Liquid Machines Promise New Era of Soft Robots

Electric fields can transform liquid metals from one shape to another. Now Chinese engineers say soft robots like the infamous T-1000 may not be far behind

In the science-fiction classic, Terminator 2: Judgement Day, the T-1000 is a robotic assassin with a liquid metal endoskeleton that can assume the form of any object or person. Its liquid nature makes it immune to attack by bullets and impervious to mechanical damage in general.

The T-1000 is an entirely fictional device that might as well be magic as far as conventional manufacturing techniques are concerned. And yet this might be about to change thanks to the pioneering work of Lei Sheng, Jie Zhang and Jing Liu at Tsinghua University in Beijing.

These guys have taken the first tentative steps to making liquid machines that work like the T-1000. Their first attempts can assume various shapes, move around and then transform into other shapes more or less without limit. And they say the work has profound implications for the design of robots, future machines and the nature of manufacturing.

While the most familiar liquid metal is the toxic mercury, there are other metals and alloys that are liquid at room temperature and much more benign. In particular, a gallium-indium-selenium alloy, with a melting point of around 10°C, has received much recent attention because it can be used for cooling microprocessors and even for liquid metal printing techniques.

Now Lei Sheng and co have made this liquid metal assume simple shapes by placing a thin film of it in water and applying an electric field.

With careful arrangement of the voltages and electrode geometries, these guys can make the metal form into a sphere. They say this is the result of the balance between the surface tension in the liquid metal and the electronic forces applied to its surface.

What’s more, they can move and rotate the sphere on the surface of the water and even merge it into other droplets. “This finding has both fundamental and practical significances which suggest a generalized way of making smart soft machines,” they say.

Much of their work involves determining exactly what kind of conditions produce which shapes and movements. But with this under their belt, the possibilities seem endless.

Lei Sheng and co suggest that these kind of liquid metal transformers could one day self-assemble into soft robots that might even be implanted into the human body, given that gallium-indium-selenium alloy is biologically benign.

One approach is to have a series of electrodes aligned in parallel which would form the liquid metal into earthworm-shaped structures. Simple modulation of the voltages would then cause the earthworm-like robot to move. This kind of fabrication is cheap, simple and highly flexible, they say.

Just how much potential it has to create smart liquid machines has yet to be seen. But Lei Sheng and co are certainly excited about the possibilities. They now plan to investigate mechanisms for transforming the liquid metal into more complex shapes and experimenting with how these might work together in a machine.

That’s exciting, early-stage technology with the potential for a variety of unusual applications. So expect to hear more about smart liquid machines, and not just from Hollywood.

Ref: arxiv.org/abs/1402.1727 : Liquid Metal Transformers