July/August_AMP_Digital

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 | J U L Y / A U G U S T 2 0 2 0 1 2 PROCESS TECHNOLOGY SELF-ASSEMBLING ULTRATHIN MEMBRANES Using a polymer-based approach, scientists at the University of Califor- nia, San Diego created flexible, ultra- thin films of nanoparticles. The new method produces ultrathin porous membranes with precisely controlled pore dimensions and surface chemis- try by growing a polymer layer, or “co- rona,” around highly porous metal-or- ganic-framework (MOF) nanoparticles. The polymer corona-coated, MOF nano- particles self-assemble into lay- ers one particle thick and into multilayer, porous films that do not require external support. The new films have high MOF particle content—87 percent by weight. The substantial particle con- tent advances efforts to produce highly functional porous mem- branes and coatings for MOF use in devices. For example, the new method could be useful in mak- ing uniform porous membranes with properties designed for spe- cific applications such as batter- ies and fuel cells. Inorganic nanoparticles have many beneficial properties for a wide range of applications in energy storage and production. However, these particles are brit- tle, and films formed fromporous nanoparticles alone or as addi- tives in polymer films tend to be relatively thick, crumbly, weak, and have lower than desired nanopar- ticle content. These attributes make them hard to use for structures that are suitable for use in devices. Research- ers have been searching for a way to produce flexible, thin films of these nanoparticles to address these chal- lenges. They have achieved some suc- cess, but the films that have all the de- sired features are still rare. The new work opens possibilities for use of this technology in various in- dustries. Researchers believe their pro- cess is the first self-assembly of porous single-layer and multilayer films that does not require external support, both made up of MOF nanoparticles. The ul- trathin, self-assembled MOF monolay- ers can be stacked to make MOF multi- layers, opening the possibility for new applications. ucsd.edu. WORLD’S FIRST LIQUID METAL LATTICE A team of researchers at Bingham- ton University, N.Y., developed what they call the “first liquid metal lattice in the world,” which is made from Field’s alloy. The alloy’s mix of bismuth, indi- um, and tin becomes liquid at a rela- tively low melting point of 62°C. Field’s alloy is currently used as a liquid-metal coolant in nuclear engineering, among other applications. The scientists com- bined the metal lattice material with a rubber shell through a hybrid manufac- turing process, integrating 3D printing, vacuum casting, and conformal coat- ing. The team made a series of proto- types that regain their shapes after be- ing heated to the melting point, includ- ing spiderweb-like mesh antennas, honeycombs, and soccerballs. The prototypes’ properties could inspire myriad uses. When the liquid metal is in a solid state, it is very safe and strong. It absorbs energy when crushed and can return to its original state, and be reused when heated or cooled. The team is exploring how to build on this metal lattice research, including differ- ent structure types and improved coat- ing materials. binghamton.edu . Scientists grew a “corona”-like polymer layer on porous metal-organic framework nanoparticles. Courtesy of Seth Cohen/U.C. San Diego. Researchers from North Carolina State University, Raleigh, and Elon University, N.C., made artificial cilia that can bend into new shapes in response to a magnetic field, then return to their original shape when exposed to the proper light source. The researchers also developed a theoretical model that allows users to predict how the shape memory magnetic cilia will respond when set into motion. In addition, the model explains why the cilia respond the way they do. ncsu.edu , elon.edu. BRIEF An array of magnetic cilia was folded and held by tweezers for this photograph. Courtesy of Jessica A.-C. Liu.