Dielectric investigations and charge transport in PS-PAni composites with ionic and nonionic surfactants

We present the preparation of polystyrene-polyaniline composites by an emulsion polymerization technique. Polyethylene glycol and dodecylbenzenesulfonic acid were used as nonionic and anionic surfactants, respectively, for emulsion preparation. Fourier transform IR spectroscopy, UV-vis spectroscopy, and thermogravimetric analysis were used to characterize the composites obtained. Surface morphological investigations by scanning electron microscopy showed that the emulsion technique using polyethylene glycol produces the most homogeneously distributed composites. Thermal analysis in conjugation with broadband dielectric spectroscopy revealed that as the composite conductivity increased, the temperature at which the maximum degradation rate was achieved gradually decreased. The dielectric investigation showed the a-relaxation process in pure polystyrene has an activation energy of 10.8 kJ/mol and is accompanied by a dielectrically determined glass transition temperature of about 366 K. After addition of polyaniline, this a-relaxation process was masked by the conductivity contribution. Moreover, polyaniline prepared with the anionic surfactant had higher electrical conductivity than that prepared with the nonionic surfactant because of its ordering effect on the structure. Surprisingly, the dependence of the conductivity of the composites on temperature, regardless of the preparation method, has two different trends, and each can be attributed to a different mechanism of charge transport.