3d printed liquid

3D-printed liquid structures pave the way for flexible electronics

A 3D printer has been adapted by a team at the US Department of Energy’s Berkeley Lab to print 3D structures composed entirely of liquids.

The modified printer injects threads of water into silicone oil - sculpting tubes made of one liquid within another liquid.

The printer could be used to construct liquid electronics that power flexible, stretchable devices, the researchers said.

The scientists also foresee chemically tuning the tubes and flowing molecules through them, leading to new ways to separate molecules or precisely deliver nanoscale building blocks to under-construction compounds.

The researchers have printed threads of water between 10 microns and 1 millimetre in diameter, and in a variety of spiralling and branching shapes up to several meters in length. What’s more, the material can conform to its surroundings and repeatedly change shape.

“It’s a new class of material that can reconfigure itself and it has the potential to be customised into liquid reaction vessels for many uses, from chemical synthesis to ion transport to catalysis,” said Tom Russell who works in Berkeley Lab’s Materials Sciences Division.

The material owes its origins to two advances: learning how to create liquid tubes inside another liquid and then automating the process.

For the first step, the scientists developed a way to sheathe tubes of water in a special nanoparticle-derived surfactant that locks the water in place.

The surfactant, which the team dubbed ‘supersoap’, prevents the tubes from breaking up into droplets.

The supersoap was created by dispersing gold nanoparticles into water and polymer ligands into oil. The gold nanoparticles and polymer ligands want to attach to each other, but they also want to remain in their respective water and oil mediums.

In practice, soon after the water is injected into the oil, dozens of ligands in the oil attach to individual nanoparticles in the water, forming a nanoparticle supersoap.

These supersoaps jam together and vitrify, like glass, which stabilises the interface between oil and water and locks the liquid structures in position.

“This stability means we can stretch water into a tube and it remains a tube. Or we can shape water into an ellipsoid and it remains an ellipsoid,” said Russell. “We’ve used these nanoparticle supersoaps to print tubes of water that last for several months.”

An off-the-shelf 3D printer was then modified by removing the components designed to print plastic and replacing them with a syringe pump and needle that extrudes liquid. It was then programmed to insert the needle into the oil substrate and inject water in a predetermined pattern.

“We can squeeze liquid from a needle and place threads of water anywhere we want in three dimensions,” said postdoctoral researcher Joe Forth. “We can also ping the material with an external force, which momentarily breaks the supersoap’s stability and changes the shape of the water threads. The structures are endlessly reconfigurable.”

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