Emeraldine Oxidation State Research Articles

Nanostructured Polyanilines Using the H2O2/CaCl2 Oxidant System

Aniline and its ring-substituted derivatives are oxidatively polymerized by H2O2 to the corresponding electrically conductive emeraldine oxidation state in dilute aqueous acids when 5 M CaCl2 is ad...

Characterization of polyaniline/polystyrene blends prepared by three different methods

A preparation and characterization of mixtures consisting of conductive polyaniline dispersed in polystyrene (PS) matrix are described. PANI was obtained by interfacial oxidative polymerization of aniline in the presence of sulfosalicylic acid, giving the protonated form the oxidation state of emeraldine (PANI-SSA). PS was synthesized by emulsion polymerization in the presence of sodium dodecyl sulfonic (SDS) as an emulsifier. Three methods were used for the preparation of PANI-SSA/PS mixtures: (1) green in-situ polymerization of aniline in the presence of SSA as a protonating agent and ammonium persulfate ((NH4)2S2O8 as an oxidant (Method I); (2) mixing PS with PANI-SSA dissolved in sulphuric acid at the temperature of 150 °C (Method II); and (3) mixing PS dissolved in dichloromethane (DCM) with PANI-SSA at room temperature (Method III). The prepared mixtures of different PANI-SSA content were characterized by FTIR, TGA, XRD and by electrical conductivity measurements. Mixing at high temperature (Method II) led to the formation of sulfonated polystyrene (PSS) or even three dimensional resins (through cross-linking of PSS) in which highly crystalline PANI particles were dispersed. The nanocomposites PS/PANI were elaborated by green in situ chemical polymerization (Method I) and by mixing with heating in the presence of sulphuric acid (Method II) at room temperature in the presence of dichloromethane at various percentages of PANI (Method III). These realized samples reported a high degradation temperature of PS which confirm that the PANI may even improve an inflammation property of polystyrene. The obtained composites proved a semi-crystalline character with a high level of crystallinity and the electrical properties range between 10–3 and 10–4 S/cm. These concepts are promising for the antistatic domain and charge dissipation domain.

Deposition Behavior of Polyaniline on Carbon Nanofibers by Oxidative Chemical Vapor Deposition.

Oxidative chemical vapor deposition (oCVD) offers unique advantages as a liquid-free processing technique in synthesizing and integrating conducting polymers, including polyaniline (PANI), by enabling conformal coatings onto nanostructured substrates, like carbon nanofibers. With relatively thick nanofiber mats, the challenge is to ensure uniform coating thickness through the porous substrates. Here, the substrate temperature during oCVD is found to be a primary factor influencing PANI coating uniformity. Coating uniformity is enhanced by operating at a higher substrate temperature, where monomer adsorption is believed to be limiting relative to intrinsic reaction kinetics. Also, a higher substrate temperature leads to significantly less PANI oligomers and more PANI in the emeraldine oxidation state. A systematic study of oCVD kinetics with substrate temperature shows a reaction-limited regime at lower substrate temperatures with an activation energy of 12.0 kJ/mol, which is believed to be controlled by the self-catalyzed PANI polymerization reaction that transitions at higher substrate temperatures above 90 °C to an adsorption-limited regime as indicated by a negative activation energy of -18.8 kJ/mol. Overall, by operating within an adsorption-limited oCVD regime, more uniform oCVD PANI coatings on electrospun carbon nanofiber mats have been achieved.

Radiation synthesis of gas sensor based on polyaniline nanoflake-poly vinyl alcohol) film for four hazardous gases (NH3, CO2, H2S and phenol)

In this study, a low-cost conductive composite membrane consisting of polyaniline nano-flake which dispersed in a polyvinyl alcohol has been prepared through in-situ polymerization technique. The polymerization of polyaniline is carried out based on polyvinyl alcohol using ammonium per sulfate as an oxidizing agent at low temperatures (–5°C) in acid medium at pH 3 1M (HCl) followed by exposure to gamma irradiation leading to crosslinging of (PVA/PANI) membranes and for enhancement formation of polyaniline nano-flake. The produced film is in the emeraldine oxidation state and fully protonated which can detect the hazardous gases (NH3, H2S, CO2 and phenol gas) through changing in the color and electrical conductivity. The gas-sensing property of (PVA/PANI) film was examined at ambient conditions of temperature and pressure. The observed is the variation in sensing property of (PANI-PVA) films corresponding to the type of gases in order NH3 ≥ H2S ≥ CO2 ≥ phenol gas. The product films of (PVA/PANI) before and after four gases adsorption were characterized by scanning electron microscopy, infrared spectroscopy, UV–Vis spectroscopy and XRD. TEM images of (PANI) obtained in form 2D-polyaniline nano-flake is confirmed. Furthermore, the incorporation of gas molecules onto the (PVA-PANI) films for four gases adsorption and their conductivity changing was examined. It was observed that the conductivity was changed according to the chemical structure changing of PANI as confirmed by FTIR data. It was found that, the electrical conductivity of all blended films decreases by exposure to the gas.

