Polyaniline Base Research Articles

The carbonization of granular polyaniline to produce nitrogen-containing carbon

Polyaniline (PANI) was prepared by the oxidative polymerization of aniline. The deprotonated product, a PANI base, was carbonized in an inert atmosphere at temperatures up to 800 °C for various times. The mass decreased to 40–50 wt.% at temperatures above 600 °C. The progress of molecular structure during carbonization was followed by infrared and Raman spectroscopies. The carbonization at 650 °C for 1 h is suggested for the optimum conversion of PANI to carbon. The product retained the original globular structure of PANI. The conductivity of the carbonized material was low for carbonizations below 600 °C, <10 −10 S cm −1, and increased to 10 −4 S cm −1 after treatment at 800 °C. The content of nitrogen, ∼10 wt.%, was not affected appreciably by the carbonization.

Polyaniline Nanoscaffolds for Colorimetric Sensing of Biomolecules via Electron Transfer Process

Biologically important analytes such as cysteine and vitamin-C were detected by electron transfer (ET) via naked eye colorimetric sensing using a tailor-made water-soluble self-doped polyaniline (PSPANa) as a substrate. Monomer (N-3-sulfopropylaniline) was synthesized via ring-opening of propane sultone with excess aniline and polymerized in water using ammonium persulfate to obtain green water-soluble polymer. Vitamin-C (ascorbic acid) and cysteine showed unexpected sharp and instantaneous color change from blue to colorless sensing action. The stoichiometry of the analyte to polymer was determined as 3:2 and 4:1 with association (or binding) constants of K = 2.1 × 10(3) and 1.5 × 10(3) M(-1) for vitamin-C and cysteine, respectively. Efficient electron transfer from vitamin-C (also cysteine) to the quinoid unit of the polyaniline base occurred in solution; as a result, the color of the solution changed from deep blue to colorless. Cyclic voltammetry analysis of PSPANa showed the disappearance of the cathodic peak at -0.21 V upon the addition of analytes (vitamin-C and cysteine) and confirms the electron transfer from the analyte to the polymer backbone. Dynamic light scattering (DLS) and zeta potential techniques were utilized to trace the molecular interactions in the electron transfer process. DLS histograms of the polymer samples confirmed the existence of nanoaggregates of 8-10 nm in diameter. The polymers possessed typical amphiphilic structure to produce micellar aggregates which facilitate the efficient electron transfer occurred between the analyte and polyaniline backbone.

Microporous carbon derived from polyaniline base as anode material for lithium ion secondary battery

Microporous carbon with large surface area was prepared from polyaniline base using K 2CO 3 as an activating agent. The physicochemical properties of the carbon were characterized by scanning electron microscope, X-ray diffraction, Brunauer–Emmett–Teller, elemental analyses and X-ray photoelectron spectroscopy measurement. The electrochemical properties of the microporous carbon as anode material in lithium ion secondary battery were evaluated. The first discharge capacity of the microporous carbon was 1108 mAh g −1, whose first charge capacity was 624 mAh g −1, with a coulombic efficiency of 56.3%. After 20 cycling tests, the microporous carbon retains a reversible capacity of 603 mAh g −1 at a current density of 100 mA g −1. These results clearly demonstrated the potential role of microporous carbon as anode for high capacity lithium ion secondary battery.

Optimizing PANi doped electroactive substrates as patches for the regeneration of cardiac muscle

