PANI Film Research Articles

Mixed doping of polyaniline with iron(III) chloride in the presence of hexafluoroacetylacetone: chemical and structural consequences

Sequential doping of polyaniline base in the oxidation state of emeraldine (abbreviated as PANI) first with iron(III) chloride and then treated with hexafluoroacetylacetone (HFAA) is described. The results obtained by using a combination of spectroscopic techniques (UV–vis–NIR, mass spectroscopy, Mössbauer effect spectroscopy, EPR) unequivocally show that complete Lewis acid-type complexation of PANI with FeCl 3 occurs only in the solid state, i.e. after removal of the solvent. In the solution an equilibrium is established between PANI complexed with FeCl 3 and FeCl 3 complexed with nitromethane. The addition of HFAA to the solution, being in equilibrium, transforms Lewis acid doped PANI into mixed doped polymer, which upon casting and solvent removal gives a solid material of a general formula: PANI(FeCl 3) x (HCl) y (HFAA) z . In this compound FeCl 3 is complexed with amine nitrogens, imine nitrogens are protonated with HCl. HFAA, dispersed in the polymer matrix, serves as a plasticizer. The determined chemical constitution is a direct consequence of the reaction of HFAA with FeCl 3 complexed on PANI imine sites to give HCl and iron(III) hexafluoroacetylacetonate. The former protonates the imine sites whereas the latter is removed from the system by extended pumping as proved by mass spectroscopy. Mössbauer spectra unequivocally show that FeCl 3 complexed on amine sites remains intact. Films of PANI(FeCl 3) x (HCl) y (HFAA) z show room temperature conductivity of ca. 3 × 10 −3 S cm −1 and improved mechanical properties as compared with PANI complexed solely with FeCl 3 due to HFAA plasticizing effects.

Chemical and Electrochemical Synthesis of Polyaniline/Gold Composites

The in situ synthesis of micrometer and nanometer gold particles in polyaniline (PANI/Au composite) using chemical or electrochemical methods, has been compared. The direct chemical synthesis of PANI/Au is initiated via the spontaneous oxidation of aniline by Gold colloid formation and subsequent reaction with PANI is monitored by in situ UV/vis spectroscopy. The emergent polymer nucleates on the gold as the PANI chain length increases, encapsulates the metal, and precipitates as its solubility limit is exceeded. Scanning electron microscopy images of these samples show relatively constant 1 μm diam gold particles. Electrochemical PANI/Au synthesis is initiated by reduction into an a priori electrochemically deposited PANI film. This method also produces a nearly uniform dispersion of Au particles but with significantly smaller 150-300 nm particles. The results indicate that electrochemical methods are more suitable for controlling particle dimensions. A minimal decrease in conductance is observed for the chemically formed PANI/Au when compared to PANI samples without the gold. A significant decrease in conductance is observed for the electrochemically formed composite. The large decrease in conductance is related to the decrease in proton doping and a greater number of oxidized units in the polymer upon electrochemical uptake and reduction of © 2004 The Electrochemical Society. All rights reserved.

Fabrication and Characterization of Schottky Junctions of Aluminum with Polyaniline Containing Hydrolysis Products

Schottky diodes based on Al/polyaniline (PANI), electrodeposited by cyclic voltammetry (CV) with two different upper oxidation potentials, 0.8 and 1.1 V, respectively, were fabricated. Auger electron spectroscopy (AES) confirms the presence of hydrolysis products of PANI, benzoquinone (BQ)/hydroquinone (HQ) for PANI film deposited with a switch potential of 1.1 V. The electrical properties of the Al/PANI (with inbuilt hydrolysis products) and Al/PANI (without hydrolysis products) junctions were evaluated at different temperatures by current-voltage characteristics and impedance spectroscopy measurements. The presence of inbuilt hydrolysis products with PANI influences the electrical properties of the junction. The junctions were found to be rectifying in both cases but with wide differences in junction parameters, such as barrier height, ideality factor, and saturation current density, between them. The temperature dependence of the impedance spectra of the devices was found to have variations. Impedance parameters of the devices were deduced from a proposed equivalent circuit. The combined analyses of current-voltage characteristics and impedance measurements reveal that the presence of hydrolysis products with PANI in Al/PANI junction increases the contact resistance, depletion layer thickness, and barrier height of the device. © 2004 The Electrochemical Society. All rights reserved.