Synthesis and thermal analysis of polyaniline (PANI)

An attempt was taken to prepare polyaniline (PANI) using chemical oxidative polymerization method with surfactant i.e sodium dodecyl sulfate (SDS) followed by treating with HCI and NH4OH dopants. Raman spectroscopy, differential scanning calorimetry (DSC) and thermogravimetry analysis (TGA) techniques were used for the characterization studies. The electrical conductivity of polyaniline was measured using two probe method. Raman spectroscopy results confirm the formation of an emeraldine oxidation state of PANI. Thermal analysis of polyaniline up to 700°C was investigated using thermo gravimetric analysis technique.

Enhanced dielectric response and thermal conduction in copper nanoparticles embedded polyaniline nanofibers

Herein we report, an easy, facile and in-situ synthesis of copper/polyaniline (Cu/PANI) nanocomposites through a chemical route via redox reaction. X-ray diffraction (XRD) confirms the characteristic peaks for polyaniline and copper. The UV–vis spectroscopy predicts the formation of emeraldine oxidation state of polyaniline, which is the only conducting state of PANI. The Cu/PANI nanocomposites have the fibril morphology and copper nanoparticles are embedded inside the PANI nanofibers. It was observed that copper reinforced polyaniline nanocomposites exhibit excellent dielectric behavior in a wide frequency range from 1.0 Hz to 1.0 MHz at room temperature. The thermal conductivity enhancement in the nanocomposites is observed in comparison to pure PANI nanofibers, which was studied in a wide temperature range 0–100 °C by Transient Plane Source method.

Simple and mass-produced mechanochemical preparation of graphene nanosheet/polyaniline composite assisted with bifunctional ionic liquid

Graphene nanosheet/polyaniline (GNS/PANI) composite was prepared by a simple and mass-produced mechanochemical method, where the functionalized ionic liquid 1-(3-sulfonic acid) propyl-3-methylimidazolium hydrogen sulfate conducts as not only the dispersant of GNS but also the dopant of PANI. The GNS/PANI composite characterized by Fourier transformation infrared spectra, UV–Vis spectra and X-ray diffraction shows that the resulting PANI in composite is in its doped, conductive emeraldine oxidation state. Scanning electron microscope images reveal that the GNS/PANI composite with PANI uniformly coated on the surface of GNS is randomly stacking. Compared with pure PANI, the GNS/PANI composite has higher electrical conductivity, better thermal stability and electrochemical activity due to the presence of GNS.

Electropolymerization of polyaniline thin films

Polyaniline (PANI) thin films have been electrochemically synthesized onto conducting glass substrates. The current study demonstrates that the properties of PANI films depend on the concentration of dopant acid. Well-adherent PANI coatings were obtained under potentiodynamic conditions during sequential scanning of the potential region between −0.35 V and +1.7 V with respect to silver/silver chloride. The structural, optical, and morphological properties of PANI films were studied with the aid of X-ray diffraction (XRD), Raman spectroscopy, ultraviolet–visible (UV-Vis) absorption spectroscopy, photoluminescence (PL) spectroscopy, and field-emission scanning electron microscopy (FESEM). Current–voltage ( I- V) measurements were performed to study the electrical properties of PANI films. The XRD peaks observed at 2 θ = 15.4°, 24.2°, and 25.1° confirm the synthesis of emeraldine form of PANI. The strong absorption peaks observed in the UV-Vis absorption spectra at 317 nm (π–π* interband transition), 371–427 nm (polaron band transition), and 750 nm (bipolaron band transition) confirm the formation of emeraldine oxidation state of PANI. A broad peak attributed in the PL spectra around 395 nm is related to the transition from polaronic band to the π band. All the intense bands attributed in the Raman spectra are associated with the emeraldine oxidation state of PANI. FESEM images reveal the formation of fibers and belts of PANI. Highly conducting thin films of PANI deposited at higher concentrations of dopant acid were confirmed by I- V measurements.

