Raman spectroscopy analysis of polypyrrole films as protective coatings on iron

In situ Raman spectroscopy was used to study the redox modifications of electropolymerized polypyrrole (Ppy) films used as protective coatings on iron. A preliminary study of the redox behavior of Ppy on platinum was carried out for highlighting the most sensitive bands to potential variations: the 1560–1620 cm⁻¹ as well as the 930 and 980 cm⁻¹ peaks show a strong dependence on the applied potential. In situ Raman spectra of Ppy on iron were recorded at different times after immersion in a 3% NaCl solution. They formally display the same peaks as those found for platinum, allowing to characterize the redox state of the Ppy film at the solution/film interface. Additional ex situ Raman spectra allowed to identify the corrosion products at the Ppy/metal interface. These results complement kinetics analysis early developed to understand the protection mechanism and its loss.     

Thermal effects on the process of electropolymerization of pyrrole on mild steel

Polypyrrole films were electrosynthesized on mild steel with oxalic acid electrolyte at varying temperatures (25–65 °C), current density (0.5–6.0 mA/cm²) and pH (2.0, 4.0, 7.0 and 8.5). The concentrations of pyrrole and oxalic acid were maintained at 0.1 M each in galvanostatic experiments. The results show that lower temperatures favor the formation of polypyrrole on mild steel in acidic media. At higher temperature and lower current densities, oscillations in electrode potentials were observed. The film quality was poorest at pH 7.0, while very adherent and compact films were obtained in alkaline medium. Higher temperature in alkaline media favors the formation of better polypyrrole films in contrast with acidic media.     

Effect of adding Pd nanoparticles to dimercaptan-polyaniline cathodes for lithium polymer battery

The electrochemical properties of 2,5-dimercapto-1,3,4-thiadiazole (DMcT)—polyaniline (PAn) composite films containing Pd nanoparticles (average diameter: 28 nm) were investigated. Compared to DMcT–PAn composite film, the DMcT–PAn composite film containing Pd nanoparticles showed enhanced redox current and discharge capacity. The enhanced activity is attributed to the nanosize dispersion of the Pd catalyst particles within the DMcT–PAn matrix. UV-Vis spectroscopy and X-ray photoelectron spectroscopy (XPS) results confirmed the interactions between DMcT and Pd nanoparticles. We have obtained the positive effect of Pd nanoparticles addition on the redox activity of the DMcT–PAn composite.     

Investigations of the redox process of conducting poly(2-methyl-5-amino-1,4-naphthoquinone) (PMANQ) film Interactions of quinone–amine in the polymer matrix

Poly(2-methyl-5-amino-1,4-naphthoquinone) (PMANQ) film is a new functionalized conducting polymer having two distinct redox systems. The polymer structure is of the polyaniline-type, bearing one methylquinone group per monomer unit. The redox mechanisms of PMANQ were investigated by in situ multiple internal reflection Fourier transform infrared spectroscopy (MIRFTIRS) and electrochemical quartz crystal microbalance (EQCM). It is shown that interactions occur between quinone and amine groups in the polymer chain.     

Physicochemical and catalytic properties of palladium deposited on polyaniline-coated silica gel

The chemical incorporation of palladium into polyaniline (PANI) deposited onto the silica gel microparticles (15-μm in diameter) was studied. The as-prepared silica particles coated with PANI–hydrochloride (AC) were treated with aqueous ammonia solution (0.1 M) to transform polyaniline to its base (BA) form. Both AC and BA samples were reacted with PdCl₂ solutions (2.3×10⁻³ M) strongly differing in the concentration of HCl (0.1 M HCl, series K; 6.6×10⁻⁴ M HCl, series Z). Two series of samples with 0.43–2.14 wt.% Pd were obtained. Fourier-transform infra red (FTIR), UV-Vis, X-ray photoelectron spectroscopies (XPS) and scanning electron microscopy have been used to examine the nature of processes involved upon insertion of Pd and to characterize palladium species in the final samples. Very similar palladium species were found in the polymer matrix independently of the acidity of PdCl₂ solutions and the extent of PANI protonation (AC and BA samples). Pd²⁺ was the only form if no more than 0.86% Pd was introduced. Incorporation of higher content of palladium resulted in the partial reduction (14.6–28.7%) of Pd²⁺ to Pd⁰. The presence of Pd²⁺ species in the form of complexes in which besides Cl⁻ ligands also nitrogen groups of PANI participated has been postulated. The catalytic properties of Pd/PANI-SiO₂ have been studied in the liquid-phase hydrogenation of 2-ethylanthraquinone (EAQ) at 60 °C under 1 atm of hydrogen. Very low activity of the as-prepared catalysts significantly increased due to reduction of the samples with NaH₂PO₂ and subsequently with dihydrogen. The specific activities of reduced series K and Z samples were comparable and the maximum activity exhibited catalysts with 1–1.5% Pd.     

