Mechanism of Charge Transport

Heavily doped polymers are of special interest, because these polymers show metallic properties such as a Pauli susceptibility, a linear temperature dependence of the thermoelectric power, a high reflectivity in the infrared region, etc., as described in Section 4.2. The temperature dependence of d.c. conductivity in heavily doped polymers is not like a metal, whereas metallic properties are observed. These results 

In the case of traw -polyacetylene (a degenerate polymer), band-structure calculations [126] indicate that a polaron lattice has a metallic band whereas a charged soliton lattice has no metallic band. An alternating polaron-charged soliton lattice [128] has been proposed for explaining the metallic properties of heavily doped states. 

It is well known that physical propeities of conducting polymers depend on 

Postscript After the manuscript of this Chapter was completed, a review book treating the polaron/bipolaron in conjugated polymers was published [129], 

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What is the relation between molecular structure and charge transport characteristics, and what is the mechanism of charge transport in such configurations ... 

In this chapter we will attempt to provide a brief but illustrative description of the various aspects of the research and technology of conducting polymers. To appreciate fully the diverse range of operations that these materials may fulfil, it is crucial to understand their basic properties. Therefore, particular attention will be devoted here to the description of the mechanism of charge transport and to the characteristics of the electrodic processes in electrochemical cells. 

Under the advisement of PhD mentor Professor Joseph T. Hupp, the PI successfully used spectroelectrochemical quartz crystal microgravimetry to elucidate the mechanism of charge transport... for both aqueous and nonaqueous sytems. This was the first demonstration of proton-coupled electron transfer at oxide semiconductor interfaces. These findings were then successfully applied to a new interpretation of photoinduced electron transfer at similar interfaces, which are of importance in the field of solar energy conversion. ... 

Another factor that strongly affects the recombination processes is the mobility of charges, or, more generally, the mechanism of charge transport in a particular system. It is normally assumed that the transport of both electrons and cations may be described as ideal diffusion. This assumption is justified in most polar systems, as well as in a part of... 

Having debated the mechanism of charge transport within the polymer film, it is now useful to consider a few examples of chemical applications of polymer modified electrodes. Electrodes coated with [Ru(bipy)2Cl(PVP)]Cl or [Ru(bipy)2(py)(PVP)]Cl2 show strong catalytic effects for the reduction of cerium(IV) and the oxidation of iron(II).52... 

It is important to note the evidence is ambiguous as to the mechanism of charge transport within these materials. It has been noted "that where insulators are concerned the origin of the charge carriers is by no means clear" (23). Possible charge carriers can... 

Refs. [i] Chance RR, Boundreaux DS, Bredas J-L, Silbey R (1986) Solitons, polarons and bipolarons in conjugated polymers. In Skotheim TA (Ed) Handbook of conducting polymers, vol. 2, Marcel Dekker, p 825 [ii] Inzelt G (1994) Mechanism of charge transport in polymer-modified electrodes. In Bard AJ (Ed) Electroanalytical chemistry, vol. 18, Marcel Dekker [iii] Lyons MEG (1994) Charge percolation in electroactive polymers. In Lyons MEG (ed) Electroactive polymer electrochemistry, Parti, Plenum, New York, p 1... 

Impedance spectroscopy (IS) is a measurement of the conductive and dielectric properties of electroactive systems over a wide range of frequencies. Its popularity and applicability has increased dramatically over the past 25 years with the advent of fast-response potentiostats and frequency response analyzers. Impedance spectroscopy has been applied extensively in electrochemistry, especially in battery and sensor research, and it has been used to study active transport in biological membranes. Skin impedance has also been investigated with IS, but many of these studies attempted to correlate impedance with hydration and provided no insight into the mechanism of charge transport. More recent studies have used IS to elucidate the pathways of ion transport through skin, with special emphasis on understanding the mechanism... 

Finally, theoretically insight into the mechanisms of charge transport should continue to improve. This will happen in concert with the development of better experimental probes of the solid state. Better understanding of the structural origins of the exceptional properties of N-polyacetylene is needed, and such work may point the way toward the syntheses of new families of materials. 

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