Characterization of 16-mer polyaniline composite Langmuir–Blodgett films A. Riul Jr. a , A. Dhanabalan a , L.H.C. Mattoso b , L.M. de Souza c , E.A. Ticianelli c , O.N. Oliveria Jr. a, * a Instituto de Fı ´sica de Sao Carlos, USP, CP 369, 13560-970, Sao Carlos, SP, Brazil b CNPDIA/EMBRAPA, CP 741, 13560-970, Sao Carlos, SP, Brazil c Instituto de Quı ´mica de Sao Carlos, USP, 13560-970, Sao Carlos, SP, Brazil Abstract A detailed structural characterization study is presented for composite Langmuir–Blodgett (LB) films containing varying compositions of the 16-mer polyaniline, processed with camphor sulfonic acid and m-cresol, and cadmium stearate. The mixed monolayer approach was selected as it has been proven to yield the most uniform LB films for conducting polymers. Because film uniformity was indeed excellent as verified by visual inspection and also using surface potential measurements, attempts were made to probe whether molecular level mixing occurred. However, X-ray diffraction (XRD) results have shown clearly that the cadmium stearate and the 16-mer molecules are phase separated. Diffractograms were obtained which are very close to that of pure cadmium stearate films, at least for low weight percentages of the 16-mer. When the 16-mer content was increased, the stacking order of the cadmium stearate domains was affected to a large extent, being no longer apparent for 75% of the 16-mer. The presence of cadmium stearate and 16-mer polyaniline in the composite LB film was also detected in a Fourier transform infrared spectroscopy (FTIR) analysis. The deposition of a layer-by-layer structure was confirmed through ellipsometry which also provided film thickness to be compared with the bilayer thickness from XRD data. The thickness was found to be dependent on the film composition, being mostly determined by the cadmium stearate domains up to 50 wt.% of the 16-mer in the composite.  1998 Elsevier Science S.A. All rights reserved Keywords: Langmuir–Blodgett films; X-ray diffraction; Fourier transform infrared spectroscopy 1. Introduction The full exploitation of conducting polymers requires the development of processing methods for obtaining thin films out of those materials. For polyaniline, for instance, a major breakthrough was the advent of functionalized-acid doping [1]. Using such acids, it has been possible to fabricate films from parent polyaniline readily in the doped state by several methods, including the Langmuir–Blodgett (LB) technique [2–4]. Despite this progress, LB films could only be obtained after a tedious, time-consuming optimization of experimental conditions for Langmuir monolayer spreading and LB transfer [5]. Such difficulties are likely to be con- siderably alleviated if oligomers of polyaniline are employed, as suggested recently [6]. Cast films from the 16-mer, for example, have been shown to exhibit similar characteristics to those observed with the high molecular weight polyaniline [6,7], with the advantage of an improved solubility in organic solvents. Furthermore, in a recent study [8] we showed that Langmuir monolayers and LB films can be produced from the 16-mer, again with similar features to the high molecular weight polyaniline LB films. In this work, the use of the 16-mer is further exploited for the fabrication of LB films. Use is made of the mixed mono- layer approach, which consists of transferring mixed mono- layers of the 16-mer and cadmium stearate, a traditional film-building material, onto solid substrates. This approach was selected because it has been proven to yield the most uniform LB films from several materials made up of macromolecules [5,9]. Macroscopic film uniformity is investigated using surface potential measurements. The for- mation of phase-separated domains of cadmium stearate and the 16-mer is demonstrated using X-ray diffraction (XRD). The LB films are also characterized by electrical conductiv- ity measurements, Fourier transform infrared spectroscopy (FTIR) spectroscopy and ellipsometry. Most results are Thin Solid Films 327–329 (1998) 576–580 0040-6090/98/$ -see front matter  1998 Elsevier Science S.A. All rights reserved PII S0040-6090(98)00716-0 * Corresponding author. Tel.: +55 16 2715365; fax.: +55 16 2713616; e-mail: chu@ifqsc.sc.usp.br