Synthesis and characterization of micrometre-sized, polypyrrole-coated polystyrene latexes

Abstract

Near-monodisperse, micrometre-sized poly(N-vinylpyrrolidone)-stabilized polystyrene latexes have been coated with polypyrrole by in situ deposition of the conducting polymer from aqueous solution. If the conducting polymer overlayer is sufficiently thin, it lies inside the steric stabilizer layer and the coated latexes retain reasonable colloid stability. The polypyrrole loading on the latex particles was systemically varied over a wide range (1–50 mass%) simply by changing the initial latex concentration. Pressed pellet conductivity measurements on the dried composites indicated an anomalously low percolation threshold of 1–2 vol. %, which is consistent with the conducting polymer component lying on the surface of (rather than within the interior of) the latex particles. IR spectroscopy studies of the composites confirmed the presence of several strong absorption bands due to the polypyrrole component. However, scanning electron microscopy (SEM) studies showed no evidence for the polypyrrole overlayer, which suggests that it must be very smooth and uniform. Disk centrifuge photosedimentometry (DCP) studies on the coated latexes revealed the presence of doublets and higher aggregates which indicates that these dispersions are weakly flocculated. However, if the polypyrrole overlayer is very thin (<10 nm) the coated particles exist in solution mainly as singlets with relatively few doublets or larger floccs. Polystyrene latex can also be coated with other conducting polymers such as polyaniline and poly(3,4-ethylenedioxythiophene). Finally, both polyelectrolytes and physically adsorbed poly(N-vinylpyrrolidone) can provide an effective steric barrier to allow controlled deposition of the conducting polymer overlayer.