Composite films of nanostructured polyaniline with poly(vinyl alcohol)

The uniform composite films of nanostructured polyaniline (PANI) (e.g. nanotubes or nanorods with 60–80 nm in diameter) were successfully fabricated by blending with water-soluble poly(vinyl alcohol) (PVA) as a matrix. The PANI nanostructures were synthesized by a template-free method in the presence of β-naphthalene sulfonic acid (β-NSA) as a dopant. The molecular structures of PANI–β-NSA and the related composite films were characterized by UV–Vis absorption spectrum, FTIR spectrum and X-ray diffraction. It was found that the electrical, thermal and mechanical properties of the composite films were affected by the content of nanostructured PANI–β-NSA in the PVA matrix. The composite film with 16% PANI–β-NSA showed the following physical properties: room-temperature conductivity is in the range 10⁻² S/cm, tensile strength ∼603 kg/cm², tensile modulus ∼4.36×10⁵ kg/cm² and ultimate elongation ∼80%.     

Conductive fibers from enzymatically synthesized polyaniline

Conducting polyaniline (PANI) fibers have been spun from a water-soluble form of PANI which was enzymatically synthesized. The enzyme, horseradish peroxidase (HRP) was used to polymerize aniline in the presence of sulfonated polystyrene (SPS) to directly form a water-soluble, conducting, PANI/SPS complex which combines moderate electrical conductivity with appreciable processability. The PANI/SPS complex was spun into fibers from aqueous solution using a dry-spinning technique. Thermal studies which included thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and DMA show that the complex has very good thermal stability and a T_g at 150°C. Mechanical properties of the fibers show a tenacity of 0.34 cN/dtex for the as-spun fibers with an increase to 0.56 cN/dtex after thermal stretch alignment. Wide angle X-Ray diffraction shows the presence of two weak peaks at d values of 4.16 Å and 2.95 Å for the drawn fibers, while no crystalline reflections were observed for cast films. The drawn fibers also show an order of magnitude improvement in conductivity. These results show that some degree of fiber orientation and crystallinity may be induced during processing.     

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.     

Corrosion inhibition performance of polymer-alloy bilayer coatings: electropolymerised polyaniline and electrodeposited ZnNi with different layer orders

Polyaniline (PANI) conducting polymer coatings have been obtained galvanostatically with various current densities (from 0·1 to 0·4 mA cm^?2) and ZnNi alloy coatings have been obtained galvanostatically at 30 mA cm^?2 current density. Corrosion protection performances of monolayered PANI and ZnNi alloy coatings and multi-layered ZnNi/PANI and PANI/ZnNi coatings on st-37 low carbon mild steel (MS) have been investigated by an open circuit potential method, Tafel extrapolation method and electrochemical impedance method in 3·5 wt-% NaCl solution. In addition, the surface morphology of the coatings has been characterised by using scanning electron microscopy (SEM). Synthesising PANI films between two metal layers provided better corrosion protection to the steel. MS/PANI/ZnNi layer formation exhibited the biggest corrosion protection performance among all layer formations of the films and protected MS for up to 72 h.     

Preparation of porous nanorod polyaniline film and its high electrochemical capacitance performance

Nano-sized polyaniline (PANI) films were electrochemically deposited onto an ITO substrate by a pulse galvanostatic method (PGM) in an aqueous solution. The morphology of the as-prepared PANI film was characterized using a field emission scanning electron microscope (FESEM). It was observed that the as-prepared PANI films were highly porous, and showed a nano-sized rod-like or coralline-like morphology depending on the charge loading performed in the electropolymerization process. Furthermore, the PANI films were electrochemically measured by the galvanostatic charge–discharge (GCD), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) tests in 1 mol L^?1 HClO₄ solution. The results showed that such PANI films had a favorable electrochemical activity and an excellent capacitance. The rod-like PANI film prepared with the charge loading of 1000 mC showed the highest discharge capacitance of 569.1 F g^?1 at a low current density of 1 A g^?1. The discharge capacitance retained 97.7% after 1000 cycles at a large current density of 10 A g^?1.     

