Synthesis and characterization of poly(aniline) and poly(o-anisidine) films in sulphamic acid solution and their anticorrosion properties

Poly(o-anisidine) (POA) and polyaniline (PANI) coatings were synthesized on platinum (Pt) surface and stainless steel (SS) in monomer containing 0.50 M sulphamic acid (SA) solution by means of cyclic voltammetry (CV) technique. Meanwhile, poly(o-anisidine) film was also deposited with a different scan rate on SS electrode. The behaviour of PANI and POA films obtained on stainless steel examined by CV was different from the one obtained for PANI and POA on Pt electrode. The corrosion performances of PANI and POA coatings in 3.5% NaCl solution were investigated with anodic polarization technique and electrochemical impedance spectroscopy (EIS). EIS measurements verified the effect of monomers and that of scan rate on corrosion inhibition of coatings on SS electrode. The results showed that POA film synthesized at low scan rate exhibited an effective anticorrosive property on SS electrode. POA synthesized at low scan rate and PANI coatings provided a remarkable anodic protection to SS substrate for longer exposure time than the one observed for POA coating produced at high scan rate as well as that of bare SS electrode.     

Electrochemical synthesis of poly(indole‐co‐thiophene) on low‐nickel stainless steel and its anticorrosive performance in 0.5 mol L−1 H2SO4

The electrochemical synthesis of poly(indole‐co‐thiophene) copolymer coatings was achieved on low‐nickel stainless steel (LN SS) with the cyclic voltammetry technique using indole and thiophene monomers in acetonitrile medium containing lithium perchlorate. The optimization of synthesis parameters such as monomer feed ratio and various scan rates was studied and also their influence on the morphology of the copolymer coatings on LN SS. For the first time, a possible radical cationic electro‐copolymerization mechanism is also proposed in order to understand the electrochemical synthesis. The bonding and structure of the as‐synthesized coatings were characterized using Fourier transform infrared and ¹H NMR spectroscopies. The surface morphology and composition of the coatings were also assessed using scanning electron microscopy and energy‐dispersive X‐ray analysis. It was observed that changes in morphology occurred which had a marked and significant effect on the electrochemical behaviour of the coated LN SS confirmed using electrochemical techniques of potentiodynamic polarization and electrochemical impedance spectroscopy in aqueous 0.5 mol L^?1 H₂SO₄ solution. The obtained results revealed that the copolymer coatings on LN SS provided significant corrosion protection in the acid medium. It was also found that a 1:1 ratio of indole to thiophene yielded the most stable and corrosion‐protective copolymer coating. © 2013 Society of Chemical Industry     

Polybithiophene and its bilayers with polyaniline coatings on stainless steel by electropolymerization in aqueous medium

For the first time, electrosynthesis of polybithiophene (PBTh) and its bilayers with polyaniline (PAni) coatings on stainless steel (SS) in aqueous oxalic acid solutions containing monomer and sodium dodecyl sulfate (SDS) was carried out by potentiodynamic synthesis technique. Smooth and adherent films were obtained on the steel surfaces. Homopolymers and bilayers were characterized by cyclic voltammetry, FTIR, UV–vis spectroscopies and SEM. Homopolymers were also characterized by means of conductivity and the number average molecular weight measurements. The effects of the scanning potential limits on electrosynthesis of PBTh and its bilayer coatings were investigated. The test for corrosion protection of the polymer coated and uncoated SS substrates were performed in highly aggressive 0.5 M NaCl and 0.5 M HCl solutions by linear potentiodynamic polarization and Tafel test technique, respectively. Corrosion test revealed that among the protective coatings obtained, PBTh as homopolymer and PAni/PBTh as bilayer exhibited the most effective anticorrosive properties. According to linear potendynamic polarization test, the dissolution current of these coatings at 1.6 V decreased to 99.8% and 99.6% in NaCl solution, respectively, when compared to that of uncoated SS surfaces.     

