Synthetic Metals (v.157, #1)

Conductive wool yarns by continuous vapour phase polymerization of pyrrole by Saeed Shaikhzadeh Najar; Akif Kaynak; Richard C. Foitzik (1-4).
Conducting polypyrrole (PPy) coated wool yarns were prepared by a continuous vapour polymerization technique, using a speed of 1 m/min with different iron(III) chloride (FeCl3) as the oxidant at different concentrations. The resistivities, tensile properties, longitudinal and cross-sectional views of PPy-coated wool yarns were investigated. Optimum specific electrical resistances of 2.96 Ω g/cm2 at 80 g/L FeCl3 and 1.69 Ω g/cm2 at 70 g/L FeCl3 were obtained for 500 and 400 twist per meter (TPM) yarns, respectively. PPy-coated wool yarns exhibited higher elongation than uncoated yarns. Longitudinal and cross-sectional views of the yarns indicate that PPy coating penetrated deep into the yarn cross-section and a uniform coating was obtained on the surface of the yarn surface.
Keywords: Polypyrrole; Wool; Conductive textiles; Continuous vapour-phase polymerization;

Silver metal has been synthesized in form of a finely divided loose nanopowder, 10–30 nm particle sizes, using a simple polyol process. In hot water, polymer molecules of polyvinyl alcohol (PVA) induce Ag+  → Ag reaction as a weak reducer (suitable to control the final particle size), forming a nanofluid of Ag nanoparticles in situ dispersing in part of PVA molecules. Ag nanoparticles do not aggregate much when casting a viscous Ag–PVA nanofluid (hot) onto a substrate in thin laminates or films. Freestanding Ag–PVA films could be obtained of 1–5 mm thickness after drying at room temperature. Dried sample can be easily peeled from a silicate glass substrate. As small as 5–10 mm Ag–PVA pieces were heated in air in order to recollect Ag nanoparticles by burning off the polymer. At 300–400 °C, Ag–PVA disintegrates and encounters combustion in air, resulting in a pure Ag-powder. As analyzed by X-ray diffraction, a single crystalline phase of an Fm3m cubic crystal structure formed. Lattice parameter a  = 0.4071 nm and density ρ  = 10.61 g/cm3 compare well the bulk values a  = 0.4086 nm and ρ  = 10.50 g/cm3.
Keywords: Metal nanoparticles; Powder; Powder metallurgy; Processing of metals; Synthetic metals;

Effect of vacuum annealing on characteristics of the DBSA-doped polyaniline pellets by Bin Cui; Hong Qiu; Kun Fang; Chunying Fang (11-16).
Powder of DBSA-doped polyaniline was pressed to pellets. The pellets were annealed in vacuum at 140, 200, 260 and 320 °C for times up to 120 min. For all the annealing temperatures, the conductivity of the pellet is sharply reduced by a factor of 2 when the annealing time reaches 15 min. For the annealing temperatures lower than 260 °C, the conductivity does not change with further increasing the annealing time. However, under the annealing condition of 260 °C/120 min, the conductivity of the pellet decreases markedly again. Furthermore, the pellets annealed at 320 °C for the times longer than 30 min exhibit an insulating characteristic. The pellets consist of many agglomerated particles. The agglomerated particles become large with thermal aging. When the annealing temperature reaches 320 °C, some small sub-particles are formed on the surface of the agglomerated particles. The annealing results in a de-doping of DBSA from the polymer backbones and promotes the formation of reduction state in the polyaniline. The DBSA-doped polyaniline pellets annealed have a more porous and cracked morphology relative to the pellet unannealed. The degradation of the conductivity of the DBSA-doped polyaniline pellets is attributed to the de-doping, the phase separation and the porous and cracked morphology.
Keywords: DBSA-doped polyaniline; Vacuum annealing; Morphology; Structure; Conductivity;

Synthesis of electrochemically and thermally stable amorphous hole-transporting carbazole dendronized fluorene by Vinich Promarak; Musubu Ichikawa; Taweesak Sudyoadsuk; Sayant Saengsuwan; Siriporn Jungsuttiwong; Tinnagon Keawin (17-22).
A novel amorphous hole-transporting carbazole dendrimer, 2,7-bis[3,6-di(carbazol-9-yl)carbazol-9-yl]-9,9-bis-n-hexylfluorene (G2CF), was synthesized by a divergent approach involving bromination and Ullmann coupling reactions. G2CF showed UV–vis absorption bands at 304 and 332 nm in chloroform solution and the photoluminescence spectra showed a maximum peak at 373 nm in a bluish-purple region. Differential scanning calorimetry (DSC) and cyclic voltammetry (CV) analysis revealed G2CF was an electrochemically and thermally stable amorphous material with a high glass transition temperature (T g) of 237 °C. The organic light-emitting device having the structure of ITO/G2CF/Alq3/LiF:Al exhibited a bright green emission with a maximum luminescence of 11,000 cd/m2 at 16 V and a turn-on voltage of 5.4 V.
Keywords: Carbazole dendrimer; Hole-transporting; Amorphous; Organic light-emitting diode;

