Polyaniline nanostructures and the role of aniline oligomers in their formation

Polyaniline (PANI) is prepared by the oxidation of aniline. Depending on the acidity conditions during the chemical oxidation, different types of products can be identified. The aniline dimers, semidines, are the first oxidation products. In the next step, aniline trimers containing a phenazine moiety, the nucleates, are produced. At moderate acidity, pH > 3.5, the reaction pathway further leads to higher brown non-conducting aniline oligomers. Alternatively, when the acidity is sufficiently high, pH  The model of phenazine nucleates is offered to explain the various supramolecular nanostructures produced by PANI. It is proposed that the hydrophobic nucleates randomly aggregate in the aqueous phase or become organized to form one-dimensional stacks stabilized by π–π interactions. This step is followed by the growth of PANI chains from the self-assembled nucleates. The evolution of the nanostructures is conveniently observed by the combination of microscopic and spectroscopic techniques. The random agglomeration of nucleates gives rise to PANI granules and regular self-assembly into stacks subsequently leads to PANI nanofibers. The growth of other nanostructures requires a starting template. A model of a flowing template combined with a helical nanotubular growth is proposed to account for the formation of nanotubes, monomer droplets serve as templates for microspheres. The detailed chemical structure of nucleates has still to be elucidated. The nucleates adsorb and self-assemble along various interfaces giving subsequently rise to additional conducting polymer morphologies. The adsorption of nucleates at solid surfaces immersed in the reaction mixture leads to PANI nanofilms or coatings of various substrates. The competition between nucleate adsorption and nucleate self-assembly may lead to more complex morphologies combining one-dimensional and three-dimensional features, such as nanobrushes, hairy spheres, etc . The control of nucleates self-assembly and of PANI growth, the involvement of various interfaces in this process, and the role of PANI conductivity are discussed. The nanostructures produced by other conducting polymers, especially by substituted PANI, polypyrrole, or poly(3,4-ethylenedioxythiophene) are also considered. Two potential extensions to the preparation of related materials, such as nitrogen-containing carbonized PANI nanostructures or the composites of conducting polymers with noble metals are outlined. The present review accounts for the latest development in the realm of PANI nanostructures in past few years and provides an upgrade in the models proposed for their formation.

Polyaniline Nanostructures and the Role of Aniline Oligomers in Their Formation

Theories of polyaniline nanostructure self-assembly: Towards an expanded, comprehensive Multi-Layer Theory (MLT)

One-dimensional nanostructured polyaniline (1D nano-PANI), including nanofibers, nanowires, nanobelts, nanotubes, nanorods, nanoneedles, and nanosticks, has been extensively studied recently due to its unique properties and many potential applications. As a continuation of our previous review on 1D nano-PANI (D. H. Zhang and Y. Y. Wang, Mater Sci Eng B 2006, 134(1), 9–19), the research and development of 1D nano-PANI, including both syntheses and applications, in the past 5 years (2006–2010) are reviewed in this paper. Newly invented chemical methods for fabrication of 1D nano-PANI, such as solid-state polymerization, seeding polymerization, UV light- and microwave-assisted polymerization, plasma-induced polymerization, porous membrane controlled polymerization, and vapor phase polymerization, are briefly reviewed, and morphology controlling of the nanostructures during several synthesizing processes are reported and discussed at first. The formation mechanisms and key factors that affect the morphology evolution of the 1D nano-PANI are discussed. Novel features of 1D nano-PANI, such as aligned or oriented, longer, self-doped, chiral, derivative, carbonized, and dendritic PANI, are summarized. Finally, newly exploited applications of 1D nano-PANI in the past few years, such as sensors (e.g., gases sensors, biosensors, moisture or humidity sensors, TNT sensors, taste sensors, and noble metal ion sensors), absorbents, catalysts, actuators, supercapacitors, batteries, fuel cells, solar cells, electrochromic devices, hydrogen storages, surface modifiers, field-effect transistors, and functional materials, are discussed in detail. © 2012 Wiley Periodicals, Inc. Adv Polym Techn 32: E323–E368, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.21283

One‐Dimensional Nanostructured Polyaniline: Syntheses, Morphology Controlling, Formation Mechanisms, New Features, and Applications

Polyaniline nanofibers were deposited on either gold or platinum electrodes and used as resistive sensors for the detection of hydrogen. In earlier work (J. Phys. Chem. B 2006, 110, 22266−22270), we showed that hydrogen interacts directly with polyaniline nanofibers to induce a small resistance decrease (−3%) at low concentrations of hydrogen (1%) using gold electrodes. This work showed that the sensor response on gold electrodes is due to hydrogen interaction with the polyaniline nanofibers. However, with platinum electrodes a much larger resistance increase (+65%) is observed under the same conditions. The sensor response on platinum electrodes is due to hydrogen interaction with platinum at the polyaniline−platinum interface. Hydrogen facilitates the formation of a Schottky barrier between platinum and polyaniline through a change in work function as platinum is converted to platinum hydride. The work function of polyaniline nanofibers was measured, and a model for sensor response is presented based on...

Hydrogen Detection by Polyaniline Nanofibers on Gold and Platinum Electrodes

Various diameters of polyaniline (PANI) nanofibers were easily made by varying the sweep rate in the electrochemical polymerization of the aniline monomer. At a sweep rate of 5 mV/s, the PANI nanofibers have an average diameter of 450 nm with a median of 440 nm. The fibers are short, on the order of a few microns in length, and exhibit a branched geometry. Increasing the sweep rate to 50 mV/s produced longer nanofibers with a smaller average diameter of 200 nm. Nanofibers synthesized at 100 mV/s were noted to be smaller with an average and median diameter of 100 nm. These results illustrate the ease in which the morphology of nanostructured PANI can be altered and indicate that the method has the potential to create multi-diameter fibers or mixed-morphology materials.

Diameter-Controlled Synthesis of Polyaniline Nanofibers

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Diameter-Controlled Synthesis of Polyaniline Nanofibers