A magnetic susceptibility study of emeraldine base polyaniline

Paramagnetic spins are found even in carefully synthesized samples of emeraldine base polyaniline. We report here magnetic susceptibility data up to a temperature of 475 K on a number of emeraldine base samples that were synthesized at different oxidant to monomer ratios. All the samples, although electrically insulating, show the presence of Pauli-like susceptibility. A simple albeit physically realistic model involving spin-pairs is shown to lead to such a dependence on temperature. The analysis of the data indicates that polarons in emeraldine base are created in pairs and that the intra-pair interactions encompass a broad distribution of antiferromagnetic exchange couplings.     

Enhanced control and stability of polypyrrole electromechanical actuators

The practical application of polypyrrole (PPy) actuators requires a stable strain response and a high degree of reproducibility from sample to sample. The use of symmetrical voltage cycling to control the actuation of polypyrrole is shown to lead to a slow net oxidation of the polymer after several tens of cycles. The result is a slow deterioration in the actuation strain. The use of current pulsing reduces this problem and gives a more stable strain response. Current pulsing in combination with an ionic-liquid (IL) electrolyte allowed a strain of 3% to be achieved repeatably for many different samples for at least 100 cycles.     

Properties of copolymer of 2,2′:5′,2″-terthiophene-5,5″-dicarboxylic acid and polyethylene oxide

A new type of alternating regular copolymer of 2,2′:5′,2″-terthiophene-5,5″-dicarboxylic acid (TDCA) with polyethylene oxide (PEO) was synthesized. The product was characterized by NMR, UV-Vis and fluorescence spectra, EPR spectroscopy, X-ray diffraction (XRD) and DSC measurements. Copolymer is dissolved in dimethylformamide (DMFA) and dimethylsulfoxide (DMSO). Using TEM, it was ascertained that due to a different chemical structure of polymeric sub-units the separated phases in the solid state are formed on a sub-nanometer level.     

Synthesis and characterization of poly (aniline-co-acrylonitrile) using organic benzoyl peroxide by inverted emulsion method

An inverted emulsion process was adopted to synthesize conducting copolymers of aniline and acrylonitrile using benzoyl peroxide (BPO) as a novel oxidizing agent. The influence of polyacrylonitrile (PAN) ratio on the properties of conducting copolymers is reported. The chemical structures of the copolymers were characterized spectroscopically by UV-Vis, FT-IR, FT-Raman and EPR. The solubility of polyaniline (PAni) and PAni–PAN copolymers in dimethyl sulphoxide (DMSO) was confirmed by electronic absorption spectra. The conductivity of these copolymers lie in the range (1.26–4.20)×10⁻² S/cm. TGA thermogram of copolymers showed multi-step thermal degradation behaviour. X-ray scattering studies reflected that the copolymers are semicrystalline and showed two crystalline peaks at 17 and 25 (2θ).     

DFT study of conjugated biheterocyclic oligomers exhibiting a very low HOMO–LUMO energy gap

Density functional theory (DFT) is applied to study the structure and electronic properties of oligomers based on bithiophene bridged by a sp² carbon substituted by a chalcogen atom (O, S, Se and Te), and their polybifurane and polybipyrrole analogues. The important reduction of the energy gap which is observed for the whole series of biheterocyclic compounds, when going down the chalcogen group, is explained on the basis of an orbital interaction analysis. Bithiophene polymers bridged by a selenium or a tellurium substituted carbon atom are expected to exhibit very low energy band gaps.     

