Preparation of polyaniline–TiO2 composite and its comparative corrosion protection performance with polyaniline

Due to strict environmental regulations on the usage of chromate in the coating industries, search for effective inhibitive pigment in replacing those chromate pigments has become necessary. In recent years it has been shown that electrically conducting polymers such as polyaniline (PANI) incorporated coatings are able to protect steel due to their passivating ability similar to that of chromates. This work presents the comparative corrosion protection performance of the coatings containing polyaniline and polyaniline–TiO₂ composite (PTC) on steel in acrylic binder. The PANI and PTC were prepared by chemical oxidative method of aniline by ammonium persulfate. The polymers were characterized by FTIR, XRD and SEM. The corrosion protection performance of the coatings containing PANI and PTC on steel was evaluated by immersion test in 3% NaCl for 60 days and salt fog test for 35 days. The performance of the coatings in both the tests was investigated by open circuit potential measurements and EIS technique. It has been found that the open circuit potential values of PTC containing coating are more nobler by 50–200 mV in comparison to that of coatings with PANI. Besides, the resistance values of the coating containing PTC were more than 10⁷ Ω cm² in the 3% NaCl immersion test after 60 days and 10⁹ Ω cm² in the salt fog test of 35 days which were two orders high in comparison to that of PANI containing coatings. The better performance of PTC containing coatings may be due to uniform distribution of polyaniline which can form uniform passive film on the iron surface.     

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.     

Preparation and characterization of polyaniline film on stainless steel by electrochemical polymerization as a counter electrode of DSSC

Polyaniline (PANI) films were electrodeposited on stainless steel 304 (SS) from 0.5 M H₂SO₄ solution containing 0.3 M aniline by potentiostatic techniques to prepare a low cost and non-fragile counter electrode in dye-sensitized solar cell (DSSC). The compact layer, micro-particles, nanorods and fibrils were observed on the top of PANI films with different applied potentials (E_appl) by SEM. Then the conductivity and electrochemical test illuminated that a polyaniline film with the highest conductivity and best electrocatalytic activity for I₃^?/I^? reaction was electrodeposited at 1.0 V E_appl. Finally, the photoelectric measurement showed that the energy conversion efficiency of DSSC with the PANI electrode was increased with the E_appl decreasing. And the efficiency of DSSC with PANI counter electrode at 1.0 V was higher than that with Pt electrode, owing to the loosely porous structure, high conductivity and excellent catalytic activity of PANI electrode.     

The influence of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) additive concentration and stretch orientation on electronic transport in AMPSA-modified polyaniline films prepared from an acid solvent mixture

We examine the effects of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA)-additive concentration, molecular weight, and specimen elongation on the temperature-dependent electronic transport properties of polyaniline films prepared with AMPSA in the presence of a great excess of a formic and dichloroacetic acid (DCAA) solvent mixture. The AMPSA-additive dependent resistivity and thermopower are reported for free-standing PANI:AMPSA_x (M_w=200,000 g mol⁻¹) films (x=0.1–0.5) in the temperature range from 2 to 325 K. The low-temperature data indicate that these samples are just on the insulating side of a disorder-induced metal–insulator (M–I) transition (dρ/dT<0), and that thermal motion at elevated temperatures is sufficient to produce a metallic state (dρ/dT>0) at room temperature. Transport occurs via variable-range hopping (VRH) for temperatures below 200 K, with hopping parameters that are a strong function of x; increased AMPSA concentration decreases the resistivity and moves the samples towards the M–I phase boundary. There is a minimum in the resistivity for all samples at a temperature T_min that is also doping dependent. Stretch orientation of PANI:AMPSA_0.5 films, prepared with higher molecular weight PANI (M_w=300,000 g mol⁻¹), along the resistivity measurement direction decreases the room-temperature resistivity at the expense of a more insulating low-temperature state. The T_min values of both stretched and unstretched PANI:AMPSA_0.5 films are pushed below 200 K, which reflects reduced disorder in film processed with higher molecular weight polyaniline. These results reflect an evolution in the underlying inhomogeneous mesoscopic disorder present in doped conducting polymers.     

