Electrochemical synthesis and characterization of polypyrrole-poly(styrene sulfonate) composite coatings on carbon fibers

Polypyrrole-polystyrene sulfonate composite coatings have been formed on carbon fibers by an aqueous electrochemical process. The effects of process parameters such as applied current density, monomer concentration, electrolyte concentration, and the reaction time, on the electrochemical polymerization of pyrrole onto carbon fibers were investigated. The rate of formation of the coatings increased with the current density and pyrrole concentration. It was, however, independent of electrolyte concentration, especially for polystyrene sulfonate concentration [PsSNa] of 0.05–0.25 M. At higher electrolyte concentration [PsSNa] ≥ 0.30 M, the rate of coatings formation increased with electrolyte concentration. The order of the rate of polymerization with respect to the electrolyte concentration was shown to be 0 and 1.0 at low and high electrolyte concentration, respectively. The polymerization potential, Ep, increased with the current density and decreased with pyrrole concentration. SEM micrographs showed that the morphology of coatings varied with the electrolyte concentration. At low electrolyte concentration, the coatings were rough and granular; however, at higher electrolyte concentration the coatings were smooth and uniform. The doping of polypyrrole films by polystyrene sulfonate ion was confirmed by infrared spectroscopy.     

Effect of electrolytes and process parameters on the electropolymerization of pyrrole onto carbon fibers

The effect of electrolytes such as toluene-4-sulfonic acid sodium salt (T₄SNa), dodecyl-benzene-sulfonic acid sodium salt (DbSNa), alzarin red S monohydrate, and dilute sulfuric acid and reaction parameters, including the monomer concentration, electrolyte concentration, applied voltage, and the reaction time, on the electrochemical polymerization of pyrrole onto carbon fibers was studied. The amount of polypyrrole coatings formed on the carbon fiber surface increased with increased monomer concentration, electrolyte concentration, applied voltage and reaction time, respectively, for each supporting electrolyte. However, the electrolyte concentration and applied voltage were shown to have a greater influence on the amount of polypyrrole coatings formed onto carbon fibers. Scanning electron microscopy micrographs show that the morphology of the coatings were dependent on the nature and concentration of the electrolyte. IR and elemental analysis of the coatings show that the counterion derived from the electrolyte was incorporated into the polypyrrole coatings. The elemental analysis of the coatings show that the ratio of pyrrole units to the counter ion is 2.64/1 for T₄SNa, 2.79/1 for DbSNa, and 5.32/1 for sulfuric acid. © 1996 John Wiley & Sons, Inc.     

Electropolymerization of 2‐methacryloyloxy(ethyl) acetoacetate on aluminum using a novel initiation method

Electropolymerization has been used as a method to form polymers on graphite fibers and metals. Most of the previous studies have involved either the use of sulfuric acid as an initiator or direct reduction or oxidation of monomers to form the polymers. In this article, α‐bromoisobutyronitrile (BrIBN) was used as a new electrochemical initiator to form polymer coatings on an aluminum cathode. The reduction of BrIBN on a glassy carbon electrode was examined using cyclic voltammetery. It was found that BrIBN could be reduced to isobutyronitrile radicals at potentials below the reduction potential of water. The reduction behavior of BrIBN was found to be similar in aqueous, semiaqueous, and nonaqueous solutions. 2‐Methacryloyloxy(ethyl) acetoacetate was then electropolymerized on aluminum using the BrIBN as the initiator and lithium perchlorate as a supporting electrolyte. Defect‐free coatings were formed at half‐cell potentials of less than −1.20 V. The effect of various process variables on the polymerization kinetics under potentiostatic conditions is reported. The coating thickness increased with polymerization time, monomer concentration, and initiator concentration. A strong dependence of thickness on monomer concentration was observed. As expected, there was weak dependence on the initiator concentration. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1665–1675, 1999     

Formation of polypyrrole coatings onto low carbon steel by electrochemical process

