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) la tex has been coated with poly(3,4-ethylenedioxythiophene) [PEDOT], an organ ic conducting polymer which exhibits good environmental stability. Despite its limited solubility, EDOT was successfully polymerized in aqueous soluti on using iron(III) tris(p-toluenesulfonate) at 85 degrees C. The PEDOT load ing was easily controlled by simply varying the latex concentration, and he nce the surface area available for deposition. Thus, a series of PEDOT-coat ed latexes was obtained with PEDOT loadings varying from 4.9 to 38.0 wt %. Pressed-pellet conductivity measurements on these composites indicated a pe rcolation threshold of ca. 5 vol %, with a conductivity plateau of 0.43 S c m(-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 obt ained. SEM studies of the PEDOT residues remaining after quantitative extra ction of the underlying PS latex reveal a "broken eggshell" morphology, whi ch is strong evidence for the core-shell morphology of the original composi te latex particles. The observed intensity enhancement of PEDOT bands in th e Fourier transform infrared spectra of the coated latexes is also consiste nt with a core-shell particle morphology. Finally, disk centrifuge studies indicate that reasonable colloidal stability of the coated latexes can be m aintained provided that the PEDOT overlayer is sufficiently thin relative t o the adsorbed steric stabilizer layer.