Study on soluble polyaniline by positron annihilation technique

The solubility, electrical conductivity, and other properties of polyaniline (PANI) are highly dependent on its oxidation state. In this work, polyaniline (PANI1) prepared by peroxodisulphate induced polymerization of aniline in acidic aqueous medium in presence of benzenediazonium chloride salt was found to exist in lower oxidation state than emeraldine form of PANI and was highly soluble in common organic solvents. This polymer was subjected to positron annihilation spectroscopic study to investigate the correlation between the oxidation state of the polymer and defect sites generated by different degrees of protonation that in turn affect its electrical conductivity. The positron annihilation lifetime data were resolved to yield a three‐component fit for PANI1 subjected to different levels of protonation. The variation of positron annihilation parameters (τ_1,I₂) and Doppler broadening parameters (R, S) as a function of protonation level of the polymer indicate the dopant sites increase initially on protonation and reach a saturation value after a certain level of acidification. The lower value of electrical conductivity and the intensity of intermediate lifetime component (I₂) for PANI1 compared to PANI in emeraldine oxidation state indicate the presence of lesser number of quinoid–imine moieties that could undergo protonation and thus yield highly enriched trapping centers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Structure and electrochemical properties of polyamide and polyaniline

Electrochemical properties of well‐defined molecular structured polyamide with amine‐capped aniline pentamer in the main chain and conventional polyaniline were investigated and discussed. CV results suggest that the synthesized polyamide shows a relatively complicated redox process than conventional polyaniline during potential cycling. Differences in ESI characterization revealed that the synthesized polyamide exhibits higher electronic conductivity and lower resistance than the conventional polyaniline. The analysis of molecular configuration based upon the quantum chemistry calculation reveal that the difference in electrochemical activity and conductivity should be ascribed to the influence of system energy, skeleton conjugation, and the Fermi energy of the bipolaron model in the polymer molecules. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Soluble polyanilines obtained by nucleophilic addition of arenesulphinic acids

Polyaniline powder and films can be modified by nucleophilic addition of arenesulphinic acids to oxidized forms of polyaniline. The FTIR spectra of modified polymers suggest the formation of sulphone and/or sulphonamide moieties linked to the polymer backbone. The modification degree increases with the increasing of the oxidation state of the polymer. The addition decreases significantly at pH above 7. It is proposed a mechanism of nucleophilic addition, which explains the effect of the oxidation state of the polymer and pH of the solution. The modification increases the solubility of the polymers in common organic solvents. The modification reaction seems to provide a simple pathway to the incorporation of organic moieties to polyaniline backbone.     

A comparative study on the electrochemical properties of ring‐substituted polyanilines

The redox behavior of polyanilines with ring‐substituted groups synthesized by chemical polymerization, poly‐2,5‐dimethoxyaniline (PDMAn), poly‐m‐chloroaniline (PmClAn) and poly‐o‐toluidine (POT), was studied and the morphology and crystal orientation of platinum particles deposited on these polymer membranes was compared. The oxidation of isopropanol on platinized polyaniline‐modified electrodes as a model reaction was also investigated to examine the electrocatalytic properties of the polymers. The results show that the first oxidation potential of the polymers increases in the following sequence: PDMAn, POT and then PmClAn, which can be explained in terms of the electronic and steric effects of ring‐substituted groups. The growth of Pt particles electrodeposited on doping‐state POT and PDMAn polymer membranes takes place by a ‘progressive nucleation mechanism’, but by an ‘instantaneous nucleation mechanism’ on PmClAn. Platinum crystallites trend towards preferred‐orientation and Pt (200) is the preferred face, but the degree of preferred orientation depends on the polymer. The oxidation potentials of isopropanol are located near 0.3 V, and the oxidation currents increase on platinized polymer‐modified electrodes, indicating that the interaction of polymer with Pt particles might improve the catalytic activity of Pt. Polyanilines act not only as dispersion media but also change the electronic properties of Pt crystalline grains. Copyright © 2005 Society of Chemical Industry     

Preparation of nanosize polyaniline by solid‐state polymerization and determination of crystal structure

