Using a modified 3D printer, the scientists injected threads of water into silicone oil — sculpting tubes made of one liquid within another liquid. 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.
So far, 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 has the potential to be customised into liquid reaction vessels for many uses, from chemical synthesis to ion transport to catalysis,” said Tom Russell, a scientist in Berkeley Lab’s Materials Sciences Division. He developed the material with Joe Forth, a postdoctoral researcher in the Materials Sciences Division, as well as other scientists from Berkeley Lab and several other institutions.
To create the material, the scientists first developed a way to sheathe tubes of water in a special nanoparticle-derived surfactant that locks the water in place. The surfactant, that the scientists call a ‘nanoparticle supersoap’, prevents the tubes from breaking up into droplets.
The supersoap was achieved by dispersing gold nanoparticles into water and polymer ligands into oil. The scientists say that 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 the 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,” added Russell. “We’ve used these nanoparticle supersoaps to print tubes of water that last for several months.”
Next, they automated the process by modifying an off-the-shelf 3D printer by removing the components designed to print plastic and replacing them with a syringe pump and needle that extrudes liquid. The printer 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,” explained 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.”