Conducting polymers electrical neutralization

Because the oxidation potential of the polymer is lower than that of the monomer, the polymer is electrochemically oxidized into a conducting state, kept electrically neutral by incorporation of the electrolyte anion as a counter-ion. This is an essential since precipitation of the unoxidized, insulating polymer would stop the reaction. Both coulometric measurements and elemental analysis show approximately one counter-ion per four repeat units. An important feature is the fact that the polymerization is not reversible whereas the oxidation of the polymer is. If the polymer film is driven cathodic then it is reduced towards the undoped state. At the same time neutrality is maintained by diffusion of the counter-ions out of the film and into the electrolyte. This process is reversible over many cycles provided that the film is not undoped to the point where it becomes too insulating. It is possible to use it to put new counter-ions into the film, allowing the introduction of ions which are too nucleophilic to be used in the synthesis. The conductivity of the film for a given degree of oxidation depends markedly on the counter-ion, varying by a factor of up to 105. 

Suppose that the metal and the semiconductor are both electrically neutral and separated from each other. Since the metal at the electron-injecting contact is assumed to have a low work function, the Fermi energy of the metal lies above that of the semiconductor, close to its conduction band. If the metal and the semiconductor are connected electrically, electrons will flow from the metal to the polymer in order to establish equilibrium, which is obtained when the Fermi energies of the two materials are aligned. Because of this flow of charge, the materials are no longer neutral after electric... 

Electrochemically stimulated conformational relaxation model (ESCR model) — This model [i, ii] describes the relaxation phenomena occurring during the charging and discharging of -> conducting polymers. It assumes that applying an anodic -> overpotential to a neutral conjugated polymer, as a first step, an expansion of the closed polymeric structure occurs. In this way, partial oxidation takes place and counter ions from the solution enter the solid polymer under the influence of an electrical field at those points of the polymer/electrolyte... 

Polaron — Polarons are charged quasiparticles with spin lf. This term has been introduced by physicists as one of the possible solutions to the equations of the relevant defect model of solids in order to describe an electron in a dielectric polarizing its environment (electron-phonon coupling), electrically situated below the conduction band, and transported together with its polarized environment. Polarons and -> bipolarons are the charge carriers in oxidized or reduced (doped) -> conducting polymers. A polaron is defined as a neutral and a charged -> soliton in the same... 

As charges are injected in the chains, electrical neutrality is maintained by counterion insertion in the polymer matrix. In this way conducting polymers resemble intercalation compounds, with the difference that usually the counterions arrange randomly. In some cases, however (more especially in poly acetylene, but also in poly aniline), ordering of the counterions, or stages, has been observed. The ion insertion can thus be compatible with a crystalline structure. It has been observed, however, that the crystallinity is degradated on cycling (see Chapter 12, Section II.C). 

In the crystalline phase, these chains pack in a hexagonal lattice in which the Lf cations are located between the chains to ensure electrical neutrality. These polymers have a conducting core made of Mo and an insulating envelope made of Se, so that they have been compared to molecular electrical wires. These wires bear a nominal charge of =0.5 e /A. Tarascon and coworkers have shown that this material could be dispersed in very polar solvents to yield a suspension of discrete chains [57]. 

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