Jacob S. Shapiro

Comparison of electronic transport in polyaniline blends, polyaniline and polypyrrole

Abstract The conductivity of PAni/PETG copolyester blends shows the expected reduction compared to unblended PAni, but PAni/PMMA (and PAni/PVC blends at lower temperatures) show a larger conductivity. SEM images indicate that the different behaviour of the blends appears to be associated with greater granularity retained by the PAni particles dispersed in PETG. The conductivities of the more highly conducting PAni blends, like PAni-CSA and its blends with PMMA measured by other authors, show a change to metallic sign for the temperature dependence near room temperature — simple models combining hopping/tunnelling with metallic conduction are consistent with the conductivity except at very low temperatures. The thermopower of PAni blends shows a remarkable similarity for blends with different insulating polymers and widely varying conductivity. For polypyrrole samples of very different conductivity, the change to metallic sign for conductivity near room temperature does not occur, indicating a much smaller ‘metallic’ resistance contribution. Nevertheless, the thermopower of polypyrrole, like that of PAni and PAni blends, is of metallic size and generally increases with temperature, as expected for metallic diffusion thermopower.

Morphological investigation by atomic force microscopy and light microscopy of electropolymerised polypyrrole films

Abstract Use of atomic force microscopy (AFM) together with light microscopy (LM) provides an ideal opportunity for studying the initial growth of wrinkles on polypyrrole films. In situ experiments, where continuous AFM image data acquisition was carried out during growth of thin polypyrrole films on indium–tin oxide (ITO) anodes, proved unsuccessful because the height changes occurring during the deposition proved to be too large to handle by the instrument cantilever and fell outside of the range of the z-piezo transducer. However, ex situ experiments have yielded valuable information on the earliest stages of film formation. Parallel in situ experiments where growth was followed by dynamic light microscopy imaging complemented the AFM study to yield a clear picture of the mechanism of formation of wrinkles. Additionally, the experiments confirmed that wrinkles are an integral part of the film and are not an artefact induced in films, consequent to shrinkage or drying out.

Some insights into the microstructure of polypyrrole

Abstract Estimation of the molecular weight between crosslinks and determination of the average conjugation length in polypyrrole are reported. By applying the Flory equation to dimethylsulphoxide-swollen dedoped polymer, it was found that the molecular weight between crosslinks is larger than previously thought and lies in the range of 25–65 pyrrole units. U.v. and resonance Raman spectroscopy indicate that the average conjugation length is short. The upper limit is about 6 pyrrole units.

A morphological study of polypyrrole films grown on indium-tin oxide conductive glass

Abstract In this study a detailed examination was carried out of variables that control the winkle morphology observed in p-toluenesulfonate doped polypyrrole films formed by electropolymerization on tin-doped indium oxide (ITO) coated glass using either methanol/water or water alone as solvents. Results are in agreement with an earlier study in which the porous nature of the substrate was identified as the most influential of the factors controlling the morphology. Other factors found to be important included: nature and size of the dopant ions, solvent, and concentrations of pyrrole and dopant. Examination of still-moist free-standing conductive films by light microscopy demonstrated that the wrinkles are not an artifact due to post-deposition shrinkage.

Investigations of the feasibility of constructing a polypyrrole-mercury/mercury chloride reference electrode

Abstract A polypyrrole-mercury/mercury chloride reference electrode was initially constructed by in situ electropolymerization of pyrrole on a mercury pool anode in a 0.5 M sodium para-toluene sulfonate and 1.0 M sodium chloride mixture solution. However, in this procedure, insufficient amount of mercury was incorporated in the polypyrrole film for reaction with chloride ions to yield a mercury/mercury chloride half cell. Alternatively, a polypyrrole film was galvanostatically deposited on a glassy carbon electrode in the presence of sodium para-toluene sulfonate. Mercury was electrochemically deposited from mercury(I) nitrate at the polypyrrole-coated electrode. The resulting film was deprotonated in 5 M NaOH. Cyclic voltammetry was then carried out in 10 M HCl in order to exchange the para-toluene sulfonate ions with chloride ions and to oxidize mercury for the formation of mercury chloride within the film. A reproducible null potential difference was obtained when the polypyrrole-mercury/mercury chloride electrode was employed as an indicator electrode against a saturated calomel reference electrode in saturated potassium chloride solution.

