Terminator-Like Liquid Metals Enable Elastic Electronics

Technology is about to get squishy.

Aug 4 2016, 12:30pm

Image: YouTube screengrab

Smartphones are getting pretty goofy. While I'm content with an easily pocketable iPhone SE, the larger trend is toward carting around liquid-crystal lunch trays. It's hard not to think that we're reaching some form factor climax in which millions of technology consumers all at once realize they kind of look like idiots.

This looming climax puts into relief a very old limitation in computer engineering: the rigidity of circuits. They don't bend, they break. If one were to, say, forget about the 7-inch phablet just barely squeezed into one's back pocket and then, say, sit down, we all know who would lose the battle between ass and Chipotle stool: the $500 allegedly portable computing device. No squish, no flex—just crack.

Flexible electronics have been long-sought, but silicon, in particular, is as brittle as glass. Even reasonably malleable materials like copper still aren't really "soft" or elastic in the desired sense. Enter liquid metals. As described this week in Nature Communications, researchers at RMIT University in Melbourne, Australia have developed a technique for enabling liquid metals to move and arrange themselves autonomously in response to varying external conditions. The resulting electronics aren't just soft and free-flowing, but are highly reconfigurable as well.

"Room-temperature liquid metals have shown to be remarkable platforms for makeshift mechanical components, reversible electrochemical systems, soft sensors, electrical components in microfluidic channels, three-dimensional printing, as well as stretchable and reconfigurable electronics," the paper notes. "Controlling the motion and deformation of liquid metals is the key to the successful realization of these applications."

This sort of control has been demonstrated through various means, but never before like this. Here, the liquid metals are driven by altering the distribution of electrical charge on their surfaces. This is done chemically.

So, by tweaking the surrounding chemistry, the Australian group was able to create "moving objects, switches, and pumps" on-demand. With a conductive metallic core and a surrounding semiconductive oxide skin, the free-flowing metal, an alloy of gallium called galinstan, meets the requirements of functional electronics quite well.

A press release accompanying the new paper, meanwhile, is sure to note a similarity to a certain highly badass model of Terminator.

To better understand how liquid metals move, the researchers began by immersing liquid galinstan droplets in liquid 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," offers Kourosh Kalantar-zadeh, the study's lead author, in the release.

"We adjusted the concentrations of acid, base and salt components in the water and investigated the effect," he explains. "Simply tweaking the water's chemistry made the liquid metal droplets move and change shape, without any need for external mechanical, electronic or optical stimulants."

As far as liquid metals go, gallium has the advantage of being fairly non-toxic. While it's melting point of 29.8 degrees Celsius is a bit too warm to be suitable for everyday use, when mixed with indium and tin, as in the case of its galinstan alloy, that melting point drops to 0 degrees Celsius. This isn't so far-fetched.

That said, the T-1000 didn't need to exist in a carefully controlled bath of electrolytes to function. It didn't even need pants. Still, squishable electronics are now a bit closer, even if that means somewhat less ridiculous personal electronics more than it does amorphous death robots.