One-step electrochemical process for the formation of poly(N-methylpyrrole) coatings on steel in different media

Poly (N-methylpyrrole) coatings have been successfully formed on steel by a one-step electrochemical process in different media. Electropolymerization was performed in aqueous medium with low monomer concentration and in a mixed aqueous/organic media with higher monomer concentrations. Ethanol (EtOH) and N,N-dimethylformamide (DMF) were chosen as the organic components of the mixed solvents and oxalic acid was used as the electrolyte. The effect of process parameters on the formation of poly(N-methylpyrrole) was systematically investigated. The composition and morphology of the coatings were also studied by elemental analysis, FT-IR and scanning electron microscopy (SEM). Our results reveal that the formation and properties of poly (N-methylpyrrole) coatings were all dependent on the solvent composition and other process parameters. The amount of poly(N-methylpyrrole) formed on steel increased with time and applied current for all the solvent-electrolyte systems. For the electropolymerization performed in distilled water-oxalic acid solution, the amount of polymer coatings formed decreased with increased electrolyte concentration. In contrast, the amount of polymer coatings formed on steel in distilled water:ethanol (1:1)-oxalic acid and distilled water:DMF (1:1)-oxalic acid systems, increased with increasing electrolyte concentration. By controlling the electrochemical parameters, smooth, uniform and strongly adherent coatings could be formed onto steel substrates.     

Poly(N-methylaniline) coatings on stainless steel by electropolymerization

Poly(N-methylaniline) (PNMA) coatings have been electropolymerized on 304 stainless steel alloy by potentiodynamic, galvanostatic and potentiostatic synthesis techniques from aqueous solutions of 0.1 M N-methylaniline (NMA) and 0.3 M oxalic acid. Characterization of PNMA coatings was carried out by cyclic voltammetry, UV-Vis and FTIR spectroscopy techniques. Corrosion behavior of PNMA coated stainless steel electrodes was investigated using linear anodic potentiodynamic polarization, Tafel test, chronoamperometry and electrochemical impedance spectroscopy (EIS) techniques in 0.5 M aqueous HCl solutions. Corrosion test results showed that PNMA coatings possessed protection to uncoated stainless steel against corrosion.     

Electrochemical synthesis and corrosion behavior of poly(N-ethyl aniline) coatings on Al-2024 alloy

Poly(N-ethyl aniline) coating was electrodeposited onto Al-2024 by using cyclic voltammetry. The coating was characterized by infrared spectroscopy, cyclic voltammetry and UV-Vis spectroscopy. The corrosion resistance of the film was evaluated by dc polarization studies. These coatings were formed in aqueous solution of oxalic acid. The concentration of monomer and oxalic acid were kept constant at 0.1 and 0.3 M, respectively. The formation of the polymer coating was monitored by cyclic voltammetry and infrared spectroscopy. Preliminary dc polarization results show that poly(N-ethyl aniline) has a corrosion rate of about 0.004 mmpy, which is significantly lower (about one order of magnitude) than that for the non-coated Al-2024.     

Ionic liquid doped poly(N-methyl 4-vinylpyridine iodide) solid polymer electrolyte for dye-sensitized solar cell

Ion conducting polymer electrolyte, poly(N-methyl 4-vinylpyridine iodide) (PVPI) is synthesized for dye-sensitized solar cell (DSSC) application. A new solid polymer electrolyte composite containing low viscosity ionic liquid (IL) 1-ethyl 3-methylimidazolium dicyanamide (EMImDCN) doped PVPI is developed and its structural, electrical and photoelectrochemical studies are presented in detail. Fourier transform infrared (FTIR) spectroscopy, proton NMR and atomic force microscopy (AFM) affirms the modified polymer and its composite nature with porous surface morphology. The developed solid polymer electrolyte shows enhancement in ionic conductivity (σ) due to IL doping. The maximum σ value of 9.12 × 10^?6 S cm^?1 was obtained at 40 wt% IL concentration. The redox behavior of the electrolyte has been verified by the cyclic voltammetry studies. For device application, we have fabricated a DSSC using this solid polymer–IL electrolyte system which shows energy conversion efficiency of the solid-state cell as 0.65% under irradiation of simulated sunlight (AM 1.5, 100 mW cm^?2).     

