Researchers at the Department of Energy’s Lawrence Berkeley National Laboratory have figured out a way to 3D print structures made entirely of liquids. According to the researchers, this advance is the first step toward creating liquid electronics that can conform to any shape and be implemented in stretchable devices.
As detailed in Advanced Materials, the 3D printed tubes of water were up to a millimeter in diameter and could be printed in spiraling shapes that were several meters long. To create these threads, the researchers used an off-the-shelf 3D printer that they modified by adding a syringe that would inject water into a small box of silicone oil.
This wasn’t just your run of the mill tap water, however. The Berkeley lab researchers seeded the water with gold nanoparticles and dispersed polymer ligands (a ligand is a group of atoms that binds to a metal atom) in the oil. Thus, when the gold-laced water and polymer ligand-laced oil were combined, the ligands are attracted to and bind with the gold nanoparticles.
This, in effect, creates a nanoparticle sheathe around the water that prevents it from breaking up into droplets and maintains the shape of the water tube. The researchers refer to this combination as a nanoparticle supersoap.
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Like a normal dish soap, this combination is technically a “surfactant,” which is a fancy way of describing a substance that reduces the surface tensions of the liquids it comes in contact with. For example, even though vegetable oil and water don’t mix if you combine them, adding a surfactant like dish soap reduces their surface tension and allows them to emulsify, or mix, which is why you can use soap to clean your greasy dishes. A similar effect is at work in this experiment.
Yet unlike dish soap, vegetable oil and water, when the ligands and gold nanoparticles jam together to form the supersoap, this results in vitrification (the same thing that happens when glass cools) and the water tubes maintain their shape. When this supersoap was combined with the automated processes of a 3D printer, the DoE researchers were able to print the water in any predetermined pattern.
Although the technique is still experimental, the researchers hope that a similar process could pave the way for liquid electronics in the future.