Surface Composition of Surfactant - stabi I ised Polypyrrole Colloids

We have examined a colloidal dispersion of surfactant-stabilised polypyrrole particles by surface-enhanced Raman spectroscopy (SERS), time-of-flight secondary ion mass spectroscopy (TOF-SIMS) and X-ray photoelectron spectroscopy (XPS). These surface-specific techniques have enabled us to probe the surface composition of the conducting polymer particles. Al l three techniques indicate that the polypyrrole component is present at (or near) the particle surface : this observation is consistent with the relatively high pressed-pellet conductivities exhibited by these colloids. Our TOF-SIMS results suggest that the surfactant stabiliser is the dominant component in the first monolayer. Similarly, our wide-scan XPS spectra indicate that the sulfur/nitrogen surface atomic ratio of the polypyrrole colloid is significantly higher than that of polypyrrole bulk powder; curve fitting of the corresponding core-line sulfur spectra confirm that a significant proportion of this excess sulfur is due to the sulfonate-based surfactant. Thus, both our TOF-SIMS and XPS studies confirm that the surface of the polypyrrole particles is distinctly 'surfactant-rich ', which is consistent with the observed long-term colloidal stability of these dispersions.