Effect of current density on the corrosion protection performance of polyaniline coated AISI 4140 steel

The present work reports on electropolymerisation of aniline onto AISI 4140 steel substrate at room temperature in oxalic acid media by the potentiodynamic electrodeposition method. The effect of coating current density on the morphology of conductive polymer films and their corrosion behaviour has been investigated. The electrolyte solution comprised 0.1 M aniline?+?0.3 M oxalic acid. The effects of deposition current density changes (0.1, 0.2, 0.3, 0.4 and 0.5?mA cm^?2) on the films were investigated. The PANI film was characterised using cyclic voltammetry and optical microscopy; it was covered with a dark green-yellow homopolymer film of strongly adherent homogeneous characteristic. The corrosion behaviour of steel electrodes with and without polyaniline (PANI) film in 3.5 wt-% NaCl solution was investigated through anodic polarisation curves. The results indicated that the PANI coating obtained under 0.2?mA cm^?2 was the most corrosion protective.     

High dielectric constant polyaniline/poly(acrylic acid) composites prepared by in situ polymerization

An ultra-high dielectric constant composite of polyaniline, PANI–DBSA/PAA, was synthesized using in situ polymerization of aniline in an aqueous dispersion of poly-acrylic acid (PAA) in the presence of dodecylbenzene sulfonate (DBSA). The water-soluble PAA served as a polymeric stabilizer, protecting the PANI particles from macroscopic aggregation. A very high dielectric constant of ca. 2.0 × 10⁵ (at 1 kHz) was obtained for the composite containing 30% PANI by weight. The influence of the PANI content on the morphological, dielectric and electrical properties of the composites was investigated. The frequency dependence of dielectric permittivity, dielectric loss, loss tangent and electric modulus were analyzed in the frequency range from 0.5 kHz to 10 MHz. SEM micrograph revealed that composites with high PANI content (i.e., 20 wt%) consisted of numerous nano-scale PANI particles that were evenly distributed within the PAA matrix. The high dielectric constants of these composites were attributed to the sum of the small capacitors of the PANI particles.     

Effect of Aspergillus niger Tiegh. L-10 on the physical and chemical properties of a polyaniline coating in the growth substrate

The influence of the growth of Aspergillus niger Tiegh. fungi on the morphological, chemical and electrochemical properties of the polyaniline (PANI) modified Ni surface has been investigated. The strain of Aspergillus niger Tiegh. L-10 was cultivated on the malt extract agar (DIFCO OXOID). A PANI film was synthesized by potentiodynamic polymerization in an aqueous 0.3 M H₂C₂O₄ solution containing 0.1 M aniline on the Ni electrode. The electrochemical behaviour of polymer films was determined in a 0.05 M H₂SO₄ solution by the cyclic voltammetry method. The composition of PANI and Aspergillus niger Tiegh. treated PANI surfaces have been characterized using X-ray photoelectron spectroscopy (XPS). The morphology has been studied using scanning electron microscopy (SEM). The attachment of a polymer film via the metabolic product resulted in oxidation of the surface. It was estimated that at the PANI/microorganism interface, a Ca-complexed carboxylate interfacial reaction product was formed.     

Redox behaviour of polyaniline–palladium catalytic system in the presence of formic acid

Redox behaviour of polyaniline (PANI) films containing chemically incorporated palladium particles in the presence of formic acid was studied. Two types of PANI–Pd hybrids were prepared: PANI-PdHA and PANI-PdLA, depending on the acidity of the PdCl₂ solution used for the introduction of palladium into the polymer matrix. UV–vis spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to examine the nature of processes involved upon the decomposition of formic acid on polyaniline–palladium hybrids. In particular, UV–vis changes of both kinds of films were followed in situ (in 1 M aqueous HCOOH solution) as a function of time. Rather unexpectedly, the redox properties of polyaniline films are found to be significantly altered in the presence of palladium particles. Particles of Pd⁰ promote the reduction of PANI from the most oxidized and semi-oxidized states to the most reduced one with simultaneous decomposition of formic acid.     

