Conducting polymers spin dynamics methods

An intrinsic conductivity determined for the highly doped PANI-PTSA sample at T > 170 K is described by Eq. 15 with /tcOpi, = 0.022 eV (Fig. 12). The value calculated at 300 K, 1.3 X 10 S cm", exceeds the OiD and O3D values assessed above, and indicates that the saturation method cannot be applied for the study of spin dynamics in highly doped polymers. 

In some conductive polymers, pairs of polarons can merge into spinless bipolarons. In this case, the method of spin-label and probe, especially at D-band ESR, seems to be more effective for the study of their structure and dynamics. 

A new method has been recently proposed for spin dynamic studies in conducting polymers [33]. It basically relies on the following. Collisions between moving spins (species A) and unlike spins (species B), instead of giving rise to a motional narrowing, can result in a broadening of the line. Such an effect can be observed in two cases. First, in the slow exchange case, i.e., when the spin flip-flop frequency Larmor frequencies of the two species < Soab = weA Wcb. Second, in the fast... 

As single crystals are not available in conducting polymers, the use of the spin echo technique is more complicated and interpretation of the data is quite model-dependent. However, electron spin echo studies of spin dynamics in polyacetylene were reported in the early 1980s [30]. The results on the soliton diffusion rate, which were not consistent with those obtained by the other methods, gave rise to a long controversy. They were recently carefully discussed and invalidated [31]. 

After more than 15 years of use and development, spin dynamics has proved to be an efficient method for transport property studies in conducting polymers. Numerous novel results have been obtained that would not have been obtained by conventional methods. 

There has been extensive effort in recent years to use coordinated experimental and simulation studies of polymer melts to better understand the connection between polymer motion and conformational dynamics. Although no experimental method directly measures conformational dynamics, several experimental probes of molecular motion are spatially local or are sensitive to local motions in polymers. Coordinated simulation and experimental studies of local motion in polymers have been conducted for dielectric relaxation,152-158 dynamic neutron scattering,157,159-164 and NMR spin-lattice relaxation.17,152,165-168 A particularly important outcome of these studies is the improved understanding of the relationship between the probed motions of the polymer chains and the underlying conformational dynamics that leads to observed motions. In the following discussion, we will focus on the... 

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