Liquid metal printing

3D printing is just starting to become a household concept, as developments push the technology relentlessly forward. Luckily, the printing of physical objects comes with lots of great pictures and videos, and this helps spread the word, and the fun.

Here at Materia, we’re very enthusiastic about a new technique, developed in the United States, for printing liquid metal, which is even more impressive because, unlike most metals, it’s liquid at room temperature.

This hasn’t been easy, or indeed possible, before, because liquids have the tendency to ‘bead up’, or form into tiny droplets. This is no good when you’re trying to make long fibres, sheets or solid objects any larger than a few micrometers across. The problem doesn’t occur with ‘normal’ 3D printing, because those printers use polymers, which are huge strings (on a molecular level) that don’t bead up.

The trick, according to NC State University scientists, is to use a metal that forms a protective layer when exposed to air. A 75% – 25% by weight alloy of gallium and indium does just that. Squeezing a tiny droplet of the alloy (EGaIn) onto a substrate causes it to form a very thin skin that keeps the metal safely in shape. This oxidised layer is just 1 nm thick, but has a huge advantage for the printed matter.

The metal can be printed in any required shape, using a fairly standard syringe needle that extrudes the liquid. The print flow can be cut off by applying a vacuum to the nozzle.A variation of this technique is to inject the alloy into a template, made of a polymer for example. This gives the metal a particular shape. The plastic template is then removed, leaving the bare metal in the required position.

In these ways, it is possible to create tiny, 3D micro-electronic components. Or, perhaps, flexible transistors, solar cells, and much more. The next step shows some of this potential. Covering the liquid metal with another material means that the metal keeps its value (for instance, being electrically conductive) while the case gives the combination another function, such as insulation, stretch, heat resistance etc. Consider wearable electronics in stretch clothing, that keep functioning while your body is moving, even halfway up a mountain. Or add the metal to a casing made of graphene for flexible computers. Put them in a dynamic environment to measure change in real-time.

Again, we can see almost endless possibilities. As the researchers’ work shows, novel techniques in 3D printing (or ‘direct-writing’ to use the jargon) can be used to form metals into shapes previously thought to be unstable because of surface tension issues. Where next – Terminator 2, anyone? For now, thought this really is a great, new step into an unknown world of potential.A video of the printing process is here.