In-situ electrochemical polymerization of multi-walled carbon nanotube/polyaniline composite films for electrochemical supercapacitors

Multi-walled carbon nanotube (MWCNT)/polyaniline (PANI) composite films were prepared by in-situ electrochemical polymerization of an aniline solution containing different MWCNT contents. The supercapacitive behaviors of these films were investigated with cyclic voltammetry (CV), charge–discharge tests, and ac impedance spectroscopy. The results revealed that the MWCNT/PANI films show much higher specific capacitance (SC), better power characteristic, better cyclic stability, and more promising for applications in supercapacitors than a pure PANI film electrode. The highest specific capacitance value of 500 F g^?1 was obtained for the MWCNT/PANI composite film containing MWCNT of 0.8 wt.%. The improvement mechanisms of the capacitance of the composites are also discussed in detail.     

PEDOT/PAMPS: An electrically conductive polymer composite with electrochromic and cation exchange properties

Poly(3,4-ethylenedioxythiophene) (PEDOT)/poly(2-acrylamido-2-methyl-l-propane sulfonate) (PAMPS) composite films were electrochemically prepared from a mixture of water and N,N-dimethylformamide (DMF) containing 3,4-ethylenedioxythiophene (EDOT) and the polyelectrolyte, PAMPS. The presence of PAMPS in the PEDOT matrix was confirmed by spectroscopic and electrochemical methods. Depending on the current density, the conductivity of PEDOT/PAMPS free standing composite films reached values of 80 S/cm. Spectroelectrochemistry of neutralized PEDOT/PAMPS composite films showed a maximum absorption at 2.0 eV (615 nm) and a band gap of 1.65 eV, as calculated from the onset of the π–π* transition. Thin PEDOT/PAMPS composite films were found to switch rapidly between oxidized and reduced states in less than 0.4 s with an initial optical contrast of 76% at λ_max: 615 nm. The morphology of the polymer composites demonstrates a cauliflower structure. Despite the high molecular weight of the polyelectrolyte, the film density was found to be similar to classical PEDOT (i.e., ca. 1.4 g/cm³), while the surface roughness averaged below 5%. As expected with the use of a sulfonated polyelectrolyte as dopant, cation exchange properties were observed with hexaammineruthenium(III) chloride as an active electrolyte.     

Solubility and rheological characterization of polyaniline base in N-methyl-2-pyrrolidinone and N,N′-dimethylpropylene urea

The thermodynamic ‘goodness’ of N-methyl-2-pyrrolidinone (NMP) and N,N′-dimethylpropylene urea (DMPU) as solvents for polyaniline (PANI) (emeraldine base) were compared by studying the dilute solution viscometry of solutions of PANI in NMP and DMPU. The intrinsic viscosity of PANI polymer in NMP was found to be 0.71 dl g⁻¹, whereas the same polymer in DMPU had an intrinsic viscosity of 0.77 dl g⁻¹, which indicates that DMPU is a ‘better’ solvent for PANI. The rheology and rheological stability of solutions of PANI in NMP and DMPU were studied by cone and plate rheometry. A 10% PANI solution in NMP gelled within 60 min, whereas a 17.5% solution in DMPU did not show any change in its viscosity for as long as 400 min. Solutions of PANI (10–17.5%) in DMPU displayed prominent shear thinning behaviour at lower shear rates (below 3 s⁻¹ and Newtonian behaviour at higher shear rates (3–15 s⁻¹). A solution of 10% PANI in NMP showed a similar prominent shear thinning followed by a gradual decrease in viscosity with an increase in shear rates, presumably due to breaking of the ‘weak’ thixotropic gel.     

Electro-Synthesis of Nano-Colloidal PANI/ND Composite for Enhancement of Corrosion-Protection Effect of PANI Coatings

The polyaniline/nanodiamond (PANI/ND) nanocomposite coating was prepared on mild steel via electrochemical polymerization using cyclic voltammetry technique. The ultrasonic irradiation was used for effectively dispersing ND particles in electropolymerization solution. The prepared nanocomposite films were found to be nano-colloidal, and very adherent with low porosity. The corrosion performance of the coatings was investigated in 0.5 M H₂SO₄ solution by electrochemical impedance spectroscopy and polarization methods. The obtained results showed that the presence of ND particles significantly enhanced the corrosion protection performance of the PANI films in 0.5 M H₂SO₄ corrosive medium. X-ray diffraction and FT-IR techniques confirmed the intercalation of the nanoparticles in PANI matrix.     

