Oriented Electronically Conducting

PREPARATIVE METHODS AND PROPERTIES OF WELL ORIENTED ELECTRONICALLY CONDUCTING POLYMERS... 

Rotations around torsional barriers induce changes in chain conformation. For conjugated systems like polydiacetylenes, flow-induced changes in chain conformation can have a profound influence on the photon absorption and electronic conductivity properties of the material [73]. Flow-induced changes in molecular conformation form the basis for several technically important processes, the best known examples are the production of oriented fibers by gel spinning [74], the compatibility enhancement [75] and the shear-induced modification of polymer morphology [76]. 

Fig. 25 (A) Tight-binding calculation (dashed) and EHMO (plain) of the electronic conduction, for the naked anthracene (a) when the two NO2 groups are perpendicular to the molecule (b), when one N02 is rotated (c) and when the two N02 are rotated (d). (B) Tunneling current intensity for the NOR gate (a) and the AND gate (b) depending on the orientation angle of the two N02 groups...

The distance between two cluster molecules is 1.3 nm, i.e., between the naked base and apex of gallium atoms of two clusters, whereby two parallel oriented toluene molecules bridge the intermediate space. Although four-point measurements for electrical conductivity in the temperature range 350 K to 2 K have been carried out, the mechanism of electron conductivity cannot be conclusively explained 83 is... 

The electrical properties of the pyrolyzed polymer differ in a number of ways from those of polyacrylonitrile. The overall conductivity increases, while the activation energy of conductivity decreases. A rough correlation is found between a0 and E of equation 15 in that a high a0 was associated with a low E (57). Increasing the degree of orientation causes an increase in conductivity but the activation energy remains unaffected. This is typical of electronic conductivity. 

Modification and functionalisation of natural polyenes, the carotenoids, is an efficient way for the molecular engineering of polyenic chains. Terminal bis-pyridinium carotenoids, termed caroviologens, represent an approach to electron conducting molecular wires (5). Fitting polyconjugated chains with an electron donor group on one end and an electron acceptor on the other end yields push-pull systems of type 1 that may be considered as polarized, unidirectional (oriented) molecular wires and also possess marked NLO properties. 

These polymeric heterocyclic nanotubes and nanowkes have redox properties similar to those of parent, bulk polymers and thek electronic conductivity is enhanced with respect to analogous bulk polymers (due to the preferential orientation of the polymer chains along the fibrils). 

We discuss the interaction of a partially filled electronic conduction band in a segregated donor-acceptor stack system with libra-tional modes of the solid. The orientational Peierls instability predicted by us earlier leads to the formation of chiral charge density waves, which interact and phase-lock below the metal-insulator transition via the Coulomb interaction. The effect of the resulting order on the physical properties of the system and the implications for the understanding of the recent neutron scattering data for the occurrence of several transitions in TTF-TCNQ will be discussed. 

We note at the outset our reasons for believing that orientational modes (librons) couple strongly to the tt electron conduction band ... 

If the electronic correlation between the primary metallic phases could be extended without barriers, there would be a drastic increase in conductivity. This appears to be the case in oriented highly conductive PAc. 

Highly oriented carbon fibers ( graphite fibers ) are a very convenient starting material for preparation of microelectrodes, namely because of their mechanical stability, high electronic conductivity and good biological compatibility. Preparation of encapsulated microdisc electrodes with diameter up to 1 /xm will be discussed. 

The orientation of n-nonoxyethyl octa-substituted liquid-crystalline material was explored by X-ray diffraction. The molecules were found to structurally order in columns such that the macrocyclic planes tilt at an angle of 46° to the columns (Figure 2) The intricacy of the structure was further elaborated for the n-decoxyl derivative. The interfacial porphyrin-porphyrin distance was found to be 3.98 A, and the intercolumn. separation was 23.59 A (Figure 3). This structure has been suggested as a one-dimensional molecular wire motif for electronic conduction. ... 

Built-up multilayers can be obtained only for transfer achieved at a surface far beyond the plateau regime, generally around 35 mN/m. Hence the resulting films are just a disordered superposition of oken monocrystals, with a random orientation in the plane of the support, as shown in Fig. 2b. As a consequence, the normal to the support behaves as an axis of full rotation. Such a macroscopic configuration is easy to investigate. This was done by the use of two different resonance methods, namely, linear dichroism and electron spin resonance, with the following result TCNQ radical anions lie completely flat on the substrate in the dimeric form [9]. Obviously, such a structure is not compatible with an in-plane conductivity, for which TCNQ molecular planes should be perpendicular to the substrate. In addition, the complete charge transfer between pyridinium and TCNQ prevents any kind of electron conductivity in the film and, as expected, the electrical properties of the pristine film are those of an insulator. 

Nevertheless, the hydrothermal method provides nanotubes with different sizes and random orientations, thus hindering the electronic and ionic transport. Hence, it makes necessary the presence of a conductive second phase mix uniformly even if it is present as a nanostructured material. The electron-conductive additive must be intimately mixed or even better, as nanostructured as the active material. Otherwise, the electron transport may remain limited. For this purpose, nanocomposited... 

Heat is developed within the polymer by the imaginary component of the dielectric constant. If the field is allowed to be effective for a very long time, then, because of the poor heat conductivity of the material, the heat produced may not be dissipated and the material may become hot. The imaginary component results from out-of-phase orientation of polar groups in the polymer or from conduction arising from impurities. These impurities must be of an ionic nature, since the conductivity of the polymer depends very much on the temperature. On the other hand, the electronic conductivity varies much less with temperature. Because of the strong... 

---