BACKGROUND: Nanosize polyaniline has several advantages in both the fabrication of nanodevices and for preparing nanoscale electrical connections in highly conducting polymer composites. RESULTS: Nanosize polyaniline with a diameter of 30–60 nm was prepared using a solid‐state polymerization process (PANI‐S) by mixing an equimolar quantity of ammonium persulfate and anilinium chloride crystals with a mortar and pestle. Polyaniline was also synthesized using a conventional oxidative polymerization method (PANI‐C) in an aqueous medium for comparison. Conductivity and contact angle measurements, infrared spectroscopy, ultraviolet spectroscopy, transmission electron microscopy and thermogravimetric analysis were carried out. An in‐depth investigation of the crystal structure of these polymers was carried out through powder X‐ray diffraction analysis. CONCLUSION: PANI‐S exhibited lower conductivity due to the presence of less emeraldine base form, lower crystallinity, greater d‐spacing and greater inter‐chain separation than PANI‐C. The hydrophilicity and thermal stability of PANI‐S were higher than those of PANI‐C. The unit cell volume of PANI‐S was much higher, resulting in a larger crystallite size and a greater number of atoms in the unit cell than PANI‐C. Copyright © 2009 Society of Chemical Industry     

Characterization of polyaniline via pyrolysis mass spectrometry

In this work, direct insertion probe pyrolysis mass spectrometry technique was applied to investigate the thermal and the structural characteristics of electrochemically prepared HCl and HNO₃‐doped polyaniline (PANI) films. It has been determined that the thermal degradation of both samples showed three main thermal degradation stages. The first stage around 50–60°C was associated with evolution of solvent and low‐molecular‐weight species adsorbed on the polymer, the second stage just above 150°C was attributed to evolution of dopant‐based products, and the final degradation stage at moderate and elevated temperatures was associated with evolution of degradation products of the polymer. Chlorination and nitrolysis of aniline during the electrochemical polymerization were detected. Extent of substitution increased as the electrolysis period was increased. Furthermore, for the HNO₃‐doped PANI, the evolution of CO₂ at elevated temperatures confirmed oxidation of the polymer film during electrolysis. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Electrochemical incineration of dyes using a boron‐doped diamond anode

The electrochemical oxidation of a synthetic wastewater containing the model dyes alizarin red (an anthraquinone) and Eriochrome black T (an azoic compound) has been studied on a boron‐doped diamond electrode (BDD) by both cyclic voltammetry and bulk electrolysis. The influence of the current density and dye concentration were investigated. The results obtained show that complete chemical oxygen demand (COD) and colour removal was obtained for both wastewaters. However, the nature of the pollutant, and specially the presence of functional groups (such as the azoic group) seems to strongly influence the performance and efficiency of the electrochemical process. The electro‐oxidation of alizarin red behaves as a mass‐transfer‐controlled process. In such a system, an increase in the current density leads to a decrease in the current efficiency. This can be explained by direct or hydroxyl radical mediated oxidation. The contrary tendency has been observed in Eriochrome black T electro‐oxidation. In this case, higher efficiencies were obtained working at high current densities. This may indicate that the mediated oxidation by electrogenerated reagent (such as peroxodisulphate) is the main oxidation mechanism involved in Eriochrome black T treatment. These compounds have a longer average lifetime than hydroxyl radicals, and it allows the reaction to be extended to the whole wastewater volume. This study has shown the suitability of the electrochemical process for completely removing the COD and total organic carbon and effectively decolourising of wastewaters containing synthetic dyes. Copyright © 2007 Society of Chemical Industry     

Thermotropic color changing nanoparticles prepared by encapsulating blue polystyrene particles with a poly‐N‐isopropylacrylamide gel

