Oxidative doping polyaniline

Wang H, Hao Q, Yang X, Lu L, Wang X (2009) Graphene oxide doped polyaniline for supercapacitors. Electrochem Common 11 1158-1161... 

The basic structure of a typical dc-biased bilayer OLED is shown in Figure 1.5. The first layer above the glass substrate is a transparent conducting anode, typically indium tin oxide (ITO). Flexible OLEDs, in which the anode is made of a transparent conducting organic compound, e.g., doped polyaniline (see Fig. 1.2),44 or poly(3,4-ethylene dioxy-2,4-thiophene) (PEDOT)-polystyrene sulfonate (PEDOT-PSS) (see Fig. 1,2)45 deposited on a suitable plastic, e.g., transparency plastic, have also been reported. 

FIG. 25 Scanning above two lines of an interdigitated array generated previously by bromine-mediated oxidation of polyaniline in stripes. The 25 /am Au tip reduces iodine under diffusion control in 5 mM I2, 20 mM KBr, 100 mM HC1 at scan speed vx = 10 gm/s. High currents indicate the doped and therefore conducting parts of PAni. (Adapted from Ref. 63.)... 

Polyaniline holds a special position among conducting polymers in that its most highly doped form can be reached by two completely different processes protonic acid doping and oxidative doping. Protonic acid doping of emeraldine... 

For aU samples, a very interesting phenomenon was observed the Bronsted acid-doped samples remain doped after treatment with a NH4OH 1.0 mol dm solution. This fact can be verified by inspection of the oxide sample with the naked eye or with an optical microscope (the doped polyaniline samples exhibit a characteristic green color, whereas the undoped samples are blue) or by UV—Vis spectra of the samples before and after treatment with 1.0 mol dm NH4OH solution. As an example, the UV—Vis spectra for BaO-polyaniline samples are shown in Fig. 5.5. 

However, when Pani samples are doped with SnCU or FeCls somewhat different results are obtained. SnCU-doped samples exhibit an absorption band at 370 nm, and a broad absorption band with maximum at 1530 nm. On the other hand, FeCla-doped samples exhibits an extremely broad absorption band extending toward NIR with a maximum around 1700nm. This is evidence of the influence of the Lewis acid on the UV-Vis/NIR (near-infrared) spectra of Lewis acid-doped polyaniline. In the present case, the UV—Vis spectra for the oxide—Pani samples resemble those obtained for Pani doped with Hthium salts. 

Lateral charge propagation in a monolayer of polyaniline has been monitored with an SECM [129] kinetic data could be extracted by modeling. The charge transfer between a dissolved redox mediator and polyalkylterthiophene films has been studied [130]. In the oxidized (/ -doped) state of the film, redox reactions proceeded at the film/solution interface, not inside the film. In the reduced state the film behaved like a completely passivating film and penetration of redox mediator ions into the film was obviously completely inhibited. 

High quality thin films of doped polypyrrole and doped polyaniline can be conveniently deposited during a few minutes at room temperature on glass and plastic substrates from dilute aqueous solutions of the respective monomer as it undergoes oxidative polymerization (5-5,75). We find that the deposition rate and the properties of the films are greatly dependent on the nature of the substrate surface, e.g., whether deposited on hydrophilic or hydrophobic surfaces. 

Leucoemeraldine base, the completely reduced form of polyaniline base, can be controllably oxidatively doped to the highly conducting regime/analogously to (CH)x,viz.,... 

Electrochemical oxidation and reduction of polyanilines has been extensively studiedlO,23,24 by cyclic voltammetry techniques, usually in aqueous acid solutiorv using either electrochemically synthesized polyaniline films/ or chemically synthesized powders. This is a convenient method for the electrochemical doping of extremely small amounts of leu-coemeraldine but it is not well suited for the synthesis of large quantities of oxidatively doped polymer in a known oxidation state. 

The fundamental difference between the oxidative and non-oxidative doping methods for synthesizing the highly conducting form of polyaniline is illustrated diagrammatically below for emeraldine hydrochloride ... 

When an enantiomer of CSA is used in the polymerization, such as R-CSA, it is possible to create chiral polyaniline nanofibers. Figure 7.20 shows the circular dichroism (CD) spectrum of a water dispersion of as-prepared R-CSA doped polyaniline nanofibers. The positive peak at 450 nm is characteristic of chiral polyaniline [66-70], and is consistent with water s effect on the direction of the CD signals previously observed [71]. The peak at 290 nm is due to excess R-CSA in the dispersion. Recently, Wang et al. discovered that highly chiral polyaniline nanofibers can be produced by incremental addition of the oxidant, ammonium peroxydisulfate, into aniline solution with aniline oligomers and concentrated chiral dopants (>5 M R- or S-CSA) [72]. Chiral polyaniline nanofibers are very interesting for chiral recognition studies [68]. 

It was later shown by MacDiarmid et al. [166] that these doped polyaniline-poly(ethylene oxide) electrospim fibers could be deposited onto an oxidized silicon wafer. They demonstrated that it was possible to measure the conductivity of individual electrospun fibers by depositing gold electrical contacts onto the wafer using a shadow mask evaporation process. It was found that the room temperature conductivity for a 1.3 pm diameter CSA-doped polyaniline-polyfethylene oxide) electrospun fiber was 33 S/cm, which is two orders of magnitude higher than the conductivity of the corresponding thermally annealed film prepared from the same solution. This result indicates that... 

Copper chloride (CuCy-doped polyaniline (PANI)/multi-walled carbon nanotubes (MWCNTs) nanocomposite (PANI C2 CNT), CuCy doped PANI (PANI C2) and pure PANI were synthesized by in-situ oxidative polymerization method. The maximum specific capacitance of 724 F/g... 

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