Conducting charge-transport theories: soliton

For charge transport along chains with conjugated double bonds the mechanism of soliton motion has been proposed (this would be a theory for R-j in the terminology of the previous section). If the conjugation defect of Fig. h is called soliton , this term is used to stress two features of this defect it does not disperse while it moves (just as solitary water waves do not disperse. This is where the name comes from) and it has certain symmetry properties. If most polymer chains in today s polyacetylene films are very short, solitons will not be able to move very far since they are confined to the polyene chains. Therefore the non-dispersivity will be hard to test. In addition solitons will not be important for electrical conductivity under these circumstances. 

One attractive aspect of the soliton theory of charge transport is that the carriers (cations or anions) carry no spin, i,e, the conducting compositions do not contain unpaired electrons, ESR experiments on the doping of PA(49) show that in certain intermediate doping regimes the spin concentration is much lower than expected from the observed conductivity values this phenomenon is referred to as spinless conductivity. If the conduction involved a normal process of defect-induced hole or electron transport, there would be a direct correlation between ESR determined spin concentration and conductivity. The same conclusion of spinless conduction is obtained from ESR experiments on doped PPP(61) however the soliton theory is not applicable to the PPP system(25). In Section VII, we present an alternate transport mechanism based on bipolarons (dications or dianions) which is applicable to all conducting polymer systems(26),... 

The dimensional structure of these materials. If we consider that there is no reticulation, these materials can appear one-dimensional in relation to both charge transfer and vibrational energy. This apparent anisotropy should be considered only local (at a short distance) because the study of conduction phenomena shows an isotropy of transport properties, which is quite well explained with the theory of interchain hopping mechanisms (Kivelson model [22] for solitons polaron lattice introduced by Bredas and coworkers [23,24]). 1 will show that the heterogeneous polymers model may also be used. 

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