Electropolymerization and characterization of poly(N-methylaniline) and poly(N-butylaniline) in mixtures of aqueous and organic solvents

Electropolymerization of N-methylaniline (NMA) and N-butylaniline (NBA) was studied on glassy carbon and optically transparent tin oxide electrodes in mixtures of aqueous and organic solvents. Five different organic solvents, dimethyl formamide, dimethyl sulfoxide, tetrahydrofuran (THF), propylene carbonate (PC) and acetonitrile (ACN) were mixed with aqueous 1.0 M HClO₄ solutions. Our results show that NMA and NBA can be electropolymerized in aqueous–organic solvent mixtures with maximum 30 and 50% (v/v) organic solvents, respectively. The choice of organic solvent strongly influences the film formation. With addition of 10–20% THF, ACN and PC to the aqueous polymerization solution, the film formation was highly improved. The poly(N-methylaniline) and poly(N-butylaniline) films were characterized with cyclic voltammetry, in situ UV–vis spectroscopy, size exclusion chromatography and with electrical conductivity measurements.     

Characteristics of poly(vinyl acetate) as a gate insulating material in organic thin film transistors

We report the physical characteristics of poly(vinyl acetate) (PVAc) as a polymeric gate insulator in the organic thin film transistors (OTFTs), in which the OTFTs require not only a simple packing process with a relatively low cost compared to conventional inorganic electronics but also their compatibility with flexible substrates. The PVAc gives dielectric constant values in the range of 3.2–8.3, which can be adopted as a good gate insulator for OTFTs. The fabricating condition of OTFTs using the PVAc was improved by both adjusting its viscosity with that of a medium, and controlling the surface morphology and spin coating conditions. All these meet the requirement for a new organic gate-insulator, which can improve the performance of the present OTFTs.     

High contrast ratio organic light-emitting devices based on CuPC as electron transport material

In this paper, a high-contrast-ratio organic light-emitting device (OLED) of high brightness is demonstrated. In this device, reflection from the cathode is reduced by inserting a copper-phthalocyanine (CuPC) layer between the emitting layer (EML) and the cathode called the Black Cathode™ technique. The absorption and the destructive interference effect caused by this layer lead to the decrease of the ambient light. With the same injection current density at 6 mA/cm², the contrast ratio of this device increases from 1.9 to 2.5 under 1000 lx illumination, when compared with a conventional device. Although the thickness of this device increases by 54.5%, its driving voltage is nearly the same as that of a conventional device. This result implies the high electron mobility in the inserted CuPC layer.     

Effects of annealing of poly(3-hexylthiophene) film on the performance of double-layered EL devices of ITO/polymer/Alq3/Mg–Ag

Double layer devices with a structure of ITO/pHT/Alq3/Mg–Ag (ITO = indium tin oxide, pHT = regio-regular or random poly(3-hexylthiophene), Alq3 = tris(8-hydroxyquinoline)aluminium) were fabricated. The device with a random pHT film emitted a green-yellow light in all voltage region, while that having a regio-regular pHT film exhibited a color change from green to red by applying the bias voltage higher than 15 V. Annealing the pHT films prepared on ITO at 200 °C for 1 h in nitrogen, prior to vapor-deposition of the Alq3 layer, improved the device performance with lowering the onset bias voltage by 2–3 V. The EL colors and spectra were also affected by annealing. X-ray reflectivity measurements before and after annealing the pHT film on ITO indicated increased density of the pHT layer and structural changes in the pHT/ITO interface by annealing, which seems to be responsible for the improved EL device performance.     

New n-type rigid rod full aromatic poly(1,3,4-oxadiazole)s and their application in organic devices

By introducing linear or branched alkoxy groups as side chains into the backbone, it is possible to synthesize rigid rod fully aromatic poly(1,3,4-oxadiazole)s which are soluble in organic solvents. Two different synthetic routes are used. First, a classical polycondensation reaction is developed involving an aromatic diacid dichloride and a dihydrazide followed by a ring closure reaction. As another polymerization reaction, the Suzuki coupling reaction is applied to synthesize polymers with a well-defined structure. The charge transport and optical properties are investigated by cyclic voltammetry (CV), current–voltage measurements and both absorption and photoluminescence spectroscopy. According to the CV-measurements, the oxadiazoles possess electron transport properties. First results will be presented about the application of these polymers in diodes.     