Thin polypyrrole coatings (∼ 10 μm thick) were formed on low carbon steel by an aqueous constant current electrochemical polymerization using oxalic acid as the electrolyte. The amount of polypyrrole coatings formed on steel increased with the applied current and monomer concentration. No significant change in the electropolymerization of pyrrole occurred as a result of increased electrolyte concentration. The induction time for electropolymerization decreased significantly with current density but was unaffected by the initial monomer and electrolyte concentration. The electropolymerization potential of pyrrole increased with increased current density (Cd), i.e., Ep = 0.62 + 0.41 [Cd], and decreased exponentially with increased monomer and electrolyte concentration, Ep = E₀ exp^-[M]. Scanning electron microscopy (SEM) showed that the microstructure of the polypyrrole coatings formed on steel was dependent on the current density to the extent that smoother and more uniform coatings are formed at low current density. © 1997 John Wiley & Sons, Inc. J Appl Polm Sci 65:417–424, 1997     

CARBON FIBER-POLYANILINE COMPOSITES: KINETICS OF ELECTRODEPOSITION OF POLYANILINE ONTO CARBON FIBERS BY CYCLIC VOLTAMMETRY

Homogeneous and uniform coatings of polyaniline were successfully deposited on carbon fibers by an aqueous electrodeposition technique using p-toluene sulfonic acid as the electrolyte. Electrochemical deposition of aniline was carried out by cyclic voltammetry in the potential range of -0.2 V to 1.0 V versus saturated calomel electrode (SCE). The electrochemical deposition parameters such as the number of cycles, scan rate (SR), initial monomer ([M]), and electrolyte concentration ([E]) were systematically varied. The amount of composite coatings on carbon fibers was dependent on the electrochemical deposition parameters. From a weight gain analysis, the rate of the reactions (R p ) was calculated. As the aniline concentration was increased up to 0.35 M and electrolyte concentration up to 0.5 M, the deposition rate also increased, whereas an increase in scan rate decreased the deposition rate. Kinetic analysis showed that the rate equation for the p-toluene sulfonic acid system is R p ∝SR -1.25 [M] 0.73 [E] 0.95 . IR spectra also showed an increase in the deposition of polyaniline coatings on carbon fibers with a decrease in the scan rate and an increase in both monomer and electrolyte concentration. The ratio of two oxidation states of polyaniline obtained during electrodeposition, namely emeraldine and pernigraniline, can be varied by changing the electrochemical deposition parameters.     

Carbon fiber-polyaniline composites: Kinetics of electrodeposition of polyaniline onto carbon fibers by cyclic voltammetry

Homogeneous and uniform coatings of polyaniline were successfully deposited on carbon fibers by an aqueous electrodeposition technique using p-toluene sulfonic acid as the electrolyte. Electrochemical deposition of aniline was carried out by cyclic voltammetry in the potential range of ?0.2 V to 1.0 V versus saturated calomel electrode (SCE). The electrochemical deposition parameters such as the number of cycles, scan rate (SR), initial monomer ([M]), and electrolyte concentration ([E]) were systematically varied. The amount of composite coatings on carbon fibers was dependent on the electrochemical deposition parameters. From a weight gain analysis, the rate of the reactions (R p ) was calculated. As the aniline concentration was increased up to 0.35 M and electrolyte concentration up to 0.5 M, the deposition rate also increased, whereas an increase in scan rate decreased the deposition rate. Kinetic analysis showed that the rate equation for the p-toluene sulfonic acid system is R p ∝SR ?1.25 [M] 0.73 [E] 0.95 . IR spectra also showed an increase in the deposition of polyaniline coatings on carbon fibers with a decrease in the scan rate and an increase in both monomer and electrolyte concentration. The ratio of two oxidation states of polyaniline obtained during electrodeposition, namely emeraldine and pernigraniline, can be varied by changing the electrochemical deposition parameters.     

A one-step electrochemical synthesis of polyaniline-polypyrrole composite coatings on carbon fibers

Polyaniline-polypyrrole composite coatings were formed on carbon fibers by potentiostatic electrochemical polymerization. Electropolymerization was done by varying the applied potential and molar feed ratio of monomers. The dual nature of the composite coatings was deduced from the current-time (I-t) curves traced during polymerization. I-t curves were also used to predict the mechanism of the formation of composite coatings. UV-vis absorption spectroscopy was used to study the electronic structure of the composite coatings.     

The effect of process parameters on the morphology of polypyrrole coatings formed on carbon fibers

Polypyrrole coatings have been electropolymerized onto carbon fibers. Several process parameters, including the type of electrolyte, the monomer concentration, the electrolyte concentration, the applied voltage, and the electropolymerization time were systematically varied, and their effect on the morphology and composition of the coatings assessed. The SEM micrographs of the coated samples revealed several distinguishable morphologies. The presence of the counterion, derived from the electrolyte, in the coatings was confirmed by EDAX analysis, elemental analysis, and infrared spectroscopy. The doping and formation of the polypyrrole coatings occurred concuriently. The morphology of the coatings was greatly influenced by the type of electrolyte, electrolyte concentration, and the applied voltage.     