Water‐dispersed thermotropic nanoparticles with core‐shell structures were synthesized by the in situ polymerization of a lightly crosslinked shell of poly(N‐ isopropylacrylamide) [poly(NIPAM)] onto blue polystyrene cores. At room temperature, the thermal responsive outer shell is hydrophilic and is in a fully swollen gel state; but as the temperature is raised above 31°C, it becomes increasingly hydrophobic and eventually collapses as the temperature reaches the lower critical solution temperature (LCST) of the poly(NIPAM). Passing through the LCST has a drastic effect on the color of the latex solution, which exhibited an intense blue color at room temperature and gradually pales or lightens as the temperature is raised above 31°C. Analysis using spectroscopic and dynamic light scattering techniques showed that it is a reversible process. Microscopy evaluation of samples dried by the evaporation of water at temperatures above and below the LCST revealed that the swollen/collapse state of the polymer shell influenced the morphology of the dry state. Drying at room temperature resulted in thin films in which only particles of sizes corresponding to the polystyrene core are clearly seen in the microscopy images; but for samples prepared above the LCST, the images revealed a morphology made of much larger particles with diameters of 400–500 nm. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

聚苯胺溶解性研究

以苯胺氧化聚合和乳液聚合两种方法合成聚苯胺(PAn),研究了溶剂、聚合方法、反应温度、导电态、十二烷基苯磺酸用量等因素对聚苯胺溶解性的影响。结果表明,N-甲基吡咯烷酮是本征态聚苯胺的良溶剂,用乳液聚合法合成的聚苯胺其溶解性明显高于化学氧化法合成的聚苯胺,当乳液中十二烷基苯磺酸∶苯胺(摩尔比)=2.0∶1,聚合温度25℃时合成溶解率大的PAn。     

Step‐strain stress relaxation of carbon black‐loaded natural rubber vulcanizates

Step‐strain stress relaxation experiments were performed on natural rubber vulcanizates of various carbon black (HAF) concentrations by subjecting the samples to a very rapid strain and fixing its length at the deformed state. Time–temperature superposition in the viscoelastic region was evaluated to investigate the effect of temperature on the relaxation times of the rubbery composites. Remarkably, it was observed that, at higher HAF concentrations, increasing the temperature had a lesser effect on decreasing the overall stress values. That was attributed to the lower number of elastomeric chains per unit volume due to the agglomeration of the carbon black particles. The energy barrier resulting from the adsorption of the rubbery chains on the filler particles was insufficient to drastically reduce the diffusion and rearrangement of the polymer chains. The activation energy of the rubber‐like deformation calculated from the time–temperature superposition was shown to be independent of temperature. Interestingly, the viscosity coefficients showed a large increase with a modest addition of the carbon black. This is due to the long‐range nature of the temporary bonds formed between the polymer molecules and the surface‐active carbon black. The stress–strain of the rubbery composites was shown to behave in a Gaussian manner in accordance with the Mooney–Rivlin relationship. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3387–3393, 2004     

In situ Raman spectroelectrochemical study of redox processes at poly(Toluidine blue) modified electrode

Electrooxidation of hydroquinone and ascorbic acid at a gold electrode modified with electropolymerized layer of phenothiazine dye Toluidine blue (PTB) has been studied with the use of in situ Raman spectroelectrochemical technique, surface enhanced resonance Raman spectroscopy (SERRS). It was shown that the redox state of PTB at any electrode potential can be determined in pH 1.0 and 4.0 solutions following specific changes in Raman spectra of these modifier layers. Electrooxidation of hydroquinone at PTB modified electrode in pH 1.0 solution, and of ascorbic acid in pH 4.0 solution, proceed without any detectable changes in a net redox state of modifier layers. It has been concluded that, under the conditions studied, both anodic oxidation processes occur most probably at the modifier/electrolyte interface rather than within the modifier film, as opposed to electrooxidation of same species at polyaniline modified electrodes studied earlier.     

