Infrared Reflection-Absorption Study of the Aniline Electropolymerization on Stainless Steel
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INFRARED REFLECTION-ABSORPTION STUDY OF THE ANILINE ELECTROPOLYNERISATION ON STAINLESS STEEL F.
GAILLARD,
G. BOUYSSOUX AND S.N.
KUMIAR*
D~partement de Chimie Appliquee et G~nie Chimique, CNRS-UJRA 417 Universit• Claude Bernard LYON, 69622 Villeurbanne Cedex, France. •Laboratoire de Physique de Ia Mati~re, Institut National des Appliqu~es de Lyon, 69621 Villeurbanne Cedex, France.
Sciences
ABSTRACT Polyaniline (PANI) films were grown on 304 L steel and studied by FTIR spectrometry. The spectra of the films formed carry evidence for quinonic/aromatic alternating structure involving head-to-tail coupling. The coupling is quite independent of the thickness of the polymeric layer. The quinonic/aromatic ratio can be varied when the film is subjected to further dedoping treatments (electrochemical reduction or KOH immersion). INTRODUCTION The polyaniline family of polymers is attracting increasing interest owing to its applications in electrochromic, organic storage and microelectronic devices [1,2]. In addition, PANI obtained by electropolymerisation on metals are known to act as a good intermediate film for strong adhesion of subsequent coatings, such as, varnish, glue etc. [3]. The properties dealing with adhesion are highly dependent on surface chemistry of the relevant treated substrates. Consequently, a detailed chemical characterisation is required. For this purpose the best suited spectrometric tools seem to be photoelectron (XPS and UPS) and Fourier transform infrared (FTIR) spectrometries [4,5]. In this paper, results dealing with surface characterisation by FTIR of aniline electropolymerised on 304L stainless steels are presented. Such results are to be considered in conjunction with our recent XPS data (6]. EXPER IMENTAL The PANI films were grown electrochemically on 304L stainless steel substrates by electropolymerisation of aniline in an aqueous solution containing sodium sulfate as the supporting electrolyte. The 304L substrates were solvent degreased and some of them anodised in nitric acid solution in order to form a chromium enriched oxide film, about 20 nm in thickness [7]. The electropolymerisation solution contained 0.1MI aniline in a 0.5 M solution of Na2 SO4 with the final pH adjusted to 1.0 by the addition of H, S04. Films were grown either at constant voltage or constant current density. The FTIR spectra were obtained using a Nicolet 740 spectrometer, at a resolution of 4 cm-'. Using a DTGS detector and a reflexion-absorption device (70" incidence angle) each spectrum is made from 256 scans. RESULTS The narrow scan spectra shown in Fig. I are relative to PANI prepared chemically by (NH4 ) 2 S2 0, method (a) and by electropolymerisation on 304L (b). The main bands respectively correspond to :i) C-C stretching of quinoid (A) and benzoid (B) structures, ii) C-N stretching for aromatic amines •C, illl band referred to by MacDiarmid et al. as 'electronic like band' and considered as a measure of the degree of delocalisation of electrons (8] (0) and iv) C-H out of plane bending on 1,4 substituted
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