Synthetic Metals 144 (2004) 229–234 An FTIR study of the role of H 2 O and D 2 O in the aging mechanism of conductive polypyrroles S. Lamprakopoulos a , D. Yfantis a,∗ , A. Yfantis b , D. Schmeisser b , J. Anastassopoulou a , T. Theophanides a a Department of Chemical Engineering, National Technical University of Athens, 9 Ir. Polytechniou str, Zografou Campus, Greece b Applied Physics-Sensors, Technical University of Cottbus, PO Box 101344, D-03013 Cottbus, Germany Received 16 January 2004; received in revised form 1 March 2004; accepted 10 March 2004 Available online 12 May 2004 Abstract In the present work the role of H 2 O was studied by conductivity measurements and FTIR spectroscopy using the isotopic effect of deuterium in order to elucidate the aging mechanism of conductivity of polypyrroles. Polypyrrole was prepared with PTS as a dopant, by using deuterated water. Conductivity measurements showed changes due to structural water and atmospheric humidity. The FTIR absorption spectra indicated that the most probable structure of polypyrrole is the two-dimensional one. This finding could be attributed to the inhibition of polypyrrole’s IR modes. The infrared spectrum analysis show that the ␥-NH bending mode of pyrrole has significantly changed after polymerization of pyrrole and this result is in accordance with XPS measurements. © 2004 Elsevier B.V. All rights reserved. Keywords: Polypyrrole; Conductivity; FTIR; Isotopic effect 1. Introduction Polypyrrole (PPy) is one of the most stable known con- ducting polymers and also one of the easiest to synthesize. Polypyrrole can be prepared by chemical or electrochem- ical oxidation [1]. By inserting doping anions like PTS (para-toluene-sulfonic acid) the conductivity of the poly- mer is controlled [2]. It is assumed that this control is most likely due to the formation of polarons, which are the charge carriers. This is due to the interaction of doping anions with the polymer chain. Chemically prepared polypyrrole doped with PTS,showed high specific conductivity of the order of 10 2 S/cm [2]. The industrial applications of these polymers are the sub- jectof extended research with respect to its structure and its synthesis. PPy has already been used as an electrode for rechargeable batteries [3], as electromagnetic shield to electronic equipment [4], in printed circuit boards [5,6] and many other diversified applications. It is known that fluoride and metal-fluorocomplexes, such as Ti, Zr,Al play a very important role in the chemistry of the aluminum surface [7]. ∗ Corresponding author. Tel.: +30-210-772-1444; fax: +30-210-772-3090. E-mailaddress: dyfantis@central.ntua.gr (D. Yfantis). On this basis we have used these metal-fluorocomplexes in anticorrosive conversion coatings with PPy in situ [8,9]. For the industrial applications of the polymer the criti- calparameters that should be considered are conductivity changes and thermal stability. The role of H 2 O in the struc- ture of the polymer both as a constituent or as atmospheric humidity is very important, because it affects the above mentioned properties considerably [10]. The structure of polypyrroles has been found to be one-dimensional as well as two-dimensional [11],depending on the conditions of synthesis [12]. The one-dimensional structure is referred to polymerization mainly in ␣–␣ positions (low oxidant con- centration). On the other hand, the two-dimensional struc- ture is referred to polymerization mainly in ␣–␥ position (high oxidant concentration) [2] (Fig. 1). Fourier transform infrared (FTIR) spectroscopy has been extensively used for studying the properties and the structure of polypyrrole. This powerful technique was very efficient for investigating the molecular structural changes of PPy during the electrochemical polymerization [13–15]. More- over, X-ray photoelectron spectroscopy (XPS) has been ex- tensively used in these studies [16]. In the present work, the role of H 2 O in the structure of polypyrrole was studied by using FTIR spectroscopy. Since PTS is considered as the classical dopant we have used it in our experiments in order 0379-6779/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.synthmet.2004.03.006