Self-assembly growth of oriented polyaniline arrays: A morphology and structure study Jihuai Wu * , Qunwei Tang, Qinghua Li, Jianming Lin The Key Laboratory for Functional Materials of Fujian Higher Education, Institute of Material Physical Chemistry, Huaqiao University, Quanzhou 362021, China article info Article history: Received 25 June 2008 Received in revised form 27 July 2008 Accepted 6 September 2008 Available online 7 October 2008 Keywords: Polyaniline Array Self-assembly abstract Highly ordered polyaniline (PANI) array was prepared by self-assembly method and using inorganic acids as dopants. The PANI array was characterized by scanning electron microscopy, Fourier transform infrared spectra, and X-ray diffraction, and the influence of preparation conditions on the morphology and structure of the PANI arrays is discussed. It is found that the morphology and structure of the PANI arrays strongly depend on the kinds of dopant. The resulted PANI has a emeraldine molecular structure and highly oriented arrangement. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Polyaniline (PANI) is one of the most promising electrical conductive polymers due to its ease of synthesis, low cost, versatile processibility, relatively stable electrical conductivity, and can be exploited in various applications including batteries, capacitors, electrochromic windows and displays, actuators, photovoltaic cells, and light-emitting electrochemical cells [1–3]. Recently, ordered PANI has aroused widely attention since ordered PANI possesses better properties and more application than PANI does [4–10]. Template synthesis is a common and effective method for synthesizing the ordered micro-/nano-conducting polymers. However, to get pure conducting polymers, the template has to be removed after the polymerization. This is difficult in most cases, and the ordered structure of resulting materials is altered or even destroyed during recovery from the templates [11–14]. Wan et al. [15–18] developed a self-assembly technique for PANIs in the presence of organic acids with long molecular chains such as b-naphthalene sulfonic acid and azobenzenesulfonic acid as dopants. Different from the template synthesis method, the long chain acids do not need to be removed after polymerization because they are used as dopants of PANI at the same time. Compared with template synthesis, the self-assembly method is simple and inexpensive. However, the structures and shapes of PANI synthesized by self-assembly method are always random and misaligned, which limit the application for PANI [19]. In this paper, an ordered PANI array was prepared by self- assembly method using inorganic acids as dopants. The PANI arrays were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectra, and X-ray diffraction (XRD). It was found that the morphology and structure of PANI arrays depend on the aniline concentration, inorganic acids concentration and kinds. 2. Experimental 2.1. Materials Aniline (ANI) monomer was distilled under pressure prior to use. Potassium peroxydisulfate (K 2 S 2 O 8 , KPS) as a radical oxidant for PANI, was purified by recrystallization from 66 wt.% ethanol/ water solution. Inorganic acids such as hydrochloric acid (HCl), sulfuric acid (H 2 SO 4 ), nitric acid (HNO 3 ) and phosphoric acid (H 3 PO 4 ) were used as the dopants for PANI. All aqueous solutions were prepared in 18 MU water obtained by purification of deion- ized water with a Millipore Milli-Q system. All the reagents were purchased from Shanghai Chemical Reagents Co., China. 2.2. Synthesis of PANI arrays The oriented PANI fiber was synthesized by an aqueous solution polymerization method. 1 ml ANI monomer was mixed with 125– 400 ml deionized water and 16.5–200 ml HCl (or H 2 SO 4 , HNO 3 , H 3 PO 4 ) (1 M) aqueous solution. Under a surrounding atmosphere and stirring, the ANI solution was heated to 80  C in a water bath, and then 2.97 g KPS was quickly added to the ANI solution. After the system was kept at 80  C for 10 min and all the KPS was dissolved, * Corresponding author. Tel.: þ86 595 22693899; fax: þ86 595 22693999. E-mail address: jhwu@hqu.edu.cn (J. Wu). Contents lists available at ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer 0032-3861/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2008.09.044 Polymer 49 (2008) 5262–5267