IOP PUBLISHING NANOTECHNOLOGY Nanotechnology 18 (2007) 115607 (6pp) doi:10.1088/0957-4484/18/11/115607 Self-assembled polyaniline nanotubes grown from a polymeric acid solution Lijuan Zhang, Hui Peng, Chyong Fang Hsu, Paul A Kilmartin and Jadranka Travas-Sejdic 1 Polymer Electronics Research Centre, Chemistry Department, The University of Auckland, Private Bag 92019, Auckland, New Zealand E-mail: j.travas-sejdic@auckland.ac.nz Received 10 November 2006, in final form 4 January 2007 Published 7 February 2007 Online at stacks.iop.org/Nano/18/115607 Abstract Polyaniline (PANI) nanotubes were obtained by a self-assembly process, from a solution containing poly(methyl vinyl ether-alt-maleic acid) (PMVEA) by oxidative polymerization using ammonium persulfate as the oxidant. The size of the nanotubes was greatly affected by the weight ratio of polymeric acid to aniline as measured by SEM images. The outer diameter of the nanotubes increased from 65 to 160 nm as the weight ratio of PMVEA to aniline increased from 1 to 4 wt/wt%. The structural features of the nanotubes were characterized by FTIR, XPS and EPR spectroscopies, which confirmed the presence of the polymeric acid in the PANI nanotubes and their electronic conductive nature. The electrochemical properties were further analysed using cyclic voltammetry. (Some figures in this article are in colour only in the electronic version) 1. Introduction Recent advances in nanoscience and nanotechnology have opened up new research fields, both at a fundamental and an applied level, focused around the development of novel, minia- turized devices based on nano-sized materials. Among these, conducting polymer nanostructures, including nanotubes and nanowires, are receiving growing attention due to the unique properties of these organic conductors combined with flexible chemical functionalization. Promising potential applications in electrical nanodevices, such as actuators [1], drug delivery sys- tems [2], tissue engineering [3], gas sensors and biosensors [4] have already been demonstrated. Several recent studies have focused on polyaniline (PANI) nanostructures for improved sensors and catalytic materials [5, 6]. Various methods, such as template-synthesis [7], electron-spinning [8], nano-fibre seed- ing [9], interfacial polymerization [10], electrochemical poly- merization [11] and template-free methods [12] have been used to prepare PANI micro/nanostructures. Among these methods, the template-free method [13] has attracted much attention due to its simplicity. Different acids, including organic and inor- ganic acids [14, 15], have been used in the preparation of PANI nanotubes by this method. Polymeric acids and other large molecular weight molecules have been shown to be easily incorporated 1 Author to whom any correspondence should be addressed. as dopants within conducting polymers during synthe- sis; the most common examples being PANI doped with poly(styrenesulfonic acid) and poly(2-acrylamido-2- methylpropane sulfonic acid) [16, 17] and poly(3,4-ethylenedi oxythiophene) doped with poly(styrenesulfonic acid) [18]. The large size of macromolecular dopants ensures their permanent entrapment within the conducting polymer material. To our knowledge, no attention has been focused so far on the use of polymeric acids as dopants for conducting polymer nanostructured materials. The presence of such macromolecules in conducting polymer nanostructures can bring novel properties to the material, as well as additional functionality for building further specific recognition or catalytic sites. Here, we report on the preparation of PANI nan- otubes that incorporate poly(methyl vinyl ether-alt-maleic acid) (PMVEA). Maleic acid bears closely spaced diacid func- tionality and therefore can provide a high density of acid func- tional groups. The PANI/PMVEA nanotubes were prepared by oxidative polymerization using ammonium persulfate (APS) as the oxidant. The external diameter of the nanotubes was found to be highly dependent upon the concentration of PMVEA present in the reaction solution. The structural features of the nanotubes were characterized by FTIR, ESR and XPS spectro- scopies and the electrochemical properties were investigated using cyclic voltammetry. 0957-4484/07/115607+06$30.00 1 © 2007 IOP Publishing Ltd Printed in the UK