Electrodepositions and capacitive properties of hybrid films of polyaniline and manganese dioxide with fibrous morphologies

Electrocodepositions were conducted in solutions of aniline and MnSO₄ through potential cycling to afford hybrid films of polyaniline (PANI) and manganese dioxide (PANI/MnO₂). The films obtained displayed characteristic redox peaks of PANI on cyclic voltammograms in acidic aqueous solution. While in 1.0 M NaNO₃ at pH 1, the films showed pseudocapacitive behaviors from 0 to 0.65 V vs. SCE. MnO₂ was detected through XRD and XPS measurements on the films. The codeposition of PANI with MnO₂ had dramatic effects on morphologies of the obtained hybrid films that displayed fibrous morphologies instead of granular one of PANI. Hybrid film PM50 obtained in the presence of 50 mM Mn²⁺ displayed a specific capacitance of 532 F g⁻¹ at 2.4 mA cm⁻² discharging current, 26% higher than that of similarly prepared PANI. It showed a coulombic efficiency (η) of 97.5% over 1200 cycles with 76% specific capacitance maintained.     

Raman based pH measurements with polyaniline

The reversible acid–base equilibrium between the emeraldine salt (ES) and the emeraldine base (EB) form of thin electropolymerized films of polyaniline (PANI) has been studied between pH 2 and 9 with in situ Raman spectroscopy using the 514, 633 and 780 nm laser excitation wavelengths. The electropolymerization of PANI was done with cyclic voltammetry in a flow cell from a solution consisting of 50 mM aniline and 1.0 M HCl. It is shown that the Raman signal of the CN stretching vibration at 1439 cm⁻¹, originating from the quinoid units of the EB form, can be used for pH measurements between pH 3 and 6 with the 633 nm laser. This vibration is strongly resonance enhanced by the 633 nm laser and its intensity grows therefore considerably in the pH interval where the ES–EB transition mainly takes place (pH 3–6). The influence of the film conditioning pH was also studied as well as the reproducibility of the Raman spectra when pH was changed several times from pH 6 to 3.     

Preparation and characterization of polyaniline with high electrical conductivity

In the present paper, polyaniline (PANI) was polymerized by ammonium persulphate using a chemically oxidative process under mild tempertures ranging from ?5–20°C. Electrical conductivity of as synthesized PANI got enhanced gradually owing to the increase in molecular weight and crystallinity with decrease in synthesis temperature. Extraction with tetrahydrofuran (THF) was employed as the purification method of emeraldine base (EB) to enhance the electrical conductivity of PANI effectively attributed to the removal of the low molecular weight fractions and defective molecular chains. Methanesulfonic acid (MSA) was used to dope EB due to its strong acidity and small molecular size, and the amount of dopant versus EB was also optimized. Using a novel “synergistic doping” process with m‐cresol, electrical conductivity of PANI is further enhanced owing to more regular molecular chains which resulted in better interchain charge carriers' conduction. The emeraldine salts obtained finally have high electrical conductivity reaching up to 32.5 S cm^?1, which is much higher than that of the conventionally synthesized sample reported previously. Copyright © 2008 John Wiley & Sons, Ltd.     

The use of trichloroacetic acid imprinted polymer coated quartz crystal microbalance as a screening method for determination of haloacetic acids in drinking water

An alternative screening method for haloacetic acids (HAAs) disinfection by-products in drinking water is described. The method is based on the use of piezoelectric quartz crystal microbalance (QCM) transducing system, where the electrode is coated with a trichloacetic acid-molecularly imprinted polymer (TCAA-MIP). This MIP comprises a crosslinked poly(ethyleneglycoldimethacrylate-co-4-vinylpyridine). The coated QCM is able to specifically detect the analytes in water samples in terms of the mass change in relation to acid-base interactions of the analytes with the MIP. The TCAA-MIP coated QCM showed high specificity for the determination of TCAA in aqueous solutions containing inorganic anions, but its sensitivity reduced in water samples containing hydrochloric acid due to a mass loss at the sensor surface. Cross-reactivity studies with HAA analogs (dichloro-, monochloro-, tribromo-, dibromo-, and monobromo-acetic acids) and non-structurally related TCAA molecules (acetic acid and malonic acid) indicated that recognition of the structurally related TCAA compounds by the TCAA-MIP-based QCM is due to a carboxylic acid functional group, and probably involves a combination of both size and shape selectivity. The total response time of sensor is in the order of 10 min. The achieved limits of detection for HAAs (20-50 μg l⁻¹) are at present higher than the actual concentrations found in real-life samples, but below the guidelines for the maximum permissible levels (60 μg l⁻¹ for mixed HAAs). Recovery studies with drinking water samples spiked with TCAA or spiked with mixtures of HAAs revealed the reproducibility and precision of the method. The present work has demonstrated that the proposed assay can be a fast, reliable and inexpensive screening method for HAA contaminants in water samples, but further refinement is required to improve the limits of detection.     

