The electrocatalytic oxidation of ascorbic acid on polyaniline film synthesized in the presence of ferrocenesulfonic acid

The catalytic oxidation of ascorbic acid on the two kinds of polyaniline electrodes (PAn and PAnFc films) has been carried out by cyclic voltammetry, constant potential and constant current methods. PAnFc and PAn films were synthesized in the presence and absence of ferrocenesulfonic acid, respectively. For the electrolysis of ascorbic acid at pH 5.64, the anodic peak potential of ascorbic acid shifts from 0.32 V (vs. SCE) on the bare platinum electrode to 0.05 V on both PAn and PAnFc electrodes. The oxidation current of ascorbic acid on the PAnFc electrode is 31 times as high as on the bare platinum electrode at the electrolysis of the constant potential. The exchange current density is 1.3 mA cm⁻² on the PAnFc electrode and 1.0 mA cm⁻² on the PAn electrode. The catalytic effect is caused by polyaniline itself. Ferrocenesulfonic acid doped in polyaniline plays an important role in enhancing the catalytic activity of polyaniline in the solution of pH >5.     

Analysis of electrochemical impedance of polypyrrole|sulfate and polypyrrole|perchlorate films

PPy|SO₄ and PPy|ClO₄ films have been synthesized and investigated in K₂SO₄, ZnSO₄ and NaClO₄ aqueous solutions by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and electron probe microanalysis (EPMA) methods. On the basis of obtained data and calculated impedance parameters as the potential functions, the role of different processes (diffusion of ions, double-layer charging, adsorption and charge transfer) in oxidized, partially reduced and reduced PPy films is estimated. The lowest pseudocapacitance values (from n × 10⁻⁶ to n × 10⁻⁴ μF cm⁻² for 1 μm film), independent of solution concentration, were established for PPy|SO₄ in ZnSO₄. This phenomenon is related with strongly aggravated film reduction process in the solution of double-charged cations. In the case of PPy|ClO₄ in NaClO₄ and PPy|SO₄ in K₂SO₄,where the mono-charged cations participate in redox process, the capacitance values are in the range from: n × 10⁻³ to n × 10⁻² μF cm⁻² and even somewhat higher for PPy|ClO₄ system at oxidized state. The calculated effective diffusion coefficients of ions D remain inside the range from n × 10⁻¹² to n × 10⁻¹⁴ cm² s⁻¹ for PPy|SO₄ in 0.1 M K₂SO₄ and PPy|ClO₄ in 0.1 M NaClO₄ aqueous solution. In the case of PPy|SO₄ film in ZnSO₄ solution the D values are essentially lower.     

Conductive polymer-coated textiles: The role of fabric treatment by pyrrole-functionalized triethoxysilane

Polypropylene (PP) and viscose (VS) textiles were modified by the in situ synthesis of a conducting polypyrrole (PPy) overlayer. To improve adhesion of the conducting layer to the textile surface, a pyrrole-functionalized silane (SP) was synthesized and bonded onto the surface before polypyrrole formation. Moreover, to introduce hydroxyl groups into the surface, PP was pretreated by grafting vinyltrimethoxysilane by means of a radiofrequency plasma discharge. The study is focused on the influence of SP on the washing fastness of a PPy layer and, consequently, on the overall conductivity of the textiles after washing. In the case of viscose, PPy was found to penetrate the substrate. A compromise was found between the influence of SP and penetration phenomenon (best conductivity after washing: wVS–0.2SP/25Py = 3 × 10⁻⁵ S/square). In the case of polypropylene the effect of pretreatment with SP is much better than for viscose, and a higher concentration of SP leads to improved fastness of the conductive layer (wmPP–0.2SP/25Py = 3 × 10⁻⁵ S/square; wmPP–1SP/25Py = 8 × 10⁻⁵ S/square), which indicates that the coating promoted by means of SP is more favoured than for viscose.     

