Physica B 354 (2004) 224–227 Composite of polyaniline containing iron oxides Juan Carlos Aphesteguy, Silvia E. Jacobo à LAFMACEL, Facultadde Ingenierı´a, Universidad de Buenos Aires, Paseo Colo´n 850, C1063EHA, Capilal Federa, Buenos Aires, Argentina Abstract A composite of polyaniline (PANI) containing iron oxides with nanometer size was prepared by a chemical method. Polymer adsorption on the surface of magnetite particles was investigated. The electrical and ferromagnetic properties of the composites were measured as a function of the pH value of the reaction solution during polymerization. The conductivity of the composites at room temperature decreases with the increase of the pH as the doping level in the composite decreases. For the basic preparation conditions, the resulting PANI-Fe x O y composite can be attracted by a magnet at room temperature and shows an insulating behavior. Doping of PANI with acids leads to electrical conducting properties of ferromagnetic composites. r 2004 Elsevier B.V. All rights reserved. Keywords: Polyaniline (PANI); Electrical-magnetic properties; Nanometer materials 1. Introduction Materials having both electrical and magnetic properties are required for the application of electrical and magnetic shielding, molecular elec- tronic, nonlinear optics, sensor and microwave absorbent [1–3]. Recently, polyaniline (PANI) has attracted much attention because of its several unique properties. It is highly stable in air and soluble in various solvents, and exhibits dramatic changes in its electronic structure and physical properties at protonated state. Depending on the oxidation level, PANI can be synthesized in various insulating forms such as the fully reduced leucoemeraldine base (LEB), half-oxidized emer- aldine base (PANIEB) and fully oxidized perni- graniline base (PNB). Of these three forms, PANIEB is the most stable and widely investigated polymer in this family. PANIEB differs substan- tially from LEB and PNB in the sense that its conductivity can be tuned via doping from 10 10 up to 100 Scm and more, whereas the LEB and PNB form cannot be conducting. The conducting emeraldine salt form (PANIES) is achieved by doping with aqueous protonic or functionalized acids where protons are added to the –NQ sites. This leads to an increase in the conductivity by more than ten orders of magnitude depending on the strength of the acid and method of processing ARTICLE IN PRESS www.elsevier.com/locate/physb 0921-4526/$-see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2004.09.053 à Corresponding author. E-mail address: sjacobo@fi.uba.ar (S.E. Jacobo).