Polyanilines optical properties

Intercalation of electroactive polymers such as polyaniline and polypyrrole in mica-type layered silicates leads to metal-insulator nanocomposites. The conductivity of these nanocomposites in the form of films is highly anisotropic, with the in-plane conductivity 10 to 10 times higher than the conductivity in the direction perpendicular to the film. Conductive polymer/oxide bronze nanocomposites have been prepared by intercalating polythiophene in V2O5 layered phase, which is analogous to clays. °° Studies of these composites are expected not only to provide a fundamental understanding of the conduction mechanism in the polymers, but also to lead to diverse electrical and optical properties. 

F. Yakuphanoglu, R. Mehrotra, A. Gupta, and M. Munoz, Nanofiber organic semiconductors The effects of nanosize on the electrical charge transport and optical properties of bulk polyanilines, J. Appl. Polym. Sci, 114, 794-799 (2009). 

J. Libert, J. Comil, D.A. Dos Santos, and J.L. Bredas, From neutral ohgoaniUnes to polyanilines a theoretical investigation of the chain-length dependence of the electronic and optical properties, Phys. Rev. B, 56, 8638 650 (1997). 

Prior studies demonstrated that the properties of chemically synthesized polyaniline could be modified by the type of synthesis -electrochemical, chemical, or potential cycling methods (1-5). In addition the optical properties of polyaniline could be controlled by the substituents on the nitrogen or aromatic ring (6,7). Enzyme-catal5rzed polymer syntheses in organic solvents with different amounts of water were described in earlier publications (7-10), and nonlinear optical properties of some of these pol5miers were reported (11). This paper describes the horseradish peroxidase-catalyzed synthesis of polyaniline and the evaluation of its optical properties to determine differences, if any, between this polyaniline and those chemically synthesized. 

In summary, polyaniline was S3mthesized by an enzymatic process and optical properties, including third order nonlinear susceptibility was assessed, x values as high as 7.6x10" (esu) were observed for one of the poljmiers. Based on the time-resolved nonlinear optical response of the poljmier solutions to the laser pulse delay, the electronic nonlinearity is the major component of the x values observed. 

Composites of conducting polymers, e.g., polyaniline and PEDOT, with polyacids, e.g., poly (2-acrylamido-2-methyl-l-methyl-l-propanosulfonic add) (PAMPS), have been shown to be electro-chromic. The polyadd acts as a dopant for the polymer film with the optical properties of the composite being contributed by the conducting polymer. The composites are formed by dther chemical or electrochemical polymerization of the electrochromic component monomer in the presence of the polyacid. Films of polyaniline-PAMPS switch from yellow to green and finally to blue on oxidation [228,229]. Composite films of PEDOT and PAMPS show similar electrochromic properties to PEDOT with the films switching from dark blue in the neutral state to Kght sky blue in the oxidized state [140,230,231]. 

Similar to the PB-conducting polymer composites, composite films can be prepared with conducting polymers and transition metal oxides. Composite films have been prepared by the electrostatic layer-by-layer technique with polyaniline and vanadium oxide with the electrochemical properties dominated by the vanadium oxide layers and the optical properties dominated by the polyaniline layers [245,246]. Composites have also been made between the water-soluble poly(2-(3-thienyloxy)ethanesulfonic acid) and vanadium oxide by mixing the two materials at different mole ratios in aqueous solutions. These films switched between an orange color when fully reduced, to yellow-green at intermediate potentials, and to dark blue when fully oxidized [247]. 

Barbero, C., and R. Kotz. 1994. Nanoscale dimensional changes and optical-properties of polyaniline measured by in-situ spectroscopic ellipsometry. J Electrochem Soc 141 859. 

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. 

Polyaniline/p-cyclodextrin inclusion complex (PANT/p-CD IC) and its relation with optical properties were investigated using solid-state NMR. Dynamics were interpreted in terms of chain motion. 

Figure 9.9 In Situ Vis-NIR absorption spectra recorded upon doping of poly(3-decylthiophene). Reprinted with permission from /. Pron, P. Rannou, M. Zagorska, Spectroscopy and spectroelectrochemistry of polyanilines and polythiophenes, in Electronic and Optical Properties of Conjugated Systems in Condensed Phases, Research Signpost, Trivandrum, 2003. Copyright (2003) Research Signpost...

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