High yield preparation of a soluble polyaniline derivative

The effect of pH, temperature, monomer/oxidant molar ratio, catalysts and ionic strength on the reaction yield and electrical conductivity of chemically synthesized poly (o-methoxyaniline) was studied. Based on this, poly (o-methoxyaniline) was prepared in the presence of p-toluene-sulfonic, dodecyl-benzene-sulfonic and dodecylsulfuric acids. Poly(o-methoxyaniline) was obtained with 90% yield and a conductivity of 0.1 S cm⁻¹ when p-toluene-sulfonic acid was used. The use of functionalized acids increased the thermal stability of the polymer in relation to HCl with no changes in the electric conductivity. The polymer is soluble in common organic solvents, enabling the preparation of films by casting. We also discuss the polymerization kinetics of o-methoxyaniline in the presence of HCl and of the functionalized acids as a function of monomer/oxidant ratio.     

Effect of electrolyte solvent on the morphology of polypyrrole films: Application to the use of polypyrrole in pH sensors

Electrochemical and morphological characteristics of polypyrrole (PPy) films electro-deposited from three different electrolyte solutions (acetonitrile, water and acetonitrile + water) have been investigated using atomic force microscopy and scanning electron microscopy. Experimental parameters including the electrolyte and the deposition time were shown to affect the morphologies of polypyrrole films. After characterization of the polypyrrole film morphologies, these polymer films were successfully tested as sensitive layers in pH sensors since the pH sensor responses were fast, linear and sensitive to pH changes. More, these responses of the pH sensors were dependent on the experimental conditions of the electro-deposition (thickness and solvent).     

Functionalized magnetic nanoparticle with poly(3-thiopheneacetic acid) and its application for electrogenerated chemiluminescence sensor

Polymer-coated magnetic nanoparticles (MNPs) have been prepared and used as an immobilization matrix for the fabrication of solid-state tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) electrogenerated chemiluminescence (ECL) sensor. The pre-synthesized maghemite (γ-Fe₂O₃) MNPs were coated with poly(3-thiopheneacetic acid) based on an oxidative polymerization method using KMnO₄. The poly(3-thiopheneacetic acid)-coated MNPs have formed the clusters with average diameter of 200–500 nm. The multilayer films of poly(3-thiopheneacetic acid)-coated MNPs were uniformly formed on the surface of a Pt electrode by an external magnet. The Ru(bpy)₃²⁺ was rapidly incorporated into the multilayer films within 5 min through the electrostatic interaction between the Ru(bpy)₃²⁺ and the negatively charged carboxylates of 3-thiopheneacetic acid at pH 7.0. Due to the fast mass transport in the multilayer films of the functionalized MNPs, the present Ru(bpy)₃²⁺ ECL sensor based on the functionalized MNPs showed improved ECL sensitivity for tripropylamine (TPA) compared to the Nafion-based ECL sensor. The present ECL sensor exhibited a quite low limit of detection for TPA (49 nM). The sensor-to-sensor reproducibility was very good (R.S.D. = 5%).     

Korrosionsuntersuchungen an chemischen Sensoren mittels elektrochemischer Rauschanalyse

Investigation of corrosion on chemical sensors by means of electrochemical noise analysis Electrochemical noise analysis has been used increasingly for investigation of electrochemical systems in recent years. In this paper results of noise measurements on different potentiometric electrochemical sensors are presented. The experimental arrangement consists mainly of a high-resolution multimeter and a series connected differential amplifier with a very high input resistance. Miniaturized pH glass electrodes, pH thick film electrodes, ISFET pH sensors as well as miniaturized reference electrodes have been investigated by means of electrochemical noise measurements. The results confirm that measurement of electrochemical noise can be used as an additional method for testing and characterization of electrochemical sensors.     

Über die Anwendung von Ionensensitiven Feldeffekttransistoren zur Untersuchung von Korrosionsvorgängen

On the application of ion sensitive field-effect transistors for the investigation of corrosion phenomena Ion sensitive field-effect transistors (ISFET) are chemical sensors based on semiconductor technology. They exhibit small dimensions, a plane measuring surface and have short response times. Thus, they are very suitable for the determination of local changes of the pH value at electrochemical corrosion studies. The described in this paper experimental set-up allows in situ measurements of the pH value by means of ISFET sensors in amounts of liquids below 1 mm³; the active surface area of the material under test may be below 1 mm². In model tests preferably changes of the pH value of dist. water due to the corrosion of steel St 38 have been investigated. After an initial short-time rise caused by oxygen reduction a decay of the pH value to pH = 3 ?4 was obseved. Furthermore, ISFET sensors have been used as a potential probe for electrochemical polarization measurements in low conductive media. It was shown, that the dynamic behaviour of potentiostatic control circuits may be influenced favourably by the low output resistance of the ISFET.     

