Synthetic Metals 158 (2008) 883–887 Contents lists available at ScienceDirect Synthetic Metals journal homepage: www.elsevier.com/locate/synmet Microwave study of chemically synthesized conducting polyaniline on alumina S.V. Jadhav, Vijaya Puri ∗ Thick and Thin Film Device Lab, Department of Physics, Shivaji University, Kolhapur 416004, India article info Article history: Received 2 August 2007 Accepted 17 June 2008 Available online 26 July 2008 Keywords: Polyaniline Microwave Alumina Conductivity Shielding effectiveness Dielectric constant abstract Polyaniline (PANI) thin film on alumina was prepared by the chemical oxidation of aniline with ammonium peroxydisulphate in acidic aqueous medium. DC conductivity, microwave transmission and reflection, microwave conductivity, shielding effectiveness and microwave dielectric constant of the conducting PANI films are reported. DC conductivity was between 0.15 × 10 -3 and 3.13 × 10 -3 S/cm. Microwave conductivity was between 0.2 and 10S/cm. The PANI films coated on alumina gave shielding effectiveness value of -1 to -4 db. The ε ′ was between 2 and 350 whereas ε ′′ was between 437 and 60. Measurements have been carried over the frequency range of 8.2–18GHz. © 2008 Elsevier B.V. All rights reserved. 1. Introduction The electronic communication industry recognizes a require- ment of large area and smart surface at which the microwave transmittance, reflectance and absorbance can be controlled. There are number of studies which indicate that conducting polymers have electromagnetic shielding [1] and absorption properties [2]. In addition conducting polymers are relatively light-weight and corrosion-resistant conducting materials which may be easily pro- duced in large scale at low cost. Basically many polymers are insoluble in the common solvents which restrict the practical application of the conducting polymers in the various fields. This can be removed or minimized by the polymer blend or dispersion [3]. Among the various conducting polymers polyaniline (PANI) has good environmental stability and high electrical conductivity associated with the protonation and can be synthesized at low cost. An important concern of practical application of PANI is the strong dependence of its conductivity on the synthesis method and its parameters, nature of electrolyte, time of deposition, etc. In the case of chemical polymerization, the main goal of many studies is to increase the conductivity of polymer. One way to achieve this is by performing the synthesis at low tempera- ture. The molecular weight of PANI can be increased by decreasing the reaction temperature [4]. ∗ Corresponding author. E-mail address: vrp phy@unishivaji.ac.in (V. Puri). Alumina is the most preferred material for substrate in microwave integrated circuit (MIC). The metallization are usually gold, copper and silver. Except for gold all others tend to react with environment and conductivity decreases with time. It is felt that the conducting polymers can replace these metals in MIC, since these have the mechanical strength of polymers and conductivity simi- lar to metals. For these types of application it is necessary to study the microwave properties of the conducting polymer deposited on alumina. The microwave aspects of thin film polyaniline are sparse. Towards this aim, this paper reports the microwave trans- mittance, reflectance, shielding effectiveness and microwave conductivity and microwave dielectric constant of the chemically synthesized conducting polyaniline coated on alumina. To the authors’ knowledge, there is no report on microwave properties of conducting polyaniline on alumina. The broad frequency range from 8 to 18GHz is reported in this paper. 2. Experimental All the chemicals used were of analytical reagent (AR) grade and distilled water was used to prepare the solutions. PANI emeraldine salt was synthesized by chemical polymerization in HCl by oxida- tion of aniline monomer (99%, S. d. Fine, India) using ammonium peroxidisulphate, while temperature was kept between 0 and 4 ◦ C. The molar ratio of aniline to ammonium peroxidisulphate concen- tration was 1.25 due to large yield of polyaniline [5]. PANI films with different thickness were obtained on alumina surface immersed for different time periods in the reaction mixture, during the oxida- tive polymerization. Aniline oligomers adsorbed at the substrate 0379-6779/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.synthmet.2008.06.010