ELSEVIER Synthetic Metals 101 (1999) 809-810 Study of the conduction mechanisms at the PAN1 /PAME interface. Role of m-cresol M.-C. Bernarda, V. T. Bichb, A. Hugot-Le Gof?* aWR 15 dtc CNRS ‘Physique des L&tides etElectrochimie”, Universitt? Pierre et Marie Curie, 3 place Jussieu, 75252 PARiS Cede.r 05 Frarlce b ISA!, NCST, Hanoi’, VietNnm Abstract The interface between polyaniline (PANI) and a polymer electrolyte (PAMPS) containing functionalized sulfonate anions (AMPS) presents a particular structure (doublestrand polymer) allowingthetransfer of carriers, evenwhen PANI is oxidizedup to aninsulating form. Theconduction is detected by thegrowth of anIR opticalabsorption. Therole of a PANI treatment by m-cresol is investigated. Keywords: Polyaniline, Raman spectroscopy, opticalspectroscopy, m-cresol, camphorsulfonic acid 1 Introduction The good performances of all-solid state electrochromic devices (ECD)using PANI polarized in high pH (3 -5) PAMPS are partly due to the transfer of carriers at the interface. The influence of a treatment by m-cresol of PANI doped with camphorsulfonic acid(HCSA) on this interfacial transfer is studied. 2 Experimental PANI films were ektrochemically polymerjzedin 0.2 M aniline+ 1 M HCSA solution; afterwards, the films were exposed to m-cresol vapors [ 11. They werestudied by Raman spectroscopy usingthe 514.5 run laserline during their polarizationin HCSA solution. The ECD preparation was described elsewhere 12, 31.The optical characteristics of PANI- CSA /m-cresol fiis polarizedin HCSA solutions arecompared to the opticalcharacteristics of ECD. 3 Results As alreadydisplayed [4], the m-cresol treatment improves the perfectionof leucoemeraldine structure in the as-prepared film shown in figure la (two sting phenyl stretching modes, together with a quasi-absence of other spectral features). As soon as the film is p&rized in pH 4.7 HCSA solution, even in cathodic polarization, the Raman spectrum of the oxidized form is obtained; however,a band at 1330 cm**remains, corresponding to polaronic sites stretching mode,it is a difference with the PANI-Cl spectra obtained in inorganic acidsolutions with identical PI-I[5]. Theoptical properties of films during their polarization in a pH 3 HCSA solution are compared in figure 2 to the properties of untreated PANI-CSA fiis andthe properties of ECDusing either treated or untreated PANI-CSA. A special attentionis paid to the polaron opticalband (fig 2a and2b) as well as to the LR absorption tail (fig 2c and2d). For ECD,the potential is thepotential at the PANI /PAMPS interface (differentof the total cell potential). Duringthe polarization in HCSA, the two features associated to conduction in film (or ECD) pass by a maximum at a potential of- 350mV. This potential corresponds to themaximum polaronic t I (A. U,) ! k i ! I ! I I , I I I , i 1200 1400 1600 cm-1 Figure 1 Ex-situ Raman spectra of PANI- CSA /m-cresol films, a: as prepared before polarization; after polarization in pH 4.7 HCSA at b: -500:c: 0; d: 150;e: 250; f: 3.50 mV/SCE 0379-6779/99/S - see frontmatter 0 1999 Elsevier Science S.A. All rights reserved. PII: SO379-6779(98)00846-7