Electropolymerization of poly(N-ethyl aniline) on mild steel: Synthesis, characterization and corrosion protection

Poly(N-ethylaniline) (PNEA) coatings on the mild steel electrode were synthesized by electrochemical oxidation of N-ethylaniline using aqueous oxalic acid solutions as reaction medium. Electrodeposition was carried out by potentiodynamic, potentiostatic and galvanostatic synthesis techniques. Smooth, adhesive and thick PNEA coatings on mild steel could be electrosynthesized during sequential scanning of the potential region between −0.5 and 1.4 V versus SCE, with scan rate of 20 mV s⁻¹. The electrodeposited coatings were characterized by cyclic voltammetry, FT-IR and UV-vis techniques. Corrosion behavior of PNEA coated steels was investigated by linear anodic potentiodynamic polarization technique and Tafel test. Anodic potentiodynamic polarization results showed that electrodissolution current value of PNEA coated steel decreased about 90% compared to that of the uncoated steel in 0.5 M H₂SO₄ aqueous solution. Tafel plots showed also strong decrease of corrosion current for the PNEA coated electrode compared to the uncoated steel electrode in 3% NaCl as corrosive medium.     

Corrosion inhibition by poly(N-ethylaniline) coatings of mild steel in aqueous acidic solutions

Poly(N-ethylaniline) (PNEA) coatings on mild steel have been electrodeposited from 0.1 to 0.5 M aqueous oxalic acid solutions containing 0.1 M N-ethylaniline (NEA) using potentiodynamic synthesis technique. The effect of oxalic acid concentration on the corrosion behavior of PNEA coated mild steel surfaces were investigated by DC polarization and electrochemical impedance spectroscopy (EIS) techniques in 0.1 M HCl and 0.05 M H₂SO₄ solutions. Corrosion test results showed that corrosion resistance of PNEA coatings decreases with increasing concentrations of oxalic acid in polymerization solution. Decreasing acidity of the polymerization solution causes more effective protection against corrosion in aqueous acidic corrosive medium.     

Poly(N-ethylaniline) coatings on 304 stainless steel for corrosion protection in aqueous HCl and NaCl solutions

Poly(N-ethylaniline) (PNEA) coatings were grown by potentiodynamic synthesis technique on 304 stainless steel (SS) alloy from 0.1 M of N-ethylaniline (NEA) in 0.3 M oxalic acid solution. Characterization of adhesive and electroactive PNEA coatings was carried out by cyclic voltammetry, FT-IR spectroscopy and scanning electron microscopy (SEM) techniques. The protective properties of PNEA coatings on SS were elucidated using linear anodic potentiodynamic polarization, Tafel and electrochemical impedance spectroscopy (EIS) test techniques, in highly aggressive 0.5 M HCl and 0.5 M NaCl solutions. Linear anodic potentiodynamic polarization test results proved that PNEA coating improved the degree of protection against pitting corrosion in HCl and NaCl solutions. Tafel test results showed that PNEA coating appears to enhancement protection for SS in 0.5 M NaCl and 0.5 M HCl solutions. However, according to long-term EIS results, PNEA coating is better for the protection of SS electrodes during the long immersion period in NaCl compared to that in HCl medium.     

Electrochemical synthesis of poly(N-methylaniline) on an iron electrode and its corrosion performance

Synthesis of poly(N-methylaniline) (PNMA) on pure iron and Pt electrodes was carried out from aqueous 0.3 M oxalic acid solution containing 0.1 M N-methylaniline (NMA) by potentiodynamic and galvanostatic techniques. It was found that when compared to polyaniline (PAni) and its ring- and N-ethyl-substituted derivatives, PNMA can be electrosynthesized with lower upper scanning potential (upper potential limit, E_upp) of 0.8 V vs. saturated calomel electrode (SCE) on an Fe electrode. PNMA coatings were characterized by electrochemical, scanning electron microscopy (SEM) and FTIR techniques. Linear anodic potentiodynamic polarization results proved that increasing the acidity of the polymerization solution causes more effective protection against corrosion in 0.5 M H₂SO₄ medium for PNMA. Moreover, PNMA exhibited similar protective properties with PAni under the same corrosion test conditions. Tafel test results reveal that the PNMA coating appears to enhance protection for iron in 0.5 M NaCl and 0.1 M HCl solutions. According to EIS results, the PNMA coating is able to offer protection to Fe electrodes in NaCl compared to that in HCl medium over a long immersion period.     

