A method was developed for printing 3D structures composed entirely of liquids. Using a modified 3D printer, threads of water were injected into silicone oil, sculpting tubes made of one liquid within another liquid. Threads of water between 10 microns and 1 millimeter in diameter were printed, as well as a variety of spiraling and branching shapes up to several meters in length. What's more, the material can conform to its surroundings and repeatedly change shape.
The material owes its origins to two advances: learning how to create liquid tubes inside another liquid, and then automating the process. First, a method was developed to sheathe tubes of water in a special nanoparticle-derived surfactant that locks the water in place. The surfactant, called a 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 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 stabilizes the interface between oil and water and locks the liquid structures in position. This stability means that the water can be stretched into a tube, and it remains a tube. The water also can be shaped into an ellipsoid, and it remains an ellipsoid.
An off-the-shelf 3D printer was modified by removing the components designed to print plastic, and replacing them with a syringe pump and needle that extrudes liquid. The printer was programmed to insert the needle into the oil substrate and inject water in a predetermined pattern. Liquid can be squeezed from a needle, and threads of water can be placed anywhere in three dimensions. The material also can be “pinged” with an external force that momentarily breaks the super-soap's stability, and changes the shape of the water threads.