Interchain electronic processes

Similar to the case of transition to supersonic velocities discussed above, this interchain transport process is also nonadiahatic. To pass through the barrier, the electron has to undergo an electronic transition from the polaron level localized to chain 1 to the TT -level localized to chain 2. The energy needed for this transition, the activation energy, is taken from the phonon system. Actually, the process is very similar to that treated by the Holstein theory discussed in Section 2.2 the electronic coupling between the chains is weak enough to force the electronic states to localize on individual chains. 

Not only are the solitons highly mobile, but in addition the motion is highly one-dimensional. Since Ti" throughout the experimental frequency range, the cutoff frequency is smaller than the smaller frequency used, that is, < 6 x 10 rad/s. Estimates of Wc have been obtained from Tip measurements (wc 4.5 x 10 rad/s), from the residual (diffusive) ESR linewidth (Wf 3 X 10 rad/s) [25], and from the data of AH versus (o [o>c (6-8) X 10 rad/s] [57]. The cutoff frequency (i)c is an upper limit for the transverse diffusion rate D , but that may be due to another process more efficient than transverse soliton diffusion. The interchain electronic dipole-dipole interactions are large enough to account for the observed o)c- In fact, owing to the actual nature of the soliton-like species, namely (CH), seg-... 

At higher polymer concentration, an interchain interaction yields aggregation [42] or the lamellar structure similar to the comblike one in the solid state [182]. If the electronic processes are studied in the semidilute solution, the interchain carrier transport in the solution is expected to be detected and compared with that in the solid state (refer to section 2.3.2). Moreover, the intrachain carrier transport in heavily doped polymers in the dilute solution is also of great interest. The change in the electronic state or in the Coulorabic repulsion between carriers may well affect the intrachain carrier transport as well as the conformation of the polymer chain [28]. 

Later we will describe both oxidation and reduction processes that are in agreement with the electrochemically stimulated conformational relaxation (ESCR) model presented at the end of the chapter. In a neutral state, most of the conducting polymers are an amorphous cross-linked network (Fig. 3). The linear chains between cross-linking points have strong van der Waals intrachain and interchain interactions, giving a compact solid [Fig. 14(a)]. By oxidation of the neutral chains, electrons are extracted from the chains. At the polymer/solution interface, positive radical cations (polarons) accumulate along the polymeric chains. The same density of counter-ions accumulates on the solution side. 

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