Photovoltaic devices based on a novel poly(phenylene ethynylene) derivative

A novel poly(phenylene ethynylene) derivative containing benzothiadiazole (BT) co-monomer (PPE-BT) was synthesized, characterized and used for photovoltaic devices. Photovoltaic devices of ITO/PEDOT-PSS/pristine PPE-BT/Ba/Al and ITO/PEDOT-PSS/PPE-BT+PCBM (1/4 w/w)/Ba/Al were fabricated and their photovoltaic performances were measured and discussed. The energy conversion efficiency and incident photo-current conversion efficiency of photovoltaic device based on PPE-BT+PCBM reached 0.022% (78.2 mW/cm², AM1.5) and 1% (391 nm), respectively. Its photosensitivity reached 3.1 mA/W, which is almost one order of magnitude higher compared to that of the pure PPE-BT. The electroluminescence of pristine PPE-BT was almost completely quenched when it was blended with PCBM.     

Optical and electrical characteristics of poly(3-alkylthiophene) and polydiphenylamine copolymers: Applications in light-emitting devices

In this work, poly (3-methylthiophene) (P3MT) or poly (3-octylthiophene) (P3OT) films were synthesized electrochemically with polydiphenylamine (PDFA), in layers and blended copolymers, in non-aqueous media through the oxidation of the monomers, using a standard three-electrode cell in acetonitrile with 0.100 mol L⁻¹ LiClO₄. The polymeric thin films were deposited on platinum plates for optimal quality control of the process. The electrochemical behaviors of as-prepared and partial dedoped films obtained by these methods was verified by cyclic voltammetry (CV) and have been characterized by UV–vis reflectance, resonance Raman, electron paramagnetic resonance (EPR) and photoluminescence (PL) spectroscopy. Based on data obtained by UV–vis reflectance spectroscopy, it was possible to characterize the chemical species in the polymer matrix using the resonant Raman method. Both Raman and PL spectra results led to the characterization of three structures (aromatic, semi-quinone and quinone forms of thiophene rings) which formed the homopolymers and copolymers chain. The EPR measurements were taken to quantify the semi-quinone species stabilization at 298 and 77 K temperatures. The ionization potential (I_P), electron affinity (E.A.) and gap energy (E_g) parameters were determined based on the technical analyses carried out.     

Current–voltage (I–V) characteristics of the molecular electronic devices using various organic molecules

Organic molecules have many properties that make them attractive for electronic applications. We have been examining the progress of memory cell by using molecular-scale switch to give an example of the application using both nano scale components and Si-technology. In this study, molecular electronic devices were fabricated with amino style derivatives as redox-active component. This molecule is amphiphilic to allow monolayer formation by the Langmuir–Blodgett (LB) method, and then this LB monolayer is inserted between two metal electrodes. According to the current–voltage (I–V) characteristics, it was found that the devices show remarkable hysteresis behavior and can be used as memory devices at ambient conditions, when aluminum oxide layer was existed on bottom electrode. The diode-like characteristics were measured only, when Pt layer was existed as bottom electrode. It was also found that this metal layer interacts with organic molecules and acts as a protecting layer, when thin Ti layer was inserted between the organic molecular layer and Al top electrode. These electrical properties of the devices may be applicable to active components for the memory and/or logic gates in the future.     

Current–voltage (I–V) characteristics of the molecular electronic devices using various organic molecules

Organic molecules have many properties that make them attractive for electronic applications. We have been examining the progress of memory cell by using molecular-scale switch to give an example of the application using both nano scale components and Si-technology. In this study, molecular electronic devices were fabricated with amino-style derivatives as redox-active component. This molecule is amphiphilic to allow monolayer formation by the Langmuir–Blodgett (LB) method, and then this LB monolayer is inserted between two metal electrodes. According to the current–voltage (I–V) characteristics, it was found that the devices show remarkable hysteresis behavior and can be used as memory devices at ambient conditions, when aluminum oxide layer was existed on bottom electrode. The diode-like characteristics were measured only, when Pt layer was existed as bottom electrode. It was also found that this metal layer interacts with organic molecules and acts as a protecting layer, when thin Ti layer was inserted between the organic molecular layer and Al top electrode. These electrical properties of the devices may be applicable to active components for the memory and/or logic gates in the future.     