Chemical sensing materials based on electrically‐conductive immiscible polymer blends

Two families of electrically‐conductive immiscible polymer blends were studied as liquid sensing materials for an homologous series of alcohols. The systems studied include: multiphase matrices [containing carbon black (CB)] consisting of either polypropylene or high‐impact polystyrene as the major phase and thermoplastic polyurethane as the minor dispersed phase; and polyaniline (PANI) dispersed within a polystyrene matrix. Extruded filaments, produced by a capillary rheometer at various shear‐rate levels were used in the sensing experiments. The electrical resistance of these filaments was selectively sensitive to the various alcohols. Moreover, the responses displayed by these filaments are reproducible and reversible. The sensing behaviour of these blends is determined by the nature of the blend components, the blend composition and the processing conditions. An attempt is made to identify the dominant mechanisms controlling the sensing process in CB‐containing immiscible polymer blends and PANI‐containing blends. In addition, the sensing performances of these blends are compared in the light of their sensing mechanisms. Copyright © 2005 Society of Chemical Industry     

Polymerization of Aniline Using Iron(III) Catalyst and Ozone,and Kinetics of Oxidation Reactions in the Catalytic System

The environmentally benign polymerization of aniline provided polyaniline with an emeraldine structure by using iron(III) and ozone which is easily converted from oxygen in air. The influence of the reaction temperature upon the molecular weight of the polyaniline in this system is different from that in the polymerization of aniline using ammonium peroxodisulfate as an oxidant. Although the polyaniline prepared here has low molecular weight, the low molecular weight of the polyaniline does not significantly influence the electrical conductivity of cast films. In contrast, this can provide an advantage for the engineering of polyaniline through solution‐processing. Kinetics of oxidation reactions in the polymerization, systematically investigated here, has revealed that polyaniline is produced catalytically in terms of iron(III) and that an oxidation reaction of iron(II) to iron(III) could be a rate‐determining step in the polymerization.     

Acrylic acid‐doped polyaniline sensitive to ammonia vapors

Acrylic acid and HCl‐doped polyanilines were synthesized by chemical oxidative polymerization. The synthesized materials were used as sensors for ammonia. Comparison of the responses of the two polymers reveal that the acrylic acid‐doped polymer exhibits higher sensitivity and reversibility. Further, the resistance is observed to decrease on exposing the acrylic acid‐doped polyaniline to saturated ammonia vapors. A reversed trend is observed in the case of HCl‐doped polyaniline. The results are explained in terms of the differences in the chemical interactions of the two polymers with respect to ammonia vapors. The proposed mechanism is further supported by the X‐ray diffraction and FTIR analysis. The X‐ray diffractogram of acrylic acid‐doped polymer shows an enhancement in the crystallinity on exposure to ammonia vapors, while the HCl‐doped polymer exhibits a loss in crystallinity. The FTIR spectra shows a higher doping level in acrylic acid doped polymer as observed from the intense peak of the dopant ion at 1158 cm⁻¹, which is seen to be shifted to a lower wavenumber i.e. ∼1128 cm⁻¹ on exposing the polymer to ammonia vapors. On the other hand, in HCl‐doped polyaniline, the peak of the dopant ion ∼1120 cm⁻¹ is initially less intense, which is further suppressed on exposure to ammonia. Conductivity measurements show a large vapor‐induced increase in conductivity, in the case of ammonia‐exposed acrylic acid‐doped polyaniline, which results in the formation of a more crystalline‐conducting phase. Exactly the opposite results were obtained in the case of HCl‐doped polyaniline exposed to ammonia. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1994–1998, 2001     

Polyaniline nanofibers: a unique polymer nanostructure for versatile applications

Known for more than 150 years, polyaniline is the oldest and potentially one of the most useful conducting polymers because of its facile synthesis, environmental stability, and simple acid/base doping/dedoping chemistry. Because a nanoform of this polymer could offer new properties or enhanced performance, nanostructured polyaniline has attracted a great deal of interest during the past few years. This Account summarizes our recent research on the syntheses, processing, properties, and applications of polyaniline nanofibers. By monitoring the nucleation behavior of polyaniline, we demonstrate that high-quality nanofibers can be readily produced in bulk quantity using the conventional chemical oxidative polymerization of aniline. The polyaniline nanostructures formed using this simple method have led to a number of exciting discoveries. For example, we can readily prepare aqueous polyaniline colloids by purifying polyaniline nanofibers and controlling the pH. The colloids formed are self-stabilized via electrostatic repulsions without the need for any chemical modification or steric stabilizer, thus providing a simple and environmentally friendly way to process this polymer. An unusual nanoscale photothermal effect called "flash welding", which we discovered with polyaniline nanofibers, has led to the development of new techniques for making asymmetric polymer membranes and patterned nanofiber films and creating polymer-based nanocomposites. We also demonstrate the use of flash-welded polyaniline films for monolithic actuators. Taking advantage of the unique reduction/oxidation chemistry of polyaniline, we can decorate polyaniline nanofibers with metal nanoparticles through in situ reduction of selected metal salts. The resulting polyaniline/metal nanoparticle composites show promise for use in ultrafast nonvolatile memory devices and for chemical catalysis. In addition, the use of polyaniline nanofibers or their composites can significantly enhance the sensitivity, selectivity, and response time of polyaniline-based chemical sensors. By combining straightforward synthesis and composite formation with exceptional solution processability, we have developed a range of new useful functionalities. Further research on nanostructured conjugated polymers holds promise for even more exciting discoveries and intriguing applications.     