Application of polyaniline as enzyme based biosensor

Abstract The PANI films have been synthesized electrochemically and are used as matrix for immobilization of glucose oxidase (GOD) and lactate dehydrogenase (LDH) enzymes. The temporal aspects of anion self-exchange in PANI films have been investigated. The exchange of bulkier tosylate–ferricyanide ion with Cl − ion has been monitored by photometry and electrochemical techniques. The relative changes in porosity brought about by self-exchange have been experimentally determined to be 323 and 2125/ k in tosylate-exchanged and ferricyanide-exchanged polyaniline films, respectively. It is seen that the polyaniline films exhibit enhanced loading of glucose oxidase after a self-ion exchange, and, hence they can be used for the fabrication of a third generation glucose biosensor. Lactate is determined by the photometric detection of NADH formed in the reaction catalysed by LDH. Studies have been carried out with PANI as a matrix for the immobilization of LDH and its feasibility as a biosensor. The results of the photometric and amperometric measurements conducted on such LDH/PANI electrodes show a response to pyruvate concentration upto 0.45 mM, a response time of 90 s and a shelf life of about two weeks.

Preparation and Electrochemistry of SWNT/PANI Composite Films for Electrochemical Capacitors

Single-walled carbon nanotube/polyaniline (SWNT/PANI) composite films were prepared by in situ electrochemical polymerization of an aniline solution containing different SWNT contents. Surface morphology and structural properties of these PANI-based films were examined by a scanning electron microscope and X-ray photoelectron spectroscopy. The electrochemical capacitance properties of these films were investigated with cyclic voltammetry, charge-discharge tests, and ac impedance spectroscopy. The composite film, based on the charge-transfer complex between well-dispersed SWNT and PANI matrixes, shows much higher specific capacitance, better power characteristics, and is more promising for applications in capacitors than a pure PANI film electrode. © 2004 The Electrochemical Society. All rights reserved.

Molecular-Level Manipulation of V2O5/Polyaniline Layer-by-Layer Films To Control Electrochromogenic and Electrochemical Properties

This work describes how manipulation at the molecular level of V2O5/polyaniline (PANI) nanocomposites built with the layer-by-layer (LBL) technique promotes enhancement of charge storage capability, new electrochromic effects, and control of ionic flux. By changing the film architecture we control the amount of PANI participating in the redox processes of the LBL films. As a consequence, the films display the electrochemical profile of V2O5 and the chromogenic properties of PANI. Impedance spectroscopy data show the presence of distinct phases in the nanocomposite, which allows a conducting path for the whole potential range between 0.5 and −1.5 V. Further control of the properties of the nanoarchitectures is achieved by adsorbing V2O5/PANI LBL films onto a cast PANI film. By changing the time of immersion of the PANI−V2O5/PANI system into a solution of LiClO4/propylene carbonate (PC), we were able to monitor the mass gain/loss (Δm) with an electrochemical quartz crystal microbalance (EQCM) as a function ...

Electrocatalytic properties and electrochemical stability of polyaniline and polyaniline modified with platinum nanoparticles in formaldehyde medium

We report the electro-oxidation of formaldehyde on polyaniline films modified with Pt nanoparticles (PANI-Pt films) in an aqueous sulfuric acid solution. The electrodeposition of Pt particles on the PANI matrix was found to promote a mass loss of the film, with a similar effect occurring after cycling the PANI films in the acidic medium containing formaldehyde. However, despite the electrochemical instability of PANI-Pt films, on films containing larger amounts of incorporated Pt particles, the oxidation of formaldehyde produces adsorbed CO species (CO ads) at a lower positive potential than on bulk Pt. Our findings also indicate that electro-oxidation of CO ads on the PANI-Pt film surface depends not only on the thickness of PANI film but also on the amount of Pt particles incorporated into the PANI matrix.

Doping level change of polyaniline film during its electrochemical growth process

AbstractPolyaniline (PANI) films doped with hydrochloric acid have been electrochemically deposited on mirrorlike platinum electrode surfaces by a cyclic voltammogram method. The Raman spectra of doped PANI films were investigated by excitation with a 633‐ or 785‐nm laser beam. It was found that the overall features of the Raman spectra depend strongly on the film thickness, due mainly to that the doping level of PANI film increases during the film‐growth process. X‐ray photoelectron spectroscopic (XPS) analysis and ultraviolet (UV)‐visible absorption spectrum results also confirmed this finding. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 171–177, 2004

Reduction of Cr(VI) Using Polyaniline–Polystirene-Divinyl Benzene Gels

Wastewaters generated by electroplating, Industry of Pigments, Tannins, etc. contain Cr(VI).The removal of Cr(VI)from wastewaters is necessary due to its toxicity; the admissible concentration being 10 ppm.This work studies quantitatively and qualitatively the possibility of treating waste waters that have a concentration of 0.1 g/l Cr(VI), by using DVB gels coated with Pani films.The Pani films were applied on the DVB's surface both by polymerization of aniline in acid medium, using ammonium peroxodisulphate as the oxidizing agent and by treating the DVB gels with Pani solutions in N,N-dimethylformamide.During reaction, the reduction rate of Cr(VI)decreases because the Pani films are degrading. This degradation is generated by over-oxidation, phenomenon that leads to a series of secondary hydrolysable products.

