Emeraldine Salt Form Research Articles

Effect of Template Type on the Trametes versicolor Laccase-Catalyzed Oligomerization of the Aniline Dimer p-Aminodiphenylamine (PADPA).

Many previous studies have shown that (i) the oxidation of aniline or the aniline dimer p-aminodiphenylamine (PADPA) in a slightly acidic aqueous solution can be catalyzed with heme peroxidases or multicopper laccases and that (ii) subsequent reactions lead to oligomeric or polymeric products, which resemble chemically synthesized polyaniline in its conductive emeraldine salt form (PANI-ES), provided that (iii) an anionic “template” is present in the reaction medium. Good templates are anionic polyelectrolytes, micelles, or vesicles. Under optimal conditions, their presence directs the reactions in a positive way toward the desired formation of PANI-ES-type products. The effect of four different types of anionic templates on the formation of PANI-ES-like products from PADPA was investigated and compared by using Trametes versicolor laccase (TvL) as a catalyst in an aqueous pH 3.5 solution at room temperature. All four templates contain sulfonate groups: the sodium salt of the polyelectrolyte sulfonated polystyrene (SPS), micelles from sodium dodecylbenzenesulfonate (SDBS), vesicles from a 1:1 molar mixture of SDBS and decanoic acid, and vesicles from sodium bis(2-ethylhexyl)sulfosuccinate (AOT). Although with all four templates, stable, inkjet-printable solutions or suspensions consisting of PANI-ES-type products were obtained under optimized conditions, considerably higher amounts of TvL were required with SDBS micelles to achieve comparable monomer conversion to PANI-ES-like products during the same time period when compared to those with SPS or the two types of vesicles. This makes SDBS micelles less attractive as templates for the investigated reaction. In situ UV/vis/near-infrared, electron paramagnetic resonance (EPR), and Raman spectroscopy measurements in combination with an high-performance liquid chromatography analysis of extracted reaction products, which were deprotonated and chemically reduced, showed seemingly small but significant differences in the composition of the mixtures obtained when reaching reaction equilibrium after 24 h. With the two vesicle systems, the content of unwanted substituted phenazine units was lower than in the case of SPS polyelectrolyte and SDBS micelles. The EPR spectra indicate a more localized, narrower distribution of electronic states of the paramagnetic centers of the PANI-ES-type products synthesized in the presence of the two vesicle systems when compared to that of the similar products obtained with the SPS polyelectrolyte and SDBS micelles as templates. Overall, the data obtained from the different complementary methods indicate that with the two vesicle systems structurally more uniform (regular) PANI-ES-type products formed. Among the two investigated vesicle systems, for the investigated reaction (oxidation of PADPA with TvL and O2), AOT appears a somewhat better choice as it leads to a higher content of the PANI-ES polaron form.

Synthesis and properties composites zeolite/polyaniline of the doping sulfuric acid

Polyaniline and polyaniline-mineral composites on the base of zeolite with low polymer content have been synthesized chemically methods. The formation of composites zeolite/polyaniline was confirmed by results of X-ray phase, FTIR spectral and thermogravimetric analysis. The comparative analysis spectral, thermal and electrical properties of the synthesized samples of polyaniline and composite zeolite/polyaniline has been carried out. It was shown that the structure of samples of polyaniline synthesized is amorphous. The structure of polyaniline in composites zeolite/polyaniline is also mainly crystalline-amorphous with the inclusion of crystalline particles of zeolite as matrices on which particles of polyaniline in the form of emeraldine salt of sulfate acid are formed. It was found that weak interphase interaction between macromolecule of polyaniline and particles of zeolite is possible thanks to interaction hydrogen bonds between surface hydroxy groups of zeolite and imino atoms of the macromolecular chains of polyaniline. The thermal stability of composites zeolite/polyaniline is much higher than pure polyaniline, due to the content of zeolite in the composite. It was established that the electrical conductivity of chanically synthesized samples of polyaniline and composites zeolite/polyaniline is several times higher than the electrical conductivity of chemically synthesized samples. The physico-chemical analysis of samples properties has been carried out using a Dron-5-04 diffractometer (Cu Kα radiation; l=1.54060 Å) in the reflection mode. Fourier-transform infrared (FTIR) spectrа of powders sample were recorded in the range of 4 000–650 cm –1 using a NICOLET IS 10 ATR spectrophotometer in the mode of reflection, which was later transformed into transmission mode. Thermal properties of synthesized samples has been analyzed using Q 1 500-D Derivatograph (MOM Paulik - Paulik - Erdei , Hungary) in the temperature range of 20–900 °C under a heating rate of 10 K/min in the atmosphere of air (corundum crucibles; standard – Al 2 O 3 ; weight of samples – 100 mg). The electrical conductivity of the pelleted samples was determined by measuring their resistance in the "sandwich" type cells at a temperature of 293±1 K using a Rigol DM 3 068 set of equipment for resistance measuring. Keywords: synthesis, polyaniline, zeolite, composite, structure, thermal stability, conductivity.