In scaffold aided regeneration of muscular tissue, composite materials are currently utilized as a temporary substrate to stimulate tissue formation by controlled electrochemical signals as well as continuous mechanical stimulation until the regeneration processes are completed. Among them, composites from the blending of conductive (CPs) and biocompatible polymers are powerfully emerging as a successful strategy for the regeneration of myocardium due to their unique conductive and biological recognition properties able to assure a more efficient electroactive stimulation of cells. Here, different composite substrates made of synthesized polyaniline (sPANi) and polycaprolactone (PCL) were investigated as platforms for cardiac tissue regeneration. Preliminary, a comparative analysis of substrates conductivity performed on casted films endowed with synthesized polyaniline (sPANi) short fibres or blended with emeraldine base polyaniline (EBPANi) allows to study the attitude of charge transport, depending on the conducting filler amount, shape and spatial distribution. In particular, conducibility tests indicated that sPANi short fibres provide a more efficient transfer of electric signal due to the spatial organization of electroactive needle-like phases up to form a percolative network. On the basis of this characterization, sPANi/PCL electrospun membranes have been also optimized to mimic either the morphological and functional features of the cardiac muscle ECM. The presence of sPANi does not relevantly affect the fibre architecture as confirmed by SEM/image analysis investigation which shows a broader distribution of fibres with only a slight reduction of the average fibre diameter from 7.1 to 6.4 μm. Meanwhile, biological assays--evaluation of cell survival rate by MTT assay and immunostaining of sarcomeric α-actinin of cardiomyocites-like cells--clearly indicate that conductive signals offered by PANi needles, promote the cardiogenic differentiation of hMSC into cardiomyocite-like cells. These preliminary results concur to promise the development of electroactive biodegradable substrates able to efficiently stimulate the basic cell mechanisms, paving the way towards a new generation of synthetic patches for the support of the regeneration of damaged myocardium.

Evaluation and selection of sensing materials for carbon dioxide (CO2) sensor by molecular modeling

We report a molecular modeling study to evaluate and select conducting polymers (CPs) as the sensing materials of carbon dioxide (CO2) sensor. The interaction between polymer and gas and the adsorption of the gas molecules in the polymer matrix are investigated. Polymers considered for this work include emeraldine base polyaniline (EB–PANI) and unprotonated sodium polyaniline salt (NaSPANI) with sulfur to nitrogen ratio (S/N) of 0.4, 0.5 and 0.6. Gases studied include CO2, humidity (H2O) and carbonic acid (H2CO3). The interaction energies of polymer-gas and the loading number of the analytes predict that the NaSPAN is more suitable for CO2 sensing than the EB–PANI.

The role of solvent on the doping of polyaniline with Fe(III) ions

The products formed from the reaction of emeraldine base polyaniline (EB-PANI) with Fe(III) ions in N-methyl-pyrrolidone (NMP), dimethylacetamide (DMA), dimethylformamide (DMF) and m-cresol media have been investigated using UV–VIS–NIR and resonance Raman ( λ 0 = 632.8 and 1064 nm) spectroscopies. Through these results it was verified that the different PANI forms in solution can be formed by the suitable choice of the solvent. The behavior of Fe(III)/EB-PANI in different solvents was rationalized in terms of the interactions among Fe(III) ions, EB-PANI and solvent. In basic NMP, DMA and DMF media, the reaction of Fe(III) with EB-PANI yields EB-PANI doping giving ES-PANI and/or the EB-PANI oxidation to PB-PANI. The formation of ES-PANI is favored in DMF while PB-PANI is formed in a greater extension in NMP and DMA. In acidic m-cresol, only ES-PANI is produced in Fe(III)/EB-PANI solutions indicating the important role played by the solvent in the nature of the product.

High‐temperature oxidation of aniline to highly ordered polyaniline–sulfate salt with a nanofiber morphology and its use as electrode materials in symmetric supercapacitors

AbstractIn this study, for the first time, aniline was oxidized by ammonium persulfate (APS) at higher temperatures without any protic acid, and APS acted as an oxidizing agent and a protonating agent. During the oxidation of aniline by APS, sulfuric acid formation occurred, and the sulfuric acid was incorporated into polyaniline (PANI) as a dopant. PANI–sulfate samples were characterized by IR spectroscopy, X‐ray diffraction, and scanning electron microscopy techniques. In this methodology, a highly ordered PANI–sulfate salt (H2SO4) with a nanofiber morphology was synthesized. Interestingly, a PANI base was also obtained with a highly ordered structure with an agglomerated netlike nanofiber morphology. PANI–H2SO4 was used as an electrode material in a symmetric supercapacitor cell. Electrochemical characterization, including cyclic voltammetry (CV), charge–discharge (CD), and impedance analysis, was carried out on the supercapacitor cells. In this study, the maximum specific capacitance obtained was found to be 273 F/g at 1 mV/s. Scan rate from cyclic voltammetry and 103 F/g at 1 mA discharge current from CD measurement. Impedance measurement was carried out at 0.6 V, and it showed a specific capacitance of 73.2 F/g. The value of the specific capacitance and energy and power densities for the PANI–H2SO4 system were calculated from CD studies at a 5‐mA discharge rate and were found to be 43 F/g, 9.3 W h/kg, and 500 W/kg, respectively, with 98–100% coulombic efficiency. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Formation of Nanoparticles in Organic Materials used in Semiconductors Optoelectronic Devices

