Polypyrrole-bearing conductive composite prepared by an inverted emulsion pathway involving nonionic surfactants

Abstract

Polypyrrole-rubber composites were prepared in two steps using an inverted emulsion pathway. In the first step, an inverted emulsion was generated by dispersing an aqueous solution of FeCl 3 (as oxidant and dopant) in an organic solution (six different solvents have been employed) of a host polymer (styrene-butadiene-styrene (SBS), styrene-ethylenebutylene-styrene (SES) or styrene-isoprene-styrene (SIS) and nonionic surfactant (six different surfactants have been employed) with stirring. In the second step, a solution of pyrrole in toluene was introduced dropwise in the emulsion generated in the first step and polypyrrole was thus formed rapidly (10–15 min). Methanol was introduced to precipitate the composite after polymerization was completed. The ratio of pyrrole/host polymer, the surfactant and the organic solvent employed in the inverted emulsion, the ratio of aqueous phase/organic phase in the inverted emulsion, the nature of the host polymer and even the organic solvent used to wash the composite are important factors that affect the conductive and mechanical properties of the composites. When a small amount (0.007 g/ml organic phase of the emulsion) of Span 80 and isooctane/toluene (1:1 vol./vol.) were employed as surfactant and solvent for the continuous phase, respectively, of the inverted emulsion and the volume ratio of aqueous phase/organic phase in the inverted emulsion was 0.4, the composites consisting of polypyrrole and SBS washed finally with petroleum ether had good conductivities, as well as good mechanical properties. The conductivities were in the range 2.4-3.5 S/cm with tensile strengths 10.9-7.8 MPa and elongations 166-38% at break point. The morphology of the composites was investigated by scanning electron microscopy (SEM), and their compositions determined by energy-dispersive spectroscopy (EDS) and elemental analyses.