A spectroelectrochemical study on polaron transformations in polyaniline in sulphuric and p-toluenesulphonic acids

The electrochemical processes involved in the oxidation of polyaniline in sulphuric and p-toluenesulphonic acids were studied under steady potential and during a potentiostatic current transient using UV-Vis absorption spectroscopy. It was found that sulphate ions are reversibly inserted into the polymer film on oxidation and removed during reduction, while tosylate ions are irreversibly accumulated slowly in the film and protons are exchange instead. The redox peaks involve two independent transformation equilibria of three main species: reduced species, polaron and bipolaron of different chain lengths. While the charge involved in the polaron transformation is less than 20% of the charge involved safely in the oxidation of polyaniline before the onset of degradation, a significant capacitive contribution 40–60% was detected before the start of further oxidation of the polaron to bipolarons. Nernstian analysis of the redox process was possible only for the reverse scan and with the absorption peak of the reduced form. The spectroscopic transients showed that the oxidation, which is much slower than the reduction, is essentially the same in both acids without a significant contribution of the diffusion of dopant species in contrast with the reduction process. ©1997 SCI     

Reduction of hexavalent chromium using polyaniline films. Effect of film thickness, potential and flow velocity on the reaction rate and polymer stability

Reduction of very toxic hexavalent chromium (Cr(VI)) to its trivalent state (Cr(III)) is necessary to facilitate the treatment of wastewater by precipitation or adsorption. The present study proposes the use of thin films of polyaniline on a conducting substrate for this purpose. The reduction rate of hexavalent chromium and the degree of degradation of the polyaniline film were studied as a function of the solution flow velocity, applied potential and film thickness. The reduction rate was significantly affected by the flow velocity, while the film thickness was observed to have little effect. The potential had no effect on the reduction rate within the range studied. The current efficiency was 100% in all experiments and no significant degradation of polyaniline was observed.     

Comparison between different conditions of the chemical polymerization of polyaniline on top of PET films

Composites produced during the in situ chemical polymerization of aniline on top of a poly(ethylene terephthalate) (PET) film, in different conditions, were studied by open‐circuit potential (Voc), ultraviolet‐visible, and infrared spectroscopy, electrical conductivity measurements, scanning electron microscopy, and atomic force microscopy. The polymerization monitoring by Voc showed a maximum associated with the intermediate pernigraniline oxidation state and a final formation of polyaniline (PANI) in the doped emeraldine salt (ES) form. Furthermore, high electrical conductivity values were obtained for the PANI–ES coating prepared under selected conditions. A globular formation was observed for the doped PANI–ES coating with globules of sizes of the same order and same shape of the PET, demonstrating the influence of the substrate on the coating morphology. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1220–1229, 2001     

X-ray photoelectron spectroscopy of conducting polyaniline and polyaniline–polystyrene blends

Conductive polyaniline solutions were chemically prepared using bis (2-ethylhexyl) hydrogen phosphate (DiOHP) as the dopant chemical species. The codissolution method leads to conductive polyaniline–polystyrene (PANI–PSt) composites with good mechanical properties. The electronic structure of both conducting PANI films and PANI–PSt blends was investigated by X-ray photoelectron spectroscopy, which allowed one to quantify the proportion of benzenoid amine, quinoid imine, and protonated units. Blending polyaniline with PSt does not involve important modifications in the polymer electronic structure. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1209–1214, 1998     

Shrinking rate of conducting grains in HCl–protonated polyaniline,polypyrrole, and polypyrrole/polyaniline blends with their thermal aging

The dc electrical conductivity (σ) of HCl‐protonated polyaniline, polypyrrole, and their blends was measured from 80 to 300 K for thermal aging times between approximately 0 and 600 h. The thermal aging took place at 70°C under room atmosphere. The change of σ with the temperature (T) and the decrease of σ with the thermal aging time (t) are consistent with a granular metal type structure, in which conductive grains are randomly distributed into an insulating matrix. Aging makes the grains shrink in a corrosion‐like process. From σ = σ(T) measurements the ratio s/d, where s is the average separation between the grains and d their diameter, as well as the rate d(s/d)/dt of their decrease with t were calculated. These revealed that the conductive grains consist of a shell, in which aging proceeds at a decreasing rate, and a central core, which is consumed at a much slower rate. Our measurements not only permitted the estimation of the shell thickness, which lies between 0 and 5 Å, but also gave quantitative information about the quality of the shells and the cores from their aging rates. The shells are consumed with an average rate of d(s/d)/dt = 6.6 × 10^?4 (h^?1), which is about 5 times greater than the more durable cores. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 117–122, 2005     

Preparation and electroanalytical characterization of polyaniline: Polyacrylonitrile composite films

