Disordered media, transport

Druger, S.D., Ratner, M.A., Nitzan, A. (1985) Generalized hopping model for frequency-dependent transport in a dynamically disordered medium, with applications to polymer solid electrolytes. Physical Review B, 31, 3939. 

The filled upper and free lower orbitals in PVC belong to the carbazole groups. So one can consider PVC as a disordered organic medium. The side chromophore groups play the role of traps for hopping charge carrier transport. 

The transport properties of such disordered materials (see Section II) are difficult to study, for several reasons. One is that the microscopic theory of transport is not clear even for perfectly ordered CPs, as discussed in the reviews mentioned above. Another is that a dc or low-frequency conductivity measurement on an inhomogeneous material can be viewed as measuring several resistances in series, the larger playing the major role. For instance, in a fibrillar material interfibril transport is important, in a mixed crystalline-amorphous medium the amorphous regions may limit... 

Charlaix et al. (1988) also conducted a study of NaCl and dye transport in etched transparent lattices. A fully connected square lattice with a lognormal distribution of channel widths and a partially connected hexagonal lattice (a percolation network) were considered. They concluded that the disorder and heterogeneity of the medium determined the characteristic dispersion length. From experimental data on the percolation network, they showed that this dispersion length was close to the percolation correlation length, p. 

Vlad, M. O. Moran, R Ross, J. Effective medium approximation of Taylor transport in systems with static disorder././ fiy5. Chem. B 2Wi, 105, 11710-11718. 

A question of great interest is the influence of disorder in the medium on the universality class of dissolved flexible polymers, namely ire the imiversal exponents (1) in this c ise the same as in the pure case The question of how line tr polymers behave in disordered media is not only interesting from a theoretical point of view, but is also relevant for understanding transport properties of polymer chains in porous media, such as an oil recovery, gel electrophoresis, gel permeation chromatography, etc. [14]. 

Since there is no principle difference between an ion and an optically excited yet neutral molecule embedded within a polarizable medium, the disorder concept applies to optical transition to molecular chromophores as well. In fact, the observation of inhomogeneously broadened absorption and photoluminescence spectra is a direct and simple experimental probe of the DOS distribution [14]. For this reason time resolved photoluminescence is a useful analogous tool for checking the validity of concepts for analyzing charge transport in random organics. 

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