The Organic Devices Optically Transparent (ODOTs) are the base Polyaniline (PANI) and were electrodeposited on substrates of the materials optically transparent covered with ITO and characterized by UV-Visible Spectroscopy (UV-Vis), Electrical Measurements (EM) and Scanning Electron Microscopy (SEM). The deposition of the PANI films was prepared in perchloric acid solution and identified by PANIX1. The results obtained by UV-Vis shows that the PANI-X1 does not have displacement of optical absorption for wavelengths greaters. The EM of PANI-X1 have stability after electrodeposition, because the thickness of the sample is equivalent conductive layer. After 466 hours of electrical tests, there was the appearance of nanoparticles visible for images by SEM due to the migration process of Organic Semiconductor Materials (OSM). Similar to the phenomenon of electromigration observed in connections and interconnections of microelectronic devices, the results reveal a new mechanism of migration that arises with the passage of electric current in ODOT.

Activated carbon prepared from polyaniline base by K2CO3 activation for application in supercapacitor electrodes

An activated carbon was prepared from a polyaniline base using K2CO3 as an activating agent. The morphology, surface chemical composition, and surface area of the as-prepared carbon materials were investigated by scanning electron microscope, X-ray photoelectron spectroscopy, and Brunauer–Emmett–Teller measurement, respectively. Electrochemical properties of the as-prepared sample were studied by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy measurements in 6 mol L−1 KOH aqueous solution. Compared with the non-activated carbon, activated carbon showed superior capacitive performance. The activation carbon presented a high specific gravimetric capacitance of 210 F g−1. The good electrochemical performance of the activated carbon was ascribed to well-developed micropores, high surface area, the presence of nitrogen and oxygen functional groups, and larger pore volume.

The reduction of silver nitrate to metallic silver inside polyaniline nanotubes and on oligoaniline microspheres

Polyaniline (PANI) reduces silver nitrate to metallic silver. Composites based on conducting polymer and silver have been prepared with equimolar proportions of reactants. Polyaniline bases having different morphologies – granular or nanotubular – and oligoaniline microspheres have been left to react with silver nitrate in acidic, neutral, and alkaline media. The content of silver, typically 20–30 wt.%, was determined by thermogravimetric analysis. Clusters of 40–80 nm silver particles are produced in the granular form of PANI. The formation of silver inside PANI nanotubes has been observed. With oligoaniline microspheres, silver was produced on their surface, and on PANI agglomerates accompanying them. The highest conductivity, 943 S cm −1, was found with silver reduced by nanotubular PANI base in 0.1 M nitric acid at 17.3 wt.% silver content. The standard granular PANI, used as a reference material, yielded a composite having a much lower conductivity of 8.3 × 10 −5 S cm −1 at 24.3 wt.% Ag. There is no simple correlation between the conductivity and silver content. Infrared and Raman spectroscopies have been used to study the changes in the molecular structure of the PANI bases of various morphologies before and after reaction with silver nitrate.

Effect of hydrophilicity of polyaniline particles on their electrorheology: Steady flow and dynamic behaviour

Electrorheological properties of suspensions are considerably affected by hydrophilicity of suspension particles. As a model material, polyaniline base powder protonated with sulfamic, tartaric, or perfluorooctanesulfonic acids provided particles of various hydrophilicity. The experiments revealed that, in the absence of electric field, due to a good compatibility of hydrophobic polyaniline particles with silicone-oil medium, their interactions were limited and the viscosity of suspension was low. When the electric field was applied, the rigidity of the polarized chain structure of the particles increased and, consequently, viscosity increased as well. In the contrast, the field-off suspension viscosity of highly interacting hydrophilic particles, which are incompatible with the oil, and where particle aggregation may set in, was high especially at low shear rates, and the material had a pseudoplastic character. Then, a relative increase in viscosity due to the polarization of the particles or their clusters in the electric field was much lower than in the former case. Due to a different primary structure of suspension, depending on the particle compatibility with the oil the field-off storage modulus of suspensions of hydrophobic particles was lower than the loss modulus, while in suspensions of hydrophilic particles the former modulus dominated. In both cases, an increase in elasticity with increasing electric field strength was higher than that in viscosity.