Electrically conducting composite films of polyaniline:polyacyrlonitrile (PANI:PAN) prepared with varying composition ratios of aniline mixed with a fixed amount PAN. The films of optimum thicknesses (0.10 mm) were obtained using an electrically operated automatic pressure machine. The films polymerized by oxidative polymerization using 0.1M potassium persulphate (K₂S₂O₈), undoped in 1M aqueous ammonia (NH₄OH) and doped in 1M hydrochloric acid (HCl). The conductivity of composite films was studied by keeping it in 1M HCl for different time period using 4-in-line probe DC electrical conductivity measuring instrument and the temperature dependence of DC electrical conductivity was studied using isothermal technique. The PANI:PAN composite film is used as a working electrode in an electrochemical cell. Chemically doped composite film is used as cathode (working electrode), aluminum metal foil as anode (counter electrode) and platinum foil as reference electrode. The electrolyte is of 0.05M aluminum chloride (AlCl₃) in dimethyl sulfoxide (DMSO). The voltage of the working electrode is stabilized with respect to the reference electrode and current applied between the working and counter electrode through a 9-V battery. The change in voltage versus time is plotted as the discharge curve and reversing the cell processes results in the doping of the composite films. The diffusion coefficient of the dopant ion (Cl⁻) present in the fully doped films were estimated by the galvanostatic pulse technique and found to bedifferent in different samples in the range of 10⁻¹⁶ to 10⁻¹² cm² s⁻¹. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Influence of chemical polymerization conditions on the properties of polyaniline

The chemical polymerization of aniline in aqueous solutions was studied as a function of a wide variety of synthesis parameters, such as pH, relative concentration of reactants, polymerization temperature and time, etc. The polymer was synthesized using a number of different oxidizing agents and different protonic acids. It was found that the reaction yield was not sensitive to most variables. By contrast, the inherent viscosity of the polymer, measured in solutions in concentrated sulphuric acid, was strongly dependent on the synthesis parameters. Optimum reaction conditions are outlined for the chemical polymerization of aniline, for post-treatment with aqueous HCl solutions, and for compensation of the emeraldine salt into its base form. Under such conditions, high-quality polyaniline base was synthesized with an inherent viscosity (0.1% w/w polymer in sulphuric acid) as high as 2.32 dl g⁻¹.     

Optical and conductivity studies of Pseudo‐doped chitin‐polyaniline blend

In this article, we report the preparation and characterization of self‐doped conducting chitin, polyaniline blends by solution blending method. The characterization of the blends was done by UV–vis absorption spectrum, FTIR, and conductivity studies. Conductivity of the self doped blends increases from less than ～10^?7 S/cm to 2.15 × 10^?5 S/cm, depending on the percentage of polyaniline in the blend. Spectroscopic analysis shows interaction between chitin and polyaniline and the electronic states are similar to those of the emeraldine and protonically doped forms of polyaniline. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Frequency‐dependent conductivity and dielectric permittivity of polyaniline/CeO2 composites

The PANI/CeO₂ composites were synthesized using in situ deposition technique by placing fine graded CeO₂ in polymerization mixture of aniline. This is the single step polymerization process for the direct synthesis of emeraldine salt phase of polymer. Low frequency dielectric studies were carried out on pressed pellets of PANI/CeO₂ with various concentrations of cerium oxide (10, 20, 30, 40, and 50 wt % of CeO₂ in PANI). The results are interpreted in terms of polarons and bipolarons, which are responsible for the dielectric relaxation mechanism and frequency dependence of conductivity. It is found that a.c. measurements at room temperature may well serve as a parallel way to the time consuming d.c. conductivity versus temperature technique, to detect the thermal degradation of the transport properties in conducting polymers. It is observed that the charge motion via creation/annihilation of polarons and bipolarons increases as the weight percentage of the composite is increased. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1403–1405, 2006     

Synthesis and humidity sensitivity of conducting polyaniline in SBA‐15

Conducting polyaniline (PANI) was synthesized in mesoporous silica SBA‐15. The investigations of XRD, N₂ adsorption–desorption, and IR spectra confirm the existence of polyaniline in the channels of SBA‐15 hosts. The impedance of PANI/SBA‐15 composites was studied at different relative humidity (RH) levels, ranging from 11 to 95% RH. The loadings of PANI as well as the concentration of HCl solution have substantial influence on the impedance values. The variation in impedance value of all PANI/SBA‐15 composites is more obvious than that of bulk PANI samples at the same RH. All these results imply that PANI/SBA‐15 composites may have better humidity‐sensitive properties than those of bulk PANI samples. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1597–1601, 2004     

Effect of composition on the conductivity and morphology of ligno sulfonic acid sodium salt doped polyaniline