The preparation and properties of sodium and organomodified-montmorillonite/polypyrrole composites: A comparative study

Two montmorillonites, an inorganic sodium montmorillonite (NaMMT) and an organo-modified montmorillonite (OMMT), were used for the preparation of montmorillonite/polypyrrole (MMT/PPy) composites. MMT particles were modified by the in situ polymerization of pyrrole in water, in aqueous solution of dodecylbenzenesulfonic acid (DBSA) used as anionic surfactant, and in water/methanol. Ferric chloride was used as oxidant in each case. Wide angle X-ray scattering (WAXS) measurements proved the intercalation of PPy into the galleries of NaMMT regardless the reaction media. In contrast, for OMMT/PPy composites, the increase of interlayer spacing depends on the preparation conditions, the highest increase in interlayer spacing was achieved in water/DBSA solution. The WAXS patterns of OMMT/PPy composites synthesized in methanol/water showed no change in interlayer spacing and the electrical conductivity of these composites was low, similar to that of NaMMT/PPy composites prepared under the same conditions. Conductivity about 1.1 S cm⁻¹ was reached for OMMT/PPy composites containing 13.3 wt% PPy prepared in the presence of DBSA. The NaMMT/PPy composite containing 15.6 wt% PPy and prepared under the same conditions showed a conductivity of 0.26 S cm⁻¹. X-ray photoelectron spectroscopy (XPS) proved that the surface of NaMMT/PPy composites is rich in MMT, whereas more PPy was found on the surface of OMMT/PPy composites. The conductivity of composites correlated with the N/Si atomic ratio determined from XPS results, which was taken as a semi-quantitative measure of the PPy surface fraction.     

Mechanism of polypyrrole and silver nanorod formation in lauric acid–cetyl trimethyl ammonium bromide coacervate gel template: Physical and conductivity properties

Polypyrrole (PPy) and silver (Ag) nanorods are synthesized in cetyl trimethylammonium bromide–lauric acid (CTAB–LA) complex coacervate gel template. When PPy–CTAB–LA system is polymerized with AgNO₃, Ag nanorods are produced while use of ammonium persulphate (APS) as initiator yields PPy nanorods. Ag-nanorods are produced from the initial stage while PPy nanorods take a longer time. The average diameter of Ag nanorods varies from 60 to 145 nm by increasing AgNO₃ concentration from 0.27 M to 1.08 M and that of PPy varies from 145 nm to 345 nm by changing pyrrole concentration from 1 × 10^?4 to 2 × 10^?4 M, respectively. Fourier transformed infrared (FTIR) spectra indicate stabilization of Ag nanorods through complexation of PPy with adsorbed Ag⁺ ions. PPy nanoparticles are stabilized by adsorbed sulphate ions and lauric acid, both are acting as dopant to it. FFT pattern and EDX spectra clearly indicate the presence of Ag nanocrystals and PPy on the surface of Ag nanorods, respectively. The mechanism of nanorod formation is attributed from UV–Vis spectra showing a red shift of surface plasmon band of Ag and π–π* transition band of PPy with time. The highest dc conductivity of PPy–Ag composite is found to be 414.2 S/cm, 7 orders higher than that of PPy nanorods (9.3 × 10^?4 S/cm). PPy–Ag systems show Ohmic behavior while PPy nanorods exhibit semi-conducting behavior. The preferential formation of Ag nanorod in AgNO₃ initiated polymerization is attributed to the higher cohesive force of Ag than that of PPy. With two times higher LA and CTAB concentration in the gel the Ag nanorod diameter decreases only 12% while that of PPy nanorod decreases by 50%. Possible reasons are discussed from the hard and soft nature of the two nanorods and from the elasticity of the gel template.     

A flexible capacitor based on conducting polymer electrodes

Flexible electrodes for supercapacitors have been prepared by depositing polypyrrole (PPy) on to a gold-coated PVDF membrane. Specific capacitance values of the order of 380 F g^?1 for PPy/Nafion and 420 F g^?1 for PPy/p-toluenesulfonate were obtained. For the PPy/Nafion electrode, an energy density of 56 Wh kg^?1 and a power density of 15.50 kW kg^?1 were available after 5000 cycles.Using a self-contained fully flexible device comprising polypyrrole as both electrodes and a PVDF membrane as separator, a capacitance of 30 F g^?1 was observed after 5000 cycles.     

Effect of various parameters on the conductivity of free standing electrosynthesized polypyrrole films

Electrical characteristics of polypyrrole films electrodeposited in different aqueous electrolyte solutions including p-toluenesulfonate, naphtalenesulfonate, nitrate, tetrafluoroborate, and perchlorate anions were investigated using the Van der Pauw procedure. The polymer films were synthesized by electrochemical oxidation at a fixed potential. Experimental parameters including the pyrrole concentration, electrolyte, applied potential and substrate were shown to affect the electrical conductivity σ of polypyrrole films. Since the substrate contributes significantly to the overall conductivity of polypyrrole-coated electrodes, the results obtained with free standing polymer films appeared more reliable. The results indicated that the p-toluenesulfonate doped PPy film showed the highest average conductivity (σ_293 K = 4.5 × 10⁵ S m^?1) whereas the perchlorate doped one produced the lowest of all the films prepared (σ_293 K = 2 × 10⁴ S m^?1).     

