Hopping conduction on PPy/SiO 2 nanocomposites obtained via in situ emulsion polymerization C. P. L. Rubinger Æ L. C. Costa Æ A. C. C. Esteves Æ A. Barros-Timmons Æ J. A. Martins Received: 22 September 2007 / Accepted: 30 November 2007 / Published online: 21 March 2008 Ó Springer Science+Business Media, LLC 2008 Abstract This work describes the preparation and elec- trical characterization of conducting polypyrrole (PPy) and silica nanocomposites. Four samples were investigated: (i) pure PPy, (ii) PPy-covered SiO 2 spherical nanoparticles, (iii) PPy-covered SiO 2 spherical nanoparticles modified with 3-aminopropyltriethoxysilane (APS), and (iv) PPy- covered SiO 2 fibers. Structural characterization was made by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electrical conductivity was measured from 80 K to 300 K and three-dimensional variable range hopping conduction was observed. From the hopping parameter the mean hopping distance was obtained as well as the density of active center and the energy associated with it. Introduction The unique size dependent properties of nanoparticles, namely confinement effects and other advanced properties related to high surface area have been increasingly reported in literature for several types of inorganic materials [1]. The synthesis and characterization of new nanostructures, have been so far the main concern in this field. Therefore, processing details and possible applications for these mate- rials have become imperative. The homogeneous dispersion of nanoparticles in polymeric matrices constitutes an excellent strategy of protection, support, and easy processing of these materials [2]. Polymerization of the monomers in the presence of inorganic nanoparticles leads to new organic-inorganic hybrid nanocomposites whose characteristic properties often depend not only on the particle size, but also on the particle shape [1]. Considerable efforts have been made on the synthesis of composite nanoparticles, since these nanostructured composites have many potential applica- tions, such as in drug delivery [3, 4], gene therapy [5, 6], and catalysis [6, 7]. Amongst conducting polymers, polypyrrole (PPy) is one of the most studied conducting polymers because of its high electrical conductivity, environmental stability, and easy synthesis [7–9]. For that reason various contributions have been reported regarding the preparation of PPy-based nanocomposites using a variety of different types of inorganic oxides such as SiO 2 , NiO, CuO, ZnO, and CeO 2 and their electrical characterization [9–12]. However, no single unanimous model is so far available that can properly describe the prevailing conduction processes occurring due to the presence of nonlinear excitations like solitons, polarons, and bipolarons. As the conductivity of SiO 2 is very low compared to PPy, the change in conductivity of different PPy/silica nanocomposites and the associated conduction process is an important issue which may help clarifying the conduc- tion processes in this type of materials. Therefore, in the present work four different samples have been studied: (i) pure PPy, (ii) PPy-covered SiO 2 spherical nanoparticles, (iii) PPy-covered SiO 2 spherical nanoparticles modified C. P. L. Rubinger (&)  L. C. Costa Physics Department, I3N, University of Aveiro, 3810-193 Aveiro, Portugal e-mail: carlarubinger@yahoo.com.br A. C. C. Esteves  A. Barros-Timmons Chemistry Department, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal J. A. Martins Polymer Engineering Department, CICECO, University of Minho, 4800-058 Guimaraes, Portugal 123 J Mater Sci (2008) 43:3333–3337 DOI 10.1007/s10853-007-2367-2