Synthetic Metals (v.158, #17-18)

Tuning of the magnetism in a polyaromatic molecular semi-conductor by M. Jouini; M. Lazerges; S. Chelly; M. Billon; C. Lombard; B. Pepin-Donat; C. Pernelle (681-683).
An heterocyclic polyaromatic molecular semi-conductor, at the crossroads of molecular polyaromatichydrocarbons (PAHs) and conducting polymers (CPs), was obtained by electrochemical synthesis in organic media. The behavior of the material investigated by in situ electrochemical-ESR measurements reveals that it possesses the advantages of both classes of materials. It can be processed easily into electroactive and adhesive thin layers, like CPs, and is able to accept one spin per charge, like paramagnetic molecular salts. It is shown that the spin concentration can be accurately and reversibly tuned by controlling the material potential at room temperature.
Keywords: Organic semi-conductor; Electrochemical synthesis; Paramagnetic material;

Synthesis and characterization of aligned SiO2 nanosphere arrays: Spray method by G. Gnana Kumar; S. Senthilarasu; Dae Nyung Lee; Ae Rhan Kim; Pil Kim; Kee Suk Nahm; Soo-Hyoung Lee; R. Nimma Elizabeth (684-687).
The power of nanomaterials has been hampered by the difficulty in controlling their size and morphology. Monodispersed silica particles with different nanometer sizes synthesized by a novel spray method remove the obstacles for the commercialization of nanomaterials at a global level. The size and shape of the silica particles were effectively controlled by simple hydrolysis and condensation reaction. Morphological images (SEM and TEM) reveal the smooth and spherical shaped silica particles with homogeneous distribution. Structural and luminescence properties of the silica particles were examined by FT-IR absorption spectroscopy and photoluminescence. A very low weight percentile loss of the silica particle ensures its high thermal stability. The high surface areas of about 55 and 25 m2/g were achieved for 90 and 220 nm particle sized silica particles, respectively. The resultant silica particles can be easily suspended in water and would be useful for variety of applications.
Keywords: Nanometer; Silica; Spray; Thermal;

Bamboo charcoal coated with polyaniline was synthesized by in situ polymerization at different bamboo charcoal/aniline weight ratio (BC/Ani = 1/1, 1/2, 1/3) and introduced into epoxy resin to be a microwave absorber. The spectroscopic characterizations of the formation processes of bamboo charcoal/polyaniline composites were studied using Fourier transform infrared, ultraviolet–visible spectrophotometer, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and electron spin resonance. Microwave absorbing properties were investigated by measuring complex permittivity, complex permeability and reflection loss in the 2–18 and 18–40 GHz microwave frequency range using the free space method. The results showed that a wider absorption frequency range could be obtained by adding different polyaniline contents in bamboo charcoal.
Keywords: Polymer–matrix composites (PMCs); Electrical properties; Magnetic properties; Electron microscopy;

Synthesis of polyaniline nanofibrils using an in situ seeding technique by Tuspon Thanpitcha; Anuvat Sirivat; Alexander M. Jamieson; Ratana Rujiravanit (695-703).
Oxidative polymerization of aniline under acidic conditions, in the presence of chlorophyllin nanorods, acting as an in situ seed, results in formation of nanofibrillar polyaniline (PANI). Specifically, PANI nanofibrils, with diameters in the range 60–100 nm, were formed at mole ratios of chlorophyllin to aniline monomer of 8.14 × 10−4, 8.14 × 10−3, and 1.63 × 10−2; however, at a 4.07 × 10−2 mole ratio, extensive aggregation of PANI occurred. To obtain pristine PANI nanofibrils, acetone and aqueous NaOH were used as solvents to remove the chlorophyllin seed. Thus, with appropriate choice of solvent, PANI nanofibrils can be obtained in either emeraldine salt or emeraldine base forms, respectively. Analysis of the PANI nanofibrils indicates that the presence of the chlorophyllin seed during polymerization induces only a change in morphology and does not influence the molecular structure of the resulting PANI. The electrical conductivity of the pressed PANI nanofibrils is comparable to that of conventional PANI. A mechanism for the formation of PANI nanofibrils is also proposed.
Keywords: Chlorophyllin; Polyaniline; Nanofibrils; In situ seeding polymerization;

Vapour phase polymerisation of pyrrole induced by iron(III) alkylbenzenesulfonate salt oxidising agents by Priya Subramanian; Noel B. Clark; Leone Spiccia; Douglas R. MacFarlane; Bjorn Winther-Jensen; Craig Forsyth (704-711).
A series of iron(III) alkylbenzenesulfonate (ABS) salts were prepared by the reaction of ferric hydroxide, Fe(OH)3·xH2O, with a variety of aromatic sulfonic acids. The products were characterised by microanalysis and FTIR spectroscopy. The microanalysis data generated indicated that three of the salts were not mononuclear iron(III) compounds and were of the formula [(OH2)5Fe–O–Fe(OH2)5][C2H5C6H4SO3]4, [(OH2)5Fe–O–Fe(OH2)5][CH3C6H4SO3]4·2H2O and [(OH2)5Fe–O–Fe(OH2)5][CH3C6H4SO3]4. Some degree of condensation or cross-linking of Fe(III) centres into hydrolytic oligomers had occurred. The X-ray crystal structure of the Fe(III) toluenesulfonate salt established the formula of an oxo-centred, binuclear complex [(H2O)5Fe(μ-O)Fe(OH2)5]4+. Vapour phase polymerisation (VPP) of pyrrole monomer was carried out using iron(III) benzenesulfonate, p-ethylbenzenesulfonate, dodecylbenzenesulfonate and p-toluenesulfonate. As the chain length of the Fe(III) alkylbenzenesulfonates increased it was found that the film forming ability of the polypyrrole was enhanced, probably as a result of a decrease in polymer chain interaction resulting from increased free volume between polymer chains. Variations in the conductivity of the polypyrrole films was observed when Fe(III) p-toluenesulfonate salts obtained from different sources (two commercial samples and one synthesised in our laboratories) were used as the oxidant. Films deposited using these oxidants generally exhibited higher conductivity than those formed using the Fe(III) p-ethylbenzenesulfonate and Fe(III) p-dodecylbenzenesulfonate salts.
Keywords: Bulk polymerisation; Conducting polymers; Iron(III) alkylbenzenesulfonates; Polypyrrole; Vapour phase polymerisation; X-ray crystallography;

