Ayusman Sen
Taking a lesson from the silk production of spiders, Ayusman Sen, Professor of Chemistry, is developing materials and methods for production of new polymer fibers, bundles, tapes, and sheets on the nanometer scale under the National Science Foundation's NIRT Award entitled "Nanoreactor Processes for Manufacturing Oriented Materials." Along with his co-principal investigators, Seong Kim (Chem. Eng.), Paul Weiss (Chem.), Hank Foley (Chem. Eng.), Steve Fonash (ESM), Sen is looking to produce polymers comprised of aligned chains, which will possess increased strength over conventionally produced bulk polymers.
As shown in the upper left of the figure below, by creating fibers from different monomers and then stitching the fibers together using photon induced cross linking, Sen believes the group will be able to produce 10-50 nm diameter fibers. Moreover, by using different monomer molecules, these fibers can be tailored with different properties, from high strength to high flexibility. One of the biggest challenges facing Sen in creating these fibers is the extrusion process. On such a small scale, traditional extrusion techniques will not work so Sen and his collaborators are searching for new techniques.
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Another proposed production strategy for nanometer sized polymer fibers is represented in the top right of the figure above. Here, encasing a polymer core with a polymer sleeve produces a concentric fiber. The polymer for the core is chosen to add strength to the resulting fiber while the polymer for the sleeve can be imbedded with molecules that act as biological or chemical receptors. Sen foresees one possible application in fabrics that could be worn by workers in toxic environments that would indicate exposure levels.
Under the NIRT award, Sen's research group has been using test channels for their proposed extrusion processes fabricated at the Penn State Nanofabrication Facility, located in the MRI Building, and synthesizing test polymers in the group's lab in Chandlee Laboratory. Characterization of the fibers has been accomplished using field-emission secondary electron microscopy (FE-SEM) in the Nanofabrication Facility. To date, Sen's group has been able to produce polymer fibers with a diameter of 20 nanometers through the use of silicon molds.
Another aspect of Sen's research focuses on controlled, or living, radical polymerization. In the September 9, 2002 issue of the American Chemical Society's weekly news magazine Chemical & Engineering News, Sen was showcased for his work in atom-transfer radical polymerization (ATRP). Through ATRP, copolymers of methyl acrylate and norbornene are produced. Sen believes these copolymers may be suitable as new photoresists for photolithography with shorter wavelength light to produce smaller features and therefore increase device densities in the semiconductor industry.
Recently, Sen was awarded an MRI/MRSEC Seed Grant to investigate polymer/ceramic composites that possess anti-bacterial qualities. Sen believes these composites could be engineered such that bacteria would not develop resistances to the composite, a shortcoming of many other anti-bacterial agents. Such composites could see applications in the health care and environmental industries, as anti-bacterial surface coatings and filters, respectively.
Dr. Sen received his Ph. D. from the University of Chicago in 1978 and came to Penn State in 1979 after serving as a Research Fellow at CalTech. His research interests include; synthetic and mechanistic organotransition metal chemistry, homogeneous and heterogeneous catalysis, environmental chemistry, and synthesis of polymers, polymer/metal and polymer/ceramic composites with electronic and opto-electronic properties. He holds 18 patents and has more than 165 published works. To learn more about Dr. Sen's research, please visit his research group's Web site at http://research.chem.psu.edu/axsgroup/.