Effect of template type on the preparation of the emeraldine salt form of polyaniline (PANI-ES) with horseradish peroxidase isoenzyme C (HRPC) and hydrogen peroxide.

Horseradish peroxidase isoenzyme C (HRPC) is often used as catalyst for the preparation of the conductive emeraldine salt form of polyaniline (PANI-ES) from aniline and hydrogen peroxide (H2O2) in the presence of anionic templates in aqueous solution. Here, a direct comparison of three types of soft templates was made, (i) the sodium salt of sulfonated polystyrene (SPS), (ii) micelles from sodium dodecylbenzenesulfonate (SDBS), and (iii) vesicles from either a 1 : 1 molar mixture of SDBS and decanoic acid or from AOT (sodium bis(2-ethylhexyl)sulfosuccinate). Based on UV/vis/NIR, EPR and Raman spectroscopy measurements all three types of templates are similarly suitable, with advantages of the two vesicle systems in terms of aniline conversion degree and radical content in the final PANI-ES product. First experiments with sulfated cellulose nanocrystals (CNCs) indicate that they are promising rigid templates for the preparation of electroconductive PANI-ES-coated cellulose materials or devices.

A Self-Healing, All-Organic, Conducting, Composite Peptide Hydrogel as Pressure Sensor and Electrogenic Cell Soft Substrate.

Conducting polymer hydrogels (CPHs) emerge as excellent functional materials, as they harness the advantages of conducting polymers with the mechanical properties and continuous 3D nanostructures of hydrogels. This bicomponent organization results in soft, all-organic, conducting micro-/nanostructures with multifarious material applications. However, the application of CPHs as functional materials for biomedical applications is currently limited due to the necessity to combine the features of biocompatibility, self-healing, and fine-tuning of the mechanical properties. To overcome this issue, we choose to combine a protected dipeptide as the supramolecular gelator, owing to its intrinsic biocompatibility and excellent gelation ability, with the conductive polymer polyaniline (PAni), which was polymerized in situ. Thus, a two-component, all-organic, conducting hydrogel was formed. Spectroscopic evidence reveals the formation of the emeraldine salt form of PAni by intrinsic doping. The composite hydrogel is mechanically rigid with a very high storage modulus ( G') value of ∼2 MPa, and the rigidity was tuned by changing the peptide concentration. The hydrogel exhibits ohmic conductivity, pressure sensitivity, and, importantly, self-healing features. By virtue of its self-healing property, the polymeric nonmetallic hydrogel can reinstate its intrinsic conductivity when two of its macroscopically separated blocks are rejoined. High cell viability of cardiomyocytes grown on the composite hydrogel demonstrates its noncytotoxicity. These combined attributes of the hydrogel allowed its utilization for dynamic range pressure sensing and as a conductive interface for electrogenic cardiac cells. The composite hydrogel supports cardiomyocyte organization into a spontaneously contracting system. The composite hydrogel thus has considerable potential for various applications.