Synthesis of conductive polymeric composite coatings for corrosion protection applications

This study investigates and evaluates the protection offered by the combination of two intrinsically conductive polymers, polypyrrole and polyaniline, when applied onto pretreated Al2024-T3 substrates by a cyclic voltametric technique. All coatings produced in this work show homogeneity and strong adhesion to the substrate. The effect of the electrolyte concentration and potential sweep rate is investigated, while the composition of the deposited coatings is analyzed by the potentiodynamic data of the potentiodynamic curves; cyclic voltamograms acquired on the formed coatings, in monomer-free solutions. Scanning electron microscopy (SEM) images and EDAX analysis employed to characterize the morphology and composition of the formed coatings. The electrochemical behaviour of the coatings evaluated through Potentiodynamic and Open Circuit Potential (OCP) measurements. Evaluation of the performance of the formed coatings suggests an improved electrochemical behaviour when compared to the pretreated uncoated substrate.     

Effect of process parameters on the electropolymerization potential and rate of formation of polypyrrole on stainless steel

Polypyrrole coatings were formed on stainless steel working electrodes in aqueous oxalic acid solution. The rate of formation of polypyrrole coatings on stainless steel increased proportionately with the current density but increased slightly with increased pyrrole concentration. Increasing oxalic acid concentration also had no significant change in the polymerization rate. The electropolymerization potential of pyrrole decreased significantly from 1.5 to 0.8 V versus SCE when the working electrode was polished. The polymerization potential, E_p, of pyrrole, increased however, with increased current density and decreased exponentially with the initial monomer and electrolyte concentration, respectively. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2433–2440, 1997     

Electrodeposition of poly(n‐methylpyrrole) coatings on steel from aqueous medium

Poly(N‐methylpyrrole) coatings were formed on low carbon steel by an electrochemical method from aqueous oxalate solutions. The electrochemical reactions were performed in a wide range of pH of the reaction medium and applied current density. The formation of poly(N‐methylpyrrole) on steel occurred in three stages: (i) dissolution of the steel, followed by (ii) passivation of the steel, and, finally, (iii) electropolymerization of N‐methylpyrrole on the passivated steel. The time taken to form the passive interphase (induction time) is decreased by an increased applied current. Passivation occurred instantaneously at pH 8.4. Below pH 7, the shortest passivation time occurred at pH 2.6. The quantity of the charge consumed during passivation (passivation charge) remained independent of the applied current at pH ≈ 2.6 and decreased with the applied current at pH 4.1 and 5.7. The polymerization potential increased with the pH and the applied current. Polymerization potentials greater than 2.0 V resulted in film degradation. By controlling the electrochemical process parameters, good quality poly(N‐methylpyrrole) was formed at a controlled induction time. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1293–1302, 1999     

Characterization of coatings of poly(hexamethylene adipamide) deposited on carbon fibers by interfacial polymerization techniques

Polyamide coatings deposited on carbon fibers by means of an interfacial in situ polymerization technique have been examined. Two different coating processes were used, depending on the length of the carbon fibers (short or long). The effect of the concentration of the monomer reactants on the quantity of coating deposited on the fibers has been determined using thermogravimetric analysis (TGA). Characterization techniques used to identify the nature of the coating process product included Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and gel permeation chromatography (GPC). Using the above techniques, IR spectra were collected and identified, and important polymer properties, such as morphology, melting point, and the molecular weight of the polymer coating were determined. © 1995 John Wiley & Sons, Inc.     

Electrochemical corrosion behaviour of plasma electrolytic oxidation coatings on AM50 magnesium alloy formed in silicate and phosphate based electrolytes

PEO coatings were produced on AM50 magnesium alloy by plasma electrolytic oxidation process in silicate and phosphate based electrolytes using a pulsed DC power source. The microstructure and composition of the PEO coatings were analyzed by scanning electron microscopy (SEM) and X-ray Diffraction (XRD). The corrosion resistance of the PEO coatings was evaluated using open circuit potential (OCP) measurements, potentiodynamic polarisation tests and electrochemical impedance spectroscopy (EIS) in 0.1 M NaCl solution. It was found that the electrolyte composition has a significant effect on the coating evolution and on the resulting coating characteristics, such as microstructure, composition, coating thickness, roughness and thus on the corrosion behaviour. The corrosion resistance of the PEO coating formed in silicate electrolyte was found to be superior to that formed in phosphate electrolyte in both the short-term and long-term electrochemical corrosion tests.     