Viscoelastic and conductivity properties of thermoreversible polyaniline–DNNSA gel in m-cresol

The rheological behavior of polyaniline (PANI)–dinonylnaphthalene sulfonic acid (DNNSA) in m-cresol is studied for different weight percent (w/v) of PANI–DNNSA_0.5. From rheological viewpoint the sample behaves like viscous fluid at low concentration (2 wt%) and gel at the concentration ≥8 wt%. The 4 wt% PANI–DNNSA_0.5 in m-cresol is at typical viscoelastic percolation region which is sol in the absence of shear but show invariant storage modulus with frequency at 30 °C. SEM picture indicates fibrillar network structure in the gel and the doped polyaniline remain as nanofiber at ≤2 wt% concentrations. The complete doping of PANI in all the systems is confirmed from UV–vis spectra. The dc conductivity of the gel increases with increasing the concentration of PANI–DNNSA_0.5 in m-cresol showing a jump at ～4% concentration (percolation threshold). ac-Conductivity increases with increase in PANI–DNNSA_0.5 concentration studied here for each frequency. At lower frequency (<10⁵ Hz) ac-conductivity increase slowly with frequency but at higher frequency (>10⁵ Hz) the increase is large having a curve like behavior. The gel state shows an increase of module by ～5 orders and also an increase of ～3 orders in ac-conductivity at the same frequency. The impedance spectroscopy results suggest the formation of combined resistance and capacitance (R–C) circuits in the gel and the increase of PANI–DNNSA_0.5 in the gel increases the capacitive feature more dominantly though the path becomes less resistive. The process also signifies the preparation of DNNSA doped PANI nanofiber in the gel medium.     

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.     

Electrical,structural and magnetic properties of polyaniline/pTSA-TiO2 nanocomposites

Polyaniline (PANI)/para-toluene sulfonic acid (pTSA) and PANI/pTSA-TiO₂ composites were prepared using chemical method and characterized by infrared spectroscopy (IR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM). The electrical conductivity and magnetic properties were also measured. In corroboration with XRD, the micrographs of SEM indicated the homogeneous dispersion of TiO₂ nanoparticles in bulk PANI/pTSA matrix. Conductivity of the PANI/pTSA-TiO₂ was higher than the PANI/pTSA, and the maximum conductivity obtained was 9.48 (S/cm) at 5 wt% of TiO₂. Using SQUID magnetometer, it was found that PANI/pTSA was either paramagnetic or weakly ferromagnetic from 300 K down to 5 K with H_C ≈ 30 Oe and M_r ≈ 0.015 emu/g. On the other hand, PANI/pTSA-TiO₂ was diamagnetic from 300 K down to about 50 K and below which it was weakly ferromagnetic. Furthermore, a nearly temperature-independent magnetization was observed in both the cases down to 50 K and below which the magnetization increased rapidly (a Curie like susceptibility was observed). The Pauli susceptibility (χ_pauli) was calculated to be about 4.8 × 10^?5 and 1.6 × 10^?5 emu g^?1 Oe^?1 K for PANI/pTSA and PANI/pTSA-TiO₂, respectively. The details of these investigations are presented and discussed in this paper.     

Synthesis of polyaniline nanotubes using Mn2O3 nanofibers as oxidant and their ammonia sensing properties

In this work, a new method for the synthesis of polyaniline (PANI) nanotubes was presented. Experimentally, Mn₂O₃ nanofibers prepared by electrospinning technique were used as the oxidant template to initiate the polymerization of aniline in acid solution. After reaction, polyaniline shells were formed on the Mn₂O₃ nanofiber surface, and the Mn₂O₃ nanofibers were spontaneously removed. As a result, PANI nanotubes were obtained. As-prepared PANI nanotubes show an average diameter of 80 nm and inner diameter of 38 nm. The final PANI nanotubes were characterized by SEM, EDX, TEM, FTIR and XRD. The gas sensing of as-obtained PANI nanotubes was also investigated. It was found that the PANI nanotube sensing device could detect as low as 25 ppb NH₃ in air at room temperature with good reversibility.     

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.     