Structure–electrical property study of anisotropic polyaniline films

The relationships of the structure and electrical properties of anisotropic HCl‐doped polyaniline (PANI) films cast from N,N′‐dimethylpropylene urea (DMPU) solutions and stretched to different draw ratios were studied. The anisotropic structure of the stretched PANI films was examined by X‐ray diffraction, near‐infrared wave‐guide coupling, and polarized infrared measurements. The PANI emeraldine base (EB) films cast from DMPU solutions had a single‐phase noncrystalline structure, and stretching of the films did not cause crystallization to occur. The transition moment angles of two weakly absorbing infrared bands were determined, and the Hermans' orientation functions for the PANI EB films were calculated. The PANI films were then doped with HCl, and the electrical properties were determined by impedance spectroscopy. With a specially designed test fixture, the in‐plane and through‐plane impedance was obtained. The conductivity along the stretch direction increased with orientation. The in‐plane conductivity was significantly higher than the through‐plane conductivity. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 823–841, 2003     

Layer-by-layer self-assembly of polyelectrolyte complexes and their multilayer films for pervaporation dehydration of isopropanol

Two negatively charged polyelectrolyte complex colloidal nanoparticles (PEC⁻) and one positively charged nanoparticle (PEC⁺) were prepared and used as novel layer-by-layer (LbL) building blocks. These PEC nanoparticles include poly(2-methacryloyloxy ethyl trimethylammonium chloride)/sodium carboxymethyl cellulose (PDMC/CMCNa PEC⁻), poly(diallyldimethylammonium chloride)/CMCNa (PDDA/CMCNa PEC⁻) and PDDA/poly(sodium-p-styrenesulfonate) (PDDA/PSS PEC⁺). LbL multilayer films based on (PEC⁺/PEC⁻) were constructed on both quartz slides and modified polyamide (MPA) reverse osmosis support membranes. UV–vis spectroscopy, quartz crystal microbalance (QCM), field emission scanning microscopy (FESEM) and atomic force microscopy (AFM) were utilized to follow the thickness growth and morphology evolution of these multilayer films with increasing bi-layer numbers. LbL multilayer films deposited on MPA support membranes were subjected to pervaporation dehydration of 10 wt% water–isopropanol and effect of bi-layer numbers and feed temperature on pervaporation performance was studied. Generally, PEC⁺/PEC⁻ can be LbL self-assembled successfully on both substrates with a thickness growth rate ca. 200 nm/bi-layer. Moreover, PEC⁺/PEC⁻ multilayer films show high pervaporation performance with film thickness up to several micrometers. For example, performance of the multilayer films in dehydrating 10 wt% water–isopropanol at 50 °C is J = 1.18 kg/m² h, α = 1013 for (PEC⁺/PDMC-CMCNa PEC⁻)₂₄ and J = 1.36 kg/m² h, α = 938 for (PEC⁺/PDMC-CMCNa PEC⁻)₂₅, respectively.     