Conducting Poly(N‐propylaniline) Nanoparticles for Hydrogen Sulfide Gas Detection

SummaryWe report a sensitive, selective, and fast responding room temperature chemiresistive sensor for hydrogen sulfide detection and quantification using poly(N‐propylaniline) (PNPA). This sensor shows an excellent wide range of detection with very good selectivity and reproducibility. Organic acid and HCl doped poly(N‐propylaniline) PNPA were synthesized by chemical oxidative polymerization. It was found that the polymer synthesized using DL‐(±)‐Tartaric acid is formed in conducting emeraldine oxidation state and displayed higher doping level and crystallinity than HCl doped poly‐(N‐propylaniline). The polymers were characterized by techniques such as UV‐Visible and FTIR spectroscopy, XRD, SEM and conductivity measurement. The synthesized materials were tested as sensors for acids, bases and organic vapors etc. and categorized. Comparison of the responses of these two polymers reveals that the tartaric acid doped polymer exhibits higher sensitivity and reversibility. The result is discussed with reference to HCl doped and DL‐(±)‐Tartaric acid doped poly(N‐propylaniline). The poly(N‐propyl)aniline pellets were used as sensor by measuring change in resistance before and after exposure to analyte gas. On exposure to H2S gas (10 to 1000 ppm in air) at room temperature, it was found that the PNPA film resistance increases, while that of the PNPA pellet decreases from the respective unexposed value. These changes on removal of H2S gas are reversible in nature, and the polymer PNPA showed good sensitivity with relatively faster response/recovery time. The XRD of PNPA is found to exhibit partial crystallinity as observed from the presence of several peaks at 2θ values of 18 to 41°. The SEM figure indicates that the PNPA/TA consist of coral‐like granular particulates with diameter in the range of 50 to 100 nm.

Electrosynthesis of Polyaniline-TiO2 Nanocomposite Films on Aluminum Alloy 3004 Surface and its Corrosion Protection Performance

The direct synthesis of polyaniline-TiO2 nanocomposite coatings on aluminum alloy 3004 (AA3004) surface has been investigated by using the galvanostatic method. The synthesized coatings were characterized by FT-IR, SEM-EDX, SEM and AFM. Optical absorption spectroscopy reveals the formation of the emeraldine oxidation state form of polyaniline-TiO2 nanocomposite. The corrosion performances of polyaniline-TiO2 nanocomposite coatings were investigated in 3.5% NaCl solution by Tafel polarization and Electrochemical Impedance Spectroscopy (EIS) methods. The corrosion rate of polyaniline-TiO2 nanocomposite coating on AA3004 was found �˝ 260 times lower than bare AA3004 and corrosion potentials of these coatings have shifted to more positive potentials (105 mV). The results of this study clearly ascertain that the polyaniline-TiO2 nanocomposite coating has outstanding potential to protect the AA3004 against corrosion in a chloride environment.

PANI Conductivity: A Dependence of the Chemical Synthesis Temperature

AbstractSummary: This work evaluated the influence of the synthesis temperature on the polyaniline (PANI) properties obtained by in‐situ polymerization onto a poly (terephthalate) (PET) substrate. The residual mass of these syntheses was dried under vacuum, obtaining PANI powders for each temperature investigated. PANI/PET thin films and PANI powders were characterized by atomic force microscopy (AFM), field emission scanning electron microscopy (FEG‐SEM), X‐ray diffraction (XRD), ultraviolet‐visible spectroscopy (UV‐Vis) and four‐point probe techniques. The UV‐Vis results showed that the synthesized PANI presents the emeraldine oxidation state. By means of XRD technique, it was possible to verify that the PANI powders present crystalline form. The AFM and FEG‐SEM techniques showed that the decrease in PANI/PET and PANI powders electrical conductivity with increasing of the synthesis temperature is related to the polymeric aggregates morphology.

Nanosensors applied to water quality: developing a low-cost pH sensor for natural water, and application of other techniques

A low-cost optical sensor built-in strip has been developed from a composite obtained with application of in-situ chemical polymerisation, using polyaniline in the emeraldine oxidation state, doped with HCl onto poly(ethylene terephthalate) (PET) film, used to measured the pH of water. The absorption of UV-Vis spectra was used to evaluate the optical response to pH change of natural water. The strip showed a reversible colour change upon variation of the pH. The pH range used to calibrate the optical sensor was from 2.0 to 12.0. These kinds of sensors show the potential to investigate the pH of natural waters, with application to limnological studies, as well as to investigate the influence of the ionic strength. This paper describes new techniques that can be used to conduct research with pesticides in water using electrochemistry and biosensors, and an electronic tongue with conductive polymers for global quality evaluation.