Synthesis of novel hexagonal micro-sheet polypyrrole and micro-sheet polypyrrole with grooves in the presence of α-cyclodextrin/Acid Red G inclusion compounds

Novel hexagonal micro-sheet polypyrrole (PPy) was synthesized via the self-assembly method in the aqueous solution containing α-cyclodextrin (α-CD)/5-acetamido-4-hydroxyl-3-(phenyliazenyl) naphthalene-2,7-disulfonic acid (Acid Red G) inclusion compounds (α-CD/ARG ICs) and ferrous cations. And micro-sheet polypyrrole with grooves was obtained by dipping the micro-sheet PPy into alkaline solution for 12 h. The existence of α-CD/ARG ICs in aqueous solution was testified by UV–vis spectra. Scanning electron microscopy (SEM) images revealed that the micro-sheet PPy was over 10 μm in average length, 0.6–10 μm in broadbrim and 100–200 nm in thickness. The conductivities of the micro-sheet PPy were in the range from 2.78 to 12.50 S cm^?1 and the conductivities of the micro-sheet PPy with grooves were in the range from 3.70 to 7.69 S cm^?1. Cyclic voltammograms (CVs) were measured to examine the electrochemical behaviors of the prepared PPy, and the oxidation peak of micro-sheet PPy was increased to 1.34 V which was higher than those of other PPy samples. The experimental conditions were also optimized, and the optimization of experimental conditions was the quantities of pyrrole monomers, α-cyclodextrin and Acid Red G were 20, 4 and 4 mmol, respectively, and the perfect micro-sheet PPy was synthesized at 5 °C and no-stirring for over 12 h. It was found that the complex aggregations of α-CD/ARG ICs and ferrous cations might have the function as a “template” during the polymerization of pyrrole monomers, but this “template” was broken off from the prepared micro-sheet PPy in the alkaline condition.     

High-temperature oxidation and hot corrosion of Cr2AlC

High-temperature oxidation and hot corrosion behaviors of Cr₂AlC were investigated at 800–1300 °C in air. Thermogravimetric–differential scanning calorimetric test revealed that the starting oxidation temperature for Cr₂AlC is about 800 °C, which is 400 °C higher than other ternary transition metal aluminum carbides. Thermogravimetric analyses demonstrated that Cr₂AlC displayed excellent high-temperature oxidation resistance with parabolic rate constants of 1.08 × 10⁻¹² and 2.96 × 10⁻⁹ kg² m⁻⁴ s⁻¹ at 800 and 1300 °C, respectively. Moreover, Cr₂AlC exhibited exceptionally good hot corrosion resistance against molten Na₂SO₄ salt. The mechanism of the excellent high-temperature corrosion resistance for Cr₂AlC can be attributed to the formation of a protective Al₂O₃-rich scale during both the high-temperature oxidation and hot corrosion processes.     

Deformation behavior of Zr55.9Cu18.6Ta8Al7.5Ni10 bulk metallic glass matrix composite in the supercooled liquid region

A Zr_55.9Cu_18.6Ta₈Al_7.5Ni₁₀ bulk metallic glass (BMG) composite with an amorphous matrix reinforced by micro-scale particles of Ta-rich solid solution was prepared by copper-mold casting. Isothermal compression tests of the BMG composite were carried out in the range from glass transition temperature (∼673 K) to onset crystallization temperature (∼769 K) determined by differential scanning calorimetry (DSC). The compressive deformation behavior of the BMG composite in the supercooled region was investigated at strain rates ranging from 1 × 10⁻³ s⁻¹ to 8 × 10⁻² s⁻¹. It was found that both the strain rate and test temperature significantly affect the stress–strain behavior of the BMG composite in the supercooled liquid region. The alloy exhibited Newtonian behavior at low strain rates but became non-Newtonian at high strain rates. The largest compressive strain of 0.8 was achieved at a strain rate of 1 × 10⁻³ s⁻¹ at 713 K. The strain rate change method was employed to obtain the strain rate sensitivity (m). The deformation mechanism was discussed in terms of the transition state theory based on the free volume.     

Long-term monitoring of atmospheric corrosion at weathering steel bridges by an electrochemical impedance method

Weathering steel corrosion was monitored for one to two years under natural atmosphere by an electrochemical impedance technique. Two identical comb-shape weathering steel sheets embedded in epoxy resin were used as monitoring probe electrodes at two different bridges in Japan. Impedances at 10 kHz (Z_10kHz) and 10 mHz (Z_10mHz) were automatically measured every hour. Coupons (50 × 50 × 2 mm³) prepared from the same steel sheets were exposed together to measure the corrosion mass loss. The average (Z_10mHz)⁻¹ value for half to one year exposure correlated well with the average corrosion rate determined from the corrosion mass loss.     