The absorption and thermal behaviors of PET-SiO2 nanocomposite films

In this paper, to improve properties of Poly(ethylene terephthalate) (PET) in thermal stability and barrier to water, the films of PET, PET with micronmeter Silica/Polystyrene (SiO₂/PS) composites (SPET) and PET with nano-SiO₂/PS composites (SNPET) are prepared and their water absorption and thermal stable behaviors are investigated.In the samples, silica load is optimized as 2 wt%, at which silica not only disperses well but also forms the tough morphology in PET as investigated by SEM. The nanoeffect and thermal degradation behaviors of SNPET are firstly presented.The water absorption experiments for the samples show that the maximum absorption water weight percentage (C_∞) and the pseudo-diffusion coefficient (D) of water reduce with SiO₂ particle size varying from 440 nm to 40 nm, and the barrier property to water of SNPET is superior to those of pure PET and SPET. At the minimum silica size of 40 nm, the C_∞ and D of SNPET approach the minimum values that are 0.946% and 7.075 × 10⁻¹³ m² s⁻¹, respectively. Fixing SiO₂ size at 40 nm, with un-modified SiO₂ and modified SiO₂, the core-shell SiO₂/PS nanocomposite particles are more effective on keeping PET from absorbing water. With the increase in nano-SiO₂ load, the C_∞ and D of SNPET films reduce, proving that the nano-SiO₂ particles can inhibit water absorption. When amorphous SNPET films are annealed at 130 °C, their C_∞ and D quickly decrease with the increase in annealing time, stating that the crystallized SNPET also retards the water absorption or diffusion in PET. Under oversaturated oxygen atmosphere, the C_∞ and D of amorphous PET and SNPET, and crystallized SNPET samples are higher than those of corresponding samples without flowing oxygen, showing that oxygen promotes the films to absorb water.TGA results show that SNPET keeps similar thermal degradation behavior under the conditions of with and without both water and oxygen. But SNPET is more thermally stable than PET.     

UV-Induced Electrical and Optical Changes in PVC Blends

 2-Chloro-polyaniline (2-Cl-PANI) in its non-conducting (emeraldine base, EB) form, prepared by a chemical route, was dissolved together with poly-(vinylchloride) (PVC) in THF for casting into thin (10–50 μm) films. Upon exposure to UV radiation, the electrical conductivity of these films increased by more than 4 orders of magnitude (from 10⁻⁶ to 10⁻²S/cm). This is attributed to the dehydrochlorination of PVC by exposure to energetic photons and subsequent doping of 2-Cl-PANI (i.e. conversion to emeraldine salt, ES) by in situ created HCl. The doped films could be returned to their undoped form by exposure to NH₃ vapours. The UV-induced doping/NH₃ undoping cycles could be repeated several times. Various spectroscopic techniques were employed to follow the changes in the films upon exposure to UV radiation. The same photo-dehydrochlorination process has also been utilized for optical and/or lithographic purposes by preparing PVC blends containing methyl violet, and acid-base indicator dye. The photo-dehydrochlorination can be effectively sensitized by incorporating hydroquinone into the PVC blends containing methyl violet.     

Morphology and thermal properties of conductive polyaniline/polyamide composite films

Polyaniline (PANI) in an emeraldine‐base form, synthesized by chemical oxidation polymerization, was doped with camphor sulfonic acid (CSA). The conducting complex (PANI–CSA) and a matrix, polyamide‐66, polyamide‐11, or polyamide‐1010, were dissolved in a mixed solvent, and the blend solution was dropped onto glass and dried for the preparation of PANI/polyamide composite films. The conductivity of the films ranged from 10^?7 to 10⁰ S/cm when the weight fraction of PANI–CSA in the matrices changed from 0.01 to 0.09, and the percolation threshold was about 2 wt %. The morphology of the composite films before and after etching was studied with scanning electron microscopy, and the thermal properties of the composite films were monitored with differential scanning calorimetry. The results indicated that the morphology of the blend systems was in a globular form. The addition of PANI–CSA to the films resulted in a decrease in the melting temperature of the composite films and also affected the crystallinity of the blend systems. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2531–2538, 2002     

pH sensor based on polyaniline and aniline–anthranilic acid copolymer films using quartz crystal microbalance and electronic absorption spectroscopy

The pH sensitivity based on conducting polyaniline (PANI) and copolymer of aniline and o‐anthranilic acid (AA) films were studied using quartz crystal microbalance (QCM) technique and UV–Vis spectroscopy. The sensor was constructed from these polymer films coated on the electrode of the QCM. The resonant frequency changes as a function of pH in the range of 2–12 were measured. These changes are quantitative indication of the degree of dedoping or redoping of the polymer films upon the subsequent exposure of the electrode to 0.25 M sulfuric acid and different pH solutions. There are two linear regressions between the frequency change and pH with two different and opposite slopes in the regions from 2 to 9 and 9 to 12. The pH sensitivity of the copolymer film was found to be less than using the PANI film. Thin films of PANI and copolymer, which were chemically polymerized in a sulfuric acid solution, were deposited onto the inner walls of the quartz cuvettes. The UV–Vis absorption spectra of these films were measured in different pH solutions. Relations between the maximum absorption and its wavelength versus pH were constructed. The copolymer film shows some advantages over the PANI film. The difference between the PANI and copolymer films as pH sensors using the QCM and electronic absorption extends from the determination of pK_a for both films. Copyright © 2008 John Wiley & Sons, Ltd.     