Microwave study of chemically synthesized conducting polyaniline on alumina

Polyaniline (PANI) thin film on alumina was prepared by the chemical oxidation of aniline with ammonium peroxydisulphate in acidic aqueous medium. DC conductivity, microwave transmission and reflection, microwave conductivity, shielding effectiveness and microwave dielectric constant of the conducting PANI films are reported. DC conductivity was between 0.15 × 10^?3 and 3.13 × 10^?3 S/cm. Microwave conductivity was between 0.2 and 10 S/cm. The PANI films coated on alumina gave shielding effectiveness value of ?1 to ?4 db. The ?′ was between 2 and 350 whereas ?″ was between 437 and 60. Measurements have been carried over the frequency range of 8.2–18 GHz.     

The manufacture and properties of polyaniline nano-films prepared through vapor-phase polymerization

We succeeded in the chemical preparation of nano-level thick polyaniline (PANI) emeraldine salt films on plastic substrate by an in situ vapor-phase deposition (VDP) polymerization method under ambient conditions, using a self-assembly method which is unprecedented. Homogeneous conductive PANI thin films were uniformly fabricated at nano-level thickness (20–100 nm), but their morphologies could grow as polycrystalline grains of a highly ordered structure, depending on the deposition conditions. The grain size was also controlled between 30 and 100 μm depending on the deposition time/temperature. The surface resistance of PANI films was enhanced up to 10⁴ Ω/square with crystallization and light transmittance was increased up to 90% in the case of a film less than 30 nm thick. A typical spectrum for the oxidized PANI, the emeraldine salts form, showing π–π^* transition and a polaron lattice were observed by UV–visible/IR and infrared /Raman spectroscopy.     

Electrosynthesis of polyaniline films on titanium by pulse potentiostatic method

Polyaniline (PANI) was synthesized on titanium electrode from aqueous solution containing 0.3 mol L⁻¹ aniline and 1 mol L⁻¹ HNO₃ by pulse potentiostatic method. The chronoamperogram during polymerization process of aniline was recorded. The effects of the synthesis parameters, such as anodic pulse duration (t_a), cathodic pulse duration (t_c), lower limit potential (E_c) and upper limit potential (E_a), on the morphology and electroactivity of the PANI films were investigated by scanning electron microscopy (SEM) and cyclic voltammetry (CV). SEM results present that flake, mica-like, quasi-fibrous and nano-fibrous PANI film could be synthesized with various polymerization parameters. Under the following conditions, t_a = 0.8 s, t_c = 0.1 s, E_c = 0 V and E_a = 1.0 V, high quality nano-fibrous PANI film with the best electroactivity was obtained. The CV results show that the PANI films with different morphologies, which were prepared under the same anodic polymerization charge, have obvious different characteristics. This means that the PANI films with different morphologies have different electrochemical activity.     

In situ template polymerization of aniline on the surface of negatively charged TiO2 nanoparticles

The in situ oxidative template polymerization of aniline was performed successfully on the surface of negatively charged titania (TiO₂) nanoparticles with a mean diameter of 40 nm using ammonium persulfate and a Chem-Solv solution at pH 1 and 25 °C. SEM showed that the resulting polyaniline (PANI)/TiO₂ composites were well dispersed in solution due to the electrostatic repulsion force. Ultraviolet/visible spectroscopy, thermogravimetric analysis, Fourier-transform infrared spectroscopy, and cyclic voltammetry showed that the optical, thermal, and electrical properties of PANI/TiO₂ composites were quite different from those of pure PANI or TiO₂, which was attributed to the strong interaction between the two components. The conductivity of the PANI/TiO₂ composite was estimated to be 0.91 × 10⁻¹ S/cm at 25 °C in the range of semiconductor.     