Organic conductor: Influence of preparation temperature

The conducting polypyrrole–polyethylene glycol (PPy–PEG) composite films were produced at various polymerization temperature ranging from 5 °C to 60 °C using 1 × 10^?3 M PEG, 0.20 M pyrrole and 0.10 M p-toluene sulfonate at 1.20 V (vs. SCE). The polymerization temperature of 5 °C appeared as the optimum preparation temperature showing the highest electrical conductivity of 70 S/cm and the thermal diffusivity of 8.76 × 10^?7 m² s^?1. The electrical conductivity and thermal diffusivity exhibited a decreasing trend with the increase in polymerization temperature in the pyrrole solution used to prepare the composite films. The XRD results reveal that low temperature (5 °C) typically results in more crystalline films, which are denser, stronger and have higher conductivity. The optical microscopy of PPy–PEG shows the globular surface morphology. The surface of the of the solution side of PPy–PEG film prepared at low temperatures showed a globular morphology.     

Superplasticity in cast A356 induced via friction stir processing

Superplasticity was investigated in friction stir processed A356 alloy at temperatures of 470–570 °C and initial strain rates of 3 × 10⁻⁴–1 × 10⁻¹ s⁻¹. Maximum superplastic elongation of 650% was obtained at 530 °C and an initial strain rate of 1 × 10⁻³ s⁻¹ where a maximum strain rate sensitivity of 0.45 was observed.     

Studies on electrochemical copolymerization of aniline with o-phenylenediamine and degradation of the resultant copolymers via electrochemical quartz crystal microbalance and scanning electrochemical microscope

Electropolymerization of aniline in sulfuric acid solution in the presence of o-phenylenediamine (oPD) of various concentrations was investigated via the electrochemical quartz crystal microbalance (EQCM) technique. It was found that the polymerization occurred more favorably at high aniline-to-oPD molar ratios (F₁, 20 or above). The stabilities of the resultant copolymers against degradation were efficiently improved compared with that of polyaniline (PANI). The first-order kinetic constants for polymer degradation were estimated to be 2.07 × 10⁻³ s⁻¹ for polyaniline, and 3.91 × 10⁻⁴ and 1.28 × 10⁻⁴ s⁻¹ for copolymers with F₁ values of 50 and 20, respectively. The degradation product, benzoquinone, was also detected at the tip electrode of a scanning electrochemical microscope (SECM).     

Preparation and characterization of a polypyrrole hybrid film with [Ni(dmit)2]2−, bis(1,3-dithiole-2-thione-4,5-dithiolate)nickellate(II)

The synthesis of a hybrid material obtained by electropolymerization of a solution of pyrrole and [NEt₄]₂[Ni(dmit)₂] (dmit = 1,3-dithiole-2-thione-4,5-dithiolato) in acetonitrile solution is reported. The material was characterized by cyclic voltammetry, UV–vis and infrared spectroscopies, scanning electron microscopy (SEM), atomic force microscopy (AFM) and thermal gravimetric analysis (TGA). The FTIR spectroscopy showed that the [Ni(dmit)₂]²⁻ anion has been inserted in the polypyrrole framework and was not destroyed or modified during the polymerization process. The voltammetric analysis indicated that the material has electroactivity and undergoes redox processes associated with the conducting polymer and the counteranion. The cyclic voltammetry results also suggest that the counteranion is not trapped in the PPy matrix undergoing anion exchange during the redox cycle of PPy. The PPy/[Ni(dmit)₂]²⁻ exhibits good thermal stability and a intrinsic conductivity value in the range of semiconductors (10⁻³ S cm⁻¹).     