Electrochemical synthesis of bilayer coatings of poly(N-methylaniline) and polypyrrole on mild steel and their corrosion protection performances

Homopolymer and bilayer coatings of poly(N-methylaniline) (PNMA) and polypyrrole-dodecylsulfate (PPy-DS) have been electropolymerized on a mild steel (MS) surface by the potentiodynamic method in aqueous oxalic acid solutions. In order to include dodecylsulfate ion as dopant in the polypyrrole, sodium dodecylsulfate was also added to the polymerization solution of pyrrole. Characterization of coatings was carried out by the cyclic voltammetry, Fourier transform infrared (FTIR) spectroscopy and field emission scanning electron microscopy (FESEM). Corrosion behavior of the polymer coated MS electrodes was investigated in highly aggressive 0.5 M HCl solution by the Tafel test and electrochemical impedance spectroscopy (EIS) techniques. Corrosion test revealed that among the protective coatings obtained, the PNMA/PPy-DS bilayer exhibited the best corrosion resistance at all immersion times.     

Synthesis and characterization of soluble poly(N-heptyl indole)

In view of preparing soluble polyindole, indole was N-alkylated using bromoheptane and polymerized to poly(N-heptyl indole) which is soluble in common organic solvents. This process is being reported for the first time. Poly(N-heptyl indole) was characterized by spectral, thermal methods and it shows photoluminescence in liquid state.     

Electrosynthesis and characterization of a poly(paraphenylene) deriving from p-fluoroanisole

The electrochemical oxidation of p-fluoroanisole (p-FA) in the solvent acetonitrile leads to oligomers and polymers of poly(paraphenylene) type. The electropolymerization process involves coupling reactions of the cation radicals intermediates. The obtained polymers are separated according to their chain length by selective precipitation in cyclohexane and ether. The corresponding structures are characterized by NMR, MS, FTIR, UV and XR diffraction. A preliminary physical study shows that the polymers are photoluminescent with a maximum emission in the near infrared.     

Corrosion protective poly(o-ethoxyaniline) coatings on copper

Poly(o-ethoxyaniline) (POEA) coatings were synthesized on copper (Cu) by electrochemical polymerization of o-ethoxyaniline in aqueous salicylate solution by using cyclic voltammetry. These coatings were characterized by cyclic voltammetry, UV-vis absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The performance of POEA as protective coating against corrosion of Cu in aqueous 3% NaCl was assessed by the potentiodynamic polarization technique and electrochemical impedance spectroscopy (EIS). The results of the potentiodynamic polarization and EIS studies demonstrate that the POEA coating has ability to protect the Cu against corrosion. The corrosion potential was about 0.330 V versus SCE more positive in aqueous 3% NaCl for the POEA coated Cu than that of uncoated Cu and reduces the corrosion rate of Cu almost by a factor of 140.     

Spectroscopic studies of polymer electrolytes based on poly(N-ethylethylenimine) and poly(N-methylethylenimine)

Poly(ethylethylenimine), PEEI, was prepared from poly(ethylenimine) by reductive alkylation with acetaldehyde. Samples of PEEI and poly(methylenimine), PMEI, complexed with LiCF₃SO₃ were prepared and characterized using differential scanning calorimetry and FT-IR. Small differences in the room temperature spectra of the two complexes were noted; these differences were due to the presence of a CH₂ group in the side chain of PEEI. The predominant form of cation-anion interactions was a contact ion pair. As the samples were heated, a transition from ion pairs to “free” ions was observed, with most of the change occurring between 140 and 150 °C in both PEEI and PMEI complexes. Thermal cycling established that the transition was irreversible in the time frame of the cycling experiments. Two-dimensional correlation spectroscopy did not show any significant intensity or frequency changes in bands sensitive to cation-polymer interactions during any heating or cooling cycle.     

