Anisotropic growth control of polyaniline nanostructures and their morphology-dependent electrochemical characteristics.
Polyaniline (PANI) is one of the most widely investigated conducting polymers and is considered to be of practical use for many future applications. Here, we first demonstrate that the anisotropic growth of PANI at the nanometer scale can be kinetically controlled by employing a polymeric stabilizer, poly(N-vinylpyrrolidone). The polymerization rate became slower in the presence of the stabilizer (the rate constants calculated at the initial stage decreased with increasing concentration of the stabilizer), yielding PANI nanostructures with lower aspect ratios. Therefore, it is believed that the stabilizer sterically restricts the directional fiber growth mechanism governing PANI chain growth in aqueous solution. Three PANI nanostructures, specifically nanospheres, nanorods, and nanofibers, were fabricated and their oxidation/protonation levels were investigated systematically. It was found that the nanofibers had the most outstanding oxidation/protonation level accompanied by structural ordering (note that the only difference between the polymerization conditions in each case was the concentration of the stabilizer). We also examine the electrochemical properties of PANI nanostructure electrodes in three-electrode and two-electrode (actual capacitor cell) configurations. The intrinsic charge-transport ability of individual nanostructures strongly affected the electrochemical properties of the electrodes. Briefly, the nanofiber electrode had faster electrode kinetics and better capacitance than the nanorods and nanospheres. Lastly, an extrinsic factor, the interparticle contact resistance, also turned out to noticeably influence the capacitances of the electrodes.
Alan G MacDiarmid Energy Research Institute, Department of Polymer and Fiber System Engineering, Chonnam National University, Gwangju 500-757, South Korea.
Hyun-Woo
HW
Park
Taejoon
T
Kim
Jinyoung
J
Huh
Minjeong
M
Kang
Ji Eun
JE
Lee
Hyeonseok
H
Yoon
D000814:Aniline Compounds / Q000737:chemistry*; D016880:Anisotropy; D003460:Crystallization / Q000379:methods*; D004553:Electric Conductivity; D004579:Electron Transport; D046911:Macromolecular Substances / Q000737:chemistry; D008422:Materials Testing; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D010316:Particle Size; D013499:Surface Properties
D000814:Aniline Compounds; D046911:Macromolecular Substances; C416807:polyaniline