Characterization of poly(N-alkylanilines) by Raman spectroscopy

Thin films of poly(N-alkylaniline) were synthesized in acidic aqueous solution and in mixtures of aqueous and organic solvents. The polymer films (alkyl = methyl, ethyl, propyl and butyl) were characterized by Raman spectroscopy with the excitation wavelengths of 514.5, 632.8 and 780 nm. The main Raman bands have been characterized for the leucoemeraldine, emeraldine and pernigraniline oxidation states between −0.2 and 0.8 V (vs. Ag|AgCl). This fundamental study shows that the structure of the half-oxidized emeraldine form contains quinoid units, which supports the commonly accepted oxidation and reduction scheme of poly(N-alkylanilines).     

Cracking investigation of W and W(C) films deposited by physical vapor deposition on steel substrates

This paper presents the investigation of the cracking of coatings deposited on steel substrates. The coating on substrate systems consisted on pure tungsten films (W) and films of solid solutions of carbon in tungsten [W(C)], which were deposited by direct current reactive magnetron sputtering on stainless steel substrates. The systems were strained uniaxially with a microtensile device adapted to a scanning electron microscope. The mechanical response was analyzed from the experimental results: the straining of the samples showed an evolution of the density of cracks in the coating, which was described trough an empirical equation based on the Weibull distribution function. The density of cracks, which corresponds to the crack saturation of the coating, appeared to vary inversely with coating thickness. Critical parameters relative to their mechanical stability were also determined from the experimental results: the strain energy release rate for crack extension through the film, G^f_c, and the fracture toughness, K^f_Ic, of the coatings. These values are included between 0.2 and 14 J m⁻², and between 0.1 and 2.5 MPa m^−1/2. The fracture resistance of W and W(C) coatings was found to be correlated to their thickness and microstructure.     

Oxidative electropolymerization of pyrrole from neat monomer solution

Oxidative electrochemical polymerization of pyrrole at gold, indium doped tin oxide on glass, and stainless steel type 304 was accomplished from neat monomer solution containing only supporting electrolyte (0.05–0.3 M n-tetrabutyl ammonium perchlorate, n-tetrabutyl ammonium hexafluorophosphate, or n-tetrabutyl ammonium tetrafluoroborate) by multiple scan cyclic voltammetry. The results presented demonstrate that thick (>1–14 μm), stable, highly conductive (up to 0.6 S/cm) polypyrrole films can be readily prepared on a wide range of electrode substrates using this simple electrochemical method.     

Non-woven fabric of poly(N-isopropylacrylamide) nanofibers fabricated by electrospinning

We have succeeded in fabricating non-woven fabric of a typical thermo-responsive polymer, poly(N-isopropylacrylamide) (PNIPAM) with a low critical solution temperature (LCST) in water at 32 °C, by the electrospinning, a simple and facile method which enables to form a mat of nanofibers directly deposited on the grounded target. The PNIPAM nanofibers electrospun at concentration and applied voltage of 15 wt% and 20 kV, respectively, had an average diameter of 165 nm. The moisture sorption isotherms of the PNIPAM nanofibers belonged to the type II of IUPAC classification, in which the interaction between polymer and water molecule was stronger than that between water molecules.     

