Single-molecular-system-based selective micellar templates for polyaniline nanomaterials: Control of shape, size, solid state ordering, and expanded chain to coillike conformation

摘要

A single molecular approach has been developed to selectively template polyaniline nanomaterials via interfacial and emulsion polymerization routes to control the nanomaterials shape, size, solubility, solid state ordering, and expanded polymer chain to coil-like conformation. A new amphiphilic azobenzenesulfonic acid dopant was designed and developed from renewable resource cardanol which exists in the form of 4.3 nm spherical micelles in water. The amphiphilic micelles selectively undergo spherical or cylindrical aggregation with ammonium persulfate (APS) and aniline in water at ambient conditions. In the interfacial route, aniline molecules diffuse through the interface and get oxidized by the dopant-APS spherical pre-aggregates to produce polyaniline nanospheres of 400 nm in diameter. The oxidations of dopant-aniline cylindrical micelles by APS in the emulsion route produce polyaniline nanofibers of 150-200 nm diameters with length up to 5-8 mu M. The mechanistic aspects of the polyaniline nanomaterials formation was investigated by dynamic light scattering to trace the factors which control the morphology of the resultant materials. The aniline/dopant ratio was varied from 100 to 450 to study the effect of reactants composition on the morphology and mechanism of the nanomaterials formation. The presence of hydrophobic tail in the amphiphilic dopant increases the solubility of nanospheres and nanofibers in water as well as organic solvents such as chloroform, n-butanol, chlorobenzene, xylene, and m-cresol, etc. The absorbance spectra of the nanospheres showed a free carrier tail above 950 nm in the near IR region for the delocalization of electrons in the polaron band corresponding to expanded conformation of polyaniline chains whereas the polyaniline nanofibers showed a peak characteristics at 750-850 nm with respect to more coiled-like conformation. The solvent dependent absorption studies revealed that the conformations of the polymer nanomaterials are less influenced by the solvent in which they were suspended. WXRD patterns of nanofibers showed a peak at 2 theta = 6.4 degrees (d-spacing = 13.6 angstrom) for polyaniline chain due to the effective inter-digitations of dopant molecules in the polyaniline crystalline domain. The expanded conformation of polymer chains enhances the solid state ordering of the nanospheres and a new intense peak at 2 theta = 6.05 degrees (d-spacing 14.3 angstrom) is observed, which is absent in the case of nanofibers.