DBSA to improve the compatibility, solubility, and infusibility of cellulose nanowhiskers modified by polyaniline in reinforcing a natural rubber-based nanocomposite

In this study, the authors evaluate the potential of the reinforcement of cellulose nanowhiskers coated with polyaniline-DBSA (CNW-PANiDB) in a natural rubber latex nanocomposite. For this purpose, cellulose nanowhiskers (CNWs) were obtained by acid hydrolysis and coated with polyaniline by in situ polymerization in an acidic medium using dodecylbenzenesulfonic acid (DBSA). The nanocomposites based on natural rubber (NR) reinforced with CNW-PANiDB were obtained by a casting/evaporation method. Sample characterization was performed by DC electrical conductivity, thermogravimetric analysis, strain–stress test, UV–Vis–NIR and field emission scanning electron microscope. The UV–Vis–NIR spectrum of the NR/CNW-PANiDB nanocomposite revealed three characteristic absorption peaks around 350, 425, and 830 nm, assigned to PANiDB in emeraldine salt form. The mechanical properties of the nanocomposite, such as Young’s modulus and tensile strength, were improved by increasing the amount of CNW-PANiDB. The electrical conductivity of the nanocomposite increased by seven orders of magnitude by adding 10 mass% of CNW-PANiDB. This result indicates that CNWs coated with polyaniline-DBSA are an excellent material for use as mechanical reinforcement and to improve electrical conductivity. Thus, NR/CNW-PANiDB nanocomposite films have potential to be used as anticorrosive, electrostatic discharge, electromagnetic interference shielding materials, transducers, and electroactive materials.

Novel preparation of self-assembled HCl-doped polyaniline nanotubes using compressed CO2-assisted polymerization

Recently, extraordinary attention has been given to the preparation of strong acid-doped polyaniline in distinct morphologies, such as nanofibers, nanotubes, and nanoflowers, while seeking proper and cheap energy polymeric materials. This work introduces the CO2-supported polymerization process as an advanced and novel polymerization technique to prepare rectangular cross-sectional self-assembled HCl-doped polyaniline nanotubes (HCl-PANNT) without the need to use any surfactants for the first time. Based on the scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results, a rectangular cross-sectional HCl-PANNT with an average outer diameter and wall thickness of 110 and 35 nm, respectively, was prepared. Furthermore, X-ray powder diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR) were employed to reveal the crystallinity and the chemical structure of the prepared polyaniline, respectively. Accordingly, the produced PANNT has a partial crystalline structure and emeraldine salt form. Moreover, the produced HCl-PANNT showed a high electrical conductivity of 1.5 S/cm.

Detail Photophysical Studies of Sulfonated Polyaniline in Aqueous Medium.

Sulfonated polyaniline (SPANI) has emerged as a promising polymer in the past few decades due to its solubility in water and relatively moderate conductivity. However, to date, literature data on the optical characterization of SPANI are very limited and preliminary in nature. In the present work, SPANI is synthesized by direct sulfonation of emeraldine salt form of polyaniline with chlorosulfonic acid in an inert solvent. Detail photophysical properties of SPANI are investigated in aqueous medium by using steady state (concentration, temperature, pH, and excitation wavelength dependence) and time-resolved spectroscopic techniques. The steady state fluorescence emission measurements are carried out carefully to avoid inner filter effect (especially secondary inner filter effect or reabsorption effect) as well as scattering. Two ground state conformations of SPANI are suggested to exist in aqueous medium. Excitation wavelength dependence of the fluorescence emission spectra is attributed to red-edge effect. All these observations are nicely corroborated by the fluorescence lifetime data of SPANI obtained from time-resolved measurements. All these new findings are extremely important in view of the potential applications of SPANI in polymer optoelectronics.

Enzymatic Synthesis of Highly Electroactive Oligoanilines from a p-Aminodiphenylamine/Aniline Mixture with Anionic Vesicles as Templates.

Oligoanilines with characteristic properties of the electrically conductive emeraldine salt form of polyaniline (PANI-ES) are promising molecules for various applications. A mixture of such oligoanilines can be obtained, for example, enzymatically under mild conditions from the linear aniline dimer p-aminodiphenylamine (PADPA) with hydrogen peroxide (H2O2) and low amounts of horseradish peroxidase (HRP) in an aqueous pH = 4.3 suspension of anionic vesicles formed from AOT, the sodium salt of bis(2-ethylhexyl)sulfosuccinate. However, the simultaneous formation of undesired side products containing phenazine-type units or oxygen atoms is unsatisfactory. We have found that this situation can be improved considerably by using a mixture of PADPA and aniline instead of PADPA only but otherwise nearly identical conditions. The PANI-ES-like oligoaniline products that are obtained from the PADPA and aniline mixture were not only found to have much lower contents of phenazine-type units and not contain oxygen atoms but also were shown to be more electroactive in cyclic voltammetry measurements than the PANI-ES-like products obtained from PADPA only. The AOT vesicle suspension remained stable without product precipitation during and after the entire reaction so that it could be analyzed by in situ UV/visible/near-infrared, in situ electron paramagnetic resonance, and in situ Raman spectroscopy measurements. These measurements were complemented with ex situ high-performance liquid chromatography analyses of the deprotonated and reduced products formed from mixtures of PADPA and either fully or partially deuterated aniline. On the basis of the results obtained, a reaction mechanism is proposed for explaining this improved HRP-triggered, vesicle-assisted synthesis of electroactive PANI-ES-like products. The oligomeric products obtained can be further used, without additional special workup, for example, to coat electrodes for their possible application in biosensor devices.

