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The surface compositions of a series of five polystyrene−polypyrrole (PS−PPy) composites and three reference materials (the original poly(ethylene glycol) (PEG) stabilizer, the uncoated PEG-stabilized PS latex, and PPy chloride bulk powder) were examined by X-ray photoelectron spectroscopy (XPS). The uncoated PEG-stabilized PS latex particles had a narrow size distribution with a mean diameter of 129 nm. The N1s XPS signal is a unique elemental marker for the PPy component and was therefore used to determine its surface concentration. As the PPy loading on the PS latex particles was increased from 4.2 to 28.1 wt % the relative intensity of the N1s signal increased, as expected. However, surface doping levels calculated from the Cl/N atomic ratios were relatively low, suggesting that some oxidative degradation of the deposited PPy component had occurred. Raman studies also indicated decreased doping levels at low PPy loadings. Close inspection of the C1s envelopes indicated that the composite particles did not have the expected core−shell morphology, since even at the highest PPy loading these XPS spectra were very similar to that of the original PS latex. These observations were confirmed by scanning electron microscopy (SEM) studies, which revealed the presence of discrete PPy nanoparticles of 20−30 nm diameter. Finally, it was found that more uniform PPy overlayers could be prepared by modifying the synthesis conditions. Thus, reducing both the total latex surface area and the pyrrole monomer concentration led to PS−PPy particles with a much improved core−shell morphology, as judged by both XPS and SEM.

A conducting polymer, polypyrrole (PPy), has been deposited from aqueous media onto a submicrometer-sized poly(ethylene glycol)-stabilized polystyrene (PS) latex. Deposition experiments were carried out at two different initial pyrrole concentrations, and the latex concentration was systematically adjusted in order to control the final conducting polymer loading. Transmission electron microscopy studies showed that at a pyrrole concentration of 5.0 × 10-3 M the PPy had deposited onto the latex as discrete PPy nanoparticles of 20−30 nm diameter. These nanoparticles act as a bridging flocculant or binder, leading to heteroflocculation of the PS latex. Thus the expected “core−shell” morphology was not observed. Pressed pellet conductivity measurements indicated relatively low conductivities (∼10-2 S cm-1) for the composites at PPy loadings less than 20 wt %. This is in contrast to earlier studies (Lascelles, S. F.; Armes, S. P. J. Mater. Chem. 1997, 7, 1339) of micrometer-sized PPy-coated PS latexes which exhibited conductivities similar to PPy bulk powder (∼1 S cm-1) even at PPy loadings as low as 5 wt %. The relative colloid stabilities of the PPy−PS composites were assessed by disk centrifuge photosedimentometry (DCP) studies. For PPy loadings up to 16.6% or lower a reasonable degree of colloid stability was retained, but the PS latex particles were present as stable colloidal microaggregates, which is in good agreement with scanning electron microscopy studies. In contrast, DCP analysis confirmed that a PPy−PS composite prepared using a relatively low latex surface area and a pyrrole concentration of 5 × 10-4 M comprised mainly singlets, with a much smaller contribution from doublets, triplets, and higher aggregates.

Polypyrrole (PPy) has been deposited from aqueous solution onto two types of near-monodisperse poly(alkyl methacrylate) latexes and the resulting composite particles have been extensively characterized using SEM, DCP, XPS, FTIR, and electrical conductivity measurements. Poly(methyl methacrylate) (PMMA) latex is more difficult to coat than the polystyrene latexes previously reported by our group in that the deposited PPy overlayer is much less uniform. This difference is most likely related to the greater hydrophilicity of the PMMA surface. The poly(n-butyl methacrylate) (PBMA) latex has intermediate hydrophobic character, and, as a result, PPy overlayers on this substrate are somewhat more uniform than those obtained for PMMA particles. The PPy-coated PBMA latex is an interesting model system for understanding the behavior of PPy-coated film-forming latexes such as DSM's ConQuest (PPy-coated polyurethane particles). The lightly cross-linked outer shell of PPy hinders film formation significantly but conductive films can be obtained in the presence of coalescence aids such as N-methyl pyrrolidone. This cosolvent acts as a plasticizer for the PBMA latex and allows a reasonable degree of film formation at ambient temperature.