Influence of the pH on the Surface and Optical Properties of the Thin Film of Polyaniline / Polyethylene Terephthalate Composite. The AFM and Spectroscopies Studies

ABSTRACTThe effect of pH was investigated on the morphological and spectroscopic properties of PANI thin films on PET. PANI/PET strips were prepared by a pattern-printing technique and coated with a thin film of polyaniline in situ emeraldine oxidation state, doped with HCl (PANI-HCl), obtained by in situ polymerization. AFM, UV-VIS-NIR and FTIR/ATR spectroscopic results showed that pH has a great influence on the polymer layer morphology of the coating layers, while the intensity of vibrational bands decreases with rising pH, increase due to changes in the H-bonded structure in the polymer chain.

Study on soluble polyaniline by positron annihilation technique

The solubility, electrical conductivity, and other properties of polyaniline (PANI) are highly dependent on its oxidation state. In this work, polyaniline (PANI1) prepared by peroxodisulphate induced polymerization of aniline in acidic aqueous medium in presence of benzenediazonium chloride salt was found to exist in lower oxidation state than emeraldine form of PANI and was highly soluble in common organic solvents. This polymer was subjected to positron annihilation spectroscopic study to investigate the correlation between the oxidation state of the polymer and defect sites generated by different degrees of protonation that in turn affect its electrical conductivity. The positron annihilation lifetime data were resolved to yield a three-component fit for PANI1 subjected to different levels of protonation. The variation of positron annihilation parameters (τ1,I2) and Doppler broadening parameters (R, S) as a function of protonation level of the polymer indicate the dopant sites increase initially on protonation and reach a saturation value after a certain level of acidification. The lower value of electrical conductivity and the intensity of intermediate lifetime component (I2) for PANI1 compared to PANI in emeraldine oxidation state indicate the presence of lesser number of quinoid–imine moieties that could undergo protonation and thus yield highly enriched trapping centers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Low-cost sensors developed on paper by line patterning with graphite and polyaniline coating with supercritical CO 2

Low-cost sensors were developed in two steps: (i) using a negative template to print graphite electrodes on vellum paper and (ii) coating with conductive polymers. Thin films of polyaniline (PANI) in the emeraldine oxidation state were investigated as active layers, after being synthesized by two routes: (a) polyaniline doped with dodecylbenzenesulfonic acid (DBSA) deposited by supercritical fluid (SC CO 2) and (b) PANI doped with hydrochloric acid (HCl) by the in situ polymerization method. The electrical response (mV) was measured with dedicated circuitry, both in static laboratory air and with a flow of dry nitrogen gas (N 2) at room pressure and temperature in a closed chamber, to assess the sensors for their sensitivity and reversibility. The phase morphology (microfiber structure) was characterized by FE-SEM. Results showed a difference in behavior between the sensors obtained by SC CO 2 coating with PANI and by in situ polymerization. The voltage in the SC CO 2 sensor decreased when it was exposed to the flow of dry nitrogen, whereas the opposite effect was observed in the other sensor.

Toward a simple method for the fabrication of 1D or 3D nanostructures of polyaniline

We present a one-step chemical method for the fabrication and isolation of conjugated polymer nanostructures, in particular, polyanilines (PANIs), either in the pernigraniline or emeraldine oxidation state. The polymerization is initiated by the addition of a solid oxidant into an unstirred anilinium hydrochloride solution. This step allows a slow release of the oxidant, via its solubilization and diffusion into the undisturbed solution. The formation of visible macroscopic heterogeneous seeds promotes the homogeneous polymerization and growth of bulk nanostructures in solution. The shape of the first formed heterogeneous seeds was found to be dependent on the solubility/diffusion of the oxidant, allowing the prediction and control of the nanomorphology (1D vs. 3D or granular) of the bulk polyanilines. X-ray analyses of the as-prepared nanostructured PANIs showed that, compared to the literature data, the crystallite growth in the present study is significantly enhanced, with the 1D fibrillar morphology exhibiting a higher crystallinity per volume of nanostructure than that of a 3D granular counterpart. The electrical conductivity ( σ ) of pelletized HCl doped PANIs or emeraldine salts (ES) showed significant differences depending on the fibrillar or granular morphology, but a close relationship among number of unit cells, crystallite size and electrical conductivity is evidenced.

