Synthesis and Characterization of Micrometer-Sized, Polyaniline-Coated Polystyrene Latexes

Poly(N-vinylpyrrolidone)-stabilized polystyrene (PS) latexes have been coated with thin overlayers of polyaniline (PANi) to produce electrically conductive “core−shell” particles. In this work we focused on the morphology of the PANi overlayer, the colloid stability of the coated latexes, and electrical conductivity. PANi-coated particles exhibit a nonuniform morphology as observed by scanning electron microscopy (SEM), in comparison with the relatively smooth polypyrrole overlayers synthesized in a previous study (Lascelles, S. F. et al., J. Mater. Chem. 1997, 7, 1339 and 1349). Disk centrifuge photosedimentometry confirmed that the PANi-coated PS latexes were weakly flocculated. The underlying PS latex “core” was quantitatively removed by solvent extraction, and SEM observations of the PANi residues revealed a “broken egg shell” morphology. Vibrational bands due to the PANi component were more intense in both the FT-IR and Raman spectra of the PANi-coated PS latexes, which is also consistent with the “core−shell” morphology. No reduction in the surface roughness of the PANi overlayer was observed when the rate of the aniline polymerization was decreased or if the latex surface was pretreated with either a thin polypyrrole overlayer or a layer of adsorbed surfactant. Similarly, only rough PANi overlayers were observed when coating a sulfonated PS latex. However, a more uniform deposition of PANi and a corresponding improvement of colloid stability were obtained using aniline hydrochloride monomer in the absence of added acid.