UV-Induced Electrical and Optical Changes in PVC Blends

Summary.  2-Chloro-polyaniline (2-Cl-PANI) in its non-conducting (emeraldine base, EB) form, prepared by a chemical route, was dissolved together with poly-(vinylchloride) (PVC) in THF for casting into thin (10–50 μm) films. Upon exposure to UV radiation, the electrical conductivity of these films increased by more than 4 orders of magnitude (from 10⁻⁶ to 10⁻²S/cm). This is attributed to the dehydrochlorination of PVC by exposure to energetic photons and subsequent doping of 2-Cl-PANI (i.e. conversion to emeraldine salt, ES) by in situ created HCl. The doped films could be returned to their undoped form by exposure to NH₃ vapours. The UV-induced doping/NH₃ undoping cycles could be repeated several times. Various spectroscopic techniques were employed to follow the changes in the films upon exposure to UV radiation. The same photo-dehydrochlorination process has also been utilized for optical and/or lithographic purposes by preparing PVC blends containing methyl violet, and acid-base indicator dye. The photo-dehydrochlorination can be effectively sensitized by incorporating hydroquinone into the PVC blends containing methyl violet. Received June 23, 2000. Accepted (revised) July 31, 2000     

Thermal degradation of polyaniline films prepared in solutions of strong and weak acids and in water - FTIR and Raman spectroscopic studies

Polyaniline (PANI) films were prepared in situ on silicon windows during the oxidation of aniline with ammonium peroxydisulfate in aqueous solutions of strong (0.1 M sulfuric) or weak (0.4 M acetic) acid or without any acid. In solutions of sulfuric acid, a granular PANI is produced, in solutions of weak acids or without any acid, PANI nanotubes are obtained. The thermal stability and structural variation of the corresponding films produced on silicon windows during treatment at 80 °C for three months were studied by FTIR and Raman spectroscopies. The morphology of the films is preserved during the degradation but the molecular structure changes. The results indicate that the spectral changes correspond to deprotonation, oxidation and chemical crosslinking reactions. The films of PANI salts loose their protonating acid. PANI bases are more stable than the salt forms during thermal ageing. The films obtained in water or in the presence of acetic acid are more stable than those prepared in solutions of sulfuric acid. The protonated structure is more prone to crosslinking reactions than deprotonated one. The molecular structure corresponding to the nanotubular morphology, which contains the crosslinked phenazine- and oxazine-like groups, is more stable than the molecular structure of the granular morphology.     

The stability of polyaniline in strongly alkaline or acidic aqueous media

Polyaniline (PANI) base has been suspended in 9 M potassium hydroxide at 20 °C or 90 °C for various time intervals extending to 4 months. The fraction of acetone-soluble material increased from 1.2 wt.% to 4.5 wt.% after exposure to an alkaline medium for 60 days at 20 °C. Gel-permeation chromatography indicates that the aggregation of PANI is reduced, while the chain degradation itself is negligible. FTIR spectroscopy confirms this trend and the absence of hydrolytic changes in the PANI structure. Polyaniline retains the ability to be reprotonated with a 1 M sulfuric acid to a conducting form. No marked changes in the molecular structure have been found, even after suspension of PANI in 9 M KOH at 90 °C for 60 days.Similar immersion of PANI salt in 5 M sulfuric acid at 20 °C was responsible for changes in the protonation, and the mass increased by 11 wt.%. This was explained by the exchange of the original sulfate or chloride counter-ions for hydrogen sulfate anions or by the protonation of secondary amine sites in PANI in addition to imine ones. The changes in the molecular structure are discussed on the basis of FTIR spectra. The conductivity decreased from 1.2 S cm⁻¹ to ∼10⁻³ S cm⁻¹ but no time-dependence of conductivity was observed. There was no fraction of PANI soluble in acetone. PANI in the protonated state is thus stable also in the strongly acidic medium.The study is supplemented by the assessment of the thermal stability of PANI base, which is of importance for the processing of PANI. Loss of moisture has been observed after exposure to 250 °C for 10 h in both nitrogen atmosphere and in air. Good stability was found at 350 °C only in the nitrogen atmosphere, while a marked mass loss in weight was registered in air.     

