Indium polyaniline

Most 2,5-unsubstituted pyrroles and thiophenes, and most anilines can be polymerized by electrochemical oxidation. For pyrroles, acetonitrile,54 or aqueous55 electrolyte solutions are normally used, while the polymerization of thiophenes is performed almost exclusively in nonaqueous solvents such as acetonitrile, propylene carbonate, and benzonitrile. 0 Polyanilines are generally prepared from a solution of aniline in aqueous acid.21 Platinum or carbon electrodes have been used in most work, although indium-tin oxide is routinely used for spectroelectrochemical experiments, and many other electrode materials have also been employed.20,21... 

Other Substrates Deposition of cadmium was also studied on Bi, Sn and Pb [303], Ni [304], reticulated vitreous carbon [305], Ti [306], and indium tin oxide [307]. UPD of Cd on tellurium results in CdTe formation [270, 308]. Electrodes coated with conducting polymers were also used to deposit cadmium electrochemi-cally. In the case of polyaniline, the metal reduction potential corresponds to the neutral (nonconducting) state of the polymer, therefore cadmium was found to deposit on the substrate-glassy carbon electrode surface, in the open pores of the polymer film [309, 310]. 

Consider the polymer-on-metal interface, which might be prepared by coating a thin metal film with polymer in a polymer-based LED. The case of the counter electrode, formed by vapor-deposition, is discussed subsequently. First, assume that the substrates have clean surfaces hydrocarbon and oxide free, or naturally oxidized but still hydrocarbon free (pointed out as necessary). Typically, in connection with polymer-based LEDs, the metallic substrate could be gold, ITO (indium tin oxide) coated glass, the clean natural oxide of aluminum ( 20 A in thickness), the natural oxide which forms upon freshly etched Si( 110) wafers ( 10 A), or possibly even a polyaniline film. Dirt , which may be either a problem or an advantage, will not be taken up here. Discussions will alternate between coated polymer films and condensed model molecular solid films, as necessary to illustrate points. 

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. 

For the demonstration device in Fig. 4.2, polyaniline was chosen as the anode material because it is flexible, conducts current, and is transparent to visible light (there is no indium-tin-oxide (ITO) layer in the device of Fig. 4.2). More generally,... 

Schottky devices have recently been fabricated by thermal evaporation of indium on polyaniline, poly(o-anisidine) and poly(aniline-co-or oanisidine), respectively [103]. The values of the rectification ratio, the ideality factor and the barrier height of an indium/poly(o-anisidine) have been experimentally determined as 300,4.41 and 0.4972, respectively. The observed deviation from the Schottky behaviour for these devices seen at higher voltages has been explained in terms of either the Poole-Frenkel effect or due to the presence of a large number of defects containing the trapped charges existing at the indium/poly (aniline-co-or oanisidine) interface. 

The choice of a suitable counter-electrode for a successful EW is not easy since only a few compounds fulfil the desired operational requirements which call for an uncommon combination of electrochemical and optical properties. The most promising, and, thus far, the mostly used materials are indium tin oxide, nickel oxide, iridium oxide and cobalt oxide among the inorganic ECMs, and polyaniline (PANI) among the organic ECMs. The electrochromic properties of indium tin oxide and PANI have been described in Chapter 7. Therefore, here attention will be mainly focused on transition metal oxide counter-electrodes. 

The cyclic voltammogram of Propyl thiol polyaniline was obtained in 0.5M HCl solution using BAS Instrument Model 100, a thin film was smeared on indium tin oxide (ITO) glass slide, the working electrode, a platinum wire counter electrode, a platinum wire counter electrode, and Ag/AgCl reference electrode. 

In the case of polyaniline samples the increase in reflection coefficient is correlated to the increase in static conductivity. In the case of poly(alk)dthiophene)s, we found out that control of molecular structure permits to increase conductivity at molecular level but is not sufficient to insure high level of static conductivity of the material. Moreover no correlation was found between static conductivity and reflection coefficient in the infirared domain. In fiict static conductivity is not only influenced by molecular parameters but also by structural parameters at supramolecular scale. The effect of structural parameters on microwave properties of low conductivity sanoples ( 10 -5 S.cm ) has already heea reported (2). By increasing the conductivity we have shown that microwave properties for Ugh conductivity sanq>les will only depend on the static conductivity and thickness of samples in term of absoibed, reflected and transmitted power for a givoi fi-equency. Differoit materials such as polypyrrole, polyaniline or indium tin oxide deposits were found to give same results en the surface resistance of the deposits was k t the same. 

Additives used in final products Fillers aluminum, barium sulfote, aluminum hydroxide, glass fiber, mica, montmorillonite, Ni-BaTi03, nickel, silica, titanium dioxide, titanium fiber Plasticizers di-(2-ethylhexyl) phthalate, 2-hydroxyethyl methacrylate, 4-cyanophenyl 4-heptylbenzo-ate Antistatics copper dimethacrylate, glycerol monolaureate, indium tin oxide, lauramide diethanolamide, polyaniline, polypyrrole Antiblocking crosslinked siloxane particles Release magnesium stearate, methylpolysilsiquioxane, silicon nitride, stearic add Slip emcamide, slip ... 

In contrast to the electrochemical route to other important conducting polymers such as polypyrrole and polyaniline, which are obtained anodically and oxidize at the electrode to conducting forms that allow current to be passed continuously, PPV is obtained cathodically and the films formed at solid electrodes are insulating and halt the electrochemical process. Thus, the reduction of a,a,a, a -tetrabromo-p-xylene in aprotic solvents at indium-tin oxide (ITO) or Pt cathodes gives thin PPV films suitable only for optical studies [60, 61]. On the other hand, if the reduction is carried out using a stirred mercury pool cathode [62], the process may be operated at a preparative scale, because any film formed at the electrode is continuously broken up. 

Optical quality coatings of polyaniline have been shown to be effective as hole-injecting materials in polymer light-emitting devices (LEDs), where traditionally indium tin oxide (ITO) has been used. Indeed, these... 

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