Microfluidic‐Spinning‐Directed Conductive Fibers toward Flexible Micro‐Supercapacitors

The large‐scale fabrication of the flexible fiber‐shaped micro‐supercapacitors has received major attention from both industrial and academic researchers. Herein, conductive and robust polyaniline‐wrapped multiwall carbon tubes reduced graphene oxide/thermoplastic polyurethane (PANI/MCNTs‐rGO/TPU) composite fibers are successfully fabricated on a large scale via the combination of facile microfluidic‐spinning process and in situ polymerization of aniline. Initially, MCNTs‐rGO/TPU fibers are formed in a T‐shape microfluidic chip, relying on the fast material diffusion and exchange in the microfluidic channel. Then, PANI/MCNTs‐rGO/TPU hybrid fibers are synthesized through an in situ chemical oxidative polymerization of aniline. With the assistance of polyaniline, these PANI/MCNTs‐rGO/TPU hybrid fibers exhibit enhanced electrochemical properties in comparison with pure MCNTs‐rGO/TPU fibers, especially in high specific capacitance, which is dramatically increased from 42.1 to 155.5 mF cm^?2. Moreover, the PANI/MCNTs‐rGO/TPU hybrid fibers can endure various blending stresses, contributing to its outperforming flexibility and weavability. The best of the excellent electrochemical and mechanical properties of these conductive fibers is made to construct the flexible supercapacitors and various complicated functional fabrics.     

Influence of Process Parameters on the Conductivity and Surface Morphology of Polypyrrole Films

Influence of electrochemical process parameters such as monomer and electrolyte concentrations, current density, pH of the electrolyte, and type of electrolyte have been studied during polymerization of polypyrrole (Ppy). The changes in the conductivity of synthesized Ppy film for different electrolytes were observed by chronopotentiograms recorded during the electrochemical polymerization and it was confirmed by measuring it using four probe techniques. It was found that the electrochemical process parameters have a considerable influence on the conductivity of the film. The Ppy film was synthesized on a platinum substrate by electrochemical polymerization with different electrolytes such as potassium nitrate, sodium nitrate, sulphuric acid, hydrochloric acid, potassium chloride, sodium chloride, oxalic acid, and sodium salicylate, under galvanostatic condition over a wide range of pH of the reaction medium and applied current density. The different concentration ratios of pyrrole and sodium nitrate were considered during synthesis of Ppy films. It has been observed that the polymerization potential increases with the pH and applied current density. One could synthesize Ppy film with very good surface morphology and conductivity with optimized process parameters. The characterization of synthesized Ppy film was done by electrochemical technique, electrical conductivity, Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM).     

Electrochemical conversion of phenolic wastewater on carbon electrodes in the presence of NaCl

The electrochemical conversion of highly concentrated synthetic phenolic wastewater was studied on carbon electrodes in a batch electrochemical reactor. The effects of reaction temperature, electrolyte concentration, current density and initial phenol concentration on phenol conversion were elucidated. The wastewater was synthetically prepared and used in reactions carried out generally at 25 °C with an initial phenol concentration of 3500 mg dm^?3. Although current density increased, phenol conversion% and initial phenol conversion rate did not increase correspondingly above 35 °C and an electrolyte concentration of 90 g dm^?3. As the voltage values applied were increased, the increasing current density resulted in fast phenol conversion. Kinetic investigations denoted that overall phenol destruction kinetics was of zero order with an activation energy of 10.9 kJ mol^?1. Under appropriate conditions, phenol was completely converted within 15 min for an initial phenol concentration of 98 mg dm^?3 while 8 h was required to gain 95% conversion using 4698 mg dm^?3. Solid polymeric materials were produced at initial phenol concentrations above 500 mg dm^?3 using the appropriate current density. In the reaction medium, only mono‐, di‐ and tri‐substituted chlorophenols were formed and 100% of all species were either oxidised or contributed to the formation of a polymeric structure. Almost all of the phenol loaded to the reactor was converted into non‐passivating polymeric products, denoting a safe and easy method for the separation of phenol. © 2001 Society of Chemical Industry     