On the nature of polymer interfacesd and interphases

An abbreviated review of the current state of knowledge of polymer interfacial phenomena is given. Classical thermodynamics treats the interfacial zone (the interphase) as a “black box” and yields rigorous relationships among interfacial quantities. A recent reformulation of interphase thermodynamics, which eliminates the use of a Gibbs dividing surface, is shown to be an invaluable tool for investigating interfacial properties. Microscopic theories, such as the gradient theory, yield more details about what is in the black box, but the information is only approximate. The gradient theory has been used to: (1) relate the surface tension of a polymer liquid to its isothermal compressibility, (2) develop a quantitative theory of polymer liquid surface tension, and (3) determine the interfacial tension between two immiscible polymer liquids. The gradient theory will be shown to be in harmony with the microscopic theory of Helfand and co-workers although the latter treats polymer interfaces from a completely different point of view.     

Low‐potential electrochemical polymerization of 6‐nitroindole and characterization of its polymers

Conducting polymers bearing nitro substituents are very important from both academic and industrial viewpoints. However, it is very difficult to electrosynthesize such conducting polymers because of the strong electron‐withdrawing effect of nitro groups. In this article, we describe the electrochemical synthesis of films of a new conducting polymer, high‐quality poly(6‐nitroindole) (P6NI), by direct anodic oxidation of 6‐nitroindole in boron trifluoride diethyl etherate containing 10% (v/v) diethyl ether. The oxidation potential onset of 6‐nitroindole in this medium has been measured to be just 0.98 V versus a saturated calomel electrode (SCE), which is much lower than that determined in acetonitrile containing 0.1 mol/L tetrabutylammonium tetrafluoroborate (1.6 V vs SCE). Thermal studies have revealed that P6NI displays good thermal stability. The electrical conductivity of the P6NI films has been measured to be 0.08 S/cm. Structural studies have shown that the polymerization of the 6‐nitroindole ring occurs mainly at the 2,3‐positions. Fluorescence spectral studies have shown that the principal excitation and emission peaks of P6NI are at 416 and 535 nm, respectively, with a fluorescence quantum yield of 0.05. All these properties of P6NI films may facilitate their potential applications in various fields, such as electrochemical sensors and green‐light‐emitting materials. To the best of our knowledge, this is the first report on the electrosynthesis and characterization of 6‐nitro‐substituted polyindole films. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation and characterization of green reflective films of polyaniline analogs containing azobenzene units

Pd‐catalyzed polycondensation of aniline derivatives and 4,4′‐dibromoazobenzene affords polyaniline analogs containing azobenzene units. The polymers are red in solution and in thin films state, whereas they have a green luster in thick films. Substitution of 4,4′‐dibromoazobenzene for 4,4′‐dibromostilbene changes the reflection color from green to blue, whereas the introduction of a non‐conjugated unit slightly affects the reflection color. The glossiness of the film is dependent on the smoothness of the film surface. The reflectance measurements using polarized light reveal that reflection spectra correlate well with the complex refractive index (ñ = n + ik) of the film. These results confirm that the green luster can be attributed to the uniform surface reflection of the object, which has a large refractive index and absorption coefficient at around 500 nm. The polymer films exhibit good transmission of radio frequency signals owing to the lack of free electron carriers. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41275.