Aniline-oriented polymerization over nano-SiO2 particles

The goal of this paper is to report a systematic structural and morphological characterization of PANI-ES/nano-SiO2 hybrid composite, which was synthesized in the bulk form by surface modification of nano-SiO2 particles through in situ polymerization of aniline. The aniline-oriented polymerization was observed. XRD patterns of Polyaniline Emeraldine-salt form (PANI-ES) and PANI + nano-SiO2 nanocomposite showed some differences. The intensities of peaks indexed as (1 1 0) and (4 3 0) decreased after polymerization in the nanocomposite form, while the intensities of the peaks (4 0 0), (0 0 1) and (0 3 0) remain unchanged. The unchanged planes are parallel to the unit cell axis and therefore parallel to the polymeric chains. This fact clearly indicates an oriented polymerization of aniline over the nano-SiO2 particles. SEM images showed that the nanocomposite is made up of PANI-ES nanofibers deposited over the nano-SiO2 particles. Furthermore, the PANI-ES morphology remains unchanged after polymerization in the presence of nano-SiO2 particles. The theoretical quantum chemical calculations were performed to verify the effect of successive deposition of PANI on the regular SiO2 surface. The participation of SiO2, although weak, occurs in most of the vibrational modes. Furthermore, the MEPS of SiO2 presents medium values of electrostatic potential, but of a mostly positive character, favoring the interaction with the polymer. The DC electrical conductivity of PANI-ES + nano-SiO2 composite was found around 1.22 × 10−4 S cm−1 at 25 °C, which is 10% higher than pure polyaniline prepared under the same polymerization conditions. The better-aligned polyaniline chains over the nano-SiO2 particles may improved the charge mobility along the polymer chains.

Synthesis of polyaniline/MWCNTs by interfacial polymerization for superior hybrid supercapacitance performance

Polyaniline/Multiwalled carbon nanotubes (PANI/MWCNTs) nanocomposite was prepared via liquid-liquid interfacial polymerization method. The morphology studies of the nanocomposite using SEM and TEM techniques confirmed the presence of PANI as aggregates along with MWCNTs and X-ray diffraction studies indicated the presence of graphitic planes of MWCNTs along with PANI in semi-crystalline emeraldine salt form. The PANI/MWCNTs nanocomposite electrode exhibited specific capacitance (Cs) of 1551 F/g at a scan rate of 2 mV/s in aqueous 1 M H2SO4 in a potential window of 0–1.2 V. The material exhibited good cycle life with 95% capacitance retention in a life cycle test conducted at 5 A/g for 1000 cycles. Further, an asymmetric supercapacitor device (ASD) was fabricated using PANI/MWCNTs as positive and activated carbon as negative electrodes in aqueous 1 M H2SO4. The ASD exhibited a Cs of 142 F/g at a scan rate of 5 mV/s in a wide potential range of 0–1.6 V. The device offered high energy and power densities of 29 Wh/Kg and 7.3 kW/Kg respectively and also demonstrated an excellent cyclic stability by retaining 97% of its initial capacitance after 5000 cycles at high current density of 20 A/g.