Chromism and molecular weight of polyaniline derivatives

The striking solvatochromic shift observed in polyaniline derivatives correlates with two solvent polarity scales, donor number (DN) and hydrogen bond acceptor scale (Taft's β-scale). The large shift is caused by conformational changes in solution that result in dramatic differences in relative molecular weight values obtained by gel permeation chromatography (MW GPC) in different solvents. For example, for poly- o-toluidine base in the emeraldine oxidation state, a low transition energy solvent like NMP (excitonic transition, λ max 608 nm) yields a very high molecular weight value ( M w ∼ 15,000 g mol −1) whereas a high transition energy solvent like CHCl 3 (excitonic transition, λ max 570 nm) yields an absurdly low value ( M w ∼ 650 g mol −1). An absolute molecular weight value, M w ∼ 4700 g mol −1, was obtained for the first time using laser light scattering (MW LS) suggesting that CHCl 3 promotes a highly coiled chain conformation whereas NMP promotes a more expanded, rod-like conformation. A similar trend is observed for poly- o-toluidine base in the fully oxidized pernigraniline oxidation state (Pierels transition). This suggests that even though the Pierels and excitonic transitions have different molecular origins their conformation driven solvatochromic shifts trend in a similar fashion which is different from thermochromic trends reported in previous studies.

Electrically Conductive Nanocomposites Made from Cellulose Nanofibrils and Polyaniline

Electrically conductive nanocomposites from cellulose nanofibrils (CNF) were successfully produced by in situ polymerization of aniline onto CNF, and studied by open circuit potential (Voc), four probe direct current (dc) electrical conductivity, ultraviolet-visible (UV-Vis) spectroscopy and scanning electron microscopy (SEM). The oxidative polymerization of aniline using ammonium peroxydisulfate in hydrochloric acid aqueous solutions was realized by the addition of nanofibrils leading to an aqueous suspension of CNF coated with polyaniline (PANI). This procedure lead to stable, green suspensions of CNF coated with PANI in the emeraldine oxidation state as demonstrated by Voc and UV-Vis analyses. Electrically conductive films of this cellulose nanocomposite could be cast from aqueous solutions with conductivity close to the conducting polymer, yet with the potential for more useful flexible films.

One‐step preparation of solution processable conducting polyaniline by inverted emulsion polymerization using didecyl ester of 4‐sulfophthalic acid as multifunctional dopant

AbstractA new one‐step method of preparation of solution processable conductive polyaniline (PANI) is reported using didecyl ester of 4‐sulfophthalic acid (DESPA) as multifunctional material. It consists of inversed emulsion polymerization of aniline in water/chloroform mixture with benzoyl peroxide initiator, maleic acid (MA) as a codopant and DESPA as protonating agent, surfactant, and plasticizer. The resulting product combines reasonable conductivity (ca.0.03 S/cm) with solubility in common solvents such as tetrahydrofuran and chloroform. Elemental analysis together with spectroscopic studies show that the protonation level of emulsion polymerized PANI (0.47 per mer involving one ring and one nitrogen) is very close to that predicted for PANI in the oxidation state of emeraldine (0.5). MA is incorporated into the polymer matrix as a co‐dopant in the ratio 1:4 with respect to the DESPA dopant. PANI‐DESPA‐MA three components system shows a highly ordered, layer‐type supramolecular structure, in which planes of regularly π‐stacked PANI chains are separated by a double layer of dopants. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1051–1057, 2008

Poly(3,5‐dichloroaniline) Doped with Different Sulfonic Acids

Poly(3,5‐dichloroaniline) was prepared by chemical oxidation in the presence of various sulfonic acids as doping agent, using potassium permanganate as oxidant. 1‐Naphtalene sulfonic acid, 2‐naphatalene sulphonic acid, 1,5‐naphtalene disulfonic acid, and p‐toluenesulfonic acid were the acids of choice. Infrared and UV‐Vis spectroscopy, utilized to characterize the polymers, revealed that the compounds exist in the emeraldine (conductive) oxidation state. The level of doping, conductivity, and morphology were determined as well. The presence of a sulfonic acid produces a morphological change, from granular to microtubule structures, which is responsible for the strong increase in the conductivity of the polymer.