Feb_March_AMP_Digital

8 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 | F E B R U A R Y / M A R C H 2 0 1 8 3D PRINTSHOP 3D CATALYST PRINTING IN ONE STEP Ames Laboratory, Iowa, has devel- oped a way to print chemically active catalytic structures, a breakthrough that could dramatically improve the ef- ficiency of chemical reactions across a range of industries. Although 3D print- ing is now common in many areas, its use as a way to control chemical reac- tions is relatively new. Producing 3D catalysts is typically amultistep process in which chemically active agents are deposited onto preprinted structures. The Ames method, however, achieves structure and chemistry in a single step using inexpensive commer- cial 3D printers. Structures are designed on a computer and built by scanning a laser through a bath of customized resins that harden layer by layer. The final product is intrinsically catalytic because it is built from bifunctional ma- terials that harden in response to light, yet retain active sites where chemical reactions can occur. ameslab.gov. Clockwise, a chemically active cuvette adaptor, scale replicas of the Ames Lab logo, and a fluidic circuit component are the types of devices that can be built using a new 3D printing process that combines structure and chemistry in a single production step. REFORMULATED PHOTORESISTS IMPROVE NANOSCALE 3D PRINTING A new type of photoresist develop- ed at Lawrence Liver- more National Labo- ratory (LLNL), Calif., is helping research- ers overcome build height limitations in nanoscale 3D print- ing. Photoresists play a critical role in photo- polymerization, serv- ing to define the in- tended design features in printed parts. To optimize precision, the team is using two-photon lithography (TPL), a photo- polymerization process in which reac- tions are driven by absorption of two photons instead of one. TPL alleviates the wavelength restrictions and diffrac- tion limitations of conventional stereo- lithography, and because it is more sen- sitive to light, it can produce features that are actually smaller than the diam- eter of the scanning beam itself. Despite its advantages, TPL pres- ents a major tooling challenge that additive manufacturing has yet to over- come. The problem lies in the optical path between the light source and work plane, a space defined by a lens on one end and a glass slide coated with resist on the other. To maintain precision, the slide and lens must be in close proxim- ity, constraining build height to 200 mi- crons or less. To address this issue, research- ers developed their own photores- ists and came up with a novel way to apply them. Instead of coating slides, they place resist directly on the lens, using the polished surface as the build plane substrate. No longer limited by proximity conditions, the team has raised the bar on build height, increas- ing it by orders of magnitude to several millimeters. The crowning achievement of their work is the ability to independently tune the optical properties of photoresists, say researchers. By tuning the refractive index—for example, matching it to that of the immersion media—scientists can print 3D parts via dip-in lithography, a direct laser writing technique. On the other hand, by tuning absorption the team can make its resist—and the re- sulting 3D-printed parts—more condu- cive to x-ray imaging. X-ray tomography is a powerful tool for analyzing defects and stress, but it does not work well with conventional resists because the constituent elements have low atomic numbers. LLNL’s resists are optically clear yet radiopaque, simultaneously optimizing image quality, feature reso- lution, and part height. llnl.gov. A 3D-printed nanoscale structure sits on a pedestal similar in diameter to a human hair.