Sensors and Actuators B 138 (2009) 318–325 Contents lists available at ScienceDirect Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb Polyaniline/silver nanocomposites: Dielectric properties and ethanol vapour sensitivity Arup Choudhury ∗ Department of Polymer Engineering, Birla Institute of Technology, Mesra, Ranchi 835215, India article info Article history: Received 21 November 2008 Received in revised form 8 January 2009 Accepted 11 January 2009 Available online 21 January 2009 Keywords: PANI/Ag nanocomposite Morphology Conductivity Dielectric properties Ethanol sensor abstract Polyaniline/silver (PANI/Ag) nanocomposites were prepared by in-situ oxidative polymerization of ani- line monomer in the presence of different concentrations of Ag nanoparticles. The formation of PANI/Ag nanocomposite was characterized by UV–vis spectroscopy, energy dispersion X-ray (EDX) and transmis- sion electron microscopy (TEM). TEM images showed that the particle size increased with increasing Ag concentration in the composite, owing to the aggregation effect. The AC conductivity and dielectric prop- erties of pure PANI and PANI/Ag nanocomposites were measured in the frequency range of 10 3 –10 6 Hz. Higher conductivity, dielectric constant and dielectric loss of PANI/Ag nanocomposites than those of pure PANI were observed. The conductivity of the nanocomposites increased with increasing Ag concentration. The gas-responses of the PANI/Ag nanocomposite towards low concentrations of ethanol was examined and compared with that of the pure PANI. The nanocomposite was found to possess superior ethanol sensing capacity compared to pure PANI and it showed linear relationship between the responses and the ethanol and/or Ag concentration. The Fourier transform infrared (FT-IR) spectroscopy was used to explain the sensing mechanism. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Polyaniline (PANI) is unique among conducting polymers in that its electrical properties could be reversibly controlled both by charge transfer doping and by protonation, which makes it a potential material for applications as chemical and biological sensors, actuators, microelectronic devices, etc. [1–4]. However, the insolubility in common solvent, low processability and poor mechanical properties of PANI has obstructed its potential applica- tions. In order to fulfill the industrial demand, several strategies have been developed to overcome such problems. For instance, the preparation of conventional thermoplastic–electroconductive polymer composites is a successful approach to achieve unique properties and applications of the resultant materials [5,6]. In recent years, the development of PANI/metal nanoparticle compos- ite with synergistic chemical and physical properties has received great attention world wide from both academic and industrial point of view [7–11]. The incorporation of metal nanoparticles could effectively improve the electrical, optical and dielectric proper- ties of the polyaniline composites [12–14]. These properties are very much sensitive to small changes in the metal content and in the size and shape of the nanoparticles. It was reported that ∗ Tel.: +91 9430 732461; fax: +91 651 2276184. E-mail address: arup@bitmesra.ac.in. the nanoparticles themselves could act as conductive junctions between the PANI chains that resulted in an increase of the electrical conductance of the composites [15,16]. The electrical conductivity of such composites might also depend upon the molecular struc- ture of the conductive polymer matrix (i.e., crystallinity). Since silver exhibits the highest electrical and thermal conductivities among all the metals [17], the combination of PANI with silver could yield functional materials having enhanced electrical prop- erties. The synthesis of PANI/silver composites was accomplished either chemically or electrochemically. The chemical methods include the polymerization of aniline monomer with simultane- ous reduction of metal ions and the photo-induced polymerization [18,19], which are based on the high affinity of metal ions for PANI. The other methods are to prepare the PANI/Ag composites in the presence of Ag nanoparticles [20,21]. Recently, gas sensors based on PANI nanocomposites combined with different noble metal cat- alysts have been the subjects of considerable interest. The reason for incorporating metallic particles into conductive polymer matrix is to increase the specific area of these materials and thus improve catalytic efficiency. It has been revealed that the chemically syn- thesized PANI/copper nanocomposite gas sensor exhibited higher response values, faster response and recovery rates to chloroform vapour than those of a pure PANI sensor fabricated under the identical conditions [22]. Torsi et al. [23] reported that the con- ducting polymers doped with metallic inclusions performed better 0925-4005/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2009.01.019