Free-standing Polypyrrole Films Research Articles

Optical studies on free-standing polypyrrole films by the photopyroelectric method

Optical spectra of free-standing polypyrrole films were investigated by a novel PhotoPyroElectric (PPE) method. The reflection and absorption spectra in the range 2000–25000 cm−1 of TsO−- and ClO4su−-doped polypyrrole films were obtained with an experimental setup comprising two pyroelectric sensors. The absorption bands due to electronic transitions to the bonding and antibonding bipolaronic levels appear at 11 000 and 21 500 cm−1, respectively. Some relevant details in the polypyrrole spectrum in the 2000–5000 cm−1 range were observed. The absorption band located at 3400 cm−1 is characteristic for NH stretching vibration. The bands in the 2300–2500 cm−1 range are ascribed to the vibration of N+H groups containing positively charged nitrogen. The PPE spectra also reveal changes of the electronic and vibrational absorption bands after polymer reduction and HCl treatment.

Electron irradiation and microstructure in polypyrrole

Free-standing films of polypyrrole have been electrochemically synthesized from solutions of pyrrole andp-toluene sulphonate in water. The resulting polymer was exposed to a variety of electron-beam conditions in an analytical scanning transmission electron microscope and the interaction between the electron beam and the sample was investigated by elemental X-ray spectroscopy and electron diffraction. In transmission mode, with an 80 kV beam, the films were found to be stable with respect to the production of sulphur X-rays for up to 500 live seconds. Molecular ordering was observed to be destroyed by the action of the beam. Such techniques, together with X-ray scattering, were subsequently utilized to examine spatial variations in molecular trajectory and counter-ion content; these variations were found to be associated with the nodular surface structure that characterizes polypyrrole.

Properties of composite membranes from ion exchange membranes and conducting polymers—I. Conductivity of composite membrane from cation exchange membranes and polypyrrole

In order to prepare a free-standing polypyrrole film with high mechanical strength, Fe(III) form of Cu(II) form cation exchange membranes were immersed in an aqueous pyrrole solution. Polymerization speed of pyrrole in the Fe(III) form membrane was faster than that in the Cu(II) form membrane. A linear relationship was observed between conductivity of the composite membrane and immersion period in the pyrrole solution. Conductivity of the composite membrane from the Fe(III) form membrane reached about 10 −3 S cm −1, which was the ultimate value of this method. Properties of formed polypyrrole in the membrane matrix was discussed in relation to weight increase of the membrane and species of oxidative cation. Burst strength of the composite membrane increased with increasing polymerization period of pyrrole.

Influence of inserted anions on the properties of polypyrrole

Selected properties of supported and free-standing polypyrrole films have been studied as a function of the anion, incorporated in the polymer during electrochemical polymerization. The anion was varied in the range: Cl −, ClO − 4, benzenesulfonate (BS), toluenesulfonate (TOS), 1,3-benzenedisulfonate (BDS) and 1,3,5-benzenetrisulfonate (BTS). The degree of oxidation of polypyrrole as determined by elemental analysis, varied from ca 0.50, when Cl − or ClO − 4 is used, to ca 0.30 for the “organic” anions. Electron micrographs of the films show an increasing smoothness of the films with increasing charge of the ions. The electrical conductivity of free-standing films shows the highest value for the BTS-containing films and decreases in the series: BTS > TOS > BS ⋍ BDS > Cl − ⋍ ClO − 4. The reduction and re-oxidation of thin supported films is a slow process for TOS- and BS-containing films. In these cases, the rate of the process is determined by the diffusion of the anions in the film from Q— t 1 2 plots; diffusion coefficients of 4.3 × 10 −11 cm 2 s −1 for TOS and 4.8 × 10 −11 cm 2 s −1 for BS can be calculated. For Cl − and ClO − 4 containing films, the process is faster and determined by the transition of the polymer from the oxidized to the reduced state (or vice versa). From the linear part of the Q— t 1 2 curves a diffusion coefficient of 3.1 × 10 −9 cm 2 s −1 for Cl − and 3 × 10 −9 cm 2 s −1 for ClO − 4 can be estimated. Also for films containing BDS and BTS ions, the process seems to be determined by the transition of the polymer, instead of by the diffusion of the ions. The differences in behaviour between the various organic ions are explained in terms of a more or less polar character of the ions. Ellipsometric experiments, carried out in ClO − 4 and toluenesulfonate solutions, support the observed differences in behaviour during reduction and re-oxidation of the polymer films.

Electrocatalytic formation of conducting polymers in aqueous solutions

A novel catalytic electrodeposition of several kinds of conducting polymers in aqueous solutions is described. The anodic deposition potentials of pyrrole, N-methylpyrrole and aniline were shifted cathodically by 140–200 mV in the presence of tiron (4,5-dihydroxy-1,3-benzenedisulfonic acid) as a catalyst in the reaction mixture. The catalytic deposition of polypyrrole and polyaniline, and the composition of the produced films, were investigated. The conductivity of the catalytically prepared free-standing polypyrrole films was smaller than that of the directly prepared films. This one-step process was used to produce films holding anions (such as carboxylates) which cannot play the role of dopant in the direct oxidation of the monomer, and thus, to simplify the preparation of drug-loaded conducting polymers for a drug release device.

Catalytic electrosynthesis of conducting polymers

A novel catalytic electrodeposition of several kinds of conducting polymers in aqueous solutions is described. The anodic deposition potentials of pyrrole, N-methylpyrrole and aniline were shifted in the negative direction by 140–200 mV in the presence of tiron (4,5-dihydroxy-1,3-benzenedisulfonic acid) as a catalyst in the reaction mixture. The catalytic depositions of polypyrrole and polyaniline, and the compositions of the produced films, were investigated. The conductivity of the catalytically prepared free-standing polypyrrole films was smaller than that of the directly prepared films. This one-step process was used to produce films holding anions (such as carboxylates) which cannot play the role of dopant in the direct oxidation of the monomers, and thus to simplify the preparation of drug-loaded conducting polymers for a drug release device.