Conducting polyaromatics

To clarify the discussion further concerning conducting polyaromatics, it is worthwhile to elaborate on some principles described by the valence-bond (VB) theory. The ideas of the (VB) (resonance) theory are found to be of aid to organic chemists for rationalizing in a simple manner the facts of organic structure and reactions. However, quantitative application is much harder for the VB method than for the molecular orbital (MO) method. Indeed, for quantitative calculations, the MO method has overshadowed the VB method. The main advantage of the VB method is that it is based on the familiar chemical ideas of bonding and structure [1050]. 

Polyaromatic sodium lignosulfonate and sulfur lignin resin can be made conducting by doping. The conductivity increases by several decades through doping with electron acceptors and donors as shown in Table IV. 

Figure 11 Selected literature data for proton conductivity as a function of inverse temperature. Imidazole-intercalated sulfonated polyaromatic polymer (IISPAP) Ba2YSn05 5 (BYSO) Ba3Cai igNb 1.82O8.73 (BCN18), the curve for Y BaCe03 is a calculated estimate. The interpretation of the conductivity of Gd BaPr03 as protonic is somewhat ambiguous at present. For further explanation and discussion, see Ref 119. (Reprinted from Ref 119 1999, with permission from Elsevier)...

Carbon black is produced industrially in the form of different products (e.g., furnace black, thermal black, channel black, lampblack, acetylene black) with specific properties. In addition to the relevance of carbon black for basic research on adsorption, or as a reference sohd, appUcations of this material in fields such as elastomer reinforcement, as modifier of certain properties of plastics (UV protection, electrical conductance, color), or as xerographic toners make its surface and interfacial properties extremely important. Soot is a randomly formed particulate material similar in nature to carbon black. The main (pragmatic, rather than conceptual) difference between these two carbon forms is that soot is generally formed as an unwanted by-product of incomplete combustion of pyrolysis, whereas carbon black is produced under strictly controlled conditions. Bansal and Donnet [78] have reviewed various possible mechanisms for the formation of soot and carbon black. Soot can retain a number of tars and resins on its surface. There is therefore some interest in studying the adsorption of polyaromatic hydrocarbons in soots, especially those of environmental significance such as diesel soot. 

In addition to the above-mentioned conventional polymers, several interesting developments have taken place in the preparation of nanocomposites of MMT with some specialty polymers including the N-heterocyclic polymers like poly (N-vinylcarbazole) (PNVC) [32, 33], polypyrrole (PPY) [34, 35], and polyaromatics such as polyaniline (PANI) [36-38]. PNVC is well known for its high thermal stability [39] and characteristic optoelectronic properties [40-43]. PPY and PANI are known to display electric conductivity [44-46]. Naturally, composites based on these polymers should be expected to lead to novel materials [47,48]. 

The CP/MAS - NMR spectroscopy cannot distinguish between the ole-finic and the aromatic carbons, since signals due to these types of carbons appear in the same region of the spectra. This difference can be detected by UV-VIS. Certain types of coke, such as conducting coke or very slowly relaxing polyaromatics are not always fully detected by CP/MAS - NMR spectro-scopy ... 

Conductive conjugated polymers belonging to polyenes or polyaromatics, such as polyacetylene, polyanUine (PANl), polypyrrole (PPy), polythiophene, poly(p-phenylene), and poly(phenylene vinylene) classes, have been investigated extensively [1-3]. PANI and PPy families of conjugated polymers are of much interest due to their low cost, easy synthesis, unique conduction mechanism, good stability and environmentally benign performance [4,5],... 

Organic impurities are mainly polyaromatic hydrocarbons (PAHs) (Taylor et al., 1980). They correspond to partially unconverted fuel that has been readsorbed onto carbon black. These PAHs are present at a very low content and, because of their firm adsorption on carbon black, the extraction must be conducted in a Soxhlet apparatus with a strong solvent (toluene) and at high temperature (80°C). However, it has been demonstrated that organic impurities have no significant effect on carbon black reinforcement (Custodero et al., 1992). 

Figure 4.3. Conductivity of Nafion and a sulfonated polyaromatic membrane as a function of water content [33] at room temperature (left) and conductivity dependence on temperature and relative humidity for the E-form of Nafion [34] (right).

Often, as in Figure 4.3b, the conductivity is measured as a function of the activity of the solvent with which the membrane is equilibrated. In order to relate these measurements to the actual water content, one can use experimentally determined sorption isotherms as shown in Figure 4.4 for Nafion and a sulfonated polyaromatic membrane. The sorption isotherms will be revisited in more detail to discuss their critical role in membrane transport models [21]. 

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