Mechanical properties of polyaniline

In spite of extensive electrical characterization of polyaniline, the information on its mechanical properties is missing in the literature. Complex Young's modulus of polyaniline compressed into pellets was measured at room temperature and an influence of preparation conditions of the polyaniline pellets on mechanical properties was studied. Young's modulus of PANI hydrochloride pellets was 0.9 ± 0.2 GPa and that of polyaniline base 1.3 ± 0.2 GPa. These values are comparable with common polymers, such as bulk polystyrene, 1.8 ± 0.1 GPa, or compressed polystyrene powder, 0.80 ± 0.02 GPa. Modulus of polyaniline is independent of the compression pressure above 300 MPa, the time of compression had no effect.

Synthesis of novel optically active pyrrolidine‐containing polyaniline: A new heterogeneous organo polymeric‐base catalyst for direct Aldol reaction

AbstractAn optically active pyrrolidine containing polyaniline, poly‐(2‐anilinomethylpyrrolidine) (PANiMp) is synthesized for the first time. PANiMp material is synthesized by simple one‐pot synthetic route and is characterized by circular dichroism, NMR, FTIR, and electronic absoroption spectral techniques. This novel polyaniline base is evaluated as new heterogeneous organo polymeric‐base catalyst for direct Aldol reaction in water medium. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Oxidative polymerization of anilinium 5-sulfosalicylate with peroxydisulfate in water

AbstractAnilinium 5-sulfosalicylate was prepared and characterized by elemental analysis, and FTIR and NMR spectroscopies. It was polymerized in an aqueous solution using ammonium peroxydisulfate as an oxidant. The precipitated polyaniline 5-sulfosalicylate exhibited high thermal stability and conductivity of 0.13 S cm−1. Its mass-average molar mass and polydispersity index were determined by gel-permeation chromatography as 22,900 g mol−1 and 2.7, respectively. Elemental analysis and FTIR spectroscopy study of polyaniline 5-sulfosalicylate revealed the doping level and the oxidation state between emeraldine and protoemeraldine salt while corresponding studies of the polyaniline base indicate a small extent of the covalent bonding of 5-sulfosalicylate anions to polyaniline chains.

Forcefields based molecular modeling on the mechanical and physical properties of emeraldine base polyaniline

Molecular dynamics (MD) and molecular mechanical (MM) analysis are carried out to provide reliable and accurate model for emeraldine base polyaniline. This study validate the forcefields and model with the physical and mechanical properties of the polyaniline. The temperature effects on non-bond energy, potential energy and solubility parameter during the transformation from the rubbery to the glassy state have been analysed in this work. A new method using the solubility versus temperature (δ−T) curve for predicting the Tg of polymer are suggested.

Electrochemical Synthesis of Polyaniline as Ethylene Gas Sensor

The aim of this work is to fabricate an ethylene gas sensor based on polyaniline (PANi). The conductive layer of emeraldine base PANi was prepared by electrochemical synthesis. The aqueous aniline solution in sulfuric acid was electrolyzed by repeating potential cycling between -0.4 and 1.0 V relative to the silver reference electrode and platinum counter electrode. The conductive layers of PANi were deposited on patterned interdigited gold substrate. The numbers of repeated potential cycles on the amount of deposited layers of PANi were investigated for ethylene gas detection. The morphology of PANi films was investigated by scanning electron microscope (SEM). The ethylene gas sensing of PANi-H2SO4 was evaluated based on the changes in conductivity of PANi-H2SO4. The results revealed that the magnitude sensing provided a good sensitivity against ethylene with concentration in the parts per million (ppm) ranges. The effect of amount of deposited layer of PANi on ethylene gas sensing will be presented.

Characterization of gas sensing behavior of multi walled carbon nanotube polyaniline composite films

In this paper, we report multiwall carbon nanotube (MWNT) doped polyaniline (PANI) composite thin films for hydrogen gas sensing applications. PANI was synthesized by in- situ chemical oxidative polymerization of aniline using ammonium persulfate in acidic medium.This emeraldine salt form of PANI was converted into emeraldine PANI base and doped with MWNT (4 wt%) in presence of champhor sulfonic acid (CSA) by solution mixing method. The MWNT/PANI composite films were deposited onto ITO coated glass substrate using spin cast technique. The gas sensitivity of these composite films was evaluated by measuring the change in electrical resistance of composite films in presence of hydrogen gas for different pressures at room tempeature. It is observed that the MWNT/PANI composite film shows a higher sensitivity in comparison to pure PANI and it decreases on increasing hydrogen gas pressure. The composite films have also been characterized by X-ray diffraction (XRD) analysis and Atomic force microscopy (AFM).