Triply switchable bioelectrocatalysis based on poly(N-isopropylacrylamide) hydrogel films with immobilized glucose oxidase

Poly(N-isopropylacrylamide) (PNIPAM) hydrogel films containing glucose oxidase (GOD), designated as PNIPAM-GOD, were synthesized on the surface of pyrolytic graphite (PG) electrodes through radical cross-linking polymerization method. Cyclic voltammetric (CV) response of ferrocenecarboxylic acid (Fc(COOH)) at PNIPAM-GOD film electrodes was very sensitive to the environmental temperature, sulfate concentration, and addition of methanol solvent. For example, at 25 °C, Fc(COOH) exhibited a quasi-reversible CV peak pair with large peak currents in pH 7.0 aqueous solutions containing no sulfate for the films; while at 37 °C, the CV response was greatly suppressed. By switching the film electrodes in solutions between 25 and 37 °C, the CV peak currents of Fc(COOH) cycled between a quite large value and a very small one, showing the reversible thermo-sensitive switching property between the on and off states. Similarly, the reversible SO₄²⁻- and methanol-sensitive on–off behavior of the films toward the probe was also observed. This triply responsive property could be used to realize the thermo-, SO₄²⁻-, and methanol-controlled electrochemical oxidation of glucose catalyzed by GOD immobilized in the films and mediated by Fc(COOH) in solution. This “smart” interface may establish a foundation for fabricating a novel type of multi-controllable biosensors based on bioelectrocatalysis.     

Electrochemical and spectroscopic characterization of poly(1,8-diaminocarbazole): Part I. Electropolymerization and determination of the polymer structure by FTIR studies and DFT calculations

Poly(1,8-diaminocarbazole) (PDACz) films on the Pt electrodes were obtained from acetonitrile (0.1 M LiClO₄) and acidic aqueous solutions (0.1 M HClO₄). The changes in the shape of polymerization curves in the two media are discussed in terms of a limited conductivity window of the fully oxidized PDACz. The polymer structure of the films obtained from acetonitrile and acidic aqueous solution was proposed on the base of FTIR spectra and the results of theoretical calculations. Density functional theory (DFT) was used to calculate a distribution of unpaired-electron spin density for monomer radical cations to predict the coupling positions during polymerization. This method allowed to resolve the problems concerning the monomer linkage, still present after analysis of FTIR spectra of the polymer.     

Synthesis, characterization and corrosion protection properties of poly(N-(methacryloyloxymethyl) benzotriazole-co-glycidylmethacrylate) coatings on mild steel

The synthesis of copolymers from different feed ratios of N-(methacryloyloxymethyl) benzotriazole (MMBT) and glycidyl methacrylate (GMA) was achieved by using free radical solution polymerization technique and characterized using FT-IR and ¹³C NMR spectroscopy. The thermal stability of the synthesized copolymers was studied using thermogravimetric analysis (TGA). The corrosion performances of mild steel specimens dip coated with different composition of copolymers were investigated in 0.1 M HCl using potentiodynamic polarization and electrochemical impedance spectroscopic (EIS) method. The polarization and impedance measurements showed different corrosion protection efficiency with change in composition of the copolymers. It was found that the corrosion protection properties are owing to the barrier effect of the polymer layer covered on the mild steel surfaces. However, it was observed that the copolymer obtained from 1:1 mole ratio of MMBT and GMA exhibited better protection efficiency than other combinations.     

