that it was in its liquid state and placed it inside a circular electrode. The gallium droplet would initially sit on one side of the electrode which is slanted at an angle. The droplet is submerged in a sodium hydroxide solution and a chemical reaction is initiated with the addition of an electric field. This is known as an electrochemical oxidation reaction. Consequently, when an electrical current is allowed to pass through the electrodes, the gallium begins to oxidize. Gallium oxide has a weaker surface tension than pure gallium which means the droplet begins to squish into a pancake shape. With this movement, the droplet then begins to move away from the side of the electrode. When this happens, the droplet turns back into a spherical droplet of gallium. And the cycle continues, it rolls back because of gravity to touch the side of the electrode, it then oxidizes, pancakes and then rolls away again. As a result, the droplet of gallium looks like it is beating like a heart. By changing the amount of electric current, the rate at which the ‘gallium heart’ beats can be altered. This is the first time that liquid metal has been shown to pulse in a controlled manner with electric currents.
The best bit about the work is that Wang says it was inspired by the T-1000 shapeshifting robots in Terminator 2. With these new findings, scientists hope that pulsating gallium droplets could be used to power artificial muscles of liquid-based robots . You can check out the work of Wang and his colleagues in Physical Review Letters here.