Synthetic Metals (v.151, #1)

Polyaniline/TiO2 microspheres prepared by a template-free method by Lijuan Zhang; Meixiang Wan; Yen Wei (1-5).
Polyaniline/TiO2 microspheres with 2.5–3.6 μm in average diameter were synthesized by a template-free method in the presence of salicylic acid (SA) as the dopant. It was found that the morphology, conductivity and hydrophilicity of the PANI-SA/TiO2 microspheres were affected by the content of TiO2 nanoparticles. The micelles composed of SA anions and anilinium cations containing TiO2 were proposed to interpret the formation mechanism of the self-assembled composite microspheres.
Keywords: Polyaniline/TiO2 microspheres; Template-free method;

Thermal properties of photonic crystals by W. Belhadj; O. Boukari; D. Gamra; F. AbdelMalek; H. Bouchriha (6-9).
We report on the analysis of thermal properties of two-dimensional (2D) photonic crystal. The changes in the transmission spectra under temperature effects have been analyzed. It is shown that the band gap width depends strongly on temperature and behaviors similar to the gap width in electronic crystals. The dispersion relation and the photon lifetime corresponding to the periodic coupled cavity structure have been investigated. A high sensitivity of cavity modes to the thermal nonlinearities has been found.
Keywords: Photonic crystal; Thermal nonlinearities; Transmission spectra;

Conductive copolymers of polyaniline, polypyrrole and poly(dimethylsiloxane) by Guliz Cakmak; Zuhal Küçükyavuz; Savaş Küçükyavuz (10-18).
Two step electrochemical polymerization method was used to obtain various conductive homopolymers, composites and copolymers of Polyaniline (PAn), Polypyrrole (PPy) and Poly(dimethylsiloxane) (PDMS). PAn/PPy, PDMS/PAn/PPy, PPy/PAn and PDMS/PPy/PAn conductive polymer films were synthesized with different compositions and their properties were compared. Films were characterized by conductivity measurements, cyclic voltammetry (CV), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) techniques. When both PPy and PAn existed in the films, the major contribution to the conductivity was due to the PPy component. PDMS/PPy/PAn films were more conductive than PDMS/PAn/PPy films similar to their binary counterparts without PDMS. When PPy was coated over PAn, thermally more stable films were obtained than the films synthesized in reverse order. The characterization tests implied the formation of chemically bounded new structures such as crosslinking copolymer structures. SEM microphotographs of PDMS/PAn/PPy films indicated a clear double layer structure. Hence, changing the order of coating had significant effects on the structure and properties of films.
Keywords: Polyaniline; Polypyrrole; Thermal properties; Morphology; Cyclic voltammetry;

Modification of corrosion behavior of stainless steels with a poly-m-methoxytoluene coating by Wassim Trabelsi; Leila Dhouibi; Fatma Matoussi; Ezzeddine Triki (19-24).
Poly-m-methoxytoluene (PMMT) coating is deposited on stainless steel. PMMT is synthesized via the anodic oxidation of the corresponding monomer, m-methoxtoluene (MMT) in acetonitrile solution containing tetrabutylammonium tetrafluoroborate (TBAF). The efficiency of PMMT coating against stainless steel corrosion has studied by standard electrochemical methods, electrochemical impedance spectroscopy (EIS) and SEM analysis. The results obtained suggest that PMMT film forms a sacrificial layer but the efficiency against corrosion is limited.
Keywords: Stainless steel; m-Methoxytoluene; Corrosion; Impedance;

Polyaniline actuators by Elisabeth Smela; Wen Lu; Benjamin R. Mattes (25-42).
Drawn polyaniline films and fibers doped with 2-acrylamido-2-methyl-propane-1-sulfonic acid, PANI(AMPS), were electrochemically cycled in HCl and their material properties and actuation performance comprehensively characterized. The Young's modulus was obtained as a function of applied voltage. Actuator figures of merit were derived from isotonic and isometric measurements, including strain, stress, work, power, creep, and efficiency. The effects of sample length, solution pH, electrochemical driving method, frequency, and load were studied, as well as the response of current to applied load for sensing applications. This work presents a complete picture of a polyaniline actuator for the first time. The behavior of the actuator is discussed in terms of the changes in the oxidation and protonation states of polyaniline.
Keywords: Polyaniline; Fiber; Actuator; Strain; Modulus; Metrics;