Synthesis and characterization of polythiophenes prepared in the presence of surfactants by Ayşegül Gök; Mária Omastová; Ayşe Gül Yavuz (23-29).
In this study homopolymers of thiophene were synthesized by chemical oxidative polymerization in the presence of three different surfactants (anionic, cationic and non-ionic) and an oxidant in an anhydrous medium. An anionic surfactant, sodium dodecylbenzenesulfonate (DBSNa), a cationic surfactant, tetradecyltrimethylammonium bromide (TTAB) and a non-ionic surfactant, poly(ethylene oxide) (20) sorbitan monolaurate (Tween 20), were used as additives. The properties of the polythiophenes (PTs) prepared were studied and compared with those of surfactant-free polythiophene (PT). PTs were characterized by different techniques: FTIR spectroscopy, elemental analysis, scanning electron microscopy, thermogravimetry and conductivity measurement. The scanning electron micrographs of PT prepared in the presence of surfactants showed differences in the surface morphologies for different surfactants. PT prepared in the presence of cationic and non-ionic surfactants exhibited smooth surfaces, while a typical globular structure was found for surfactant-free PT. PT synthesized with a cationic surfactant showed the highest thermal stability of all the samples.
Keywords: Polythiophene; Surfactant; Conducting polymers; Structure;

Fluorescence and anisotropy dynamics of a ―CHO substituted terthiophene by D. Anestopoulos; M. Fakis; G. Mousdis; V. Giannetas; P. Persephonis (30-34).
We report steady-state spectroscopic and femtosecond time resolved fluorescence and anisotropy measurements on a ―CHO substituted terthiophene in order to study the effect of aggregates on its properties. Aggregates are formed in concentrated solutions causing a broadening and a red-shift of the absorption and fluorescence spectra. Terthiophene molecules exhibit a fluorescence lifetime of 250 ps while in the presence of aggregates the fluorescence dynamics are governed by rapid energy transfer from the isolated terthiophene molecules to the aggregates within 10 ps. Finally, anisotropy dynamics in concentrated solution exhibit a slower decay than in dilute solution, which is related to the existence of aggregates.
Keywords: Oligothiophenes; Time resolved fluorescence; Time resolved anisotropy; Aggregates;

Molecular glasses possessing a phenyl-1,2,3,4-tetrahydroquinoline moiety as hole transporting materials for electrophotography by Vytautas Getautis; Jolanta Stumbraite; Valentas Gaidelis; Vygintas Jankauskas; Almantas Kliucius; Valdas Paulauskas (35-40).
The new hole transporting materials which comprise molecules consisting of two hydrazone branches linked with flexible thiobiphenyl or thiophenyl sulphide and two hydroxyl groups containing central bridge were synthesized and investigated. These transporting materials possessing phenyl-1,2,3,4-tetrahydroquinoline moieties are low molecular glasses and allow preparing stable to crystallization layers. The ionization potentials of these compounds are ca. 5.3 eV as determined by the electron photoemission method. These low molecular glasses can be used as hole transporting materials with or, in the case of a solid substrate, without binder polymer. The hole drift mobility of the newly synthesized compounds, measured by xerographic time of flight method, exceeds 10−5  cm2/V s at an electric field of 106  V/cm.
Keywords: Hydrazone; 1-Phenyl-1,2,3,4-tetrahydroquinoline; Molecular glasses; Charge transport; Hole drift mobility;

In this paper wool and polyester fabrics were pretreated with atmospheric plasma glow discharge (APGD) to improve the ability of the substrate to bond with anthraquinone-2-sulfonic acid doped conducting polypyrrole coating. A range of APGD gas mixtures and treatment times were investigated. APGD treated fabrics were tested for surface contact angle, wettability and surface energy change. Effect of the plasma treatment on the binding strength was analyzed by studying abrasion resistance, surface resistivity and reflectance. Investigations showed that treated fabrics exhibited better hydrophilicity and increased surface energy. Surface treatment by an APGD gas mixture of 95% helium/5% nitrogen yielded the best results with respect to coating uniformity, abrasion resistance and conductivity.
Keywords: Polypyrrole; Textile; Plasma treatment; Abrasion;