Identification of the best chemical equivalent ratio to produce emeraldine salt exhibiting better pseudo capacitance

This work details the effect of varying the ratio of concentrations of oxidant-to-monomer, in the process of synthesizing Polyaniline (PANI) in emeraldine salt (oxidation state) form for pseudo capacitor application. The formation of emeraldine salt is confirmed by analytical characterizations such as Fourier Transform Infrared spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS) and Raman analysis techniques. The UV/Vis spectroscopic (UV) technique was employed to elucidate the optical band gap of variants. Both DC and AC measurements have shown a maximum total conductivity of 1.296 × 103 S cm−1. The cyclic voltammetry (CV) of variants exhibit reversible redox reactions due to back and forth transitions between emeraldine and pernigraniline oxidation states and high diffusion of ions in the fabricated polyaniline thin films. The electrochemical impedance spectroscopy has shown their low solution resistances and charge transfer resistances behaving like a near ideal capacitor and the specific capacitances of CER variants have been calculated by performing constant current discharge cell test showing a maximum specific capacitance of 30.2 Fg−1. The variants also exhibit better coulombic efficiencies.

Comparative analysis of properties of mechanochemical and chemically synthesized polyaniline and zeolite/polyaniline composites

Polyaniline and polyaniline-mineral composites on the base of zeolite with low polymer content have been synthesized mechanochemically (by solid phase synthesis) and chemically (by liquid phase synthesis). The formation of zeolite/polyaniline composites was confirmed by the results of X-ray phase, FTIR spectral and thermogravimetric analysis. The comparative analysis of spectral, thermal and electrical properties of the synthesized samples of polyaniline and zeolite/polyaniline composites has been carried out. It was shown that the structure of samples of polyaniline synthesized both by mechanochemical and chemical methods is amorphous. The structure of polyaniline in zeolite/polyaniline composites is also mainly crystalline-amorphous with the inclusion of crystalline particles of zeolite as matrices on which particles of polyaniline in the form of emeraldine salt of sulfate acid are formed. It was found that weak interphase interaction between macromolecule of polyaniline and particles of zeolite is possible due to the interaction of hydrogen bonds between surface hydroxy groups of zeolite and imino atoms of the macromolecular chains of polyaniline. The thermal stability of zeolite/polyaniline composites is much higher than pure polyaniline due to the presence of zeolite in the composite. Chemical composition of the composites is practically identical. It was established that the electrical conductivity of mechanically synthesized samples of polyaniline and zeolite/polyaniline composites is several times as high as the electrical conductivity of chemically synthesized samples. The physico-chemical analysis of samples properties has been carried out using a Dron-4 diffractometer (Cu Kα radiation; l=1.54060 Å) in the reflection mode. Fourier-transform infrared (FTIR) spectrа of powders sample were recorded in the range of 4 000–650 cm –1 using a NICOLET IS 10 spectrophotometer in the mode of reflection, which was later transformed into transmission mode. Thermal properties of synthesized samples have been analyzed using Q 1 500-D derivatograph (MOM Paulik - Paulik - Erdei , Hungary) in the temperature range of 20–900 °C under a heating rate of 10 K/min in the atmosphere of air (corundum crucibles; standard – Al 2 O 3 ; weight of samples – 100 mg). The morphology and composition of the polyaniline and zeolite / polyaniline composites were studied by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) methods respectively (accelerated voltage – 20 kV). For these studies, the samples were dispersed by ultrasound in water, put on the platinum plate and dried at room temperature. The electrical conductivity of the pelleted samples was determined by measuring their resistance in the "sandwich" type cells at the temperature of 293±1 K using a Rigol DM 3 068 set of equipment for resistance measuring. Keywords: synthesis, polyaniline, zeolite, composite, structure, morphology.

Morphological and Structural Analysis of Polyaniline and Poly(o-anisidine) Layers Generated in a DC Glow Discharge Plasma by Using an Oblique Angle Electrode Deposition Configuration.

