CHARACTERIZATION OF POLYANILINE AND POLYPYRROLE PREPARED IN INVERSE MICROEMULSION

Abstract

A novel method for preparing and thereby substantially increasing the electrical conductivity of polyaniline and polypyrrole has been established. The method involves the principle of oxidative and electrochemical polymerisation of aniline and pyrrole in a stable inverse microemulsion via diffusion of reactants at the interfaces. The interfaces may arise from the contacts of microemulsion/microemulsion, microemulsion/membrane and microemulsion/electrode. The conductive polyaniline and polypyrrole can be prepared in the forms of ultra-fine spherical particles, polymer-coated electrodes and polymer-membrane composites. The resulting polymers show high electrical conductivity especially the latter two. The fine particles of polyaniline and polypyrrole were produced directly in the specially prepared w/o inverse microemulsion. Two microemulsions, each contained monomer or oxidant, were prepared separately and polymerisation occurs readily after the mixing of both microemulsions. The resulting fine polyaniline arid polypyrrole particles showed conductivity of 8 S cm-1 and 4 S cm-1 respectively. The sizes of these poly aniline and polypyrrole microparticles were 10-35 nm and 70-100 nm in diameter, respectively. The polyaniline films firmly coated on electrodes were obtained by electrochemical polymerisation in inverse microemulsion. All films were grown potentiodynamically from -0.2 to 0.8 V vs SCE using a sweep rate of 50 mV s-1. The electrical conductivity of these polyaniline films can be as high as 300 S cm-1. The polyaniline-membrane composites and polypyrrole-membrane composites were also made from two microemulsions, each contained monomer or oxidant respectively, which are separated by a cellulose membrane. The interfacial polymerisation occurred via diffusion of the reactants across the membrane. The cellulose membn.ne would eventually coat with polyaniline or polypyrrole to give conductive composites. The electrical conductivity of polyaniline-membrane composite was 400 S cm-1 and 24 S cm-1 for the polypyrrole-membrane composite. The residual surfactant in polyanilines and polypyrroles prepared from microemulsion could be easily removed by washing with alcohol and water. The washed products were then redoped to maximize electrical conductivity. X-ray photoelectron spectroscopy (XPS), thermogravimetry (TG), transmittence electron microscopy (TEM), scanning electron microscopy (SEM), elemental analysis, Fourier-transform infra-red spectroscopy (FT-IR) and cyclic voltametry (CV) have been employed to characterize various properties of the conductive polyanilines and polypyrroles.