Nano-emulsion use for the synthesis of polyaniline nano-grains or nano-fibers

We report that nano-emulsions can be creatively used as a morphology selective synthesis method to prepare not only nano-grains but also nano-fibers with high selectivity. Synthesis of the two different morphological materials was demonstrated using polyaniline synthesis as a model case. Polyaniline nano-grains were synthesized from aniline molecules in nano-size aqueous droplets as polymerization sites whose droplets were generated by inverse water-in-oil nano-emulsion use, and polyaniline nano-fibers were synthesized from aniline in aqueous nano-dimensional channels as polymerization sites whose channels were generated by direct oil-in-water nano-emulsion use containing high population of oil droplets. Using the approaches, we successfully synthesized nano-fibers of 60nm diameter with 0.5 mu m length and also nano-grains having diameter of 60-80 nm. The two different polymerization sites of nano-scale dimension were made by changing the ratio among surfactant, aqueous aniline/HCl solution, and oil, i.e. organic solvent. We found the nano-fibers synthesized from the channels formed by the direct oil-in-water nano-emulsion have higher bulk electrical conductivity than the nano-grains which were synthesized from the droplets formed by the inverse water-in-oil emulsion. We also found that the emulsion use allows us to use a room temperature synthesis unlike conventional synthesis methods which require to use ice bath temperature. Physical properties of both nano-fibers and nano-grains synthesized were characterized by Fourier transform infrared (FTIR), UV-Vis spectra, scanning electron microscopy (SEM), and four probes conductivity measurement. Copyright (C) 2009 John Wiley & Sons, Ltd.