Preparation and characterization of polyaniline films in the presence of N-phenyl-1,4-phenylenediamine

The chemical oxidation of aniline to form polyaniline (PANI) films was made in the presence of N-phenyl-1,4-phenylenediamine (PPDA) in aqueous hydrochloric acid medium. The PANI films were monitored by using the quartz crystal microbalance (QCM) technique. The effect of PPDA and its concentration on the film formation was investigated. It was found that PPDA decreases the yield of the PANI film, the induction period and the depletion time of the polymerization. However, the growth rate of the film formation was found to increase by increasing PPDA concentration. These results were justified by measuring the UV-VIS absorption spectra for the in situ PANI films and the in situ UV-VIS absorption spectra for the polymer in the bulk during the polymerization. The conductivity for the PANI films at different concentrations of PPDA was measured. Also, the IR spectra, X-ray and the thermal gravimetric analysis for the PANI powder formed in the bulk in the presence of PPDA were measured and discussed.     

Different experimental results for the influence of immersion angle on the resonant frequency of a quartz crystal microbalance in a liquid phase: with a comment

This paper presents different experimental results of the influence of an immersion angle (θ, the angle between the surface of a quartz crystal resonator and the horizon) on the resonant frequency of a quartz crystal microbalance (QCM) sensor exposed one side of its sensing surfaces to liquid. The experimental results show that the immersion angle is an added factor that may influence the frequency of the QCM sensor. This type of influence is caused by variation of the reflection conditions of the longitudinal wave between the QCM sensor and the walls of the detection cell. The frequency shifts, measured by varying θ, are related to the QCM sensor used. When a QCM sensor with a weak longitudinal wave is used, its resonant frequency is nearly independent of θ. But, if a QCM sensor with a strong longitudinal wave is employed, the immersion angle is a potential error source for the measurements performed on the QCM sensor. When the reflection conditions of the longitudinal wave are reduced, the influence of θ on the resonant frequency of the QCM sensor is negligible. The slope of the plot of frequency shifts (ΔF) versus (ρη)^1/2, the square root of the product of solution density (ρ) and viscosity (η), may be influenced by θ in a single experiment for the QCM sensor with a strong longitudinal wave in low viscous liquids, which can however, be effectively weakened by using the averaged values of reduplicated experiments. In solutions with a large (ρη)^1/2 region (0-55 wt% sucrose solution as an example, with ρ value from 1.00 to 1.26 g cm⁻³ and η value from 0.01 to 0.22 g cm⁻¹ s⁻¹, respectively), the slope of the plot of ΔF versus (ρη)^1/2 is independent of θ even for the QCM sensor with a strong longitudinal wave in a single experiment. The influence of θ on the resonant frequency of the QCM sensor should be taken into consideration in its applications in liquid phase.     

Influence of the settling of the resin beads on diffusion gradients in thin films measurements

Binding resin beads used in DGT (diffusion gradients in thin films) tend to settle to one side of the resin during casting. This phenomenon might be relevant for metal accumulation when partially labile complexes dominate the metal speciation, especially after recognizing the important role played by complex dissociation in the resin domain. The influence of the inhomogeneity of the binding agent distribution on metal accumulation is here assessed by numerical simulation of DGT devices with binding beads in only one half of the resin disc, as a reasonable model of the standard resin discs. Results indicate that a decrease in mass accumulation of less than 13% can arise in these inhomogeneous devices (as compared with an ideal disc with homogeneous dispersion of the resin beads) when complexes with stability constant K < 10² m³ mol⁻¹ (K < 10⁵ L mol⁻¹) dominate the metal speciation. The loss increases as K increases, but the percentage of mass loss always remains lower than the volume fraction of resin disc without beads. For very labile or inert complexes, the impact of the inhomogeneous distribution of binding resin beads is negligible. As kinetic dissociation constants of complexes can be estimated from the distribution of the metal accumulation in a DGT device with a stack of two resin discs, the influence of the inhomogeneity on the recovered kinetic constant is also assessed. For the cases studied, the recovered kinetic dissociation constant, k_d,recovered, retains the correct order of magnitude, being related to the true k_d by k_d ≈ f⁻¹ k_d,recovered, quite independently of K and k_d values, being f the fraction of volume of the resin disc where resin beads are dispersed.     