Development of poly(vinylcarbazole)/alumina nanocomposite coatings for corrosion protection of 316L stainless steel in 3.5% NaCl medium

Poly(vinylcarbazole) (PVK) and PVK‐alumina (Al₂O₃) nanocomposite coatings were electrochemically coated on 316 L stainless steel (SS) substrates for corrosion protection of 316 L SS in 3.5 weight (wt) % NaCl medium. The formation of PVK and incorporation of nanoalumina particles in PVK‐Al₂O₃ nanocomposite coatings were confirmed from attenuated total reflectance‐infrared spectroscopy (ATR‐IR). Thermal analysis (TG) results showed enhanced thermal stability for the composites relative to PVK. Incorporation of Al₂O₃ nanoparticles enhanced the micro hardness of PVK coated 316 L SS. The dispersion of alumina nanoparticles was examined via scanning electron microscope (SEM) and tunneling electron microscopy (TEM) and revealed distinct features. The influence of nanoparticles on the barrier properties of PVK and PVK‐Al₂O₃ nanocomposites was evaluated in aqueous 3.5 wt % NaCl by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) studies. The results proved that PVK nanocomposite coatings provided better protection for 316 L SS than PVK coatings. The drastic increase in impedance values is due to the high corrosion resistance offered by the PVK nanocomposite coatings that arises due to the interaction between Al₂O₃ nanoparticles and PVK. The highest corrosion protection shown by the 2 wt % nano Al₂O₃ incorporated PVK composite coatings proved enhanced corrosion resistance compared to PVK. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44937.     

Electrical conductivity enhancement of spin‐coated PEDOT:PSS thin film via dipping method in low concentration aqueous DMSO

The electrical conductivity of poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) was enhanced by dipping the thin films prepared by spin coating technique in an aqueous DMSO solution. The low concentration range of DMSO in water between 0–5 vol % was studied in comparison with pure water and pure DMSO. It was found that the electrical conductivity dramatically increased as increasing the concentration of DMSO and reached the constant value of 350 S cm^?1 at 2 vol % of aqueous DMSO solution. This could be explained by the conformational change of PEDOT chains from the coil structure to the linear or expanded coil structure as confirmed by Raman spectra. Further, white patches were obviously noticed on the surface of the films dipped in pure DMSO, indicating the phase separation of conductive PEDOT grains and associated PSS. The sulfur element of the dipped film surface was investigated by XPS. The XPS S2p core‐level spectra displayed that the unassociated PSS was considerably removed from the surface of PEDOT:PSS films dipped in pure water and 2 vol % of aqueous DMSO solution, indicating that the presence of water in the solvents is important to prominently promote the washing effect. Finally, UV–Vis spectra revealed the improved transparency of the films probably owing to the decreased film thickness. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42108.     

Electrochemical characterization of hydroxyapatite coatings on HNO3 passivated 316L SS for implant applications

Type 316L SS play a key role in the bone replacement surgery due to its excellent mechanical features, availability at low cost and ease of fabrication. However it fails miserably in vivo conditions due to corrosion-related problems. Hence an alternative method on the development of hydroxyapatite (HAP) coatings has been elucidated to impart corrosion resistance of the base metal and ensure biocompatibility of the ceramic on the metal surface. This also could not match the implant at the host site due to the continuous interaction of hostile environment with the implant and results in the dissolution of both ceramic and metal. An artificially induced passive layer on the metal surface prior to coating may improve the nature of implant on the resistance to corrosion. In the present study, the effect of HNO₃ treatments on 316L SS and the coatings on passivated 316L SS is being explored. Electrochemical studies involving cyclic anodic polarization experiments and impedance analysis in Ringer's solution were done to determine the corrosion resistance of the coatings. The leach out characteristics of the coatings was determined at the impressed potential. The results have indicated the efficiency of HAP coatings on HNO₃-treated surface.     