A systematic approach is developed to study the ligno sulfonic acid sodium salt (LSA) protonation or doping process with polyaniline emeraldine base (Pani‐EB) in organic solvents like dimethyl sulfoxide, and the influence of LSA‐doping on the properties of polyaniline was investigated in detail. The composition of Pani‐EB and LSA was varied in the weight ratio of 1:1 to 1:50 to investigate the effect of the dopant concentration on the conductivity and morphology. The doping process was confirmed by UV–vis and FTIR spectroscopes. The composition analysis indicates that only 50% of the LSA is used for the doping process irrespective of the weight ratio of LSA/Pani‐EB in the feed. The four probe conductivity measurement suggests that the conductivity of the doped samples are increasing with the increase in the ratio of Pani‐EB/dopant composition, and the high conductivity of the doped material was obtained in the range of 1.0 × 10^?2 S/cm. Scanning electron microscopy reveals that LSA induces a selective aggregation in the polyaniline chains to produce needlelike or rod‐shape morphology of sizes having ～0.2 μm diameter and 1 μm length. At very higher amount of LSA, the microrods are completely collapsed and form uniform continuous morphology. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2650–2655, 2006     

Flame retardancy afforded by polyaniline deposited on wood

Wood scantlings were coated with polyaniline (PANI) during the in situ polymerization of aniline with ammonium peroxydisulfate in an aqueous medium. The coating was made in hydrochloric or phosphoric acid solutions in both the absence and presence of stabilizers, poly(N‐vinylpyrrolidone) or colloidal silica. The PANI‐coated wood was placed in a flame or in a furnace operating at 400 or 600°C, and the decrease in the mass was determined. The wood coated with PANI was less reduced in its mass than uncoated samples and was converted to charcoal rather than to ashes. The deposition of related polymers, polypyrrole and poly(1,4‐phenylenediamine), provided similar protection against heat exposure. Fourier transform infrared and Raman spectra of the residues after the burning of PANI‐coated wood were compared. The soaking of wood in PANI colloids did not result in similar protection of wood against fire; the coating of the cellulose fibers with PANI during the polymerization was needed for the enhanced stability of wood at elevated temperatures. The concept of carbonization processes at the surface layer of PANI‐coated cellulose fibers leading to the formation of carbonaceous microtubes is offered to explain the improved stability of wood against flame and heat exposure. © 2006 Wiley Periodicals, Inc. J Appl PolymSci 103: 24–30, 2007     

Role of a chelating agent in the formation of polyaniline films on aluminum

A chelating agent, alizarin, was used to pretreat an aluminum surface before the electrochemical synthesis of polyaniline. Alizarin had two main effects on the process: (1) it suppressed the hydrogen evolution reaction and increased the current efficiency and (2) it stabilized the open‐circuit potential in a corroding environment, such as in 0.1M NaCl. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 819–823, 2003     

Electrochemical supercapacitor properties of polyaniline thin films in organic salt added electrolytes

We demonstrate optimized supercapacitive characteristics of electrodeposited polyaniline by adding organic salt into electrolyte. The optimum amount of the organic salt is found to be 2 wt % which provides better ionic conductivity of the electrolyte, leading to the improved specific capacitance of 259 Fg^?1. This capacitance remains at up to 208 Fg^?1 (80% capacity retention) after 1000 charge–discharge cycles. The optimized organic salt added electrolyte causes better rate performance and higher cyclability. Significantly reduced electrochemical charge transfer resistance at the electrode/electrolyte interface results in the increased ionic conductivity, which can be useful in electrochemically preferred power devices for better applicability. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40306.     

Thermal behavior of polyaniline films and polyaniline–polystyrene blends

In this article, a study of the thermal behavior of polyaniline films and polyaniline–polystyrene blends is presented. Transport measurements (electrical conductivity and thermoelectric power) at high temperature and thermogravimetric analysis show that an irreversible degradation is observed near 450 K for films doped with DiOHP and near 500 K for films doped with CSA. In both cases, the thermoelectric power is the most sensitive parameter to electrical degradation during the heating of conducting films. Electrical conductivity measurements during heating–cooling cycles show a diminution of the room temperature conductivity after evaporation of the solvent (water, m‐cresol). A model of cluster with a variable diameter allows interpreting this phenomenon by assuming the existence of a sensitive frontier to the solvent at the periphery of conducting clusters. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1848–1855, 2002; DOI 10.1002/app.10468     

Dielectric properties of thin films of Babassu‐based polymer and polyaniline blends

In the present work, we describe the preparation and subsequent characterization of polymeric blends consisting of a monoglyceride (MG) synthesized from the Babassu's oil and the already commonly employed polyaniline (PAni). By following changes in the complex impedance of capacitor‐like devices we observe that the presence of MG in the PAni/MG blends decreases electrical conductivity and that this decrease is a function of the content of MG in the blend, i.e., the blend with 30% of MG shows Z′ about seven times greater than the one with 10% of MG. Fourier transform infrared measurements prove the formation of MG and the presence of secondary amine groups (N? H bonds) in the blends, which allow for the chemical doping of PAni by protonation, further studies are necessary to access the viability of employing this new material as active layer in electronic organic devices. Atomic force microscopy images show the formation of agglomerates due to the presence of MG. In addition, the polymeric mixture acts only as a blend, providing a physical interaction between different components. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46198.     

