Intrachain carrier conduction

Metallic properties are also observed in columnar stacked complexes in which the intrachain separation is too long for conduction to be associated with the formation of a band from overlap of the metal dz2/pz orbitals. For these complexes the conduction process involves carriers present in the delocalized MOs extending over die whole complex. The conduction process in these compounds may be described by a hopping mechanism in which the on-site Coulomb repulsion energy has been reduced by the delocalization of the charge over the whole molecule. 

Electrical conductivity in PPy involves the movement of positively charged carriers and/or electrons along polymer chains and the hopping of these carriers between chains. It is generally believed that the intrachain hopping resistance is much greater than the interchain transport resistance. 

Both coil and linear or expanded-coil conformations exist in untreated PEDOT-PSS films, whereas the linear or expanded-coil conformation becomes dominant in high-conductivity PEDOT-PSS films. This conformational change results in an increase in the intrachain and interchain charge carrier mobility, so the conductivity is enhanced. ... 

We previously noted that both intrachain and interchain transport of carriers mdst be considered when examining the electronic conductivity of conjugated polymer materials. We now describe a theoretical model recently developed by Pearson and coworkers that can be used to examine the effect of polymer molar mass and polymer orientation on the conductivity behavior of conjugated polymer materials. 

The mechanisms by which these polymers conduct electricity have been a source of controversy ever since conducting polymers were hrst discovered. At first, doping was assumed to remove electrons from the top of the valence band, a form of oxidation, or to add electrons to the bottom of the conduction band, a form of reduction. This model associates charge carriers with free spins, unpaired electrons. This results in theoretical calculations of conduction that are much too small (59). To account for spinless conductivity, the concept of transport via structural defects in the polymer chain was introduced. From a chemical viewpoint, defects of this nature include a radical cation for oxidation effects, or radical anion for the case of reduction. This is referred to as a polaron. Further oxidation or reduction results in the formation of a bipo-laron. This can take place by the reaction of two polarons on the same chain to produce the bipolaron, a reaction calculated to be exothermic see Figure 14.17 (55). In the bulk doped polymer, both intrachain and intrachain electronic transport are important. 

Figure 6 also shows the contribution of both ID and 3D polaron motions to the ac conductivity of the laser-modified PATAC. Its intrachain conductivity Oid was interpreted in terms of the model of the charge-carrier scattering on the lattice optical phonons proposed by Kivelson and Heeger for metal-Uke clusters in conjugated polymers, ... 

If the conducting polymer is dilutely dissolved in a solvent and an average separation among the polymer chains is larger than their hydrodynamic diameters [13], the interchain mode is completely inhibited, but the intrachain one still contributes to the electric transport (Fig. 17b). As a result, we can exclusively obtain information on the single-chain phenomena, specifically on the intrachain transport process of the electronic carriers. It is to be noted that the electric polarizability should be measured instead of the conductivity to detect the intrachain mode based on carrier transport restricted within a contour length of a polymer chain. 

---