Synthesis and characterization of micrometer-sized poly(3,4 ethylenedioxythiophene)-coated polystyrene latexes

A 1.8 mu m diameter poly(N-vinylpyrrolidone)-stabilized polystyrene (PS) latex has been coated with poly(3,4-ethylenedioxythiophene) [PEDOT], an organic conducting polymer which exhibits good environmental stability. Despite its limited solubility, EDOT was successfully polymerized in aqueous solution using iron(III) tris(p-toluenesulfonate) at 85 degrees C. The PEDOT loading was easily controlled by simply varying the latex concentration, and hence the surface area available for deposition. Thus, a series of PEDOT-coated latexes was obtained with PEDOT loadings varying from 4.9 to 38.0 wt %. Pressed-pellet conductivity measurements on these composites indicated a percolation threshold of ca. 5 vol %, with a conductivity plateau of 0.43 S cm(-1) obtained at the highest PEDOT loading. Scanning electron microscopy (SEM) studies revealed that a PEDOT subphase was present in addition to the coated particles at high PEDOT loadings, whereas at lower loadings (<12 wt %) only particles with relatively smooth, uniform PEDOT overlayers were obtained. SEM studies of the PEDOT residues remaining after quantitative extraction of the underlying PS latex reveal a "broken eggshell" morphology, which is strong evidence for the core-shell morphology of the original composite latex particles. The observed intensity enhancement of PEDOT bands in the Fourier transform infrared spectra of the coated latexes is also consistent with a core-shell particle morphology. Finally, disk centrifuge studies indicate that reasonable colloidal stability of the coated latexes can be maintained provided that the PEDOT overlayer is sufficiently thin relative to the adsorbed steric stabilizer layer.