Effect of acetonitrile on the hydration of human serum albumin films: a calorimetric and spectroscopic study

A new experimental approach based on the combination of calorimetric and FTIR spectroscopic measurements was proposed to study simultaneously the sorption of water and organic solvent, and corresponding changes in the structure of protein films in the water activity range from 0 to 1.0. Enthalpy changes (ΔH_tot) on the interaction of water with the dried human serum albumin (HSA) in the presence and absence of acetonitrile (AN) have been measured using a Setaram BT-2.15 calorimeter at 298 K. Spectroscopic data on water and organic solvent vapor sorption by the HSA films and the corresponding changes in the protein secondary structure were determined by means of a Bruker Vector-22 FTIR spectrometer. By using a water activity-based comparison we characterised the effect of acetonitrile on the hydration and structure of the HSA films. Acetonitrile (AN) sorption isotherm resembles a smooth curve. HSA film binds about 250 mol AN/mol protein at the lowest water activities. As the water activity increases from 0 to 0.8, the sorption of AN gradually decreases from 250 to 150 mol AN/mol HSA. At a_w > 0.8, the sorption of AN sharply decreases to zero. Acetonitrile decreases markedly the water content at a given a_w. This behavior suggests that the suppression in the uptake of water is due to a competition for water-binding sites on the HSA films by acetonitrile. Changes in the secondary structure of HSA were determined from infrared spectra by analyzing the structure of amide I band. Acetonitrile increases the intensity of the 1654 cm⁻¹ band that was assigned to the α-helix structure. Changes in the intensity of the 1654 cm⁻¹ band agree well with the decrease in water uptake in the presence of AN. An explanation of the acetonitrile effect on the hydration and structure of the HSA films was provided on the basis of hypothesis on water-assisted disruption of polar contacts in the initially dried protein.     

An effect of N ion bombardment on the properties of CdTe thin films

E-beam evaporated CdTe thin films were processed with N⁺ ion bombardment as in situ process. The N⁺ ion glow was generated using simple Multipurpose Al probe instead of conventional plasma sources. The prepared films were identified as nano crystalline using XRD analysis. High N⁺ ion fluence helped to grow (3 1 1) oriented CdTe thin films instead of (2 2 0) and (1 1 1). The observed results revealed the effect of N⁺ ion fluence on the structural parameters like lattice parameter, d space value, crystalline size, dislocation density, micro strain etc. The observed optical band gap values lie in between 1.47 and 1.77 eV. The effect of N⁺ ion bombardment on optical properties was also reported. Noticeable change in electrical and surface properties was also observed. The observed value shows the reproducibility as <1% and it is suggested that the N⁺ ion plasma was effectively utilized to modify the structural, optical and surface properties as in situ.     

Nanoscale measurements of conducting domains and current-voltage characteristics of chemically deposited polyaniline films

Spatial variations in electric conductivity and evolutions of band structures of polyaniline (PANI) films have been studied by use of a so-called current-sensing atomic force microscope (CS-AFM) or atomic force microscope current image tunneling spectroscopy (AFM-CITS). PANI films were deposited chemically onto indium-tin oxide- (ITO-) glass substrates, and their thickness and doping levels were controlled by polymerization and acid-doping conditions. The conducting uniformity of the PANI films depends on their doping level and thickness. Conducting domains were observed in fully doped PANI film, even when the bias voltage was reduced to as small as 30 mV. High current flowing regions gradually disappeared when conducting PANI films were partially dedoped. The point-contact current-voltage (I-V) characteristics of conducting tip-polymer/ITO systems were investigated on PANI films with different thickness and degree of doping. Various types of I-V curves representing metallic, semiconducting, and insulating states were obtained depending on the aggregation of polymer chains and doping level of the polymer film. The band gap energies (estimated from the I-V or dI/dV-V curves) of emeraldine base (EB) (undoped polyaniline) films are all higher than 3.8 eV, and a wide distribution of the band gap energies (0-1.1 eV and 0.75-1.8 eV for fully and partially doped PANI thin films, respectively) was found in a single polymer film.