Synthesis and characterization of polyaniline–Fe3O4 nanocomposite: Electrical conductivity,magnetic, electrochemical studies

Fe₃O₄ nanoparticles were prepared by hydrolysis reaction of urea in ethylene glycol as solvent at 160 °C. The prepared Fe₃O₄ nanoparticles were incorporated into polyaniline (PANI) matrix during in situ chemical oxidative polymerization of aniline with different molar ratios of aniline:Fe₃O₄ (19:1, 16:1, 12:1, 9:1) using (NH₄)₂S₂O₈ as oxidant in aqueous solution of sodium dodecylbenzene sulphonic acid under N₂ atmosphere. Room temperature conductivities of the synthesized PANI, PANI/Fe₃O₄ (19:1) and PANI/Fe₃O₄ (9:1) are 3.2 × 10^?4, 1.8 × 10^?5 and 1.0 × 10^?5 S/cm, respectively, indicating decrease of conductivity with increase of Fe₃O₄ in PANI. Saturation magnetizations of Fe₃O₄, PANI/Fe₃O₄ (19:1), and PANI/Fe₃O₄ (9:1) are 27.5, 5.5 and 6.3 emu/g, respectively, indicating an increase of ferromagnetic interaction with more incorporation of Fe₃O₄ in PANI matrix, whereas PANI is diamagnetic. Electrochemical studies shows that Zn-PANI/Fe₃O₄ (9:1) battery had delivered maximum discharge capacity (78.6 mAh/g) as compared to Zn-PANI battery (50.1 mAh/g) at constant current of 0.5 mA cm^?2. At constant resistance of 1000 Ω, discharge capacities of Zn-PANI/Fe₃O₄ and Zn-PANI battery are 73.37 and 50.8 mAh/g, respectively.     

Large-area network of polyaniline nanowires supported platinum nanocatalysts for methanol oxidation

Nanocomposites comprised of Pt nanoparticles and electrically conducting polymers were prepared and tested for the electrocatalytic performance towards oxidation of methanol. Films of polyaniline (PANI) synthesized independently by potentiostatic and galvanostatic method, PANI(V) and PANI(I), respectively, were used as the supporting matrix for loading Pt nanoparticles. PANI(V), PANI(I), PANI(V)/Pt, and PANI(I)/Pt films were characterized for structure and morphology using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). SEM image of PANI(I) reveals that the particles are highly porous and interconnected nanowires, whilst PANI(V) particles are granular. The large surface area in the nanofibrillar PANI(I) makes the dispersion of Pt particle with a lesser time for the deposition of Pt particles. The porous network structure of PANI(I) helps in effective dispersion of Pt particles (about 10–20 nm) and facilitates easy access of methanol to the catalytic sites. The electrocatalytic activity of PANI(I)/Pt is much higher (current density (24.7 mA/cm² mg) at 0.68 V) in comparison to PANI(V)/Pt and bulk Pt electrodes (the current density values of 5.5 and 7.5 mA/cm² mg).     

Studies on electrochemical copolymerization of aniline with o-phenylenediamine and degradation of the resultant copolymers via electrochemical quartz crystal microbalance and scanning electrochemical microscope

Electropolymerization of aniline in sulfuric acid solution in the presence of o-phenylenediamine (oPD) of various concentrations was investigated via the electrochemical quartz crystal microbalance (EQCM) technique. It was found that the polymerization occurred more favorably at high aniline-to-oPD molar ratios (F₁, 20 or above). The stabilities of the resultant copolymers against degradation were efficiently improved compared with that of polyaniline (PANI). The first-order kinetic constants for polymer degradation were estimated to be 2.07 × 10⁻³ s⁻¹ for polyaniline, and 3.91 × 10⁻⁴ and 1.28 × 10⁻⁴ s⁻¹ for copolymers with F₁ values of 50 and 20, respectively. The degradation product, benzoquinone, was also detected at the tip electrode of a scanning electrochemical microscope (SECM).     

