Polypyrrole Nanowire Array with High Aspect Ratio Fabricated by Block-Copolymer-Templated Electropolymerization
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Polypyrrole Nanowire Array with High Aspect Ratio Fabricated by Block-CopolymerTemplated Electropolymerization Hideaki Komiyama,1 Tomokazu Iyoda,1,* and Kaori Kamata1,2 Division of Integrated Molecular Engineering, Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8503, Japan 2 JST-PRESTO, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan 1
ABSTRACT Conducting polypyrrole (PPy) nanowire array was electrochemically fabricated by using microphase-separated block copolymer (PEOm-b-PMA(Az)n) thin film as an electrode template. Electropolymerization proceeds selectively through the perpendiculary oriented PEO nanocylindrical microdomains on an ITO electrode coated by the above polymer film. The length of the PPy nanowires was controllable in range of 10-120 nm by the thickness of the coated template film and the amount of passed charge. A 10 nm of diameter, 27 nm of periodicity, and 12 of aspect ratio of the crystalline PPy nanowires were successfully achieved. Selective removal of the template is also achieved simply by rinsing with solubility-controlled mixed solvent. INTRODUCTION Conducting polymer nanowires are of great advantage for applications in electronics, energy conversion and storage [1], and photovoltaic cell [2] because of their high electrical conductivity, large surface area, and mechanical flexibility. At present, conducting polymer nanowires have been commonly fabricated by chemical or electrochemical polymerization inside nano-scaled cylindrical pores as a template such as track-etched membranes and anodic porous alumina membranes [3-5]. Recently, the porous block copolymer membranes, of which one of the microdomains can be removed, has drawn much attention due to simple fabrication of high surface density of nanowires. However, the aspect ratio of conducting polymer nanowires fabricated by using block copolymer template has been limited to less than 4, much smaller than that of nanowires obtained by other porous templates [6,7]. The reason is the difficulty in perpendicular alignment of cylindrical microdomain with large aspect ratio in block copolymer templates. We have developed a series of liquid crystalline block copolymers consisting of poly(ethylene oxide) and poly(methacrylate) bearing azobenzene mesogens in the side chain, here denoted by PEOm-b-PMA(Az)n, which form perpendicularly aligned and highly ordered PEO nanocylinder array with very high aspect ratio in thin film [8,9]. Since the PEO of the nanocylinder is in under-cooled liquid state at room temperature and a well-known medium of ion-conducting polymers, the thin film coated on an electrode could be worked as an electrode template without removal of PEO cylindrical microdomains. The PEO nanocylinders in the template is expected as ethereal solvent and electrochemical channels. Here, we report the fabrication of nanowire array of conducting polypyrrole (PPy) with high aspect ratio through the
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PEOm-b-PMA(Az)n template. Furthermore, the nanowire length and aspect ra
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