Oriented Growth of Self-Assembled Polyaniline Nanowire Arrays Using a Novel Method** By Hongjin Qiu, Jin Zhai, Shuhong Li, Lei Jiang,* and Meixiang Wan* 1. Introduction Nanostructure materials, especially one-dimensional (1D) nanostructures, including inorganic materials (carbon, metals, ceramics, glasses) and organic materials (biomolecules, poly- mers), [1,2] have potential applications as electrical and optical materials. [3] Conducting polymer nanotubes have potential applications in the fabrication of many kinds of electronic de- vices, [4] such as batteries, capacitors, and light-emitting diodes. Micro- and nanotubes of polyaniline and polypyrrole have been reported by several groups. [5±9] Most of this work was car- ried out using microporous polymeric filtration membranes with a wide range of pore diameters and pore densities as templates. Basically, template-directed synthesis [10±12] and self- assembly growth are two typical methods for preparing 1D tubes and fibers. Martin and co-workers [13] synthesized nano- tubes/-wires of conducting polymers using polycarbonate and alumina membranes as templates. Self-assembled nanotubes/ -fibers have been reported in the literature [5,6] as well. These two methods have both merits and limitations. By using the template-directed synthesis method, unique and ordered struc- tures can be built directly, but post-processing is required in order to remove the template. On the other hand, a myriad of nanoscale morphologies can be constructed through self-as- sembly, but controlling the orientation and size (e.g., diameter) is difficult. Recently, Liu and co-workers [14] used direct electro- chemical synthesis and fabricated uniform and oriented poly- aniline (PANI) nanowires on various substrates without using a support template by controlling the current density. This pro- vides a new approach with potential for microelectronic and optical devices on the basis of electropolymerization. As for chemical synthesis, the fabrication of self-assembled conduct- ing polymer micro/-nanotubes has been developed in our group. [7,8] It provides an attractive, template-free, alternative route to nanotubes or -fibers, but obtaining oriented arrays is quite difficult. In this report, we demonstrate a simple and nov- el self-assembly process combined with a porous template to prepare highly oriented arrays of PANI nanowires. 2. Results and Discussion As the polymer to form nanowire arrays, aniline-4-(3-(4-((4- nitrophenyl)azo)phenyloxy)propyl)aminobenzene sulfonic acid (aniline/C3-ABSA) was chosen, which could be formed as free micelles in aqueous solution and self-assembled to form PANI/ C3-ABSA nanowires by the addition of the oxidant (NH 4 ) 4 S 2 O 8 (APS), as reported by us previously. [7,8] A novel dopant was used in this fabrication and the chemical structure of a PANI nanotube is shown in Scheme 1. The diameter of the wires ranged from micrometers to nanometers (4 lm to 50 nm) depending on the synthesis conditions. [8,9,15] The details of the experiment are given in the Experimental section. In order to obtain an ordered array structure, a hydrophilic track-etched Al 2 O 3 substrate with average pore diameter of 200 ± 30 nm and ca. 60 lm thickness was immersed as a tem- plate into the emulsion of aniline/C3-ABSA. The self-as- sembled nanowires of PANI-(C3-ABSA) grow oriented per- pendicular to the Al 2 O 3 template while the lengths of these wires can be roughly controlled by controlling the polymeriza- Adv. Funct. Mater. 2003, 13, No. 12, December DOI: 10.1002/adfm.200304366 Ó 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 925 ± [*] Prof. L. Jiang,Prof. M. Wan, Dr. H. Qiu, Dr. J. Zhai, Dr. S. Li Center of Molecular Sciences, Institute of Chemistry The Chinese Academy of Sciences Beijing 100080 (PR China) E-mail: jianglei@iccas.ac.cn, wanmx@iccas.ac.cn [**] The work was supported by the National Natural Science Foundation of China (No. 29634020-2; No. 29974037), State Key Project Fundamental Research (G1999064504), Special Research Foundation of National Nature Sciences Foundation of China and Center for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences (No. CMS-CX2001). A novel method for fabrication of highly oriented polyaniline (PANI) nanowires without removal of the template was devel- oped by combining self-assembly and template synthesis techniques. By using a self-assembly process under inhibition condi- tions, oriented arrays of PANI nanowires growing out of the nanoporous template were obtained, with nanowire diameters ranging from 110 to 190 nm and lengths of several micrometers. The lengths of these wires can be roughly controlled by the po- lymerization time. N H N N H N + + H A -1 A -1 A -1 =C3-ABSA: N O 2 N N OCH 2 CH 2 CH 2 NH SO 3 -1 0.5 n PANI: H Scheme 1. The chemical structures of PANI and the dopant C3-ABSA. FULL PAPER