Solid-State Reduction of Silver Nitrate with Polyaniline Base Leading to Conducting Materials

The polyaniline (PANI) base was ball-milled with silver nitrate in the solid state. Samples were prepared at various mole ratios of silver nitrate to PANI constitutional units ranging from 0 to 1.5 for three processing times, 0, 5, and 10 min. The emeraldine form of PANI was oxidized to pernigraniline, and the silver nitrate was reduced to metallic silver. Nitric acid is a byproduct, which may protonate the residual emeraldine and pernigraniline. The changes occurring in the structure of PANI are discussed on the basis of Fourier transform IR and Raman spectroscopies. Raman spectra revealed the formation of pernigraniline salt. The reaction between the two nonconducting components, emeraldine base and silver nitrate, produced a mixture of two conducting components, emeraldine or pernigraniline nitrate and metallic silver. The accompanying conductivity changes were determined. The increase in the conductivity of the original base, 10(-9) S cm(-1), up to 10(-2) S cm(-1) was found to depend on the mole ratio of silver nitrate to PANI base and on the processing time of the components in the ball mill.

The role of oxygen in the interaction of emeraldine base polyaniline with Cu(II) or Fe(III) ions in NMP solution

The influence of molecular oxygen in the interactions of emeraldine base form of polyaniline (EB-PANI) with Fe(III) or Cu(II) ions in 1-methyl-2-pyrrolidinone (NMP) solutions has been investigated by UV–vis–NIR, resonance Raman and electron paramagnetic resonance (EPR) spectroscopies. Through the set of spectroscopic results it was possible to rationalize the role of O 2 and to construct a scheme of preferential routes occurring in the interaction of EB-PANI with Fe(III) or Cu(II). Solutions of 4.0 mmol L −1 EB-PANI with 0.8, 2.0 and 20 mmol L −1 Fe(III) or Cu(II) ions in NMP were investigated and the main observed reactions were EB-PANI oxidation to pernigraniline (PB-PANI) and EB-PANI doping process by pseudo-protonation, or by a two-step redox process. In the presence of O 2, PB-PANI is observed in all Fe(III)/EB solutions and EB-PANI doping only occurs in solutions with high Fe(III) concentrations through pseudo-protonation. On the other hand, emeraldine salt (ES-PANI) is formed in all Fe(III)/EB solutions under N 2 atmosphere and, in this case, doping occurs both by the pseudo-protonation and two-step redox mechanisms. In all Cu(II)/EB solutions PB-PANI is formed both in the presence and absence of O 2, and only for solutions with high Cu(II) concentrations doping process occurs in a very low degree. The most important result from EPR spectra was providing evidence for redox steps. The determined Cu(II) signal areas under oxygen are higher than under N 2 and, further, the initial metal proportions (1:2:20) are maintained in these spectra, indicating that Cu(I) formed are re-oxidized by O 2 and, so, Cu(II) ions are being recycled. Consistently, for the solutions prepared under nitrogen, the corresponding areas and proportions in the spectra are much lower, confirming that a partial reduction of Cu(II) ions actually occurs.

A sensor of alcohol vapours based on thin polyaniline base film and quartz crystal microbalance

Thin films of polyaniline base, emeraldine base (EB), coating on the quartz crystal microbalance (QCM) electrode were used as a sensitive layer for the detection of a number of primary aliphatic alcohols such as ethanol, methanol, 2-propanol and 1-propanol vapours. The frequency shifts (Δ f) of the QCM were increased due to the vapour adsorption into the EB film. Δ f were found to be linearly correlated with the concentrations of alcohols vapour in part per million (ppm). The sensitivity of the sensor was found to be governed by the chemical structure of the alcohol. The sensor shows a good reproducibility and reversibility. The diffusions of different alcohols vapour were studied and the diffusion coefficients ( D) were calculated. It is concluded that the diffusion of the vapours into the EB film follows Fickian kinetics.