Terminator draws closer with shape-shifting liquid metal motor

Using gallium, a metal with a very low melting point, researchers have developed a self-powered, shape-shifting liquid metal motor.

Michelle Starr Science editor
Michelle Starr is CNET's science editor, and she hopes to get you as enthralled with the wonders of the universe as she is. When she's not daydreaming about flying through space, she's daydreaming about bats.
Michelle Starr
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There are some concepts from sci-fi that really should never, ever see the light of day. The T-1000 -- the murderous robot made of shifting liquid metal -- is arguably one of them, but that doesn't mean it doesn't exhibit some interesting ideas, even if they do seem impossible.

Seem, of course, being the operative word -- because researchers in China have just created the world's first liquid metal robot that can both change shape and power itself.

"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," Jing Liu from Tsinghua University in Beijing, China, told New Scientist. "These unusual behaviours perfectly resemble the living organisms in nature."

The motor is made of a gallium alloy called galinstan. Gallium has a melting point of 29.76 degrees Celsius (85.57 degrees Fahrenheit). When combined with tin and indium in proportions of 68.5 percent gallium, 21.5 indium and 10 percent tin, the resulting alloy -- galinstan -- has a melting point of -19 degrees Celsius (-2 degrees Fahrenheit). This means it's liquid at room temperature.

When placed in a sodium hydroxide solution and kept in contact with a flake of aluminium it uses as fuel, this drop of liquid can move around on its own for around half an hour.

This is achieved through two mechanisms: first, an imbalance in the charge across the droplet creates a pressure differential between the front and the back which pushes it forward. Secondly, the aluminium reacts with the sodium hydroxide solution, releasing hydrogen bubbles that provide propulsion. This has potential applications as a delivery method for materials in pipes, or environmental monitoring.

Before they were robots

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When held still, the galinstan drop acts like a pump, as demonstrated in previous research. The difference between this drop and the previous research is that the previous experiments applied external power; whereas Liu's experiment is self-powered. It can pump about 50 millilitres of water a second -- a small amount, but the concept could potentially be developed into a self-powered pump for moving water through a cooling device.

Combined with previous research, which demonstrated that the galinstan forms complex shapes when an electrical current is supplied, Liu believes the research could be used to coordinate a swarm of individual galinstan drops.

The full study, "Self-Fueled Biomimetic Liquid Metal Mollusk," can be found online in the journal Advanced Materials.