A comparative study on polyaniline degradation by an electrochemical quartz crystal impedance system: electrode and solution effects

By combining the piezoelectric quartz crystal impedance (PQCI) and electrochemical impedance spectroscopy (EIS) measurements, we conducted a comparative study on polyaniline (PANI) degradation in different media, HClO₄ and H₂SO₄, and on different piezoelectric quartz crystal (PQC) electrodes, Pt and Au. It is concluded that (1) the PANI film grown on an Au electrode is more stable than that on a Pt electrode; (2) the PANI degradation reaction abides by the zero-order kinetic law in HClO₄ with rate constants from 0.17 to 2.25 Hz s⁻¹ on Pt and 0.16 to 0.83 Hz s⁻¹ on Au, but the first-order kinetic law in H₂SO₄ with rate constants from 2.61×10⁻³ to 7.00×10⁻³ s⁻¹ on Pt and 1.00×10⁻³ to 5.00×10⁻³ s⁻¹ on Au at different ion concentrations. The contrary effects of ClO₄⁻ and SO₄²⁻ on PANI degradation may be understood from the Hofmeister series of anions; (3) the dissolution of the PANI film bulk, the increase of film porosity and the film attenuation occurred simultaneously during degradation via systematic analyses of the motional resistance (R₁)and electrochemical impedance spectra responses, etc.     

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.     

NH3 and HCl sensing characteristics of polyaniline nanofibers deposited on commercial ceramic substrates using interfacial polymerization

This paper reports the use of the interfacial polymerization method in a simple route for fabricating low-cost, highly sensitive NH₃ and HCl gas sensors made of polyaniline (PANI) nanofiber coatings on commercially available ceramic substrates. The PANI coatings consisted of uniform nanofibers and formed emeraldine salt. NH₃ gas-sensing properties of as-synthesized PANI nanofibers were also investigated in detail. The influence of PANI nanofiber acidification treatment at different HCl solutions (pH = 0, 1, 2, and 3) on NH₃-sensing properties was discussed as well. As-synthesized PANI nanofibers exhibited very low detection limit (1 ppm) and high sensing response (response S) was above 2 when the sensor was exposed to 50 ppm NH₃ gas, though a limited drift of the response appeared in the reproducibility test. For acid-treated PANI sensors, the response time increased and response S decreased with increasing pH value of HCl solutions. Response S, especially after acid-treatment, increased as testing proceeded. This is possibly due to the creation of reaction sites on the surface and/or the bulk of the sensors. When PANI was used to detect gaseous HCl, an irreversible process occurred and response S became saturated when the concentration of gaseous HCl reached 200 ppm.     

Functional electrospun nanofibres of poly(lactic acid) blends with polyaniline or poly(aniline-co-benzoic acid)

Functionalised nanofibres of a controlled fibre diameter were electrospun from solutions of polyaniline (PANI) or poly(aniline-co-m-aminobenzoic acid) (P(ANI-co-m-ABA)) with poly(lactic acid) (PLA). Soluble copolymers of aniline (ANI) and m-aminobenzoic acid (m-ABA) were prepared and the average molecular weight of the copolymers, as determined by gel permeation chromatography, was found to decrease from 13,800 g mol^?1 to 1640 g mol^?1 with an increase of m-ABA content in the copolymer. By contrast, FT-MS results revealed that homopolymerisation of m-ABA formed oligomers rather than polymeric chains due to low reactivity of m-ABA monomer. ATR FTIR, Raman spectroscopy, and conductivity measurements confirmed incorporation of the conducting (co)polymers within the PLA based nanofibres. The conductivity of the nanofibres increased significantly with increased proportion of PANI or P(ANI-co-m-ABA) to 2.0 × 10^?5 mS cm^?1 for PLA/PANI (3.27% of PANI) and 8.3 × 10^?6 mS cm^?1 for PLA/P(ANI-co-m-ABA) (5.80% of the copolymer in the blend). The nanofibre diameter decreased from 640 ± 195 nm for pure PLA fibres to 141 ± 68 nm for PLA/PANI, and to 124 ± 31 nm for PLA/P(ANI-co-m-ABA). These fibres have potential for a range of applications, such as electroactive scaffold tissue engineering and sensing.     