Relationship between permselectivity and the acidity of polyphenols pertaining to the pH response of Pt/polyphenol electrode

The permselectivity of Pt/polyphenols has been investigated. The selective permeability is found to be different for various polyphenols. Relationships of the diffusion rates, the limiting currents for the reduction of H⁺ ions and the pK_a values of the polyphenols have been established. Electron-withdrawing substituents increase the diffusion rate of the H⁺ ions with increasing acidity of the polyphenol; whereas electron-donating groups bring out the reverse effect. Poly(p-cyanophenol) and poly(2,6-dichlorophenol) are found to be better candidates to modify a Pt electrode for application as pH sensor than existing polyphenol and poly(2,6-dimethylphenol) films.     

Humidity sensitive properties of substituted polyacetylenes

Thin film resistive humidity sensors have been prepared based on a series of homogeneously doped soluble substituted polyacetylenes synthesized using palladium acetylide complex catalyst. The humidity sensitive properties of the polymers (poly(propiolic acid) (PPA); poly(propiolic acid-co-ethynylbenzene) (PA-co-EB); poly(propiolic acid-co-p-diethynylbenzene) (PA-co-DEB); poly(propiolic acid-co-propargyl alcohol) (PA-co-OHP)) doped with FeCl₃, H₂SO₄ and HClO₄ have been investigated and compared. The chemical structures of polymers and the doping agents have great influence on the sensing properties of the sensors. A sensor based on PA-co-OHP doped with HClO₄ shows the best response. Its logarithm of impedance varies linearly with relative humidity (RH) for four orders of magnitude (10⁷–10³ Ω) over a wide range of 30–95%RH, and the response time is <6 and <15 s for absorption and desorption, respectively. Furthermore, the effect of temperature on the sensing behaviour of the polymers has also been described.     

Synergistic or additive corrosion inhibition of mild steel by a mixture of HEDP and metasilicate at pH 7 and 11

Electrochemical measurements (steady‐state current‐voltage curves and AC impedance) were coupled with mass‐loss measurements, SEM examinations, and EDSX analyses to investigate the inhibition of corrosion of a carbon steel by a mixture of phosphonic acid HEDP (acid 1, hydroxyethylene, 1‐1 diphosphonic) and sodium metasilicate pentahydrate Na₂SiO₃. 5H₂O in an industrial hard water containing 3.10^?3 M Ca²⁺ ions. At pH 7, HEDP and Ca²⁺ act in a synergistic manner, by formation of a HEDP and calcium containing layer. Addition of silicate at this pH value, allows to reach an efficiency of 94% due to an additive inhibition effect. At pH 11, metasilicate, HEDP, and Ca²⁺ ions reinforce the passive layer in a synergistic way. The mixture (1.7 · 10^?5 M HEDP + 2.6 · 10^‐3 M SiO^2?₃) in the Ca²⁺ containing electrolyte is shown to be able to inhibit efficaciously the corrosion of iron at room temperature, considering uniform corrosion at pH 7 or pitting corrosion at pH 11.     

Functionalization of the surface of ceramic membranes with 3-mercaptopropyl groups using the sol-gel method

Tubular ceramic membranes based on α-Al₂O₃ were functionalized with 3-mercaptopropyl groups using the sol-gel method. The formation of the polysiloxane layer on the inner surface of the membranes was confirmed by SEM images and FTIR spectroscopy data. The functionalized membranes (identically to the original one) retain the high performance typical of highly efficient microfiltration membranes (320–690 L/m² h); however, they can be used to remove silver(I) ions from water due to the formation of complexes between thiol groups of the active layer and silver(I) ions. It was also shown that the decreasing concentration of functionalizing sol produces a thinner surface polysiloxane layer with more active sites available for the sorption of Ag⁺ ions. Thus, fourfold dilution of the starting sol results in a tenfold increase in the sorption of Ag⁺ ions calculated per mass unit of the functionalizing layer (from 23 to 203 mg/g).     

Anodic reaction characteristics of tungsten in basic phosphate solutions

DC polarization and electrochemical impedance spectroscopy techniques were used to investigate the pH dependent anodic behaviour of tungsten in basic solutions. Anodic currents of W were pH independent between pH 8 and 11. Above pH 12 as pH increased the anodic currents of W also increased. The diffusion control in pH independent regime was observed to arise from slow diffusion of the solubilized species. At higher pH levels, however, OH⁻ ion diffusion from bulk of solution was observed to control the anodic process. Hydrate layer formation, which was observed with low frequency capacitive loop formation, accelerated with increase in pH.     