Electropolymerization of m-aminophenol on mild steel and its corrosion protection effect

Poly-m-aminophenol (PMAP) films were synthesized using cyclic voltammetric (CV), chronoamperometric (CA) and chronopotentiometric (CP) methods in basic hydro-alcoholic medium on mild steel (MS). The structure and properties of these films were characterized by FTIR, UV–vis and scanning electron microscopy (SEM). SEM microphotographs reveal that the surface of MS was coated with PMAP films using CV, CP and CA methods. Some pinholes were seen in the SEM microphotograph of PMAP films prepared using CP method. The anti-corrosion behavior of PMAP films synthesized by CV, CA and CP has been investigated in 3.5% NaCl solution using potentiodynamic polarization and electrochemical impedance spectroscopy. The results show that PMAP films synthesized by CV and CA methods are much more effective in reducing the corrosion of MS than PMAP films synthesized by CP method. Corrosion performance of these films arises from the barrier effect for the diffusion of O₂.     

Potentiodynamic deposition of poly (o-anisidine-co-metanilic acid) on mild steel and its application as corrosion inhibitor

For the first time, poly (o-anisidine-co-metanilic acid) (PASM) was deposited on mild steel substrate by electrochemical polymerization of o-anisidine and metanilic acid monomers in aqueous solution of 0.1 M H₂SO₄. The electrochemical polymerization of o-anisidine takes place in the presence of metanilic acid monomer and uniform, strongly adherent coating was obtained on the substrate. The electroactivity of copolymer was studied by cyclic voltammetry and AC impedance techniques. There is an increasing anodic current due to oxidation of metanilic acid monomer at the surface of the electrode when the applied potential is cycled from −0.2 V to 0.8 V. These deposits were characterized by Fourier transform infrared (FTIR) spectroscopy, UV-vis and TG/DTA techniques. The effect of various concentrations of PASM copolymer solution in acid rain corrosive media has been studied through potentiodynamic polarization, AC impedance and I-E curve methods. The soluble form of polymeric solution provided better anti-corrosive behavior in artificial acid rain solution.     

Electrochemical preparation of self-doped poly(N-(3-sulfonicpropion) anilide) and its application in sensing ethanol

A novel containing sulfonic acid group aniline monomer, N-(3-sulfonicpropion) anilide, was synthesized in three steps and subsequently to be electropolymerized on a glassy carbon electrode (GCE). The resulting self-doped poly(N-(3-sulfonicpropion) anilide) (SPAN/GCE) held 79.5% electrochemical activity when transferred from 0.1 M pH 7.0 PBS to 0.1 M pH 10.0 PBS, indicating its remarkable extension of the redox activity. The SPAN/GCE was characterized by X-ray photoelectron spectroscopy (XPS) and found that 30% of the nitrogen atoms are sulfonated. Preliminary experimental results show that after the immobilization of alcohol dehydrogenase (ADH) on the SPAN/GCE (ADH/SPAN/GCE), the ADH/SPAN/GCE showed good electrocatalytic activity toward the oxidation of ethanol. These reveal that the SPAN/GCE is quite promising in the fields of biosensors, biofuel cells and other bioelectrochemical devices.     

Corrosion protection of carbon steel and copper by polyaniline and poly(ortho-methoxyaniline) films in sodium chloride medium. Electrochemical and morphological study

The aim of this work was to obtain polyaniline (Pani) and poly(ortho-methoxyaniline) (Poma) by chemical synthesis and to evaluate their corrosion protection properties on carbon steel (CS) and copper (Cu) in an aggressive media such as sodium chloride. The syntheses of the polymers were carried out by chemical oxidation of the monomers by (NH₄)₂S₂O₈ in nitric acid solutions. Under these conditions, the polymers were obtained in the oxidized form, dissolved in 1-methyl-2-pyrrolidone and casted by solvent evaporation onto the metallic substrates (carbon steel and copper) for corrosion evaluation. The morphology of the polymers was evaluated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The electrochemical behavior was determined by open circuit potential (OCP) measurements and polarization curves (PC). The best results were obtained with Pani because this polymer film participates in the formation of an oxide film at the polymer–metal interface, a phenomenon which is not observed with Poma. This oxide film increases the barrier effect that the polymeric film has by itself.     