涂层材料对钛合金机加工石墨型铸造工艺成形质量的影响

通过在石墨铸型内表面涂敷Y₂O₃、Al₂O₃、CaZrO₃耐火氧化物涂料,研究涂层成分对纯钛铸件界面反应和表面组织性能的影响规律。结果表明：涂敷涂料能有效克服石墨铸型对铸件的激冷作用。Y₂O₃涂料与钛液无化学反应发生,稳定性最佳,仅物理粘附于铸件表面。Al₂O₃和CaZrO₃涂料均与钛液发生了界面反应,分别生成Ti-Al-O和 Ca-Ti-O的化合物,Al₂O₃反应程度尤为剧烈。涂刷涂料后钛铸件表面晶粒尺寸、粗晶层厚度和显微硬度明显增大,变化趋势均为未涂刷< Y₂O₃< CaZrO₃< Al₂O₃。     

White light electroluminescence from PSi devices capped with poly(thiophene)(s) as top contact

For the first time, electrochemically deposited poly(3-methylthiophene) and chemically produced poly(3-methylthiophene) and poly(3-phenoxymethylthiophene) have been employed as top electrical contact on porous silicon light-emitting devices. The polymer-capped devices emitted white light as opposed to the uncapped devices, which emitted orange colour. The polymer-capped devices show much higher rectification ratio (up to 1×10⁵) as opposed to 1×10³ for the uncapped devices at ±10 V. The polymer-capped devices show 10³–10⁴-fold improvement in the luminous efficiency over the uncapped devices. Electrochemically deposited poly(3-methylthiophene) top contacts give a luminous efficiency of 8×10⁻⁵ lm W⁻¹ as opposed to 3×10⁻⁹ lm W⁻¹ obtained from uncapped devices. All the devices were found to fit the space charge limited current model.     

Polyaniline, polypyrrole and poly(3,4-ethylenedioxythiophene) as additives of organic coatings to prevent corrosion

The aim of this work is to compare the protection against corrosion imparted by different conducting polymers when these materials are used as anticorrosive additives in the formulation of conventional epoxy paints. Specifically, the polymers employed as anticorrosive additives are polyaniline emeraldine salt, polyaniline emeraldine base, polyaniline emeraldine salt composite with carbon black, polypyrrole composite with carbon black and poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulphonate). Initially, the structural, thermal and mechanical properties of the unmodified epoxy paint as well as the modified coatings, obtained by the addition of 0.3 wt.% of conducting polymers, have been characterized. After this, controlled accelerated corrosion assays in an aggressive solution medium were developed using coated steel panels. Results indicate that the protection against corrosion imparted by the formulations modified by the addition of poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulphonate), polyaniline emeraldine salt and, especially, polyaniline emeraldine base is significantly higher than that of the unmodified paint. In contrast, the use of conducting polymer composite with carbon black reduces the efficacy of the coating. Results indicate that some conducting polymer compositions should be considered as a suitable alternative to replace inorganic anticorrosive pigments currently used in paint formulations.     

Detection of microwaves using the organic semiconductor poly(p-phenylenevinylene)

We report a new procedure to convert the polymer precursor poly(xylylidene tetrahydrothiophenium chloride) (PTHT) into poly(p-phenylenevinylene) (PPV) using microwave irradiation. Spin-coated PTHT films were irradiated at room temperature under ambient conditions in a commercial microwave oven, with varying power from 20 W to 100 W. Complete conversion was reached within only 5 min of irradiation for powers above 50 W, yielding PPV films with absorption and photoluminescence spectra that are practically indistinguishable from the spectra of thermally converted PPV films, which require ca. 2 h of a high temperature (～200 °C) thermal treatment. In addition to a much faster conversion procedure, the irradiation with microwaves led to a red shift in the absorption spectrum of a PTHT film, which varied linearly with the time of irradiation. These films can then be used as low-cost, easy-to-use detectors of microwaves.     