Electrochemical synthesis and redox processes of poly(paraphenylene vinylene): An in situ FTIR-attenuated total reflectance and electrochemical quartz crystal microbalance study

The electrochemical synthesis and the redox reactions of poly(paraphenylene vinylene) (PPV) have been studied by in situ Fourier transform infrared (FTIR) spectroscopy using the attenuated total reflection method and by the electrochemical quartz crystal microbalance, EQCM, technique. The polymer material has been synthesized by electrochemical reduction of α,α,α′,α′-tetrabromo-p-xylene on a Pt-electrode in dimethylformamide or acetonitrile using tetraethylammoniumtetrafluoroborate or tetraethylammoniumtosylate as electrolyte salts. The IR spectra of the doped conducting state show a very large broad absorption band starting at 1700 cm⁻¹ and extending to 5000 cm⁻¹. Additional changes in the spectra can be seen in the region between 1700 and 700 cm⁻¹ where new absorption bands appear. The intensity for these infrared active vibrations (IRAV) increase with increasing n-doping level. The reversible charging–discharging reaction is characterized by the growth in intensity of the IRAV during charging and diminish during discharging of the PPV film. Results from FTIR spectroscopy obtained from the charging–discharging reaction are consistent with the results obtained from the EQCM experiments, which show movement of counter cations during n-doping.     

Sensing electrochemical activity in polymer-coated metals during the early stages of coating degradation by means of the scanning vibrating electrode technique

Application of scanning vibrating electrode technique (SVET) for corrosion studies of organic coatings on reactive metals is presented. SVET was used to monitor the electrochemical processes at painted steel immersed in either 10 mM Na₂SO₄ or 10 mM NaCl aqueous solutions. The coated samples were investigated after a scratch was operated through the polymer matrix down to the metal–substrate surface in order to simulate a defect across the coating. SVET imaging probes that the electrochemical behaviour of the system is different depending on the electrolyte employed. Enhanced coating delamination originating from the defect is observed when chloride ions are present in the environment.     

Spectroscopic studies of CSA-doped poly[C-hydroxyl-(4-N-dimethylamino)phenyl]dithienylmethine and doping effects on ionic conductivity

Protonation of poly[C-hydroxyl-(4-N-dimethylamino)phenyl]dithienylmethine with (1S)-(+)-10-camphorsulfonic acid (CSA) induced a structural change on the pendant group of the polymer and resulted in the formation of a cationic quinoid iminium moiety. This chemical transformation changed the polymer from a non-conducting polymer into a semi-conducting polymer with the maximum ionic conductivity of 2 × 10⁻⁴ S cm⁻¹ at 10 mol% CSA-doping level. The polydithienylmethines doped with various CSA loadings were characterized by UV–vis-NIR, FT-IR and Raman spectroscopy. An ion-hopping mechanism was suggested as the conduction mechanism for this CSA-doped polymer.     

Functional electrospun nanofibres of poly(lactic acid) blends with polyaniline or poly(aniline-co-benzoic acid)

Functionalised nanofibres of a controlled fibre diameter were electrospun from solutions of polyaniline (PANI) or poly(aniline-co-m-aminobenzoic acid) (P(ANI-co-m-ABA)) with poly(lactic acid) (PLA). Soluble copolymers of aniline (ANI) and m-aminobenzoic acid (m-ABA) were prepared and the average molecular weight of the copolymers, as determined by gel permeation chromatography, was found to decrease from 13,800 g mol^?1 to 1640 g mol^?1 with an increase of m-ABA content in the copolymer. By contrast, FT-MS results revealed that homopolymerisation of m-ABA formed oligomers rather than polymeric chains due to low reactivity of m-ABA monomer. ATR FTIR, Raman spectroscopy, and conductivity measurements confirmed incorporation of the conducting (co)polymers within the PLA based nanofibres. The conductivity of the nanofibres increased significantly with increased proportion of PANI or P(ANI-co-m-ABA) to 2.0 × 10^?5 mS cm^?1 for PLA/PANI (3.27% of PANI) and 8.3 × 10^?6 mS cm^?1 for PLA/P(ANI-co-m-ABA) (5.80% of the copolymer in the blend). The nanofibre diameter decreased from 640 ± 195 nm for pure PLA fibres to 141 ± 68 nm for PLA/PANI, and to 124 ± 31 nm for PLA/P(ANI-co-m-ABA). These fibres have potential for a range of applications, such as electroactive scaffold tissue engineering and sensing.     