Self-assembled polyaniline nanotubes and nanoribbons/titanium dioxide nanocomposites

Self-assembled polyaniline (PANI) nanotubes, accompanied with nanoribbons, were synthesized by the oxidative polymerization of aniline with ammonium peroxydisulfate in an aqueous medium, in the presence of colloidal titanium dioxide (TiO₂) nanoparticles of 4.5 nm size, without added acid. The morphology, structure, and physicochemical properties of the PANI/TiO₂ nanocomposites, prepared at various initial aniline/TiO₂ mole ratios, were studied by scanning (SEM) and transmission (TEM) electron microscopies, FTIR, Raman and inductively coupled plasma optical emission (ICP-OES) spectroscopies, elemental analysis, X-ray powder diffraction (XRPD), conductivity measurements, and thermogravimetric analysis (TGA). The electrical conductivity of PANI/TiO₂ nanocomposites increases in the range 3.8 × 10^?4 to 1.1 × 10^?3 S cm^?1 by increasing aniline/TiO₂ mole ratio from 1 to 10. The morphology of PANI/TiO₂ nanocomposites significantly depends on the initial aniline/TiO₂ mole ratio. In the morphology of the nanocomposite synthesized using aniline/TiO₂ mole ratio 10, nanotubes accompanied with nanosheets prevail. The nanocomposite synthesized at aniline/TiO₂ mole ratio 5 consists of the network of nanotubes (an outer diameter 30–40 nm, an inner diameter 4–7 nm) and nanorods (diameter 50–90 nm), accompanied with nanoribbons (a thickness, width, and length in the range of 50–70 nm, 160–350 nm, and ～1–3 μm, respectively). The PANI/TiO₂ nanocomposite synthesized at aniline/TiO₂ mole ratio 2 contains polyhedral submicrometre particles accompanied with nanotubes, while the nanocomposite prepared at aniline/TiO₂ mole ratio 1 consists of agglomerated nanofibers, submicrometre and nanoparticles. The presence of emeraldine salt form of PANI, linear and branched PANI chains, and phenazine units in PANI/TiO₂ nanocomposites was proved by FTIR and Raman spectroscopies. The improved thermal stability of PANI matrix in all PANI/TiO₂ nanocomposites was observed.     

Indentation modulus and hardness of polyaniline thin films by atomic force microscopy

Polyaniline (PANI) thin films with different thicknesses have been deposited on indium tin oxide (ITO) coated glass substrates by electrochemical polymerization of the aniline monomer in H₂SO₄ aqueous solution. By using the tip of an atomic force microscopy (AFM) apparatus as an indenter, cantilever deflection versus sample vertical displacement curves have been acquired and analyzed for evaluating the contact stiffness, by using an approach analogous to that developed for standard depth sensing indentation (DSI) tests. After the calibration performed using a set of polymeric reference materials, indentation modulus and hardness of PANI films have been deduced as a function of the reached maximum penetration depth. By using a model originally proposed for the analysis of standard DSI measurements, indentation modulus and hardness values of only PANI are finally deduced from the corresponding apparent values measured for the film-substrate systems, although they have to be considered as semi-quantitative estimations, since the roughness of the films does not allow a certain determination of the local thickness in correspondence of the probed points.     

Polyaniline modified electrodes for detection of dyes

Polyaniline (PANI) is one of the most extensively used conjugated polymers in the design of electrochemical sensors. In this study, we report electrochemical dye detection based on PANI for the adsorption of both anionic and cationic dyes from solution. The inherent property of PANI to adsorb dyes has been explored for the development of electrochemical detection of dye in solution. The PANI film was grown on electrode via electrochemical polymerization. The as grown PANI film could easily adsorb the dye in the electrolyte solution and form an insulating layer on the PANI coated electrode. As a result, the current intensity of the PANI film was significantly altered. Furthermore, PANI coated stainless steel (SS) electrodes show a change in the current intensity of Fe²⁺/Fe³⁺ redox peaks due to the addition of dye in electrolyte solution. PANI films coated on both Pt electrodes and non-expensive SS electrodes showed the concentration of dye adsorbed is directly proportional to the current intensity or potential shift and thus can be used for the quantitative detection of textile dyes at very low concentrations.