Impact of hydrogen bonds in polyaniline.AMPSAn/acid solutions

Water concentration in polyaniline (PANI)/acid solutions containing 2-acrylamido-2-methyl-l-propanesulfonic acid (AMPSA) significantly changes the solubility of PANI and the stability of its solutions. By varying trace amounts of water, we investigated the impact of hydrogen bonds (H-bonds) on PANI chain conformation in solutions of AMPSA/dichloroacetic acid (DCAA) or AMPSA/orthophosphoric acid. UV–vis–NIR spectral changes of these PANI solutions reveal that a competition between H-bond formation and protonation among PANI, AMPSA and water is an on-going process. The H-bonds between the PANI and AMPSA molecules can cause a large red shift in the π_b → π_q electron transition (the quinoid peak) from ∼630 nm into the near IR (NIR) region. Absent protonation peak (410–490 nm) and blue color of the solution suggest that the H-bond interaction, instead of protonation, is sufficient to cause PANI chains to adopt an “expanded coil” chain conformation in the PANI.AMPSA_n/DCAA or H₃PO₄ solutions. Protonation leads to the gelation of PANI solutions. The kinetic mechanism of protonation of the PANI.AMPSA_n/DCAA solutions is studied. The activation energy of protonation in the PANI.AMPSA_0.6/DCAA solutions is ∼60 kJ/mol.     

Electrical and magnetic properties of the Fe3O4–polyaniline nanocomposite pellets containing DBSA-doped polyaniline and HCl-doped polyaniline with Fe3O4 nanoparticles

DBSA-doped polyaniline (DBSA–PANI) powder and HCl-doped polyaniline with Fe₃O₄ nanoparticles (HCl–PANI–Fe₃O₄) powder were mechanically mixed to obtain the Fe₃O₄–polyaniline nanocomposites. Powders of the nanocomposites were pressed to the pellets. Micromorphology, electrical and magnetic properties of the nanocomposite pellets were studied by using scanning electron microscopy and by measuring the conductivity in 100–300 K and the magnetization curve at room temperature. The DBSA–PANI pellets consist of long fibrils while the HCl–PANI–Fe₃O₄ pellets consist of granular particles. Thus the Fe₃O₄–polyaniline nanocomposites pellets consist of long fibrils and granular particles. The conductivity of the nanocomposite pellets linearly decreases from 0.19 ± 0.06 to 0.05 ± 0.01 S/cm when the HCl–PANI–Fe₃O₄ content increases from 0 to 100 wt.%. The variation of conductivity with temperature reveals that the charge transport mechanism can be considered to be one-dimensional variable-range-hopping (1D-VRH). All the Fe₃O₄–polyaniline nanocomposites show the magnetization curves. The saturation magnetization monotonously increases with increasing HCl–PANI–Fe₃O₄ content while the coercivity is estimated to be about zero independent of the HCl–PANI–Fe₃O₄ content. The saturation magnetization of the HCl–PANI–Fe₃O₄ is 11 emu/g.     

In situ UV–visible spectroelectrochemical studies on electrochromic behavior of poly(2,5-dimethoxy aniline)

The electrochromic characteristics of poly(2,5-dimethoxy aniline) (PDMA), have been evaluated using cyclic voltammetry, in situ UV–visible (UV–VIS) spectroscopy, cyclic spectrovoltammetry and spectrochronoamperometry. The results from cyclic voltammetry revealed that PDMA could be easily transformed from leucoemeraldine to emeraldine state in comparison with polyaniline (PANI). The conversion of reduced PDMA form into fully oxidized state could occur at a lower positive potential for PDMA than PANI (0.70 V for PANI and 0.27 V for PDMA). UV–VIS spectrum of PDMA showed three optical transitions at λ_max=375 nm (I), 460 nm (II) and 770 nm (III). The electrochemical transitions of PDMA while cycling the potentials were simultaneously monitored through UV–VIS spectroscopy. Results of cyclic spectrovoltammetry experiments revealed that the band at λ_max^II=460 nm corresponds to intermediate state between leucoemeraldine and emeraldine forms of PDMA. Hysteresis were noticed in the absorbance-potential profile for λ_max=375, 460 and 770 nm. The derivative cyclicvoltabstogram (DCVA) deduced from spectrovoltammetry reveals the presence of residual absorbance at E=0.0 V for PDMA. A linear correlation was noticed between half intensity of absorbance (E_1/2^A) at the wavelength 375, 460 and 770 nm and scan rate (ν). Electrochromic properties of PDMA like optical contrast, columbic efficiency and electrochromic efficiency are reported.     

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.