Miscibility, thermal characterization and crystallization of poly(l-lactide) and poly(tetramethylene adipate-co-terephthalate) blend membranes

Binary blend membranes of biodegradable poly(l-lactide) (PLLA) with poly(tetramethylene adipate-co-terephthalate) (PTAT) copolymer were prepared by solution casting via air evaporation. The miscibility of PLLA/PTAT blends was studied by dynamic mechanical analysis (DMA) and thermal mechanical analysis (TMA) in a tensile mode. Differential scanning calorimetry (DSC) measurement was carried out. The surface microstructure and tensile properties of the blend membranes were examined using atomic force microscopy (AFM) and tensile tester. It was concluded that PLLA/PTAT blends should be partially miscible for all ranges of compositions. Higher roughness and porosity were observed for the blend containing 50% PTAT, suggesting more phase separation occurred. The DSC analysis showed that the fusion enthalpy and crystallinity (X_c) of the PLLA-rich phase decreased with increasing PTAT content. Solidification process strongly suggested that the crystallization rate was accelerated by blending with 25% PTAT content, which served as the nucleation agent. Furthermore, the crystallization rate coefficient (CRC) depended on the blending miscibility and cooling rate in the non-isothermal crystallization process. Besides, PTAT addition could be proved to enhance the thermal stability and elongation of resulting blend membranes, even superior to those properties of poly(lactic acid-co-glycolic acid) (PLGA).     

Electrochemical sensor based on a poly(para-aminobenzoic acid) film modified glassy carbon electrode for the determination of melamine in milk

A novel and simple sensor is developed in this paper for melamine detection, which is based on an electropolymerized molecularly imprinted polymer (MIP) of para-aminobenzoic acid (pABA). The poly(para-aminobenzoic acid) (P-pABA) film was deposited in a pABA solution by potentiodynamic cycling of potential with and without the template (melamine) on a glassy carbon electrode. The surface feature of the modified electrode was characterized by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The molecular imprinted sensor was tested by differential pulse voltammetry (DPV) to verify the changes in redox peak currents of hexacyanoferrate. Several important parameters controlling the performance of the P-pABA were investigated and optimized. In the optimal conditions, the relative redox peak currents of hexacyanoferrate were linear. The concentration of melamine ranged from 4.0 μM to 0.45 mM, with a linear correlation coefficient of 0.9992. The detection limit was 0.36 μM (S/N = 3). The MIP sensor was successfully applied to the determination of melamine in milk products and showed high selectivity, sensitivity, and reproducibility. The results of this research demonstrate that it is feasible to use the molecular imprinting methodology when preparing sensing devices for analytes that are electrochemically inactive.     

Thermally responsive poly(N-isopropylacrylamide) monolayer on gold: synthesis, surface characterization, and protein interaction/adsorption studies

This report describes a novel method for preparing a thermally responsive poly(N-isopropylacrylamide) (PNiPAM) monolayer on a gold surface, and demonstrates the function of this monolayer in aqueous media. Thiol (-SH) terminated PNiPAM was synthesized by UV polymerization followed by hydrolysis, and a monolayer of this polymer (2.84±0.2 nm) was prepared on a gold substrate by simply dipping a precleaned gold plate into an aqueous solution of the PNiPAM. Cyclic voltametry and atomic force microscopy studies showed that the gold surface was well covered by the PNiPAM chains, and X-ray photoelectron spectroscopic data showed that this monolayer was chemisorbed on the gold surface. Studies of the water contact angle, protein interaction, and protein adsorption on the PNiPAM monolayer demonstrated that this monolayer shows a temperature dependence of the interfacial properties in aqueous media.