Morphology of polypyrrole films grown in thin-layer cells and on indium-tin oxide conductive glass

Abstract Examination by atomic force microscopy and scanning electron microscopy of the non-conducting substrate poly(methyl methacrylate) and the polypyrrole free-standing film formed at its surface in a thin-layer cell has led to an understanding of how such films may be formed. A mechanism is proposed for the origin of the wrinkle morphology observed in thin-layer cells under certain conditions, and attention is drawn to its similarity to the morphology of polypyrrole films formed on indium—tin oxide glass electrodes. In both cases it is proposed that the porous surface of the substrate on which the film grows acts as a template for nucleation sites.

Degradation of oriented poly(vinyl chloride) films in the presence of metal chlorides

Abstract Films of poly(vinyl chloride) containing added stannous chloride and stretched at 90°C to elongations up to 600% discolour, in shades from purple to grey, when heated at 110°C. The electronic and resonance Raman spectra of such films show characteristic features, which are a function of sample preparation conditions, particularly the time of annealing at 110°C. Resonance Raman spectra show the presence of conjugated polyene sequences, as long as 30 units for the most extensively annealed samples. The electronic spectra are not explicable on this basis, and are probably indicative of a polyene-metal salt complex of the type proposed by Owen and Msayib in the case of poly(vinyl chloride) thermally decomposed in the presence of zinc chloride. Substitution of zinc chloride for stannous chloride with the present degradation conditions gives very similar electronic spectra, though substantially different from those reported by Owen and Msayib. This result is tentatively explained in terms of the very different degradation conditions.

Formation of surface-modified polypyrrole films by electropolymerization on non-conducting solid surfaces

Abstract Deposition of polypyrrole tosylate, synthesized potentiostatically with values of 0.5–0.8 V (relative to a standard calomel electrode) from an aqueous solution, on a solid non-conducting surface in a specially designed thin-layer cell led to the observation of two-dimensional growth of the film directly adjacent to the surface, reverting to three-dimensional dendritic growth as the film thickness increases. The significance of the two forms of morphology is discussed.

Wrinkle morphology of polypyrrole films grown in thin-layer cells

Abstract A study of polypyrrole films grown on poly(methyl methacrylate) surface in thin-layer cells and on ITO has shown that a common morphology is found in both types of films. It is proposed that the porous nature of the growth surface in each case acts as a template, leading to the observed wrinkle morphology.

Analysis of the kinetics of the thermal decomposition of poly(1,6-bis-N-carbazolyl-2,4-hexadiyne) obtained using thermogravimetric analysis

Abstract The thermal decomposition of crystalline poly(1,6-bis-N-carbazolyl-2,4-hexadiyne) was examined by thermogravimetric analysis (t.g.a.) using both isothermal and temperature-programmed methods over a temperature range of 400–600°C. Extents of decomposition versus time data were fitted to an Avrami-Erofeyev equation with the exponent equal to three. Two consecutive processes were observed, each with its own Arrhenius parameters. An independent study, reported by us elsewhere, involving a flow system, leads to results consistent with the parameters obtained by t.g.a. reported in this investigation. Differences in reactivity between polymer crystals prepared by heating and by γ-radiation have been noted and discussed. Levels of imperfection of the crystals, determined by the choice of polymerization method, appear to correlate with the observed pre-exponential factors. The numerical value of the activation energy found for the second kinetic regime, which is attributed to the chemical process itself, is consistent with a process of bond breaking at the methylene-carbazole bond being the rate-determining step of the decomposition.