Polyaniline actuators by Elisabeth Smela; Benjamin R. Mattes (43-48).
Actuation of polyaniline (PANI)/Au bending bilayers and stretched polyaniline fibers doped with 2-acrylamido-2-methyl-propane-1-sulfonic acid was studied in aqueous methanesulfonic acid. Electrochemical activity was retained even upon repeated cycling into the pernigraniline state, unlike in HCl. The polyaniline expanded 1.6% from the leucoemeraldine state to the emeraldine state, similar to the strain in HCl, and then contracted 0.2% upon entering the pernigraniline state. The polyaniline was not mechanically stable in the pernigraniline state, however: the ultimate tensile strength decreased so much that the actuators were rendered ineffective for lifting a load. In addition, in this electrolyte the creep was considerable even under small loads; the Young's modulus was only 0.4 GPa in the oxidized state, compared to 1.7 GPa in HCl.
Keywords: Polyaniline; Fiber; Actuator; Electrochemical stability; Lifetime;

The migration of ions through poly(3-octylthiophene) by J. Corish; D.A. Morton-Blake (49-59).
Molecular dynamics (MD) simulations are used to investigate the abilities of several anions (Cl, BF4 , ClO4 , SO4 2− and PO4 3−) to migrate in a matrix of oxidised poly(3-octylthiophene) formed by doping the polymer. The transport of the ions is considered when it is induced both by thermal effects and by an electric field. When a degree of disorder is introduced into the lattice, the Coulomb association of the polymer and anion subsystems retains persistent lattice domains in which the ions are intercalated between the thiophene rings of the polymer backbone forming channel sites for the ions. This order seems to be a consequence of the alkyl side chains, as it is not found in unsubstituted polythiophene. Transport of the singly-charged ions occurs readily along the channels’ encountering low barriers (4 kJ mol−1), but the motions of the SO4 2− and PO4 3− ions are precluded, presumably due to coulombic effects. Application of electric fields along the channel directions induces the motion of the SO4 2− and PO4 3− ions also, but applying fields perpendicular to the channel destroys the lattice order. The transport of BF4 ions in a molecular channel is simulated by twisting the poly(3-octylthiophene) into a helix and examining the migration of the ions both inside and outside the helix channel.
Keywords: Electroactive polymer; Ion transport; Molecular simulation; Electric field-induced mobility; Helical cavity; Migration through helix;

Electrochemically-induced fluid movement using polypyrrole by Jennifer Causley; Shannon Stitzel; Sarah Brady; Dermot Diamond; Gordon Wallace (60-64).
Initial studies on inherently conducting polymer-coated surfaces show that the surface energy can be controlled by electrochemically switching the polymer's oxidation state. This surface energy change was then used to induce fluidic movement in a 700 μm wide polymethylmethacrylate channel coated with a polypyrrole layer doped with dodecylbenzenesulfonate anions. By applying a reducing potential to the polymer-coated channel, electrolyte solution was seen to move along the channel.
Keywords: Microfluidics; Polypyrrole; NaDBS; Fluid control;

