Surface characterization of micrometre-sized, polypyrrole-coated polystyrene latexes: verification of a ‘core–shell’ morphology

Abstract

Micrometre-sized, polypyrrole-coated polystyrene latexes with various conducting polymer loadings have been extensively characterized using X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectroscopy (TOF-SIMS), Raman and UV–VIS reflectance spectroscopy, scanning force microscopy (SFM) and scanning electron microscopy (SEM). Both XPS and TOF-SIMS studies are consistent with relatively uniform, chloride-doped polypyrrole overlayers. Raman studies also indicated a 'core–shell' morphology since only bands attributable to polypyrrole were observed; no evidence was found for the underlying polystyrene component even at the lowest polypyrrole loadings. This is most likely due to remarkably efficient attenuation of the polystyrene bands by the highly absorbing polypyrrole overlayer. UV–VIS reflectance spectroscopy studies confirmed that a coated latex had a much lower reflectance (higher absorbance) than a heterogeneous admixture of polypyrrole and polystyrene with a similar polypyrrole content. High-resolution images of the polypyrrole overlayer nanomorphology were obtained using SFM. At low polypyrrole loadings (1.0 mass%) the overlayer was relatively smooth and uniform, but higher loadings (8.9 mass%) resulted in a rougher, more globular morphology. Finally, the underlying polystyrene latex 'core' was quantitatively removed by solvent extraction. SEM studies of the polypyrrole residues revealed a 'broken egg-shell' morphology, thus providing irrefutable evidence for the 'core–shell' morphology of the original polystyrene/polypyrrole particles.