The preparation and properties of dispersions of electrically-conducting polypyrrole particles

Abstract

A conventional aqueous dispersion polymerisation technique has been used to prepare polypyrrole latices having particle diameters in the size range 300–450 nm and conductivities as high as 2–3 S cm −1. Both FeCl 3 and (NH 4 2S 2O 8 have been used as initiators. High M w PEO has been used as the steric stabiliser; this may be subsequently removed to give bare polypyrrole particles dispersed in water. Much smaller polypyrrole particles ( < 70 nm) may be prepared using an inverse microemulsion polymerisation procedure with the initiator in one set of dropelts and the monomer in the other. On quenching the reaction, by diluting the microemulsion into an aqueous solution of polyvinylpyrrolidone (stabiliser), stable dispersions of small particles may be prepared. Electrophoretic mobilities, as a function of pH, and various background KCl concentrations, have been determined. The “bare” particles show an isoelectric point which depends on the initiator used. Adsorption isotherms for sodium poly (styrene sulphonate) onto the bare latices (at low pH) have also been established. Effects arising from the bulk charge density, as well as the surface charge density, may play a role. Finally, critical electrolyte (KCl) concentrations for coagulation of the “bare” particles have been found; these are very low compared to the values found, e.g., for polystyrene latex. Calculations of the zeta potentials from mobility data imply that, for the purpose of electrophoresis, conducting particles should be treated as “insulators” (confirming a suggestion made by Overbeek some 40 years ago). Finally, Hamaker constants for the polypyrrole particles have been established which agree well with those predicted for metals.