In situ polyaniline film formation using ferric chloride as an oxidant

In situ polyaniline (PANI) films were grown from an aqueous hydrochloric acid solution on glass substrates via the chemical oxidation of aniline using hydrated ferric chloride, FeCl₃.6H₂O (FC). The effect of initial molar ratios of FC/aniline on the yield of PANI films was monitored using the quartz crystal microbalance technique. The morphology of the resultant polymer film and powder was examined using scanning electron microscopy. It was found that the film possesses a porous character; however, the polymer powder consists of small particles with interconnected nanofibers. The polymer powder formed in the bulk was characterized using the energy dispersive analysis of X-ray, the X-ray diffraction, and the thermal gravimetric analysis. A comparison between the PANI produced from FC and ammonium peroxydisulfate was considered and discussed. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Doping effects of cerium ion on structure and electrochemical properties of polyaniline

Polyaniline (PANI)/Ce³⁺ and PANI/Ce⁴⁺ composites were successfully prepared by in situ polymerization in an aqueous solution of poly(2‐acrylamido‐2‐methylpropane sulfonic acid) and characterized by Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, X‐ray photoelectron spectroscopy, SEM, TEM and electrochemical methods. The results showed that the PANI/Ce ion composites had a high degree of sphericity, high electrical conductivity and good electrochemical performance. The conductivity of PANI/Ce(NO₃)₃ reaches a maximum of 46.76 S cm^?1 at 20 wt% of Ce(NO₃)₃. It is increased by 377% by comparison with that of pure PANI. In particular, the polarization results showed that the corrosion current density (0.47 µA cm^?2) and the inhibition efficiency (97%) of PANI/Ce(NO₃)₃ were better than the results for PANI and PANI/Ce(SO₄)₂ composite. This suggested that the PANI/Ce(NO₃)₃ composite has promising applications in conductive materials, anticorrosion coatings and other related fields. © 2017 Society of Chemical Industry     

Electrochemistry of polyaniline: Study of the pH effect and electrochromism

Polyaniline was electrochemically synthesized from an aqueous medium with various acid electrolytes via potentiodynamic and potentiostatic techniques. The electrochemical synthesis of polyaniline was studied over various substrates, including Pt, Ti, Ni, and SnO₂ coated glass, and in various acid electrolytes. Cyclic voltammograms of electrochemically synthesized polyaniline were studied in HCl in a pH range of 1–4. Probable electrochemistry and chemical changes were deduced that occurred when polyaniline film was electrochemically oxidized and reduced between ?0.2 and 1.0 V versus a Ag/AgCl reference electrode in an acidic electrolyte at pH 1, and three corresponding oxidation and reduction peaks were described instead of two redox peaks (as observed by W. S. Huang, B. D. Humphrey, and A. G. MacDiarmid, J Chem Soc Faraday Trans 1 1986, 82, 2385). The electrochromic property was studied with changes in the chemical states of polyaniline during electrochemical oxidation and reduction. A new viscous electrolyte, aqueous AlCl₃ (pH 2), saturated with AgCl was used for the construction of an electrochromic display device. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 378–385, 2002     

Fabrication and characterization of hybrid films based on polyaniline and graphitic carbon nitride nanosheet

Hybrid films of polyaniline/graphitic carbon nitride (PANI/g‐C₃N₄) deposited on titanium was fabricated. First, g‐C₃N₄ as a two‐dimensional graphite‐like structure was synthesized by the stepwise condensation reaction of melamine and cyanuric chloride in the presence of N,N‐dimethylmethanamide as a high boiling point nonnucleophilic base. Then composite films of PANI/g‐C₃N₄ were prepared by in situ electrochemical polymerization of an aniline solution containing g‐C₃N₄. Different concentrations of g‐C₃N₄ were utilized to improve the electrochemical performances of the hybrids. The resulting PANI/g‐C₃N₄ composite films were characterized by X‐ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and ultraviolet–visible diffuse reflection spectroscopy techniques. The electrochemical performance of the composites was evaluated by cyclic voltammetry (CV). Application of the prepared samples has been evaluated as supercapacitor material in 0.5 M H₂SO₄ solution using CV technique. The specific capacitances of PANI/g‐C₃N₄ composite films were higher than obtained for pure PANI films. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44059.