X-ray photoelectron spectroscopy characterization of submicrometer-sized polypyrrole - Polystyrene composites

The surface compositions of a series of five polystyrene-polypyrrole (PS-PPy) composites and three reference materials (the original poly(ethylene glycol) (PEG) stabilizer, the uncoated PEG-stabilized PS latex, and PPy chloride bulk powder) were examined by X-ray photoelectron spectroscopy (XPS). The uncoated PEG-stabilized PS latex particles had a narrow size distribution with a mean diameter of 129 nm. The N1s XPS signal is a unique elemental marker far the PPy component and was therefore used to determine its surface concentration. As the PPy loading on the PS latex particles was increased from 4.2 to 28.1 wt % the relative intensity of the N1s signal increased, as expected. However, surface doping levels calculated from the Cl/N atomic ratios were relatively low, suggesting that some oxidative degradation of the deposited PPy component had occurred. Raman studies also indicated decreased doping levels at low PPy loadings. Close inspection of the Cls envelopes indicated that the composite particles did not have the expected core-shelf morphology, since even at the highest PPy loading these XPS spectra were very similar to that of the original PS latex. These observations were confirmed by scanning electron microscopy (SEM) studies, which revealed the presence of discrete PPy nanoparticles of 20-30 nm diameter. Finally, it was found that more uniform PPy overlayers could be prepared by modifying the synthesis conditions. Thus, reducing bath the total latex surface area and the pyrrole monomer concentration led to PS-PPy particles with a much improved core-shell morphology, as judged by both XPS and SEM.