This work is focused on the structural and morphological investigations of polyaniline and poly(o-anisidine) polymers generated in a direct current glow discharge plasma, in the vapors of the monomers, without a buffer gas, using an oblique angle-positioned substrate configuration. By atomic force microscopy and scanning electron microscopy we identified the formation of worm-like interlinked structures on the surface of the polyaniline layers, the layers being compact in the bulk. The poly(o-anisidine) layers are flat with no kind of structures on their surfaces. By Fourier transform infrared spectroscopy we identified the main IR bands characteristic of polyaniline and poly(o-anisidine), confirming that the polyaniline chemical structure is in the emeraldine form. The IR band from 1070 cm−1 was attributed to the emeraldine salt form of polyaniline as an indication of its doping with H+. The appearance of the IR band at 1155 cm−1 also indicates the conducting protonated of polyaniline. The X-ray diffraction revealed the formation of crystalline domains embedded in an amorphous matrix within the polyaniline layers. The interchain separation length of 3.59 Å is also an indicator of the conductive character of the polymers. The X-ray diffraction pattern of poly(o-anisidine) highlights the semi-crystalline nature of the layers. The electrical conductivities of polyaniline and poly(o-anisidine) layers and their dependence with temperature are also investigated.

Superior capacitive properties of polyaniline produced by a one-pot peroxidase/H2O2-triggered polymerization of aniline in the presence of AOT vesicles

The development of novel electrode materials for electrochemical capacitors requires innovative approaches with an imperative to produce highly active materials while holding to simple and scalable synthetic approaches. For the first time we have addressed capacitances of polyaniline (PANI) obtained by enzymatic polymerization. PANI was synthesized in an aqueous system containing aniline, horseradish peroxidase isoenzyme C (HRPC)/hydrogen peroxide (H2O2) as catalyst/oxidant, and 80-100 nm-sized vesicles formed from sodium bis(2-ethylhexyl) sulfosuccinate (AOT). The vesicles served as templates to produce PANI in its emeraldine salt (ES) form. Electrochemical properties of the obtained material were investigated using cyclic voltammetry and galvanostatic charge/discharge experiments. Under galvanostatic conditions and the current load of 1 A g−1 a specific capacitance of 770 F g−1 was measured in 0.5 M H2SO4 solution. We observed that the presence of AOT vesicles in the reaction mixture is crucial for the synthesized polymer product to exhibit redox activity. The applied mild enzymatic PANI-ES synthesis procedure led to a highly stable and processable PANI-AOT vesicle suspension which can be applied directly for the production of active electrodes without any isolation and purification of the reaction products. We believe that the presented results can open a new perspective in the production of conductive polymers for application in electrochemical capacitors.

Facile fabrication of conductive polyaniline nanoflower modified electrode and its application for microbial energy harvesting

A facile strategy for fabrication of conductive polyaniline (PANI) nanoflower modified carbon cloth electrode was developed and its application for microbial energy harvesting was also demonstrated. By simply tuning the concentration of aniline monomer, uniformly distributed PANI nanoflowers assembled from PANI nanoflakes anchored on the surface of carbon cloth electrode were fabricated with in-situ polymerization. Electrochemical and spectral analyses indicated that the synthesized PANI nanoflower was in conductive emeraldine salt form. Electrochemical impedance spectroscopy (EIS) analysis revealed PANI nanoflower modification reduced the charge transfer resistance of carbon cloth electrode, indicating the PANI nanoflower had excellent electrochemical activity. Furthermore, the PANI nanoflower modified electrode was used as the anode of microbial fuel cells (MFC), which delivered 2.6 and 6.5 times higher voltage and power output than these of pristine carbon cloth electrode, respectively. This work provided a controllable synthesis strategy for PANI nanostructure and demonstrated its promise in microbial energy harvesting.

Polyaniline-CuO hybrid nanocomposite with enhanced electrical conductivity

A hybrid nanocomposite based on a polymer matrix constituted of Polyaniline Emeraldine-salt form (PANI-ES) reinforced by copper oxide II (CuO) particles was obtained by in situ polymerization. Structural, morphological and electrical properties of the pure materials and nanocomposite form were investigated. The presence of CuO particles in the nanocomposite material affected the natural alignment of the polymer chains. XRD technique allowed the visualization of the polymer amorphization in the nanocomposite form, suggesting an interaction between both phases. The FTIR spectra confirmed this molecular interaction due to the blue shift of the characteristic absorption peaks of PANI-ES in the nanocomposite form. SEM images revealed that the polymer nanofiber morphology was no longer observed in the nanocomposite. The CuO spherical particles are randomly dispersed in the polymer matrix. The density functional theory plus the Coulomb interaction method revealed a charge transfer from PANI to CuO slab. Moreover, the density of states (DOS) has revealed that the nanocomposite behaves as a metal. In agreement, the electrical conductivity showed an increase of 60% in the nanocomposite material.