Transparent,conductive polymer blend coatings from latex-based dispersions

Flexible, transparent and conductive polymer blend coatings were prepared from aqueous dispersions of poly(3,4-ethylenedixoythiophene)/poly(styrenesulfonate) [PEDOT/PSS] gel particles (∼80 nm) and latex (∼300 nm). The stable dispersions were deposited as wet coatings onto poly(ethylene terephthalate) substrates and dried at 80 °C. Microstructure studies using tapping mode atomic force microscopy (TMAFM) indicate that a network-like microstructure formed during drying at 0.03 volume fraction PEDOT/PSS loading. In this network-like structure, the PEDOT/PSS phase was forced into the boundary regions between latex. In addition, migration of the PEDOT/PSS particles towards coating surface is likely during drying of the aqueous dispersions. The addition of a small amount of dimethyl sulfoxide (DMSO) in dispersions altered the distribution of the PEDOT/PSS phase. As PEDOT/PSS concentration increases to 0.15 volume fraction, the coating surface is dominated by the PEDOT/PSS phase. The effect of DMSO on microstructure becomes less apparent as PEDOT/PSS concentration increases. The conductivity of the polymer blend coatings increases in a percolation-like fashion with a threshold of ∼0.02 volume fraction PEDOT/PSS. The addition of DMSO in dispersions enhanced the coating conductivity beyond the threshold by more than two orders of magnitude. The highest conductivity, ∼3 S/cm, occurs at 0.20 volume fraction PEDOT/PSS concentration. The polymer blend coatings have good transparency with only a weak dependence of transparency on wavelength due to the small refractive index difference between filler and matrix.     

Hierarchical polymer nanocomposite coating material for 316L SS implants: Surface and electrochemical aspects of PPy/f-CNTs coatings

Biocompatible nanocomposite coatings can be synthesized to offer improved surface properties for biomaterials and biomedical implants. Nanocomposite coatings containing polypyrrole (PPy) matrix reinforced with functionalized multi-wall carbon nanotubes (f-CNTs) were deposited on 316L SS substrates using electrochemical route. FT-IR, XRD, SEM, and TEM were employed to characterize the nanocomposite microstructure. High resolution imaging showed relatively uniform dispersion of the CNTs in the nanocomposite with a typical tubular structure. Micro-indentation tests revealed improvement in the hardness of the PPy/CNTs coatings. Measurement of the contact angle indicated enhanced surface wettability of the nanocomposite coatings. The corrosion behavior of 316L SS samples coated with PPy/CNTs was studied in SBF medium. The corrosion potential and the breakdown potential of coated 316L SS substrates shifted to more noble values as compared to uncoated 316L SS samples. The results suggest that incorporating CNTs as reinforcements in PPy coatings can provide enhanced properties in terms of surface hardness, biocompatibility, and corrosion resistance.     

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.     

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.     

Inhibition of steel corrosion by electrosynthesized poly(o-anisidine)-dodecylbenzenesulfonate coatings

Poly(o-anisidine)-dodecylbenzenesulfonate (POA-DBSA) coatings were synthesized on stainless steel from aqueous solution containing o-anisidine and dodecylbenzene sulfonic acid by using cyclic voltammetry. These coatings were characterized by Fourier transform infrared spectroscopy (FTIR), UV-vis absorption spectroscopy, scanning electron microscopy (SEM) and cyclic voltammetry (CV). Corrosion tests of these coatings were carried out in aqueous 3% NaCl solution by using open circuit potential (OCP) measurements, potentiodynamic polarization technique, cyclic potentiodynamic polarization measurements and electrochemical impedance spectroscopy (EIS). The results reveal that POA-DBSA acts as a corrosion protective coating on steel and reduces the corrosion rate (CR) of steel almost by a factor of 14.5.     

Evaluation of the protective nature of GO–BCP nanocomposite coatings on 316L SS in artificial body fluid

This work reports on a novel approach to deposit composite coatings based on biphasic calcium phosphate (BCP) incorporating graphene oxide (GO) on 316L stainless steel (316L SS) and on its protective nature against corrosion in the simulated body fluid (SBF). For this purpose, 2-dimensional GO was successfully incorporated in 1% and 3% weight ratios as mechanical strength enhancer and pore size reducer for the prepared coatings. It was observed that upon increasing the GO content, the corrosion rate was drastically decreased when compared to pristine BCP coating. The corrosion resistance polarization results are in good agreement with the test results obtained for SBF immersion study. The size of the particles has significantly decreased, as shown by transmission electron microscopy (from 190 to 27 nm). The experimental results indicate that the composite hydroxyapatite–β-tricalcium phosphate–GO (HAp–β-TCP–GO) coatings enhanced the corrosion resistance of the surgical grade 316L SS, turning it a better implanting option for orthopedic applications.     

