Synthesis And Characterization Of Polyaniline Micro/Nanostructures

Polyaniline is a conjugated polymer. After chemical/electrochemical treatment, polyaniline can change from an initial insulating state to an electrically conducting sate. One-dimensional micro/nanostructures possess the advantages of both low-dimensional systems and organic conductors. They have potential applications in polymeric conducting molecular wires, chemical sensors or actuators, and gas-separation membranes. Based on the self-assembly of surfactants and the rigid molecular chain of polyaniline, one-dimensional micro/nanostructures have been synthesized by "soft template" and "template free" methods, respectively. The structures and formation mechanism of polyaniline micro/nanostructures have been investigated. The main results are concluded as follows:(1) Dendritic polyaniline nanofibers with diameters of 60-90 nm have been synthesized by chemical oxidative polymerization of aniline in acetic acid, using hexadecyltrimethylammonium chloride (C16TMA) as structural directing molecule. It is found that the diameters of polyaniline nanofibers decrease with decreasing the concentrations of C16TMA.(2) Polyaniline nanobelts have been prepared by chemical oxidative polymerization of aniline in acetic acid, using cetyltrimethylammonium bromide (CTAB) as structural directing molecule. The thickness, widths and lengths of PANI nanobelts are in the range of 40-50 nm, 300-400 nm and about several micrometers, respectively. When the concentration of CTAB is more than 0.2 M, bending belt-like PANI nanostructures with widths of about 100-200 nm are formed.(3) Net-like polyaniline nanofibers have been fabricated in aqueous solution with equimolar CTAB and sodium dodecylbenzenesulfonate (SDBS) as structural directingagents. The porous film cast on a quartz substrate from the as-synthesized sample suspension is composed of polyaniline nanofibers with diameters in the range of30-60 nm and lengths up to several micrometers. The diameters of polyaniline nanofibers increase with the molar fractions of CTAB increased.(4) Submicrometer-sized polyaniline tubes have been formed in aqueous solution using SDBS as structural directing molecule. The walls of polyaniline tubes become draped with increasing the time of sonification.(5) Polyaniline nanofibers and nanotubes have been synthesized by "template free" method using p-aminobenzenesulfonic acid and tartaric acid as dopants, respectively. The diameters of polyaniline nanofibers decrease from 80-120 nm to 30-60 nm with the concentration of p-aminobenzenesulfonic acid decreased. Using tartaric acid as dopant, the assembly of polyaniline is highly reminiscent of a sea urchin which is composed of radially aligned uniform nanotubes and a core. The core seems to be composed of vestigial nanorods and nanoparticles. These nanotubes are often linked together to form Y-junctions and then assemble into polyaniline dendrites. The geometrical shape of the individual branch is a cone with length of several micrometers. At the early stage of polymerization, the radially nanofibers are vestigial.(6) Fe3O4/P(St/AA) microspheres with average diameter of 542 nm have been prepared by dispersion polymerization. The inner structures of magnetic microspheres are investigated through dissolution experiment. Hollow titania microspheres and copper micro-amygdalae have been synthesized using polystyrene particles as templates.