Rapid one-step chemical synthesis of polyaniline-manganese ferrite nanocomposites without external initiator and mechanical agitation Emmanuel F. C. Chimamkpam * , Thomas Schweizer ** , Andreas Schilling *** and José M. F. Ferreira * * CICECO, Centre for Research in Ceramics and Composite Materials, Department of Ceramics and Glass Engineering, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal, jmf@ua.pt ** ETHZ, Swiss Federal Institute of Technology, Department of Materials Science, Institut f. Polymere, HCI H531 Wolfgang-Pauli Str. 10, CH8093 Zurich, Switzerland *** Institute of Physics, University of Zurich, Winterthurerstrasse 190, CH8057 Zurich, Switzerland ABSTRACT We describe a rapid one-step, room temperature method to chemically synthesize bulk quantities of nanocomposites comprising specifically of manganese ferrite (MnFe 2 O 4 ) and polyaniline (conductive form). Typically a chemical agent, for example ammonium peroxydisulfate, is used to start the polymerization of aniline in the presence of ferrites, and stirring of the reaction system for several hours is also very common. Our approach allows for the nanocomposites to be formed in less than thirty minutes without adding an external polymerization initiator and applying any form of mechanical agitation. This process affords the possibility to grow thin films of polyaniline- MnFe 2 O 4 directly on device substrates. Structural, thermal, magnetic and electrical studies did reveal significant chemical interactions between MnFe 2 O 4 and polyaniline matrix. The nanocomposites are magnetic semiconductors with long rod-shaped structures of average diameter in the nanometer scale range and optical properties resembling that of conductive polyaniline. They exhibit a positive magnetoresistance across all temperature ranges with a minimum at around 250 K, corresponding to the temperature for their uniform-to-irregular transition in dynamic stability behavior and likewise coinciding with a minimum in their profile of electrical conduction mechanism (one-dimensional variable range hopping below 250 K) – these complementarities are important for hybrid spintronic applications. Keywords: organic conducting polymers, ferrites, polyaniline, manganese ferrite, magnetic, semiconductor, nanocomposites 1 INTRODUCTION Nowadays, all attention is particularly directed towards making use of structural, optical and electrical properties of organic conducting polymers in electronic devices, where their roles could be either active or passive. Combination of members of this polymer family with magnetic materials, for example ferrites, brings forth multifunctional products that can equally serve for magnetic purposes in addition to tunable optical and electrical functions [1-6]. The challenge to arrive at such multifunctional materials, however, is on choosing a straightforward combinatorial approach that is less time-consuming, cost-effective, and does not require too many external chemical ingredients like surfactants and initiating agents. Polyaniline (PAni) which is amongst the most interesting conducting polymers has been blended with ferrites to produce magnetic composites: this was mainly carried out in-situ in the presence of an external initiator and/or a surfactant while stirring the reaction continuously for a prolonged period of time [1-6]. Mechanical agitation, however, does contribute to aggregation of polyaniline and can indeed be precluded during synthesis [7, 8]. Here, we demonstrate the preparation of magnetic semiconducting nanostructured composites of polyaniline and MnFe 2 O 4 under a short reaction time frame and by circumventing the aforementioned conventional method of synthesis. The final characteristics of the resulting composites are evaluated. Figure 1. Response of PAni-MnFe 2 O 4 nanocomposites to external magnetic field. 2 METHOD MnFe 2 O 4 was prepared by a coprecipitation method [9], and for a typical synthesis, the ratios [Fe 3+ ]/[Mn 2+ ] = 2 and ([Fe 3+ ]+[Mn 2+ ])/[OH - ] = 0.06 were used. The suspension was digested at 100 °C for 90 minutes, and the magnetic nanoparticles were thereafter washed several times with water. For the preparation of polyaniline-MnFe 2 O 4 nanocomposites, 0.042 M MnSO 4 + 0.084 M Fe 2 (SO 4 ) 3 in magnet MnFe 2 O 4 PAni-MnFe 2 O 4 magnet NSTI-Nanotech 2011, www.nsti.org, ISBN 978-1-4398-7142-3 Vol. 1, 2011 527