Electrochemical Polymerisation of Aniline on Skeleton Nickel Electrodes

The polyaniline(PAni)coating was electrochemically deposited on nickel skeleton electrode and nickel foil by potential sweep between − 0.2 V and 1.2 V/SCE, with a scan rate of 20 mV s−1; acid aqueous solutions containing 0.027 mol L−1aniline in 1 mol L−1sulphuric acid were used. The PAni film was studied by IR Spectroscopy, UV-VIS Absorption, Scanning Electron Microscopy, X-Ray Diffraction and Cyclic Voltammetry. The X-Ray studies suggest that the PAni films present a good cristalinity, as well as high molecular weight, possible high or intermediate crosslinked.

Microwave Conductivity Measurements of High Conductive Polyaniline Films

This article presents several techniques for determining the complex conductivity of highly electrically conducting polymer films at microwave frequencies. The advantages and disadvantages of these techniques are discussed. Microwave measurements were investigated using resonant cavity, reflection/transmission, and impedance surface techniques. The dc conductivity was measured using the four wires technique. Polyaniline (PANI/DEHEPSA) films of 120 μm thickness have conductivity of (5000–6000 S/m) and permittivity of 6000±1000 over X and S bands. The high values of the measured conductivity and its weak dependence on frequency at least up to 12 GHz confirm the metallic character of Pani films and their efficient use in microelectronic technology such as microwave integrated circuits (MMIC) and microwave devices.

Sensing Mechanism of Conducting Polymer Sensor for Volatile Organic Compounds

In this study, the chemically polymerized PPy and PANi films with different selectivity by controlling dedoping time were fabricated. Additionally, the sensing properties and mechanism of VOCs adsorption to conducting polymers were investigated with contact angles measurement, a scanning probe microscope (SPM) and a UV-Vis-NIR spectrophotometer. The thin sensor had higher sensitivity compared to the thick one, which the dedoped sensor at 1-minute had the highest ; sensitivity. Upon gas absorption, polypyrrole exhibited positive sensitivity while polyaniline had negative sensitivity. PPy film showed hydrophilic property and PANi film showed hydrophobic property. After gas absorption, the sensitivity increased as a function of the polarity of the absorbed molecules. These behaviors are due to the polar molecules absorbed with the movable polaron or free carrier, which then interrupts or generates the movement of polaron and carrier, and then changes the conductivity of the polymer. We found that conducting polymer sensors are very sensitive to the difference in polarity of gas molecules.

XPS study of aged polyaniline films

AbstractIn this article, a study of the aging of conducting Polyaniline–Polystyrene blends using X‐ray photoelectron spectroscopy (XPS) and UV‐visible‐near IR analysis is presented. The physicochemical results are compared to those obtained by electrical measurements. XPS results confirm the existence of an oxidation process also deduced by the electrical conductivity studies. The N1s and S2p core level spectra decomposition allows to show that a deprotonation process and cyclization of tertiary amine occur during aging. The absorption spectrum shows a decrease of delocalized charges and the apparition of localized polarons after a long aging time. All these mechanisms are responsible of the electrical conductivity decrease observed during aging at elevated temperature. The results are presented for films of PANI–CSA–PSt blends, but the conclusions can be extended to pure conducting PANI–CSA films. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3730–3736, 2003

Doping of polyaniline by thermal acid–base exchange reaction

Conducting polyaniline (PAni) films were prepared by heat treatment of the cast film from the homogeneous solution of the emeraldine base and the ammonium or alkylamine salts of various acids in N-methyl-2-pyrrolidone (NMP). Doping of the PAni was proceeded by the removal of the low boiling ammonia or alkylamine bases upon heating the cast film at 80–120 °C. Conductivity of the resulting PAni films was in the range between 0.01 and 5 S/cm depending on the structure and ratio of the dopants. Easy preparation of conducting composites was realized.

Improved surface properties of polyaniline films by blending with Pluronic polymers without the modification of the other characteristics

Films of conductive polyaniline and amphiphilic Pluronic (P105) copolymer blends were prepared by dissolving the two polymers in N-methylpyrrolidinone (NMP) followed by a slow solvent evaporation at 55 °C. The characteristics of both doped and undoped films were determined by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), water droplet contact angles, differential scanning calorimetry (DSC), thermal gravimetry analysis (TG), wide-angle X-ray diffraction (WAXD), and tensile strength measurements. The surface of the blends became more hydrophilic than that of the hydrophobic PANI film, but the other properties of the blends did not change appreciably for Pluronic content lower than 50 wt%. Compared to PANI films, the more hydrophilic surfaces decreased the amount of bovine serum albumin protein adsorbed. By preventing biofouling, the polyaniline–Pluronic blends can become more useful as biosensors than the polyaniline films.