Effect of pH on the Electrochemical Behavior of Tantalum in Borate Buffer Solutions

In this research, various electrochemical methods were used to investigate the electrochemical behavior of tantalum in borate buffer solutions of various pH values, ranging from 9.0 to 6.5. Potentiodynamic polarization curves revealed that tantalum showed excellent passive behavior in borate buffer solutions. The potentiodynamic polarization and electrochemical impedance spectroscopy results showed that the passive film formed on tantalum offered its best protective behavior when the pH is 8.0, with the passivity undergoing a drastic change as the pH moved toward higher values. The semiconductive behavior of the passive films formed on tantalum was investigated by employing Mott-Schottky analysis in conjunction with a point defect model. The results indicated that the passive film exhibited n-type semiconductive behavior and that donor densities were in the range of 1.958-7.242 × 10²⁰ cm^?3. Moreover, this analysis showed that the donor density and flat band potential were quite sensitive to the pH.     

Amperometric alcohol biosensors based on conducting polymers: Polypyrrole,poly(3,4-ethylenedioxythiophene) and poly(3,4-ethylenedioxypyrrole)

Alcohol biosensors based on conducting polypyrrole (PPy), poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(3,4-ethylenedioxypyrrole) (PEDOP) were constructed. Alcohol oxidase (AlcOx, from Pichia pastoris) was immobilized during electropolymerization of the monomers in sodium dodecylsulfate (SDS) and phosphate buffer electrolysis medium. Optimization of several parameters was carried out. The highest affinity was observed for the PEDOT/AlcOx sensor. Lowry protein determination method was also used to calculate the amount of immobilized enzyme in sensors. Before testing the biosensors on alcoholic beverages effects of interferents (glucose, acetic acid, citric acid, and l-ascorbic acid) were determined. The alcohol contents of the distilled beverages (vodka, dry cin, whisky, and rak?) were determined with the sensors constructed. A good match with the chromatography results was observed.     

Preparation and Conductivity of Triheteropoly Tungstozincoaluminic Acid

Heteropoly acids (HPA) have been widelyused as e1ectrochroAnc and conducting materi-als, new modified electrodes, comPonents inconversion of solar energy, new materials foroxidation catalysis, cormsion resistant coatings,dyes or pigments, sorbents of gases, and cationexchangers etc. according to their unmatchedmolecular and electronic simctural versatility[l--4]. Because of their high-proton conductivi-ties, they are of special interest as new materi-a1s. There are two kinds of protons in th…     

PMMA-based patternable gate insulators for organic thin-film transistors

In order to prepare patternable polymer gate insulators, two methods of photo-crosslinking the polymer insulator were investigated. In the first method, poly(methyl methacrylate-co-2-hydroxyethyl methacrylate) [poly(MMA-co-HEMA)] functionalized with cinnamate groups was synthesized and photo-crosslinked. In the second method, a semi-interpenetrating PMMA network was prepared using a 25 wt% solution of PMMA/dipentaerythritol hexa-acrylate (DPEHA)/diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) by photo-crosslinking. Both of the photo-crosslinked insulator layers showed a high pattern resolution, indicating that physically and chemically stable crosslinking was accomplished. The field-effect mobilities of the pentacene-based OTFTs fabricated with the functionalized poly(MMA-co-HEMA) (60/40) and PMMA/DPEHA as gate insulators were 0.98 and 0.71 cm²/V s, respectively. It was found that patternable polymer gate insulators having good electrical properties could be prepared by using the functionalized poly(MMA-co-HEMA) and the PMMA/DPEHA solution.     

Surface charge properties of red mud particles generated from Chinese diaspore bauxite

Acid/basic potentiometric titration can be used to quantify the red mud surface charge properties. The amount of surface active --OH groups and surface charge density on the red mud particles generated from Chinese diaspore bauxite were evaluated from the acid/basic potentiometric titration data in 0.1 mol/L or 0.5 mol/L NaCl solution. The results show that the adsorption of sodium polyacrylate（SPA） on the red mud surface causes the increase of the surface active --OH groups, which makes the point of zero charge（PZC） shift to a lower pH value. However, the adsorption of polyacrylamide（PAM） causes little change. As the concentration of NaCl solution increases, the surface charge becomes more positive in acidic solution and more negative in alkaline solution, which can be attributed to the presence of a porous surface gel coating on the red mud particles.     

XANES studies of the formation of Ag-nanoparticles in LbL deposited polyelectrolyte thin films

Layer-by-layer polyelectrolyte multilayer thin films, composed of poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) were used as polymeric nanoreactors for the nucleation and growth of Ag-nanoparticles. The effects of precursor conditions like the pH on the corresponding size, distribution and fractional composition of the embedded silver were studied before, during and after reduction process by means of NaBH₄. X-ray absorption near edge structure (XANES) investigations enabled to distinguish between metallic Ag in the particles, dissolved Ag⁺-ions and Ag⁺-ions coordinated with carboxylic acid groups via a metal-ion exchange mechanism. The detailed analysis of the X-ray data showed that fractional composition of the embedded silver is determined by the processing conditions of the multilayer assembly during the nucleation and growth of Ag-nanoparticle PAH/PAA multilayer films. When the unreduced Ag-loaded PAH/PAA samples were exposed to ambient light, small Ag particles were formed within the polyelectrolyte multilayer films by reduction due to UV exposure. The formation of Ag-nanoparticles was confirmed by means of TEM and the characteristic plasmon resonance absorption peak in the UV-Vis range.     

