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The electrochemical properties of poly (3,4-ethylenedioxythiophene) are studied using the bending beam method to detect volume changes during electrochemical transformations of the material. Thin films of poly (3,4-ethylenedioxythiophene) immersed in different supporting electrolytes first contract very rapidly and then expand on doping, while upon undoping they contract directly, or first expand and then contract, to their original positions. It is clearly observed that the oxidation or reduction of the polymer contains two steps, one due to a redox potential close to -0.5 V vs Ag/AgCl, and another potential around 0 V. We find that the volume changes cannot be understood as a simple consequence of ion transport but must be due to the structural change of the polymer between the different states. A hypothetical picture is that during the transition from the neutral to the polaron state, the polymer is slightly charged and thus contracted; on further doping to the bipolaron and to the metallic state, the coulomb repulsion between charged sites become stronger, and the polymer expands.

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Articles you may be interested inLowtemperature deposition of cubic BN:C films by unbalanced direct current magnetron sputtering of a B4C target Effects of nitrogen pressure and ion flux on the properties of direct current reactive magnetron sputtered Zr-N films J. Vac. Sci. Technol. A 13, 2808 (1995); 10.1116/1.579709Preparation and characterization of epitaxial gold films deposited on mica by direct current magnetron sputteringThe effects of growth processes on the chemical bond structure, microstructure, and mechanical properties of carbon-nitride ͑CN x ͒ thin films, deposited by reactive magnetron sputtering in a pure N 2 discharge, are reported. The film deposition rate R D increases with increasing N 2 pressure P N 2 while N/C ratios remain constant. The maximum N concentration was ϳ35 at. %. R D was found to be dependent upon the film growth temperature T s . For a given P N 2 , R D decreased slightly as T s was increased from 100 to 600°C. The variations in R D with both P N 2 and T s can be explained by ion-induced desorption of cyano radicals CN x from both the target and growth surfaces during deposition. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy ͑FTIR͒ analyses showed that N atoms in films grown at T s Ͼ350°C with low nitrogen partial pressures P N 2 , ϳ2.5 mTorr, were bound to C atoms through hybridized sp 2 and sp 3 configurations. For low T s ϭ100°C and higher P N 2 , 10 mTorr, triple-bonded CwN was detected by FTIR. Two types of microstructures were observed by high-resolution transmission electron microscopy, depending on T s : an amorphous phase, containing crystalline clusters for films deposited at T s ϭ100°C, while a turbostraticlike or fullerenelike phase was observed for films deposited at T s Ͼ200°C CN x films deposited a higher T s and lower P N 2 were found to have higher hardness and elastic modulus.

The electronic structure of some poly͑phenylenevinylene͒s have been investigated by resonant and nonresonant x-ray inelastic scattering spectroscopies. The nonresonant as well as all resonant spectra for each polymer demonstrate benzene-like features, indicating a local character of the x-ray emission in which the phenyl ring acts as a building block. Theoretical simulations of x-ray energies and intensities taking the repeat unit as a model molecule of the polymer agree with the experimental spectra fairly well. The edges of the occupied bands have been identified in the nonresonant spectra of each polymer. By subtracting the emission energy of the highest occupied molecular orbital in the nonresonant spectrum from the core excitation energy in the resonant spectrum an alternative way to determine the optical band gap is obtained. As for free benzene the outer band in the polymer spectra show a depletion of the emission going from the nonresonant to the resonant x-ray emission spectra. It is demonstrated that this transition, which is strictly symmetry forbidden for free benzene, becomes effectively forbidden in the polymer case as a result of strong interference effects, and it is argued that this is the general case for resonant x-ray emission of conjugated polymers as far as the frozen orbital approximation holds.