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6 0 A D V A N C E D M A T E R I A L S & P R O C E S S E S | M A Y / J U N E 2 0 1 8 3D PRINTSHOP LIQUID PRINTING OOZES WITH POTENTIAL Scientists at the DOE’s Lawrence Berkeley National Laboratory, Calif., developed a way to print 3D struc- tures composed entirely of liquids. Using a modified 3D printer, they in- jected threads of water into silicone oil to sculpt tubes made of one liquid within another liquid. The scientists envision their all-liquid material could be used to construct liquid electronics that power flexible, stretchable devic- es. The team also foresees chemically tuning the tubes and flowing molecules through them, leading to new ways to separate molecules or precisely de- liver nanoscale building blocks to un- der-construction compounds. So far, researchers printed threads of water between 10 microns and 1 mm in diameter in a variety of spiraling and branching shapes up to several meters in length. The material can conform to its surroundings and repeatedly change shape. First, the scientists developed a way to sheathe tubes of water in a spe- cial nanoparticle-derived surfactant that locks the water in place. The sur- factant, essentially soap, prevents the tubes from breaking into droplets. The supersoap is made by dispersing gold nanoparticles into water and polymer Printing water in oil using 2D nanoparticle surfactant (NPS) assemblies. Left, 3D printing NPS-stabilized aqueous threads in a silicone oil. Right, schematic of interfacial assembly of NPSs and the elastic films they form. Courtesy of Forth et al., doi: 10.1002/adma.201707603. ligands into oil: The nanoparticles and 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 inject- ed 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—stabilizing the in- terface between the oil and water and locking the liquid structures into posi- tion. To automate the process, the team modified an off-the-shelf 3D printer by removing the components designed to print plastic and replacing them with a syringe pump and needle that extru- des liquid. Then they programmed the printer to insert the needle into the oil substrate and inject water in a prede- termined pattern. lbl.gov. PRINTING COMMERCIAL QUALITY GLASS OPTICS Researchers at Lawrence Liver- more National Laboratory (LLNL), Calif., report successfully 3D printing opti- cal-quality glass on par with commer- cial glass products currently available on the market. Because the refractive index of glass is sensitive to its thermal history, it can be difficult to ensure that glass printed from the molten phase will result in the desired optical per- formance, say researchers. Depositing the LLNL-developed material in paste form and then heating the entire print to form the glass achieves a uniform refractive index, eliminating optical dis- tortion that would degrade the optic’s function. The custom inks—aimed at form- ing silica and silica-titania glasses— allow researchers to tune the optical, thermal, and mechanical properties of the glass, explains principal inves- tigator Rebecca Dylla-Spears. For the study, researchers printed small, sim- ply shaped optics as proof of concept, but Dylla-Spears says the technique eventually could be applied to any de- vice that uses glass optics and could result in optics made with geometric structures and compositional changes unattainable with conventional manu- facturing. For example, gradient refrac- tive index lenses could be polished flat, replacing more expensive polishing techniques used for traditional curved lenses. The team is nowmixing and pat- terning different material compositions in hopes of gaining control over mate- rial properties and making gradient re- fractive index lenses. llnl.gov. A new 3D-printing technique could allow scientists to print glass that incorporates different refractive indices in a single flat optic, making finishing cheaper and easier. Courtesy of Jason Laurea/LLNL.