Study of pitting corrosion on mild steel during wet–dry cycles by electrochemical noise analysis based on chaos theory

Electrochemical noise (EN) was used to investigate the corrosion behaviour of mild steel (Q235) in 0.1 M Na₂SO₄ and 0.1 M NaCl aqueous solutions during wet–dry cycles. The positive fraction and value of the Largest Lyapunov Exponent (LLE) of electrochemical current noise (ECN) were found out to represent the number and isolation degree of the pits formed in two electrolyte conditions. The calculated results indicate that metastable pits are more plentiful and uniformly distributed in wet cycles and in Na₂SO₄ solution than those in dry cycles and in NaCl solution respectively.     

Fabrication and characterization of Schottky diodes and thin films based on poly(o-toluidine) deposited by spincoating technique

Poly(o-toluidine) (POT) thin films were fabricated by spin coating on bare glass and indium–tin–oxide (ITO)-coated glass substrates, from a solution of poly(o-toluidine) in chloroform. The optical transmittance of the as-deposited and doped films was measured in the 250–1200 nm wavelength range. These measurements showed that the optical band gaps of the undoped and doped polymer films are on the order of 3.28 and 2.7 eV, respectively, and that doping increases absorption in the near infrared region. The FT-Raman measurement on spincoated POT film is comparable to that of polyaniline. The electrochemical properties of those thin films are presented using cyclic voltammetry. ITO/POT/Al devices were fabricated by thermal evaporation of aluminum circular contacts on films deposited on ITO-coated glass. The current–voltage characteristics of the devices indicate a Schottky diode-type behavior. The current–voltage characteristics can be fitted using the modified Shockley equation. The diode parameters were calculated from I–V characteristics and discussed. On the other hand, capacitance of these structures decreased with increasing frequency.     

Synthesis of an optically active poly(aryleneethynylene) bearing galvinoxyl residues and its chiroptical and magnetic properties

We synthesized an optically active poly(binaphthyl-6,6′-diylethynylene-1,3-phenyleneethynylene) with pendant galvinoxyl residues. The hydrogalvinoxyl precursor polymer was given by polymerization of (1,3-diiodophenyl)hydrogalvinoxyl and 6,6′-diethynyl-2,2′-dihexyloxybinaphthyl using Pd(PPh₃)₄ catalyst (M_w = 4.6 × 10⁴, M_w/M_n = 3.0). The polymer yielded the corresponding polyradical with high spin concentration by treatment of the polymer solution with PbO₂. In the CD spectra of the polymer and polyradical taken in various solutions, clear Cotton effects were observed in the absorption region of the binaphthyl chromophore, while no Cotton effect was observed in that of the galvinoxyl chromophore. On the other hand, in the MCD, Faraday effects were observed in the absorption region of the backbone and galvinoxyl chromophore. The static magnetic susceptibility of the chiral polyradical was measured using a SQUID magnetometer, and showed weak antiferromagnetic interaction.     

FTIR study of chemically synthesized poly(N-methylpyrrole)

A FTIR study has been carried out on poly(N-methylpyrrole) chemically synthesized in water and in acetonitrile with 10% water. Conductivity of the polymer has been measured in pellets formed by pressing the powder obtained in the synthesis. The FTIR of the pellet is very different from that of the powder showing that there has been a pressure-induced conformational change. Evolution of the IR spectra with temperature shows that the polymer is stable up to 403 K and from that temperature conformational changes followed by decomposition of the polymer take place.     

Electrosynthesis of 2,7-linked polycarbazole derivatives to realize low-bandgap electroactive polymers

