2 - Technologies

Electrosynthesis of electroconducting conjugated polymers (ECPs. Details are described on polypyrrole example.

The current is proportional to the anion concentration caused by different chemical reaction. Changing the current the number of counterions changes. The doping/dedoping mechanism is a two-way reaction. We could define either p and n type doping. Polypyrrole is a p-type semiconductor

Electroconducting polymers concerned here are not composite plastics filled with conductive particles, but organic materials that exhibit intrinsic electronic conductivity, reflecting their delocalized electronic structure along the conjugated backbone. Polyacetylene, polyaromatic and polyheterocyclic chains can provide such a structure (see Figure 1). Macroscopic conduction through these polymers takes place by charge hopping both along the polymer chains and also between the macromolecules that make up individual fibres and between the fibres themselves. However, in the neutral (undoped) state these materials are only semiconducting. The electronic conductivity appears when the material is doped, i.e., when electrons or holes are injected into the superorbital. For reasons of electroneutrality, counter ions called dopants are simultaneously inserted into the polymer matrix. Conductivity can be varied in a wide range this way (Figure 2). Film deposition possibility using electrosynthesis (see animation): the electrochemical oxidation of a monomer solution (pyrrole, thiophene or aniline derivatives under appropriate conditions gives a doped conductive polymer film deposited at the surface of the electrode. The control of the growth rate and film thickness is simply achieved by counting the electrical charge used for the synthesis. The doping/dedoping mechanism is the possibility to associate ionic movements stoichiometrically with electrical currents.