Polyaniline interfaces/surfaces

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. 

Liljeroth et al. [80] used SECM in the feedback mode to study the electronic conductivity of a film of gold nanoparticles deposited at various pressures on a nonconductive substrate. They were able to observe an insulator-to-metal transition associated with a change in surface pressure. Unwin Whitworth et al. [83] have also developed a method to determine the electronic conductivity of ultrathin films using SECM under steady-state conditions. They obtained analytical approximations for the fitting of approach curves. The usefulness of their approach was demonstrated by investigating the effect of surface pressure on conductivity of a polyaniline monolayer at the water-air interface. 

The system was further characterized by in situ electrochemical/surface plasmon resonance (SPR) measurements, " and surface plasmon resonance spectroscopy was introduced as a means to follow bioelectrocatalytic transformations. Surface plasmon resonance spectroscopy (SPR) is a useful method for the characterization of the refractive index and thickness of interfaces associated with Au surfaces (or Ag surfaces). " In fact, SPR spectroscopy is a common practice in biosensing, and numerous examples that follow the formation of biorecognition complexes on SPR active surfaces have been reported.The redox transformations of polyaniline... 

The tenuous network of conducting polyaniline that self-assembles in blends of PANI with insulating host polymers results from a compromise the counter-ions want to be at the interface between the polar PANI (a salt) and the weakly polar (or nonpolar) host (5,d,7,5). On the other hand, the PANI and host tend to phase separate because there is no entropy of mixing for macromolecules. The result is a phase-separated structure with high surface area and with holes on every length scale (9). 

According to the theory of the metastable adsorption of de Gennes [172], when an adsorbed polymer layer is in contact with a pure solvent, the layer density diminishes from the substrate (e.g., metal) surface. The behavior of several polymer film electrodes (e.g., poly(tetra-cyanoquinodimethane) [173], poly(vinyl-ferrocene) [21, 92], polypyrrole [174], and polyaniline [37, 175]) has been explained by the assumption that the film density decreases with the film thickness, that is from the metal surface to the polymer/solution interface. During electropolymerization (e.g., in the case of polyaniline) first, a compact layer (thickness L 200 nm) is formed on the electrode surface via a potential-independent nucleation and a... 

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