Highly anisotropic conducting polymer

Fig. 2.9 shows that in highly oriented and heavily doped r-PA conductivity values in excess of 105 2 1 cm-1 can be obtained. The samples were prepared with care and stretched by a factor 5 so that they were highly oriented. The high conductivity suggests that they are metallic. The metallic nature was confirmed by the 100% reflectivity observed with similar samples. The conductivity is highly anisotropic. With a draw ratio of 15, the ratio cry/a reached value 250. Absorption of light polarized perpendicular to the chains is also small. These observations suggest that the polymers are semiconductors... 

The first method is to manufacture a malleable polymer that can be easily converted into a conjugated polymer. This is done when the initial polymer is in the desired form and then, after conversion, is treated so that it becomes a conductor. The treatment used is most often thermal treatment. The precursor polymer used is often made to produce highly aligned polymer chain which are retained upon conversion. These are used for highly orientated thin films and fibres. Such films and fibres are highly anisotropic, with maximum conductivity along the stretch direction. 

An LCAO (linear combination of atomic orbitals) local-density functional approach was used to calculate the band structures of a series of polymer chain conformations unsubstituted polysilane in the all-trans conformation and in a 411 helical conformation, and all-trans poly(dimethylsilane). Calculated absorption spectra predict a highly anisotropic absorption for the all-trans conformation of polysilane, with the threshold absorption peak arising strictly from polarizations parallel to the chain axis. The absorption spectrum for the helical conformation is much more isotropic. Results for the dimethyl-substituted polysilane chain suggest that the states immediately surrounding the Fermi level retain their silicon-backbone a character upon alkyl-group substitution, although the band gap decreases by I eV because of contributions from alkyl substituent states both below the valence band and above the conduction band to the frontier states. 

Intercalation of electroactive polymers such as polyaniline and polypyrrole in mica-type layered silicates leads to metal-insulator nanocomposites. The conductivity of these nanocomposites in the form of films is highly anisotropic, with the in-plane conductivity 10 to 10 times higher than the conductivity in the direction perpendicular to the film. Conductive polymer/oxide bronze nanocomposites have been prepared by intercalating polythiophene in V2O5 layered phase, which is analogous to clays. °° Studies of these composites are expected not only to provide a fundamental understanding of the conduction mechanism in the polymers, but also to lead to diverse electrical and optical properties. 

A triumph of the Durham route was the preparation of oriented crystalline polyacetylene (107-109) by stretch orientation of the polymer during the transformation reaction. This material has highly anisotropic optical properties, but the anisotropy of the conductivity of the doped polymer was low. Oriented fibers as well as films were prepared. 

Recently anchoring nanosized SnO on anisotropic nanostructures of conducting polymers has attracted much attention, emerging the ID or 2D nanocomposites as high-performed anode materials. Zhang et al. employed a facile two-step electrochemical reaction method including electropolymerization and electrodeposition to fabricate SnO -nanoparticles-decorated PPy nanowires [108]. SEM and TEM reveal that the surface of PPy nanowires was densely coated with SnO nanoparticles (Figure 7.15). 

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