Preparation and characterization of polyaniline–cadmium sulfide nanocomposite for gas sensor application

Polyaniline (PANI) was prepared by chemical oxidative polymerization of aniline monomers as emeraldine salt form. By the same method, polyaniline–cadmium sulfide nanocomposites were synthesized in the presence of different percentages (10–50 wt.%) of cadmium sulfide (CdS) which was prepared by using sol–gel method. The optical band gap was decrease with increasing of CdS concentration, that is obtained from UV-VIS measurements. From SEM and AFM, there is uniform distribution for cadmium sulfide nanoparticles in the PANI matrix. The electrical measurements of nanocomposites exhibit the effect of crystallite size and the high resistivity of CdS on the resistivity of nanocomposites. Emeraldine salt PANI, CdS and PANI–CdS nanocomposites were investigated as gas sensors. From this investigation, the sensitivity of PANI–CdS for NO2 gas increase with the increasing of operation temperature and the optimum sensitivity was obtained at 200[Formula: see text]C. The sensitivity of nanocomposites at best temperature (200[Formula: see text]C) was increased and faster response time with the increasing of CdS contents.

Sisal fibers coated with conducting polyaniline: Property and structural studies

Sisal (Agave sisalana) fiber was extracted by manual process. These fibers were subjected to surface coating with conducting polyaniline, through in situ oxidative polymerization. The polyaniline modified sisal fibers were characterized by thermal, spectroscopic and microscopic techniques. It was shown that the fiber was coated with polyaniline through in situ oxidative polymerization and the latter had a smoothing effect on the surface as compared to uncoated sisal fiber. Besides, it was confirmed that polyaniline was deposited in conductive form of emeraldine salt. This in turn verified the introduction of active functionalities to the system, which is helpful to tune up surface chemistry of polyaniline for water treatment applications.

Self-sustaining hybrid electrode prepared from polyaniline, carbon nanotubes, and carbon fibers: morphological, structural, and electrochemical analyses

The self-sustaining hybrid electrode was prepared via chemical polymerization of aniline in acid medium containing dispersed carbon nanotubes (CNT), using carbon fiber (CF) as conducting substrate. The ternary composites called PAni/CNT/CF were characterized in order to evaluate their morphologies, structures, and thermal properties. The influence of the polyaniline (PAni) layer in the ternary composite properties was studied considering different deposition times on CF samples (30, 60, and 90 min). The ternary composite morphologies were observed by scanning electron microscopy while thermal structural analyses were obtained using thermogravimetric measurements. The structural features were analyzed by Raman scattering spectroscopy and Fourier transform infrared spectroscopy (FTIR). The possible interactions between PAni and CNT were discussed on the basis of Raman and FTIR spectra. These spectroscopic analyses also confirmed that the PAni present in the composite is in the emeraldine (ES) salt form. Furthermore, the ternary composites were also evaluated by electrochemical measurements such as cyclic voltammetry (CV), galvanostatic charge–discharge, and electrochemical impedance spectroscopy (EIS) techniques. The results showed good charge storage capacity for ternary composites, in particular, for PAni/CNT/CF obtained with 90 min of deposition time, which exhibited specific capacitance of around 500 F g−1. Therefore, this electrode was selected to build a prototype of type I supercapacitor. This device presented specific capacitance of around 143 F g−1 after 3200 charge/discharge cycles.

Furthering Our Understanding of the Doping Mechanism in Conjugated Polymers Using Tetraaniline

Polyaniline is known for reversible acidic doping. However, despite extensive work, little experimental evidence exists for the initial doping mechanism mainly due to the difficulty of synthesizing polyaniline with a uniform chain length. In this study, we partially dope aniline tetramers in order to investigate the initial stage of doping in both solution and the solid state. In solution, we discovered a method for visualizing the doping level due to solvent density differences. The optical results in both the liquid and solid state suggest that the partially doped aniline tetramers are physical mixtures of aniline tetramer in the emeraldine base and emeraldine salt forms. Electron paramagnetic resonance confirms the formation of spinless bipolarons as the major carriers. Therefore, we postulate that the doping mechanism proceeds via a continual increase in the number of doubly doped tetraanilines.