F. Genoud

The effect of the oxidation conditions on the chemical polymerization of polyaniline

Abstract Chemical polymerization of aniline with four oxidizing agents ((NH4)2S2O8, H2O2, K2Cr2O7 and KIO3) was studied in HCl solutions. It was established that the redox potential of the oxidizing agent is not a dominant parameter. Products of similar quality have been obtained with (NH4)2S2O8, K2Cr2O7 and KIO3. However, KIO3 seems the most convenient, because it yields good quality samples in a wide range of polymerization conditions.

Polarons, bipolarons and charge interactions in polypyrrole: Physical and electrochemical approaches

A quantitative study of polaron and bipolaron formation in polypyrrole upon electrochemical doping is presented. The steady-state spin concentration has been measured as a function of the electrical potential in an in situ ESR-electrochemical experiment and the charge injection has been determined by coulometry and by optics. The data are analysed from both physical and electrochemical points of view. It is shown that the energy for creating a bipolaron is about the same as for creating two polarons. The non-Nernstian behaviour that is observed for the redox process is explained by the introduction of interparticle charge repulsion interactions. The shape of these interactions is specified.

Polyaniline: A material still under discussion

Abstract Several studies ( 13 C NMR, vibrational spectroscopy, acidic titration, etc.) have been considered in this coherent description of the structure and the chemical composition of polymers of the polyaniline family. Among the different processes (oxidation, protonation, etc.) which relate the five polymers of this family, three are characterized by insulator-to-conductor transitions. The chemical aspects of these processes are explained in the framework of the preceding descriptions. Then, the variation of the magnetic and transport properties related to these transitions, as well as the models which have been proposed to account for these properties, are discussed. Special attention is paid to the problem of homogeneity of the material, after different types of doping.

On the nature of the conducting state of polyaniline

Abstract The role of disorder in the polyaniline properties is emphasized. Evidences are given against a true metallic state: the presence of two types of acidic functions is not compatible with a regular periodic lattice; the spin dynamics behavior reflects incoherent carrier motion. Pulse and CW ESR data are consistent with high spin concentration clusters (conducting islands), and it is concluded that a conducting island just consists of a single conducting polymer chain.

ESR investigation of polarons and bipolarons in conducting polymers:: the case of polypyrrole

Abstract In situ ESR-electrochemical experiments in conducting polymers are presented. Spin concentration has been measured as a function of doping level. Quantitative data are presented for the case of polypyrrole. Analyses of the data in terms of quasiequilibrium polaron and bipolaron populations with different models -Nernst law, “box” model including charge interactions, and complete mechanical statistics derivation- lead to the convergent conclusion that polarons and bipolarons are nearly degenerated and undergo important inter-particle charge interactions.

Alternate copolymers of head to head coupled dialkylbithiophenes and oligoaniline substituted thiophenes: preparation, electrochemical and spectroelectrochemical properties

New processable, electroactive, alternate copolymers consisting of dialkylbithiophene units and oligoanilinethiophene units have been prepared by post-polymerization functionalization of a specially prepared precursor polymer, namely poly[(4,4″-dioctyl-2,2′∶5′,2″-terthiophene-3′-yl)ethyl acetate], carried out via its hydrolysis and consecutive branching aniline dimer or tetramer through the amidation reaction. The precursor polymer is interesting by itself because it gives a very clear spectroelectrochemical response over a very narrow potential range. The proposed method enables the preparation of regiochemically better defined alkylthiophene-oligoanilinethiophene copolymers with higher content of oligoaniline side groups as compared to previously used methods. Cyclic voltammetry investigations combined with UV–vis–NIR, EPR and Raman spectroelectrochemistry show that both the oligoaniline side groups and poly(thienylene) main chain are electrochemically active. Significant differences for the side group electrochemistry are observed in acidified and nonacidified electrolytes making the prepared new copolymer a good candidate for electrochromic applications in diversified electrolytes.

Highly conductive composites of polyaniline with plasticized cellulose acetate

Abstract Highly transparent, conductive blends can be prepared from plasticized cellulose acetate and polyaniline protonated with sulphonic acids, phosphonic acids and phosphoric acid diesters. Films cast from m-cresol solution exhibit percolation threshold below 0.5 wt% and excellent mechanical properties of plasticized cellulose acetate.

Grafting of oligoaniline on CdSe nanocrystals: spectroscopic, electrochemical and spectroelectrochemical properties of the resulting organic/inorganic hybrid

We have synthesised a new organic/inorganic hybrid, in which electroactive aniline tetramer is grafted on the surface of quasi-monodispersed CdSe nanocrystals. The grafting reaction consists of two steps. First initial nanocrystal surface ligands (TOPO) are exchanged for 4-formyldithiobenzoate linker ligands, which contain an anchor function (the dithioate group) and an aniline grafting function (the aldehyde group). The condensation reaction between the primary amine group of aniline tetramer and the aldehyde group of the linker ligand results in the grafting of the former with simultaneous formation of an azomethine linkage between both reagents. The grafting reaction is nearly quantitative as demonstrated by 1H NMR, FTIR and XPS studies. Voltammetric, UV-visible and EPR spectroelectrochemical studies of the hybrid compound show that after the grafting process the polyconjugated molecule retains its electrochemical activity i.e. electrochemical switching between the completely reduced state (leucoemeraldine), the semi-oxidised state (emeraldine) and the completely oxidised state (pernigraniline) is possible.

Simultaneous “In situ” conductivity and ESR measurements: evidence for spinless conducting state in polyaniline

Abstract In conducting polymers the correlation between spin concentration and conductivity is of great interest to describe the nature of the conducting state. In the present work we report and discuss recent results obtained from “in situ” conductivity and ESR measurements on polyaniline during electrochemical doping of the polymer. The spin susceptibility in the conducting state depends on the mode of sample preparation. Observation of spinless conductivity is reported.

Spin susceptibility in polyaniline: Temperature and doping dependence

Abstract Using a special electrochemical cell compatible with an ESR variable temperature insert, the temperature dependence of the spin susceptibility of polyaniline films has been measured for different doping levels. It is shown that in the conducting Emeraldine Salt the spin susceptibility decreases, with in particular zero Pauli susceptibility. The data of the spin suscpetibility versus doping are compatible with a polaron/bipolaron equilibrium, with a polaron concentration being essentially temperature independent.