Durability of aminosilane-silica hybrid gas-barrier coatings on polymers

Aminosilane solutions with pH equal to 8 and to 11 were applied and cured on SiO₂-coated poly(ethylene terephthalate) (PET) films. The permeability of the silane-silica hybrid coating on PET was reduced twofold compared to that of the SiO₂/PET film, at solution concentrations as low as 1 wt.%, irrespective of the pH. This concentration level led to a dense silane monolayer crosslinked to the silica surface. The oxygen transport mechanisms in the hybrid coatings were determined based on the thermally activated rate theory. Permeation experiments were also performed under tensile loading, and the critical strain for loss of barrier performance was found to be improved by a factor of two, only in case of basic pH. The defect population and morphology of the hybrid coating subjected to hydrothermal aging were analyzed using a reactive ion etching method and atomic force microscopy, respectively. These experiments confirmed the defect healing action of the aminosilane at low concentrations in solution, through the formation of a densely crosslinked polysiloxane layer at the silane-silica interface for both pH8 and pH11. The influence of the silane treatment was emphasized in case of basic pH due to the dissolution of superficial oxide layers.     

Suitability of emeraldine base polyaniline-PVA composite film for carbon dioxide sensing

A CO₂ sensor based on a composite thin film of emeraldine base polyaniline and poly (vinyl alcohol) cast from N-methyl pyrrolidone on an interdigitated electrode was characterized using impedance spectroscopy. The response of the sensor was slow and smaller in magnitude as compared to reports in the literature for similar sensors. Materials characterization indicated that the desired emeraldine base phase was not present after heat treatment. In addition, the mechanism for carbon dioxide detection previously reported in the literature cannot explain the CO₂ sensitivity, because the pH established between CO₂ and carbonic acid in the water dissolved in the poly (vinyl alcohol) matrix is not sufficient to induce a significant change in the conductivity of the emeraldine base polyaniline.     

TiO2薄膜的低温制备及有机半导体对其光催化活性的提高

采用具有锐钛矿晶粒的TiO2溶胶,通过浸渍提拉的方法,在载玻片上低温制备了具有光催化活性的TiO2薄膜.为进一步提高薄膜的光催化活性,采用掺杂了聚苯乙烯磺酸盐的聚乙撑二氧噻吩作为TiO2薄膜的涂膜基底,采用SEM、PL光谱等测试方法考察了该有机半导体基底对TiO2薄膜性能的影响,并就TiO2薄膜厚度对两种基底上薄膜光催化活性的影响及其机理进行了讨论.结果表明电子从有机半导体向TiO2的迁移使得光生电荷较好地分离,从而增加了表层TiO2的空穴浓度.同时发现合适的TiO2厚度能够有效地提高薄膜的光催化活性.     

Toward intelligent polymers: DNA sensors based on oligonucleotide-functionalized polypyrroles

A conjugated polymer can be considered as tri-dimensional network of intrinsically conducting macromolecular wires, able to transport signals. When further functionalized with prosthetic groups showing recognition properties, such polymer architecture mimics the nervous system existing in living beings. With this aim, we have developed a new type of electrochemical sensors, based on electroactive polypyrrole functionalized with oligonucleotide (ODN). At first, we analyzed the experimental conditions for building such modified electrode, showing a high electroactivity in aqueous medium. We developed a new route for the functionalization of polypyrrole, involving a precursor polypyrrole bearing an easy leaving ester group, on which an amino-labelled ODN can be directly substituted. The electrochemical response of this polypyrrole electrode functionalized with an ODN probe has then been analyzed in various aqueous media, containing either complementary or noncomplementary ODN targets. Results show that the cyclic voltammogram of ODN-functionalized polypyrrole is not modified when in presence of a noncomplementary ODN in solution. On the other hand, a significant modification of the voltammogram is observed upon addition of a complementary ODN target, to the electrolytic medium, which indicates that specific hybridization has occurred between the polypyrrole-grafted ODN probe and its complementary ODN target in solution. This biological recognition can be quantitatively determined by an amperometric analysis, and the limit of detection of this electrochemical biosensor is about 10⁻¹¹ mol, without any signal processing. These results confirm that functionalized polypyrroles act as macromolecular wires able to transduce biological information into molecular signals.