Poly(2,7-carbazole) derivatives have been synthesized because they have more extended conjugation lengths and lower energy bandgaps than poly(3,6-carbazole)s; however, few studies regarding electrochemical synthesis of poly(2,7-carbazole)s have been reported. Here, a series of N-alkylated-2,7-di(2-furyl)carbazoles, N-butyl-2,7-di(2-thienyl)carbazole, and N-butyl-2,7-di(2-(3,4-ethylenedioxthienyl))carbazole, were synthesized to obtain electroactive films of poly(2,7-carbazole) derivatives by electrochemical polymerization. Cyclic voltammetry revealed that these monomers have excellent polymerization activity, due to their low oxidation potentials (<0.57 V vs. ferrocene (Fc/Fc⁺)), and the corresponding polymers exhibit good redox properties. The energy bandgaps of the polymers obtained from optical absorption spectra range from 2.1 to 2.3 eV. Among the polymers, poly[N-butyl-2,7-di(2-(3,4-ethylenedioxthienyl))carbazole] shows the lowest bandgap energy of 2.1 eV, which is lower than that of previously reported poly(3,6-carbazole) analogues (2.4 eV). This polymer exhibits a significant color change from red in the oxidized state to blue in the reduced state during an electrochemical redox process. The electrochemical and optical properties of the monomers are dependent on external heteroaromatic rings attached to the 2 and 7 positions of the carbazole unit.     

Photovoltaic properties of poly(terthiophene) doped with light-harvesting dyes and photocurrent generation mechanism

A range of commercially available anionic dyes were successfully incorporated as dopants during the electrodeposition of poly(terthiophene) (P(TTh)). Photovoltaic testing revealed that the best photoelectrochemical cell (PEC) was based on P(TTh) doped with Sulforhodamine B, which showed short-circuit-current (I_sc) = 178 μA cm⁻², open-circuit-voltage (V_oc) = 318 mV, fill-factor (FF) = 29.6% and power-conversion-efficiency (PCE) = 0.0334% under white light illumination intensity of 500 W m⁻². Photocurrent action spectroscopy of the PECs based on dye-doped P(TTh)s prepared here, and of the PECs prepared in a previous study, showed that only a cationic dye directly contributed to photocurrent, while anionic dyes did not. It is proposed that these observations are due to attractive or repulsive electrostatic interactions between dyes and the electron acceptor I₃⁻ at the polymer/electrolyte interface.     

Synthesis of a boron-containing conducting polymer from the anodic oxidation of Tris(pyrrolyl)borane

The electrochemical oxidation of Tris(N-pyrrolyl)borane (1) in THF yielded a conducting polymer film with an electron conductivity of ca. 7×10⁻⁴ S cm⁻¹. The coulometric measurements indicated that the three pyrrolyl units were not totally coupled during the electropolymerization reaction. From further UV–VIS and FT-IR spectroscopy data, a structure of poly(1) was then proposed.     

A comparative investigation between poly(1-ethynylpyrene) and poly(1,6-(3-ethynylpyrenylene)): Influence of the structure on the thermal,optical, electrochemical properties and conductivity

A comparative investigation between trans-poly(1-ethynylpyrene) (trans-PEP) obtained chemically and poly(1,6-(3-ethynylpyrenylene) (E-PEP) prepared electrochemically was carried out. Thermal and optical properties of the polymers were studied by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and absorption spectroscopy. Electrochemical properties were evaluated by cyclic voltamperometry, in a 0.1 M Et₄NClO₄/THF solution at 10 mV/s, using a Pt disc as working electrode and Ag/AgCl as reference electrode. On the other hand, the conductivity of both polymers was measured in pressed pellet. Trans-PEP (T₁₀ = 369 °C) showed a higher thermal stability than its homologue E-PEP (T₁₀ = 256 °C). DSC of the polymers showed that trans-PEP exhibits a softening point at 330 °C, whereas E-PEP does it at 117 °C. Absorption spectra of the polymers revealed that trans-PEP exhibits two absorption bands at λ = 336 nm and λ = 580 nm due to the pyrene moieties and the highly conjugated polyacetylene main chain, respectively. By contrast, E-PEP showed only an absorption band at λ = 358 nm followed by a tail, which reveals that this polymer possesses a lower degree of conjugation. Molecular modelling performed in short segments of these polymers confirmed this hypothesis. Regarding the electrochemical properties, trans-PEP showed an anodic peak at 1500 mV and a conductivity value σ = 2.7 × 10^?2 S/cm, whereas E-PEP exhibited an anodic oxidation peak at 1670 mV and σ = 8.4 × 10^?2 S/cm.