Synthesis and characterization of submicrometer-sized polypyrrole-polystyrene composite particles

A conducting polymer, polypyrrole (PPy), has been deposited from aqueous me dia onto a submicrometer-sized poly(ethylene glycol)-stabilized polystyrene (PS) latex. Deposition experiments were carried out at two different initi al pyrrole concentrations, and the latex concentration was systematically a djusted in order to control the final conducting polymer loading. Transmiss ion electron microscopy studies showed that at a pyrrole concentration of 5 .0 x 10(-3) M the PPy had deposited onto the latex as discrete PPy nanopart icles of 20-30 nm diameter. These nanoparticles act as a bridging flocculan t or binder, leading to heteroflocculation of the PS latex. Thus the expect ed "core-shell" morphology was not observed. Pressed pellet conductivity me asurements indicated relatively low conductivities (similar to 10(-2) S cm( -1)) for the composites at PPy loadings less than 20 wt %. This is in contr ast to earlier studies (Lascelles, S. F.; Armes, S. P. J. Mater. Chem. 1997 , 7, 1339) of micrometer-sized PPy-coated PS latexes which exhibited conduc tivities similar to PPy bulk powder (similar to 1 S cm(-1)) even at PPy loa dings as low as 5 wt %. The relative colloid stabilities of the PPy-PS comp osites were assessed by disk centrifuge photosedimentometry (DCP) studies. For PPy loadings up to 16.6% or lower a reasonable degree of colloid stabil ity was retained, but the PS latex particles were present as stable colloid al microaggregates, which is in good agreement with scanning electron micro scopy studies. In contrast, DCP analysis confirmed that a PPy-PS composite prepared using a relatively low latex surface area and a pyrrole concentrat ion of 5 x 10(-4) M comprised mainly singlets, with a much smaller contribu tion from doublets, triplets, and higher aggregates.