SURFACE CHARACTERIZATION OF POLYANILINE-COATED POLYSTYRENE LATEXES

The surface compositions of seven polyaniline (PAni)-coated polystyren e (PS) latexes have been investigated by X-ray photoelectron spectrosc opy. This technique was used to assess the uniformity of the PAni over layers deposited onto micrometer-sized, poly(N-vinylpyrrolidone) (PNVP )-stabilized PS latex particles under various synthesis conditions. Pe ak fitting of the N(ls) core-line spectra provided evidence for the pr esence of both PAni and the PNVP stabilizer at the surface of the PS l atex. Nonuniform PAni coatings were obtained using conventional anilin e polymerization conditions (aniline monomer, ammonium persulfate, 1.2 M HCl at 25 degrees C). In contrast, more homogeneous PAni coatings w ere 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 coate d and uncoated PS latexes to that of a PAni ''bulk powder'' prepared i n the absence of any latex. It was shown that the relatively rapid pol ymerization at room temperature resulted in nonuniform PAni coatings a nd reduced PAni surface composition. The maximum PAni coverage was fou nd to be around 57-59%, which is much lower than the surface compositi on of 94-100% found for polypyrrole (PPy) deposited onto a similar mic rometer-sized PS latex (Perruchot et al. Langmuir 1996, 12, 3245). The se results indicate that the PAni coatings are much less uniform than the PPy overlayers. Finally, the improved uniformity of the PAni overl ayers prepared using aniline hydrochoride in the absence of HCl is con sistent with the higher coalescence temperature found for these PAni-c oated PS particles in hot-stage optical microscopy studies.