Characterization of 16-mer polyaniline composite Langmuir–Blodgett films

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.