WHMiHHIHIIMIIHlWtlHK NANOMATERIALS
FILMS IN A FLASH A pulse of light converts polymer powders into potentially useful films
G FLASH WELDING Light flashed through a copper grid mask (top) causes the exposed areas of a mat of green polyaniline nanofibers to turn smooth and golden (bottom), reproducing the grid pattern.
NATIONAL
RADUATE STUDENT JIAXING
Huang was fooling around with his digital camera in the lab one evening when he made an unexpected discovery. He took a flash photo of a vial of polyaniline nanofibers and heard a pop. "So I did it again with an even closer flash and then smoke emanated from the powder along with the odor of burning plastic, ,, he recounts. Huang soon discovered that by flashing a mat of dark green polyaniline nanofibers on a substrate, he could fuse the fibers into a smooth, golden, continuous film of cross-linked polyaniline. Huang and his thesis adviser, chemistry professor Richard B. Kaner of the University of California, Los Angeles, report their "flash welding" process in Nature
Materials [published online Oct. 24, http://dx.doi.org/10.1038/ nmatl242}. In an accompanying commentary, chemists Dan Li and Ifounan Xia of the University of Washington, Seattle, write that the discovery "provides a versatile new technique for processing polymers into potentially useful structures." Other groups previously reported that an ordinary camera flash can make single-walled carb o n n a n o t u b e s and silicon nanowires burst into flames. W h e n these nanostructures absorb light, local hot spots develop that may lead to ignition. Polyaniline, K a n e r and Huang explain, converts most of the energy it absorbs from light into heat. But the heat may
ACADEMIES
Institute Of Medicine Elects New Members
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he Institute of Medicine, part of the Nation- Rowena 6. Matthews, G~. Robert Greenberg Disal Academies, announced the election of 65 tinguished Professor of Biological Chemistry at new members and five new foreign associ- the University of Michigan, Ann Arbor. ate members.The additions bring the total I0M Established in 1970 by the National Academy membership to 1,416 and the foreign associate of Science, I0M is required by charter to select membership to 76. one-quarter of its membership from fields outOf the newly elected members, four are . ^^^^^^^m i American Chemical So: ciety members. They [. are Frances H.*Arnold;v'V^|| Dick & Barbara Dickinson Professor of Chem- ; ical Engineering & Bio- ' chemistry at California . Institute of Technology; Arnôld Laurencin Cohen Matthews Fred E. Cohen, professor in the department of cellular and molecular side the health professions. Potential members pharmacology at the University of California, San are selected by current I0M members from canFrancisco* Cato T. Lauréncin, Lillian T. Pratt Dis- didates nominated for "their professional achievement and commitment to service." tinguished Professor and chairman of orthbpe-. -SUSAN MORRISSEY die surgery at the University of Virginia; and / U
C & E N / OCTOBER 2 5 . 2 0 0 4
be diffused by the melting of the nanofibers, preventing complete structural breakdown or combustion, they suggest. T h e UCLA chemists point out that flash welding appears to be a convenient way to make an asymmetric film—that is, one having a dense skin on top and a porous layer underneath. Asymmetric films have found use in many applications, including separation membranes and chemical sensors and actuators. Such films, though, are usually made using relatively time-consuming processes and flash welding might prove faster. A key advantage of flash welding, the chemists note, is its ability to form p a t t e r n e d films. By flash-illuminating a mat of nanofibers through a patterned mask, the pattern can be transferred to the mat, just as in photolithography. This technique "will be especially useful for organic micro- or nanodevices," the researchers suggest. The heat generated by a camera flash also can be used to weld polyaniline to a n o t h e r polymer, offering a rapid and clean way to make polymerpolymer blends and composites, according to the UCLA team. For example, Huang prepared a composite film by flash welding a mixture of polyaniline nanofibers and polystyrene microspheres. Particles of polytetrafluoroethylene also can be embedded in a polyaniline matrix in this way, the researchers report. Preliminary tests on polyaniline derivatives and other conducting polymers such as polypyrrole andpolythiophene indicate that they, too, can be flash welded when nanostructures smaller than 100 nm are present. Huang, now a postdoc at UC Berkeley, says, "I wouldn't be surprised at all to start hearing 'Let's go flash our nanomateriaF in nanoscience labs."—RON DAGAN I
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