Continuous motion of a self-propelling liquid metal droplet under a pH gradient, shown at different time intervals. The droplet is placed in a fluidic channel, midway between two reservoirs filled with different electrolytes of an acidic and basic nature. (Image Credit: RMIT University) Modern electronic devices such as smart phones and computers are typically based on circuits that use solid state components, with fixed metallic tracks and semiconducting devices.
Researchers have been working to create truly elastic electronic components, in which soft circuit systems can act more like live cells and move around autonomously, communicating with one another to form new circuits rather than being stuck in one configuration.
So far liquid metals, in particular non-toxic alloys of gallium, have offered the most promising path for that dream.
Why? Any droplet of liquid metal contains a highly conductive metallic core and an atomically thin semiconducting oxide skin, which are critical elements necessary in the making of electronic circuits.
To figure out how to get liquid metal to move autonomously, Professor Kourosh Kalantar-zadeh and his group from the School of Engineering at RMIT first immersed liquid metal droplets in water.
"Putting droplets in another liquid with an ionic content can be used for breaking symmetry across them and allow them to move about freely in three dimensions, but so far we have not understood the fundamentals of how liquid metal interacts with surrounding fluid," said Kalantar-zadeh. "We adjusted the concentrations of acid, base and salt components in the water and investigated the effect.
By making tiny alterations to the water's chemistry, the liquid metal droplets moved and changed shape, without any need for external mechanical, electronic or optical stimulants.
"Using this discovery, we were able to create moving objects, switches and pumps that could operate autonomously—self-propelling liquid metals driven by the composition of the surrounding fluid,” said Kalantar-zadeh.
The research could potentially lead to the use of "electronic" liquid metals to make 3-D electronic displays and components on demand, as well as create floating electronics.
"Eventually, using the fundamentals of this discovery, it may be possible to build a 3-D liquid metal humanoid on demand—like the T-1000 Terminator but with better programming," Kalantar-zadeh added.
