Surface composition of surfactant-stabilised polypyrrole colloids

Abstract

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. All 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.