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Chinese Scientists Have Built the First Self-Propelled Liquid Metal Robot

Posted March 16, 2015

Researchers from Tsinghua University in Beijing, China have developed the world’s first liquid metal robot which can power itself and also change shapes.

Combined with some indium and tin, gallium turns into a liquid motor. Image credit: Alshaer666 via Wikipedia, CC BY-SA 3.0.

Combined with some indium and tin, gallium turns into a liquid motor. Image credit: Alshaer666 via Wikipedia, CC BY-SA 3.0.

“The soft machine looks rather intelligent and [can] deform itself according to the space it voyages in, just like [the] Terminator does from the science-fiction film,” said Jing Liu from the Tsinghua University. “These unusual behaviours perfectly resemble the living organisms in nature.”

The motor is made from galinstan – an alloy made from gallium, indium and tin (68.5%, 21.5% and 10% respectively) that has a melting point of -19 degrees Celsius, meaning it stays liquid at room temperature.

When placed in a Petri dish with sodium hydroxide, or even brine, and left in contact with a flake of aluminium, which the alloy utilizes as fuel, the liquid motor can move around on its own for about an hour, prompting its inventors to raise some new questions about the definition of life – the research group has likened their creation to a bio-mimetic mollusc.

Puzzled by the underlying mechanism of the functioning motor, the team carried out several experiments that revealed two primary drivers of propulsion: some of it comes from a charge imbalance across the drop, which in turn creates a pressure differential between the front and the back, while the rest is created by hydrogen bubbles that form as the aluminium reacts with the sodium hydroxide.

Building on previous research that suggested a stationary drop of gallium can act as a pump in an electric field, Liu has demonstrated that their self-powered motor, too, becomes a pump if held still, and is capable of shifting around 50 millilitres of water per second. According to the team, this could have immediate applications in many fields, such as moving liquid through a cooling device without the need for an external source of power.

Thanks to the alloy’s “large surface tension, desirable flexibility, high electrical conductivity and low toxicity” – it can move in a straight line, run around the circular dish and squeeze through complex shapes – a robot based on a similar device could soon be used to monitor the environment, deliver materials through pipes, or even move substances through blood vessels.

Combined with last year’s findings, which revealed that electricity makes galinstan take complex forms, Liu believes their research could be used in tandem to change the drop’s velocity or coordinate a swarm of individual drops.

The paper, released in the journal Advanced Materials and called Self-Fuelled Biomimetic Liquid Metal Mollusc, is part of a long-term effort to develop intelligent, non-rigid robots that can be reshaped on the fly, bringing fictional, shape-shifting T-1000 from the movie Terminator 2 that much closer to reality.

Sources: study preview,,,

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