Conducting polymers conduction mechanism

As for further analysis, curve fitting against the worm-like chain (WLC) model was conducted and indicated as a solid line in Figure 21.4. The model describes single polymer chain mechanics ranging from random-coil to fully extended forms, as follows ... 

Another conductivity mechanism could be suggested for LB films of this polymer with Ag+ cations. Such cations can accept or release electrons easily, so in the layer of such cations the conductivity could be caused by electron transitions between the ions with different degrees of oxidation. With tunneling microscopy an anomaly in the dl/dV(V) curves near zero bias was discovered for the LB films in Ag form with an odd number of layers there was a conductivity peak some 150-200 mV wide (Figure 7.4, Curves 1, 3) but no anomaly for these same films with an even number of layers (Figure 7.4, Curve 2). For LB films with an odd number of layers the ordered superstructure of the scale 11.5 x 11.5 x lO cm has been found in a conductivity dl/dV (x,y) measurement regime. The scale of such a structure corresponds to 3 x 2 surface reconstruction (Figure 7.5). 

Despite the initial misinterpretation in the ion conduction mechanism, it was soon realized that the ion conduction in PEG and other similar polyether-based media mainly occurred in the amorphous phases. Increasing evidences were obtained that ionic motion in these polymer ion conductors was closely... 

A polymer electrolyte with acceptable conductivity, mechanical properties and electrochemical stability has yet to be developed and commercialized on a large scale. The main issues which are still to be resolved for a completely successful operation of these materials are the reactivity of their interface with the lithium metal electrode and the decay of their conductivity at temperatures below 70 °C. Croce et al. found an effective approach for reaching both of these goals by dispersing low particle size ceramic powders in the polymer electrolyte bulk. They claimed that this new nanocomposite polymer electrolytes had a very stable lithium electrode interface and an enhanced ionic conductivity at low temperature. combined with good mechanical properties. Fan et al. has also developed a new type of composite electrolyte by dispersing fumed silica into low to moderate molecular weight PEO. 

Paddison SJ (2003) Proton conduction mechanism at low degrees of hydration in sulfonic acid-based polymer electrolyte membranes. Ann Rev Mater Res 33 289-319 Rasten E, Hagen G, Tunold R (2003) Electrocatalysts in water electrolysis with solid polymer electrolyte. Electrochimica acta 48 3945-3952... 

The literature on conductivity in poly(p-phenylene sulfide) is confused. According to Shacklette et al.74) heavy doping with AsF5 causes reduction of the polymer with the formation of fused benzothiophene structures which are responsible for conjugation. This would more properly place poly(p-phenylene sulfide) in the category of precursor polymers, discussed later. On the other hand, Friend and Giles 75) proposed an intrinsic conduction mechanism, based on optical measurements and Tsukamoto et al. 76) have presented XPS and 13C NMR measurements to support this view. 

Even though our understanding of the conduction mechanisms involved in many organic polymers is limited, these are the materials that have shown greatest promise for applications in electrical devices (Myl nikov, 1974 Gill, 1976 Schmidlin, 1976). The subject of the electrical properties of polycrystalline, non-crystalline and amorphous polymers is a vast one and no attempt will be made to cover the field in this review. However, a limited consideration will be given to the practical usefulness of a certain class of polymers and the key... 

Ionically conducting polymers and their relevance to lithium batteries were mentioned in a previous section. However, there are several developments which contain both ionically conducting materials and other supporting agents which improve both the bulk conductivity of these materials and the properties of the anode (Li)/electrolyte interface in terms of resistivity, passivity, reversibility, and corrosion protection. A typical example is a composite electrolyte system comprised of polyethylene oxide, lithium salt, and A1203 particles dispersed in the polymeric matrices, as demonstrated by Peled et al. [182], By adding alumina particles, a new conduction mechanism is available, which involved surface conductivity of ions on and among the particles. This enhances considerably the overall conductivity of the composite electrolyte system. There are also a number of other reports that demonstrate the potential of these solid electrolyte systems [183],... 

Though numerous groups have fabricated CNT-polymer composites, mechanical behaviour has not been the main focus of such studies. The bulk of the work has focused on studying the effect of the addition of CNT on the crystallization behaviour and on the electrical conductivity and improving dispersion by employing different techniques, as described earlier. 

An outline of a quantitative description of the dispersion phenomenon is given below. This theory provides a description of the backbone structure of a polymer insofar as it evaluates a distribution function for conjugation lengths on the chains. In certain cases this was found to correlate with the conductivity of the polymer after doping and thus provided important information concerning the conduction mechanism. Fig. 4.8-5b... 

However, it seems likely that a conductivity value of 10 S cm at room temperature is a goal that can only be achieved with polymer networks including organic solvents as plasticizers [96] or with polymer matrixes like polyacrylonitrile [97] or poly(methyl methacrylate) [98] entrapping a large amount of organic electrolytic solution, i.e., with hybrid and/or gel electrolytes. These electrolytes combine the advantage of the polymer s mechanical properties with the electrochemical properties of the liquid electrolytes. 

Properties of representative conducting polymers. Doped conjugated polymers have generated substantial interest in view of possible applications such as lightweight batteries, antistatic equipment, and microelectronics to speculative concepts such as molecular electronic devices.37-38 These polymers include doped polyacetylene, polyaniline, polypyrrole, and other polyheterocycles (Figure 5). While the conduction mechanism of metals and inorganic semiconductors is well understood and utilized in microelectronics, this is not true to the same... 

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. 

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