Surface characterization of polyaniline-coated polystyrene latexes

The surface compositions of seven polyaniline (PAni)-coated polystyrene (PS) latexes have been investigated by X-ray photoelectron spectroscopy. This technique was used to assess the uniformity of the PAni overlayers deposited onto micrometer-sized, poly(N-vinylpyrrolidone) (PNVP)-stabilized PS latex particles under various synthesis conditions. Peak fitting of the N(ls) core-line spectra provided evidence for the presence of both PAni and the PNVP stabilizer at the surface of the PS latex. Nonuniform PAni coatings were obtained using conventional aniline polymerization conditions (aniline monomer, ammonium persulfate, 1.2 M HCl at 25 degrees C). In contrast, more homogeneous PAni coatings were obtained when polymerizing aniline hydrochloride at 0 degrees C in water. The relative proportion of PAni at the surface of the PS latex was estimated by comparing the surface nitrogen contents of the coated and uncoated PS latexes to that of a PAni "bulk powder" prepared in the absence of any latex. It was shown that the relatively rapid polymerization at room temperature resulted in nonuniform PAni coatings and reduced PAni surface composition. The maximum PAni coverage was found to be around 57-59%, which is much lower than the surface composition of 94-100% found for polypyrrole (PPy) deposited onto a similar micrometer-sized PS latex (Perruchot et al. Langmuir 1996, 12, 3245). These results indicate that the PAni coatings are much less uniform than the PPy overlayers. Finally, the improved uniformity of the PAni overlayers prepared using aniline hydrochoride in the absence of HCl is consistent with the higher coalescence temperature found for these PAni-coated PS particles in hot-stage optical microscopy studies.