This thesis reports the results of electroabsorption measurements undertaken on three materials that are all, to some degree, conjugated: polymeric and oligomeric emeraldine base, and polysquaraine. The aim of these experiments has been to investigate the nature of the optical excitations occuring within the materials. Electroabsorption (EA) spectroscopy involves the measurement of the change in absorption coefficient of a material with the application of an external field. The fields required are high and the resulting signals small, hence to perform such experiments a dedicated spectrometer was constructed. To achieve high sensitivity lock-in amplification techniques were used, and the sample kept at low temperatures. Such techniques resulted in the spectrometer being able to resolve changes in absorption of the order 1 in 5x10(^7).The sample configuration consisted of thin films of the materials which were spun coated onto sapphire substrates, with interdigitated gold electrodes deposited on top. This configuration allowed the absorption of the material to be measured while alternating fields of up to 200 kVcm(^-1) were applied. The EA data of the oligomeric and polymeric emeraldine base are seen to closely resemble each other - indicating that the same photoexcitation processes are occurring. Using existing theories the spatial extent of the 2 eV excitation is calculated as -0.4 nm, i.e. greater than one phenyl ring repeat unit. This is consistent with previously suggested models of 2 eV photoexcitation in emeraldine base. Similar calculations suggest a spatial extent of the 4 eV transition of -0.25 nm, i.e. restricted to one phenyl ring. A feature in the EA spectra of the oligomeric emeraldine base has been observed at 1.35 eV - below the onset of linear absorption, and it is suggested that this may be evidence of a normally one photon forbidden transition becoming allowed in the presence of an external field. Due to the fully conjugated nature of polysquaraine a different model has been used to interpret the EA spectrum. An energy level scheme for the material is suggested, including the possible location of a normally one photon forbidden transition at 1.75 eV.

Polyaniline was chemically synthesized at three different temperatures of 25, 0, and -25oC, by oxidative polymerization with ammonium peroxidisulfate at equimolar of aniline to oxidant ratio and 1M HCl. The resulted polyaniline was in a powder form which was characterized by several techniques such as: electrical conductivity, elemental analysis, thermal analysis, wide-angle X-Ray diffraction, and scanning electron microscope. The solution properties of the reduced polymer were studied by viscometry, static and dynamic light scattering. It was found that as the polymerization temperature decreased, the molecular weight, crystallinity, and thermal stability of polyaniline increased, while the electrical conductivity was independent of the polymerization temperature. Moreover, the morphology of the polymer was changed from granular to tubular with reducing polymerization temperature. Viscometry and static light scattering showed that polyaniline has a flexible random coil conformation when dissolved in N-methyl-2-pyrrolidinone which proved to be a good solvent for this polymer. Dynamic light scattering indicated that the polymer solution is a polyelectrolyte with high hydrodynamic radius at low polymer concentrations. All mechanical features except Young&#039 / s modulus of polyaniline-filled low density polyethylene composites became poorer as polyaniline content increased. Moreover, a sudden increase in the electrical conductivity with increasing polyaniline contents was also observed. The conductivity of the tubular composites of multi wall nanotubes (MWNTs)-filled polyaniline increased with increasing MWNTs loading, and became weakly temperature dependent. The morphological analysis indicated that the MWNTs were well dispersed and isolated, and the tubes became crowded proportionally to MWNTs weight percent used in the composites.