On metallic characteristics in some conducting polymers by P.K. Kahol; J.C. Ho; Y.Y. Chen; C.R. Wang; S. Neeleshwar; C.B. Tsai; B. Wessling (65-72).
Polyaniline (PANI) exhibits a dc conductivity σ  ≈ 10−1  S/cm when it is doped with poly(styrenesulfonic acid) (PSSA) such that the number of sulfonate groups per two-ring PANI unit (y) is 2. On increasing the dopant amount to y  = 12, σ drops to 10−5  S/cm. The EPR-derived magnetic susceptibility of these two conducting polymers gives nearly the same density of states at the Fermi level N(E F) ≈ 0.65 ± 0.05 states/eV 2-rings. The corresponding electronic specific heat coefficient as calculated from this N(E F) value does not appear to be inconsistent with the results from low temperature calorimetric measurements. Similarly, with y′ defined as the number of sulfonate groups per three-ring PEDOT unit, PSSA-doping of poly(ethylenedioxythiophene) (PEDOT) yields different σ  ≈ 10−1 and 10−5  S/cm at y′ = 5.7 and 45.9, respectively, but the same N(E F) ≈ 0.55 ± 0.05 states/eV 3-rings. These observations suggest that the additional dopants, which help with dispersion in processing conducting polymers, do not alter the metallic domains but are located in the disordered regions surrounding them. The N(E F) values also remain practically the same between p-toluenesulfonic acid (PTSA) doped PANI and its dispersed blend in poly(methylmethacrylate) (PMMA), as well as for PEDOT–PTSA before and after its being subjected to an additional dispersion step.
Keywords: Magnetic susceptibility; Heat capacity; Density of states; Electron paramagnetic resonance; Conductivity; Organic polymers;

We present the dynamical simulation of a bond-order polaron which is associated with a ring-torsion polaron in the pernigraniline-base polymer on the basis of Baranowski–Büttner–Voit model. We find the relaxation time of forming a combined polaron is about 65 fs. The obvious difference existing in the relaxation process between this polymer and polyacetylene and its origin are discussed. Actions of the two polaron levels in the Peierls gap are also given out.
Keywords: Pernigraniline-base; Combined polaron; Electron–libron interaction; Time evolution;

The metal oxides films are widely used for CO, aromatic hydrocarbon and NO2, gas-sensing applications, but such sensors mostly lack selectivity and operate at high temperatures (300–500 °C). We focused on the use of organized ultrathin films of conducting polymers and their nanocomposites, which recognize selectively the NO2 gases with a very high sensitivity (≤ppb). Polyhexylthiophene (PHTh), poly(ethylene dioxythiophene) (PEDT), PHTh–PEDT copolymer, sulfonated polyaniline, polyaniline (PANI)–SnO2, polypyrrole (PPy)–SnO2, PEDT-SnO2, PHTh–SnO2 and copolymer (HTh-EDT)–SnO2 conducting polymer and nanocomposite thin films were fabricated and used for gas sensing applications. The physical properties (UV and FTIR) such films were investigated before and after the NO2 gas treatment. Regioregular PHTh, its copolymer P(HTh-PEDT), and their metal oxide nanocomposites films detected NO2 gas with a high sensitivity.
Keywords: Gas sensor; NO2 gas; Conducting polymers; Nanocomposites; Layer-by-layer self assembly;

Actuation behaviour of layered composites of polyaniline, carbon nanotubes and polypyrrole by Geoffrey M. Spinks; Binbin Xi; Van-Tan Truong; Gordon G. Wallace (85-91).
Layered composites of polyaniline (PAn), single-walled carbon nanotubes (CNTs) and polypyrrole (PPy) were produced by coating PAn or PAn/CNT on a PPy hollow fibre containing a platinum (Pt) helix. The actuation behaviour of PAn/PPy and PAn/CNT/PPy composites was compared with that of neat PPy. The Pt helix reduces the IR drop along the fibre, thus enhancing the actuation strain. Components of the composite with low actuation strain such as PAn and/or CNT restrict the actuation displacement of the PPy substrate causing a reduced strain in the composite. In particular, a minimal quantity of CNT (1.3 wt.%) in the composite leads to a discernible decrease in actuation strain but also increases the Young's modulus and tensile strength of the composite. Sodium nitrate (1 M) aqueous solution used as an electrolyte gives good actuation stability where the actuation strain is almost independent of applied stress (5–12 MPa). This can be explained by the unchanged Young's modulus at the reduced (contracted) and oxidized (expanded) states during the actuation process. The polyaniline/polypyrrole composite produced the highest work-per-cycle reported to date under isotonic conditions.
Keywords: Polypyrrole; Polyaniline; Carbon nanotubes; Electromechanical actuators; Composites;