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.     

Corrosion‐protection aspects of electrochemically synthesized poly(o‐anisidine) coatings on mild steel: An electrochemical impedance spectroscopy study

The corrosion‐protection aspects of poly(o‐anisidine) (POA) coatings on mild steel in aqueous 3% NaCl solutions were investigated with electrochemical impedance spectroscopy, a potentiodynamic polarization technique, and open circuit potential measurements. The POA coatings were electrochemically synthesized on mild steel with cyclic voltammetry from an aqueous salicylate medium. The corrosion behavior of the POA coatings was investigated through immersion tests performed in aqueous 3% NaCl solutions, and the recorded electrochemical impedance spectra were fitted with an equivalent circuit to obtain the characteristic impedance parameters. The use of a single equivalent circuit was inadequate to explain the various physical and electrochemical processes occurring at different exposure times. It was suggested that some characteristic element(s) should be incorporated into the equivalent circuit at different stages of the immersion to elucidate the various processes occurring at different exposure times. The evolution of the impedance parameters with the immersion time was studied, and the results showed that POA acted as a protective coating on the mild steel against corrosion in a 3% NaCl solution. From these data, the water uptake and delamination area were determined to further support the corrosion‐protection performance of the POA coating. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

H2SO4 as a passivating medium on the localised corrosion resistance of surgical 316L SS metallic implant and its effect on hydroxyapatite coatings

The localised corrosion resistance of 316L SS metallic implant due to H₂SO₄ treatment is being studied through electrochemical studies involving cyclic polarisation experiments and impedance studies. The efficiency of hydroxyapatite (HAP) coatings on H₂SO₄ treated 316L SS is also been investigated through electrochemical studies and the dissolution characteristics of the coatings. The study reveal that 15% H₂SO₄ treatment was found to be efficient in the corrosion resistance of 316L SS and dissolution of alloy is considerably reduced in the hydroxyapatite coatings on 15% H₂SO₄ treated 316L SS.     

Fabrication of composite coatings of 4-(pyrrole-1-yl) benzoate-modified poly-3,4-ethylenedioxythiophene with phosphomolybdate and their application in corrosion protection

We propose a novel composite (hybrid) organic/inorganic system that can be prepared as a coating (on 1 μm level) on glassy carbon and metal electrode substrates. Poly(3,4-ethylenedioxythiophene) or PEDOT based composite coatings were electrodeposited using cyclic voltammetry on glassy carbon and stainless steel substrates in the presence of 4-(pyrrole-1-yl) benzoic acid (PyBA) and phosphododecamolybdic acid (PMo₁₂). The coating growth was facilitated by the addition of polyoxyethylene-10-laurylether (BRIJ10) neutral surfactant at the level of 0.04 mol dm⁻¹ to improve solubility of the 3,4-ethylenedioxythiophene monomer and to form an aqueous micellear solution in the reaction medium. The fact that carboxylate-containing PyBA units link positively charged PEDOT structures tends to improve overall stability and adherence of composite coatings to stainless steel. The PEDOT/PyBA composite serves as a stable host matrix for large negatively charged polymolybdate inorganic species. Consequently, due to the formation of denser polymeric structures and to the existence of electrostatic repulsion effects, the polyanion-containing composite coatings are capable of largely blocking the access of pitting-causing anions (chlorides) to the surface of stainless steel. Interaction of phosphomolybdate with metal ions, namely with chromium(III) or even iron(III) or iron(II) that exist at the stainless steel–composite coating interface, may lead to the formation of insoluble deposits and exhibit overall passivating effect.     