Physical and chemical properties of polypyrrole–carbon fiber interphases formed by aqueous electrosynthesis

The properties of carbon fibers modified by aqueous electrochemical synthesis of pyrrole has been determined by using the dynamic contact angle analyzer (DCA), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). Electrochemical process parameters such as the initial pyrrole concentration, electrolyte concentration, applied voltage, electrolyte type, and reaction time were systematically varied, and their impact on the polypyrrole–carbon fiber interphases surface free energy and morphology was ascertained. The surface free energies of the polypyrrole–carbon fiber interphases were obtained by using single fiber filaments. SEM analysis of the interphases revealed several distinct surface structures, including smooth, porous, granular, microspheroidal, and leafoidal morphologies. The noncoated but commercially surface oxidized carbon fibers have smooth surface morphology with occasional longitudinal striations. FTIR analysis of the polypyrrole interphases confirmed that the counterions derived from the electrolytes were incorporated into the film. The surface free energies of the electrochemically formed polypyrrole–carbon fiber interphases equivalent to 60–75 dynes/cm, was determined to be up to 40% higher than that for the surface oxidized but unsized carbon fibers equivalent to 50 dynes/cm. This improvement in the surface free energies of the polypyrrole–carbon fiber interphases suggests easy wettability by polymer matrices such as epoxy resin, γ ˜ 47 dynes/cm and, polyimide matrix, γ ˜ 45 dynes/cm. © 1996 John Wiley & Sons, Inc.     

Protection of epoxy coatings containing polyaniline modified ultra-short glass fibers

Polyaniline (PANI) was covered on the surface of ultra-short glass fibers uniformly by in situ polymerization of aniline. Epoxy coatings with different contents of PANI ultra-short glass fibers and ultra-short glass fibers were formulated and their protection abilities were evaluated by means of open-circuit potential, electrochemical impedance spectroscopy and salt spray test. The results showed that the PANI ultra-short glass fibers had a significant inhibitive effect and its best volume fraction was10% in epoxy coating. XPS results indicated that a dense, stable passive oxide film of Fe₂O₃/Fe₃O₄ was formed on the steel surface beneath the coating.     

Corrosion resistance of Pb–Sn composite coatings reinforced by carbon nanotubes

Carbon nanotubes/Pb–Sn composite coatings were prepared by electrodeposition technology. The polarization curves and electrochemical impedance of the Pb–Sn coatings and carbon nanotube/Pb–Sn composite coatings were studied in 3.0 wt% HCl, 10 wt% NaOH, and 3.5 wt% NaCl electrolyte solutions, respectively. The results show that the corrosion potential of carbon nanotubes/Pb–Sn composite coatings were improved in the three kinds of corrosive medium, especially in 3.5 wt% NaCl electrolyte solution, where it increased significantly from −0.592 V (vs SCE) to −0.535 V (vs SCE). In addition, composite coatings have higher electrochemical impedance. Carbon nanotubes can improve the corrosion resistance of lead–tin electroplated coatings.     

Electropolymerization on graphite fibers

The electrodic polymerization on graphite fibers of a variety of monomers having different types of functional groups has been investigated. In addition to vinyl polymerization, some novel polymerizations of cyclic functional groups have been conducted under appropriate polymerization conditions. In many instances, the grafting of the surface polymer to the fiber has been confirmed. The stereochemical configuration of poly(methyl methacrylate) resulting from electropolymerization was measured, but conclusive evidence could not be obtained for the occurrence of stereo-regulation in electrochemical polymerization on graphite fiber surface; Composite specimens were prepared by the incorporation of the coated fibers in an epoxy matrix. It was demonstrated that the effect of electropolymerization on the interfacial properties of the resulting composite was manifested in variations of the measured interlaminar shear and impact strengths of the composite specimens. The increase or decrease in interlaminar shear was accompanied by the usually observed reverse change in impact strength. In exception to this general trend, it was also indicated that the shear and impact strengths could simultaneously be increased. Implicit in these findings is the contribution of the electrochemically formed interlayer to one or more of the toughening mechanisms that are available to fiber reinforced composites. The potential value of interphase modification by electrochemical polymerization is thus clearly indicated.