An alternative method to build organic photodiodes

We demonstrate a new method to build inverted organic photodiodes with highly conducting polymer anodes. In the inverted design the cathode is deposited first, followed by the deposition of the active material and finally the anode. A cathode of bismuth was vacuum evaporated followed by the evaporation of a capping layer of C₆₀. A semiconducting polymer, poly(3-(4′-(1″,4″,7″-trioxaoctyl)phenyl)thiophene) (PEOPT) was then spin-coated on the cathode, followed by a surface energy modification step and a subsequent spin-coating of the anode, a solution of glycerol and the conducting polymer poly(3,4-ethylenedioxythiophene) with the polyelectrolyte poly(4-styrenesulfonate) (PEDOT-PSS). As the pristine PEOPT was too hydrophobic to spin-coat the aqueous based PEDOT-PSS, the semiconducting polymer was silanized with 3-glycidoxypropyltrimethoxysilane to increase its surface energy before spin-coating of the PEDOT-PSS solution. The device geometry was proven successful by current–voltage measurements of devices in dark and under illumination.     

An EPR investigation of electrospun polyaniline-polyethylene oxide blends

The EPR magnetic susceptibility behavior of the camphorsulfonic acid doped polyaniline (PANCSA) blends with polyethylene oxide (PEO) is reported in fibers and films. In particular, EPR investigations on electrospun (PANCSA)_0.72(PEO)_0.28 nanofibers, cast films of (PANCSA)_0.72(PEO)_0.28 and cast films of (PANCSA) were performed to investigate differences in the mesoscopic disorder as induced by the process of electrospinning. The changes observed in the Pauli susceptibility, EPR lineshape, EPR linewidth, and dc conductivity are interpreted as due to increased chain alignment in the fibers compared with the cast films.     

Qualification of parallel kinematics machines in high-speed milling on free form surfaces

Serial milling machines may one day find their limits in high-speed milling due to their limited dynamic characteristics. Indeed, the major drawback of a serial structure is that it consists of a pile of actuated joints; hence the mass on board for the axis underneath can be huge. This is mainly the reason why parallel structures are of interest in milling: in order to go faster.Such structures have been developed since 1980 for robotic tasks, while the first parallel kinematics machine tool appeared only 14 years later. Since then, very few papers have been published that deal with the potential of these structures in milling. The objective of this study is to show the potentialities of parallel structures in milling and especially in high-speed milling of free form surfaces, in comparison to serial structures. To do so, experiments have been realised on four serial kinematics machines (SKMs) and four parallel kinematics machines (PKMs). These experiments were of two kinds: either a real piece has been milled, or the output axis encoder data have been saved (this method of measurement has been previously developed in our team).So far, a comparison between the two structures (serial and parallel) has been possible, which permitted us to show that PKMs can provide interesting results in terms of time and precision. Hence, the goal of this study has been reached, as the PKMs potentialities in milling free form surfaces have been highlighted. With more experiments, a generalisation, by taking into account all the parameters (shape and material of the part, structure of the machine, etc.), will be attempted. In parallel, the development of our simulator for PKMs is necessary in order to be able to predict milling on these machines.     

Synthesis and characterization of single phase LixBC (x=0.5 and 1.0), using Li hydride as a starting material

The hole-doped Li_xBC (x<1) has been theoretically predicted to exhibit superconductivity. In this report, preliminary information about the atomistic structure, thermal stability and magnetic property was presented on the single phase Li_xBC (x=0.5 and 1.0), using Li hydride as a starting material. The hydrogen concentration in Li_xBC (x=0.5) is about 0.7 mass% (Li_0.5BC-H_0.18), and the hydrogen desorption occurs around 700 K. The absence of superconductivity might originate from the modified atomistic structure, detected by Raman spectroscopy. We propose that the hydrogen concentrations can be varied for realizing superconductivity in Li_xBC (x<1).     