O,p-Polyaniline: A New Form of a Classic Conducting Polymer

A new o-PANI-co-p-PANI copolymer was prepared in order to allow for the introduction of solubilizing and function-enhancing substituents on the conducting polymer backbone without concomitant loss of conductivity. An urea-protected trimeric aniline macromonomer with para−ortho−para connectivity and bromine end groups was condensed using palladium catalysis with a di-BOC-protected trimeric aniline comonomer with all para connectivity and amine end groups to give 5p,o-PANI. The new polymer has a repeat unit consisting of five para-substituted aniline rings for every one ortho-substituted aniline ring. The regioregularity of 5p,o-PANI (Mn = 14 000, GPC in NMP, polystyrene standards) was established using 1H NMR, 13C{H} NMR, and IR spectroscopy. Analogous with p-PANI, the 5p,o-PANI exhibited three distinct oxidation states. The conductivity of blends of 5p,o-PANI and PVC was on the same order of magnitude as the conductivity of PANI films prepared under the same conditions.

Catalytic polyaniline-supported electrodes for application in electrocatalysis

Polyaniline (Pani) films prepared on Au wires were employed as substrates to deposit Pt, Pt-Ru, Pt-Os, Pt-Mo and Pt-Ru-Os or Pt-Ru-Mo by using appropriate working solutions and a potential-programmed perturbation. The atomic percentages of the different metals on Pani were determined by EDAX and their particle size and distribution by SEM. The catalytic activity was tested for adsorbed CO and CH3OH electrooxidation. Accordingly, the best binary and ternary metal combination resulted in Pt-Ru and Pt-Ru-Os.

Solution processible poly(aniline) via doping with diesters of sulfosuccinic acid

We demonstrate that similarly as in the case of poly(pyrrole), diesters of sulfosuccinic acid containing alkyl or alkoxy substituents can serve as dopants inducing solution processibility of poly(aniline) (PANI). Free-standing films of PANI doped with sulfosuccinates, cast from 2,2′-dichloroacetic acid, show excellent thermal stability and electrical conductivity exceeding 100 S cm −1 which in addition is metallic in character down to 230 K.

Determination of physical parameters of conducting polymers by photothermal spectroscopies

Photothermal spectroscopies, photopyroelectric and photoacoustic, were used to obtain physical parameters of polyaniline–emeraldine base (PANI-EB) and poly(o-methoxyaniline)–emeraldine base (POMA-EB), such as thermic parameters like thermal diffusivity, thermal conductivity, and specific heat. These studies were done for PANI-EB and POMA-EB films in the 400<λ<900 nm wavelength range. The photopyroelectric intensity Vn(f ) and the phase Fn(f ) (f being the chopping frequency) for a given λ of the saturation part of the PPES spectrum signal were independently measured, as well as the intensity Vn(λ) and its phase Fn(λ). Equations of both the intensity and the phase of the PPES signal, taking into account the thermal and the optical characteristics of the PANI and POMA films and the pyroelectric detector, were used to fit the experimental results. It was observed that, in contrast with the strong doping dependence of the electrical conductivity, the thermal parameters of PANI films remained practically unchanged under doping. This apparent discrepancy is explained by the granular metal model of doped PANI.

Comparison of simple aromatic amines for electrosynthesis of permselective polymers in biosensor fabrication

A range of simple aromatic amines were used to modify Pt microcylinders with insulating electrosynthesised polymers generated amperometrically in the presence or absence of a typical globular protein, bovine serum albumin (BSA), at neutral pH. Sensitivity to a typical interference species, ascorbic acid (AA), and the most common electrochemical signal molecule for oxidase enzymes, H2O2, was used to compare the suitability of the resulting polymer–protein modified electrodes for biosensor applications. Pt modified with poly(aminobenzene), PANI, gave the lowest sensitivity to AA (∼3000 times lower than bare Pt); incorporation of BSA into the polymer during synthesis had a detrimental effect on its AA-rejecting capability. The H2O2 sensitivity of the PANI-based electrodes was poor (∼7 times lower) compared to bare Pt. The behaviour of poly(1,2-diaminobenzene), PoPD, was different in many respects: its AA-blocking ability was enhanced 3-fold by the presence of BSA and its H2O2 sensitivity was similar to bare Pt. EQCM data recorded in PBS indicated that PANI films electrosynthesised at pH 7.4 were two orders of magnitude thicker than for PoPD. These differences may be due, at least in part, to the ‘ladder’ structure with phenazine rings proposed for PoPD, since they were not duplicated by other mono-substituted derivatives of aniline, such as 2-methylaniline or 1,3-diaminobenzene.