HCl-doped nanofibers of polyaniline (PANI) were chemically prepared by adding inorganic salts (e.g. LiCl, NaCl, MgCl2 and AlCl3) as the additives via a self-assembly process and aggregated to former chrysanthemum flower-like microstructures. The PANI nanofibers have not only thin diameter (17–23 nm), but also high conductivity (∼3.7 S/cm) at room temperature and high crystallinity due to a low rate of accretion or elongation process of the nanofibers by adding inorganic salts. The influence of the nature and concentration of the inorganic salts on the formation yield, morphology, diameter, molecular structure and conductivity of the self-assembled nanofibers was investigated.
Keywords: Polyaniline; Ammonium peroxydisulfate; Inorganic salt; Nanofibers;

A novel polymer constituted of N-substituted pyrrole was synthesized by chemical oxidative polymerization from N-vinylpyrrole monomer. The structure of the resulting polymer was characterized by FT-IR, 1H NMR and element analysis. The results indicated that the polymer was comprised of two chains, i.e. α-coupled polypyrrole and polyethylene, and the two chains were found to have the same average degree of polymerization. The investigation of the solubility showed that the polymer was soluble in common organic solvents and could be cast into thin films from a chloroform solution. Interestingly, the polymer displayed strong optical absorption in the visible region and exhibited photoluminescence as determined by UV–vis and fluorescence spectrum analysis.
Keywords: Polypyrrole; N-Vinylpyrrole; Synthesis;

Sulfamic acid doped polyaniline (abbreviated PANI-SFA), previously used as an optical sensor for reagentless nitrite determination, has been tested as a potential electrochemical sensor for this anion. Cyclic voltammetry measurements of PANI-SFA and, for comparative reasons, PANI-HCl clearly show that electrochemical activity of the former is strongly dependent on the presence of nitrite in the electrolyte, even at low concentrations of this anion (C  = 10−6  M). Inspired by this finding we have constructed an electrochemical sensor by deposition of a thin PANI-SFA layer on the Si/SiO2 substrate to obtain an electrolyte–insulator–semiconductor (E.I.S.) structure. The electrochemical sensing properties of PANI-SFA towards nitrite, in the E.I.S. configuration, have been tested in acidified (pH 2) solutions by capacitance voltage measurements C(V) method. Transfer and ion diffusion process of nitrite anions in the polymer membrane have been investigated. A specific feature of the sensor tested is a monotonic change of its flat band potential (ΔV fb) with increasing nitrite concentration, observed for the concentration range from C  = 10−6  M to C  = 10−1  M. The sensitivity of the detection is however significantly enhanced only for concentrations exceeding 5 × 10−4  M, for lower nitrite concentrations the capacitance-based detection is inferior to the previously studied optical one.
Keywords: Sulfamic acid; Polyaniline; Electrolyte–insulator–semiconductor heterostructure; Capacitance measurements; Nitrite determination;

The forward and reverse bias capacitance–voltage (CV) and conductance–voltage ( G / w – V ) characteristics of Al/polymer/PEDOT-PSS/ITO heterojunction diodes have been investigated in the frequency range of 10 kHz to 5 MHz at room temperature. The obtained CV and G / w – V characteristics of these diodes at various gate biases show fairly large frequency dispersion especially at low frequencies and forward bias due to surface states N ss in equilibrium with the polymer semiconductor and series resistance R s. These observations indicate that at low frequencies, the charges at interface states can easily follow an ac signal and yield an excess capacitance and conductance. In addition, the forward and reverse bias current–voltage (IV) characteristics of Al/polymer/PEDOT-PSS/ITO heterojunction diode were measured at room temperature. The main diode parameters such as barrier height Φ B0, ideality factor n and average series resistance R s obtained from the forward bias ln  IV characteristics were found as 0.53 eV, 4.79 and 195 Ω, respectively. Experimental results show that both N ss and R s values should be taken into account in determining frequency and voltage-dependent IV, CV and G / w – V characteristics.
Keywords: Heterojunction diode; Poly[2-(2-naphtylamino)-2-oxo-ethyl methacrylate]; Frequency dependent; Organic nanometric thin film; Polymer; Series resistance;

A hyperbranched polymer containing azo chromophore groups on the periphery has been successfully synthesized by atom transfer radical polymerization using hyperbranched polyester bearing peripheral bromoacetyl groups as the initiator and 4-[(E)-phenyldiazenyl]phenyl acrylate as monomer and CuBr/2,2′-bipyridine (bpy) as the catalyst. The resultant products were characterized by FT-IR, NMR, TEM, and EA. The photo-tunable azobenzene-functionalized hyperbranched polymer as well as the corresponding azo monomer showed photoresponsive behavior of the azobenzene type molecules. UV–vis spectra of the azobenzene-functionalized hyperbranched polymer in tetrahydrofuran showed isomerization of azobenzene units upon irradiation with UV (365 nm).
Keywords: Photo-tunable; Azo chromophores; Hyperbranched polyester; Atom transfer radical polymerization;