Supercapacitor studies of electrochemically deposited PEDOT on stainless steel substrate

There has been increasing interest on various properties and applications of electronically conducting polymers. Polyethylenedioxythiophene (PEDOT) is an interesting polymer of this type as it exhibits very high ionic conductivity. In the present study, PEDOT has been electrochemically deposited on stainless steel (SS) substrate for supercapacitor studies. PEDOT/SS electrodes prepared in 0.1M H₂SO₄ in presence of a surfactant, sodium dodecylsulphate (SDS), have been found to yield higher specific capacitance (SC) than the electrodes prepared from neutral aqueous electrolyte. The effects of concentration of H₂SO₄, concentration of SDS, potential of deposition, and nature of supporting electrolytes used for capacitor studies on SC of the PEDOT/SS electrodes have been studied. SC values as high as 250 F/g in 1M oxalic acid have been obtained during the initial stages of cycling. However, there is a rapid decrease in SC on repeated charge‐discharge cycling. Spectroscopic data reflect structural changes in PEDOT on extended cycling. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Poly(o-ethylaniline) coatings for stainless steel protection

The poly(o-ethylaniline) coatings were electrochemically synthesized on 304-stainless steel by using cyclic voltammetry from an aqueous salicylate medium. Cyclic voltammetry, UV–vis absorption spectroscopy, Fourier transform infrared spectroscopy and scanning electron microscopy were used to characterize these coatings, which indicates that the aqueous salicylate solution is a suitable medium for the electrochemical polymerization of o-ethyaniline on 304-stainless steel. The performance of poly(o-ethylaniline) as protective coating against corrosion of 304-stainless steel in aqueous 3% NaCl was evaluated by the open circuit potential measurements, potentiodynamic polarization technique, cyclic potentiodynamic polarization measurements and electrochemical impedance spectroscopy. The results of the potentiodynamic polarization and cyclic potentiodynamic polarization demonstrate that the poly(o-ethylaniline) coating provides excellent protection to both localized and general corrosion of 304-stainless steel. The corrosion potential was about 0.190 V more positive in aqueous 3% NaCl for the poly(o-ethylaniline) coated steel than that of bare steel and reduces the corrosion rate of steel almost by a factor of 20.     

Corrosion protection aspects of electrochemically synthesized poly(o-anisidine-co-o-toluidine) coatings on copper

The poly(o-anisidine-co-o-toluidine) coatings were synthesized on copper substrates by electrochemical copolymerization of o-anisidine with o-toluidine using sodium salicylate as supporting electrolyte. These coatings were characterized by cyclic voltammetry, UV-vis absorption spectroscopy, Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR) and scanning electron microscopy (SEM). The formation of the copolymer with the mixture of monomers in the aqueous sodium salicylate solution was ascertained by a critical comparison of the results obtained with the polymerization of the individual monomers, o-anisidine and o-toluidine, respectively. The corrosion protection aspects of poly(o-anisidine-co-o-toluidine) coatings to copper was investigated in aqueous 3% NaCl solution by potentiodynamic polarization technique and electrochemical impedance spectroscopy (EIS). The results of the potentiodynamic polarization measurements and EIS studies showed that the poly(o-anisidine-co-o-toluidine) coatings provided the effective corrosion protection to copper than that of respective homopolymers. The corrosion rate is observed to depend on the feed ratio of o-toluidine used for the synthesis of the copolymer coatings.     

Electrochemical synthesis and corrosion protection properties of poly(o‐toluidine) coatings on low carbon steel

Uniform and strongly adherent poly(o‐toluidine) (POT) coatings have been synthesized on low carbon steel (LCS) substrates by electrochemical polymerization (ECP) of o‐toluidine under cyclic voltammetric conditions from an aqueous sodium tartrate solution. Cyclic voltammetry (CV), UV‐visible absorption spectroscopy, Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD) measurements, and scanning electron microscopy (SEM) were used to characterize these coatings, which indicates that the sodium tartrate is a suitable medium for the ECP of o‐toluidine and it occurs without noticeable dissolution of LCS. Corrosion protection properties of the POT coatings were evaluated in aqueous 3% NaCl by the potentiodynamic polarization measurements and CV. The result of the potentiodynamic polarization demonstrates that the POT coating has ability to protect the LCS against corrosion. The corrosion potential was about 334 mV more positive in aqueous 3% NaCl for the POT‐coated LCS than that of bare LCS and reduces the corrosion rate of LCS almost by a factor of 50. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 685–695, 2005