Semiconducting polyfluorenes as materials for solid-state polymer lasers across the visible spectrum

We report a detailed study of the gain properties of three polyfluorenes: poly(9,9-dioctylfluorene-co-9,9-di(4-methoxyphenyl)fluorene (F8DP), poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT), and a Dow proprietary copolymer, Dow Red F. The emission spectra of these conjugated polymers span the full visible spectrum from 400 to 800 nm. We observe amplified spontaneous emission (ASE) with peak wavelengths at 452, 576 and 685 nm for F8DP, F8BT and Red F, respectively. Low stimulated emission thresholds in the region of 0.1–0.45 μJ per pulse are demonstrated for planar asymmetric waveguides. Variable stripe length gain measurements at the peak ASE wavelengths show large net gains up to 66 cm⁻¹. Very low loss coefficients, in the range of 3.2–14.8 cm⁻¹, were also found.     

Surface spectroscopy and temperature-programmed desorption studies of the interaction of water vapor with Ni3(Al, Ti) (100) and (111) surfaces as a function of temperature

The interaction of water vapor with single crystal Ni₃(Al, Ti) has been studied with Auger electron spectroscopy, photoemission spectroscopy and thermal desorption. Water adsorbs molecularly onto the (111) and (100) surfaces at 140 K. When warmed up to room temperature, water remains as an intact molecule on (111), but dissociates to surface hydroxyl and atomic oxygen on (100). The latter process is accompanied by the evolution of hydrogen and oxidation of Al. It appears that the dissociation of water is structure-sensitive and that Al is the active species in controlling the dissociation of water on Ni₃Al surfaces.     

Switching and memory devices based on a polythiophene derivative for data-storage applications

In this article, we report electrical characteristics of devices based on oriented and unoriented films of a polymer, namely poly[3-(6-methoxyhexyl)thiophene]. The current–voltage characteristics of sandwiched devices, based on unoriented polymer, showed hysteresis behavior, while oriented versions exhibited switching characteristics, i.e. presence of two conducting states depending on sweep direction of voltage scans. The ratio between the device current of two conducting states has been as high as 10⁵. This is comparable, if not better, than the results reported so far with complicated device architecture or doped polymeric materials. We have also demonstrated that the switching devices have an associated memory effect for data-storage applications.     

Modelling the propagation of a radar signal through concrete as a low-pass filter

The knowledge of how a dispersive, dielectric medium such as concrete affects a propagating short electromagnetic pulse used in ground penetrating radar (GPR) is helpful both in the interpretation of radar results and in the prediction/modelling of expected radar measurements. Although there are a number of published results on the frequency-dependent, dielectric properties of media such as concrete and soils, the use of this information is still relatively small, primarily due the lack of a reliable method of applying these properties to propagating radar pulses. Modelling the dielectric medium as low-pass filter is one solution to this difficulty. In this paper the propagation of short pulses in concrete with known frequency-dependent properties is studied. The extent of how the pulses are attenuated and distorted is analysed and the implications on GPR applications are also discussed.     

Preparation of nano-sized SrAl2O4 using an amorphous hetero-nucleus complex as a precursor

Nano-crystalline SrAl₂O₄ with spinel structure was successfully prepared at 700 °C using amorphous SrAl₂(diethylenetriaminepentaacetic acid (DTPA)_1.6)(H₂O)₄ as precursor. The precursor was synthesized by a simple inorganic reaction and decomposed into SrAl₂O₄ at temperatures above 500 °C, which was proved by DTA–TGA and X-ray photoelectron spectroscopy (XPS) analysis. X-ray diffraction (XRD) results illustrated that a crystalline SrAl₂O₄ phase can form at 700 °C, which is about 600 °C lower than that used in the traditional method. The crystalline SrAl₂O₄ prepared at 900 °C for 2 h had a crystal size of about 28 nm and a grain size of about 80 nm, and its BET surface area can reach 28.056 m²/g. Calcination temperature and time had a weak effect on crystal size.