Electrosynthesis of adherent poly(3-amino-1,2,4-triazole) films on brass prepared in nonaqueous solvents

The kinetics of the electropolymerization of 3-amino-1,2,4-triazole on a brass substrate in alkaline solution containing methanol was investigated using cyclic polarization, chronoamperometry, electrochemical impedance techniques and scanning electronic microscopy. The polymeric film was prepared by successive cycles of potential of a 60Cu–Zn electrode between 0 and 1.6 V. During the second cycle, the oxidation peak of the monomer disappears indicating the formation of the insulating film. We have also shown that the monomer oxidation reaction is essentially irreversible and controlled by a diffusion process. The protective effect of the film formed on brass has been studied in a 3%NaCl and 3%NaCl + S^2? solution. The results showed important inhibition efficiency, about 96% for 4 h of testing time.     

Preparation and properties of poly(arylene) containing Si unit-bridged diphenylamine

Si (monosilane, disilane, and disiloxane) unit-bridged diphenylamine-containing poly(arylene) PARs were prepared and properties of PARs were compared with the relative Si unit-bridged diphenylamine homopolymers. PARs were prepared by palladium-catalyzed polycondensation between Si unit-bridged diphenylamine and distannyl- or diboryl-aromatic compound. PAR with disiloxane unit-bridged diphenylamine was also prepared by oxidation of PAR with disilane unit-bridged diphenylamine. Optical properties and electrochemical properties of PAR depended on not only bridging Si unit but also introduced arylene unit.     

Different solvents effect on the performance of the solar cells based on poly(3-hexylthiophene):methanofullerenes

This paper reports the effect on the performance of the solar cells based on poly(3-hexylthiophene) (P3HT):[6,6]-phenyl C₆₁-butyric acid methyl ester (PCBM) with different casting solvents. These blend films are characterized by UV–vis absorption spectra, photoluminescence spectra, charge-transport dark J–V curve, X-ray diffraction pattern curve, and AFM images. The results indicate that high boiling point solvent leads to an enhanced self-organization of P3HT in the active layer, which causes an increased charge transport. Increased incident light absorption and higher carrier mobility in the active layer contribute to the enhancement in the device performance, the power conversion efficiency of 3.69% and fill factor up to 65.3% are achieved with 1,2,4-trichlorobenzene as casting solvent without further heat treatment under Air Mass 1.5, 100 mW/cm².     

A study on the preparation of poly(vinyl alcohol) nanofibers containing silver nanoparticles

In this study, two practical methods for the facile and controlled preparation of poly(vinyl alcohol) (PVA) nanofibers containing Ag nanoparticles were investigated for use in antimicrobial applications. In the first method, PVA nanofibers containing Ag nanoparticles were successfully electrospun from PVA/silver nitrate (AgNO₃) aqueous solutions after first refluxing them. The Ag nanoparticles in the PVA/AgNO₃ aqueous solutions were generated by refluxing them. Interestingly, it was found that the Ag nanoparticles were also spontaneously generated during the electrospinning process. In the second method, Ag nanoparticles were generated by annealing the PVA nanofibers electrospun from PVA/AgNO₃ aqueous solutions. Residual Ag⁺ ions and the Ag nanoparticles generated during the electrospinning process in the PVA nanofibers were diffused and aggregated into larger Ag nanoparticles during the annealing process. All of the Ag nanoparticles were sphere shaped and evenly distributed in the PVA nanofibers prepared by the two methods.     

Conductive films of tetrathiafulvalene dicarboxylate cation radicals and poly(vinyl alcohol) formed by casting

Aqueous solutions of dipotassium tetrathiafulvalene dicarboxylate (1), potassium ferricyanide and poly(vinyl alcohol) were used to cast air-stable, flexible and electrically conductive films. Casting at 80–95 °C formed a network of microcrystals oriented in the film plane. Spectroscopic studies showed that these crystals contain π-stacks of the cation radical 1⁺. No evidence for mixed valence stacks was found. A film containing 5 wt.% of 1⁺ in PVA had a four-point conductivity σ = 10⁻² S cm⁻¹ in the film plane. The structural anisotropy led to a lower conductivity (10⁻⁴ S cm⁻¹) across the plane of the film.