We report on the thermal degradation characteristics of heat treated poly(p-phenylene vinylene) (PPV) films deposited using chemical vapor deposition. It was found that no decrease in the thickness of the films (110 nm) occurred after isothermal heat treatment in vacuum at 450 °C for up to 1 h, while films treated at 500 °C for 1 h decreased to 70% of their original thickness. In situ mass spectrometry during heat treatment of the film at 500 °C showed the release of significant amounts of material including toluene and xylene ion fragments. However, Fourier transform infrared spectroscopy shows no significant change in bond structure, indicating that the decrease in film thickness after heat treatment is due to release of material and densification, not crosslinking or bond breaking.
Keywords: Poly(p-phenylene vinylene); Thermal degradation; Mass spectrometry; Ellipsometry; Fourier transform infrared spectroscopy;

The incorporation of silver nanoparticles into polypyrrole: Conductivity changes by Abdullah Alqudami; S. Annapoorni; P. Sen; R.S. Rawat (53-59).
Silver nanoparticles obtained by the electro-exploding wire technique were used to deposit on polypyrrole films prepared electrochemically. The presence of silver nanoparticles deposited was confirmed by X-ray diffraction. Energy dispersive X-ray spectroscopy was used to estimate the amount of silver nanoparticles deposited on polypyrrole.The current–voltage characteristics obtained from scanning tunneling microscopy showed remarkable changes in the electrical and the electronic properties of polypyrrole, which was also observed by the conventional two-probe method.The new approaches are the novel process used to produce pure silver nanoparticles and the simple and clean electro-deposition without the use of any chemical agents.
Keywords: Electro-deposition; Polypyrrole; Silver nanoparticles; Exploding wire;

Synthesis and electrochemical study of narrow band gap conducting polymers based on 2,2′-dipyrroles linked with conjugated aza-spacers by Cristina Pozo-Gonzalo; Jose A. Pomposo; Javier Rodríguez; Elena Yu. Schmidt; Alexander M. Vasil’tsov; Nadezhda V. Zorina; Andrey V. Ivanov; Boris A. Trofimov; Al’bina I. Mikhaleva; Alexey B. Zaitsev (60-65).
A series of 2,2′-dipyrrole monomers separated by aza-spacers (N,N′-bis-(1H-pyrrol-2-ylmethylene)-benzene-1,4-diamine; N 4,N 4′-bis-(1H-pyrrol-2-ylmethylene)-biphenyl-4,4′-diamine; N,N′-bis-[1-(1H-pyrrol-2-yl)-ethylidene]-hydrazine; and 4,4′-bis[(1H-pyrrol-2-yl)-diazenyl]biphenyl) have been synthesised using modified Schiff and azo-coupling reactions. The new 2,2′-dipyrroles linked with conjugated aza-spacers have been evaluated as precursors of narrow band gap conducting polymers. Electrochemically synthesized poly(N,N′-bis-[1-(1H-pyrrol-2-yl)-ethylidene]-hydrazine) displays a narrow band gap of just 0.7 eV, making it a suitable candidate for optoelectronic applications.
Keywords: Poly (dipyrroles); Aza-spacers; Synthesis; Cyclic voltammetry;

Electrochemical properties of the polypyrrole films doped with benzenesulfonate by Jüri Tamm; Terje Raudsepp; Margus Marandi; Tarmo Tamm (66-73).
The electrochemical redox behavior of the polypyrrole films doped with benzenesulfonate was investigated by cyclic voltammetry, the surface morphology of the films was characterized by AFM, and the interactions between pyrrole oligomers and the benzenesulfonate anion were modeled with quantum chemical methods. It is the first systematic study of the redox properties of this interesting system, somewhat of a model system with two complementing interactions (electrostatic and aromatic stacking). The influence of the electrodeposition charge and current density on the properties of the polymer film is explored. The voltammetric measurements show that redoxactivity of the polypyrrole films doped with benzenesulfonate anions is quite high, and markedly depends on the thickness of the film. Experiments with bilayered films show that electrode surface has an important but limited impact on the formation of organized compact structures.
Keywords: Conducting polymers; Polypyrrole; Benzenesulfonate; Voltammetry; AFM; Quantum chemical modeling;