Kinetic study of the electrochemical degradation of polyaniline

The kinetics of the electrochemical degradation of polyaniline (PANI) layers, deposited by electropolymerization and chemical polymerization onto platinum electrode, was investigated in an acid aqueous solution. The degradation rate was shown to depend greatly on the electrode potential applied. First-order rate constants of degradation, obtained from the kinetic data, were shown to vary between 2.87×10⁻⁵ and 3.11×10⁻³ s⁻¹ for thick PANI films, having the electrochemical charge density of 14 mC/cm², and between 2.0×10⁻⁵ and 3.60×10⁻³ s⁻¹ for thin PANI films, having the charge density of 1.5 mC/cm², within the electrode potential range of 0.3–0.9 V versus Ag/AgCl. Two linear regions were found to present on the dependencies of logarithm of the first-order degradation rate constant on electrode potential, one of them having a slope of 0.44 and 1.34 V⁻¹ within electrode potential limits of 0.3–0.6 V, and another one having a slope of 6.37 and 6.39 V⁻¹ within potential limits of 0.6–0.9 V, for thick and thin polymer films, respectively. The results obtained show that the electrochemical degradation of PANI films proceed at a remarkable rate even at low electrode potential values.     

Thermal expansion of the W5Si3 and T2 phases of the W–Si–B system investigated by high-temperature X-ray diffraction

The coefficients of thermal expansion (CTE) of the W₅Si₃ and T₂ phases of the W–Si–B system were determined using high-temperature X-ray diffraction in the 298–1273 K temperature interval. Alloys with nominal compositions 62.5W37.5Si (at%) and 58W21Si21B (at%) were prepared from high-purity materials through arc melting followed by heat treatment at 2073 K for 12 h under argon atmosphere. The highly different thermal expansion coefficients of W₅Si₃ along the a (5.0 × 10⁻⁶ K⁻¹) and c (16.3 × 10⁻⁶ K⁻¹) axes lead to a high thermal expansion anisotropy (α_c/α_a ≅ 3.3). On the other hand, the T₂-phase exhibits similar thermal expansion coefficients along the a (6.9 × 10⁻⁶ K⁻¹) and c (7.6 × 10⁻⁶ K⁻¹) axes, indicating a behavior close to isotropic (α_c/α_a ≅ 1.1).     

Z-scan measurements of third-order optical non-linearities in poly(phenylacetylenes)

Poly(phenylacetylene) (PPA) and poly(p-methoxyphenylacetylene) (PMOPPA) were synthesized by catalytic polymerization of monosubstituted alkynes and were fully characterized by conventional techniques. Linear and third-order non-linear optical properties of polymers solutions were investigated at λ=780 nm using a Z-scan set-up equipped with a femtosecond laser source at different operating regimes. A high repetition rate (76 MHz) regime was used to measure the linear and non-linear absorption coefficients by means of thermo-optical effects. Values of the linear and non-linear absorption coefficients were α=4.9×10⁻³ cm⁻¹ and β=1.1×10⁻¹¹ cm W⁻¹ for PPA and α=2×10⁻² cm⁻¹ and β=2.1×10⁻¹⁰ cm W⁻¹ for PMOPPA. Very low repetition rate (14 Hz) excitation was used to evidence the purely-optical non-linear refractive indexes, that were γ=6×10⁻¹⁸ cm² W⁻¹ and γ=11×10⁻¹⁸ cm² W⁻¹, respectively, for PPA and PMOPPA.     

Preparation and electrical–magnetic properties of polyaniline doped with ionic ferrocenesulfonic acid

Conducting polyaniline with electrical conductivity of 2.34 × 10⁻¹ S cm⁻¹ was obtained using ferrocenesulfonic acid as dopant. After the ferrocenesulfonic acid was oxidized with FeCl₃, though the electrical conductivity of the doped polyaniline decreased by 1–2 orders of magnitude, the magnetic susceptibility (χ) increased with the increase of the oxidation degree of ferrocenesulfonic acid. EPR spectra showed not only a signal with a g value of around 2, but also a so-called half-field signal with a g value of about 4 even at room temperature. Coexistence of ferromagnetic intrachain interactions and antiferromagnetic interchain interactions in the materials has been suggested.     

Environmentally assisted cracking behaviour of Al–Zn–Mg–Cu–Cr alloy bonded with polymer matrix composite stiffener

Studies were conducted to investigate the effect of polymer matrix composite stiffener (patch) on environmentally assisted cracking (EAC) susceptibility of pre-cracked alclad Al–Zn–Mg–Cu–Cr alloy in 3.5 wt.% NaCl environment. The EAC threshold stress intensity of the peak and two-step aged alloy was reduced from 26 to 7 MPa m^1/2 and 31to 8 MPa m^1/2 respectively under the influence of patch. The plateau crack velocity was increased from 2.5 × 10⁻⁹ to 5.1 × 10⁻⁹ m/s for peak aged and 1.2 × 10⁻⁹ to 2.0 × 10⁻⁹ m/s for two-step aged tempers in patched condition. The significant increase in EAC susceptibility was attributed to crevice effect generated by the stiffener.