Properties Of Polypyrrole Films Research Articles

Influence of electropolymerization temperature on corrosion, morphological and electrical properties of PPy doped with salicylate on iron

In this work, the influence of the electropolymerization temperature on corrosion, morphological and electrical properties of polypyrrole (PPy) film is studied. Polypyrrole is electrochemically synthesized on iron in the presence of sodium salicylate. The X-ray diffraction and scanning electron microscopy are performed in order to study the structure and morphology of electrodeposited PPy. The electroactive surface area, corrosion performance and resistance of the PPy film on iron are also investigated as a function of electropolymerization temperature. The results show that the synthesis temperature significantly affects the properties of the PPy film on iron. It is observed that at 25°C amorphous PPy is formed, whereas lowering the temperature leads to the formation of a film containing crystallites of salicylic acid. The latter reveals lower corrosion protection and a much higher level of resistance compared to the amorphous one. These characteristics were associated with the presence of insulating salicylic acid crystals in the layer structure.

Tuning the Surface Properties of Polypyrrole Films for Modulating Bacterial Adhesion

Tuning the physical–chemical properties of polypyrrole (PPy) opens up potentially exciting new applications, especially in the area of bacterial adhesion. Polypyrrole is electrochemically synthesized under various conditions and the physical properties of the films and their effects on bacterial adhesion are characterized. Five types of dopants—chloride (Cl), perchlorate (ClO4), p‐toluene‐sulfonate (ToS), dodecylbenzene sulfonate (DBS), and poly sodium styrene sulfonate (PSS)—are used to fabricate PPy films at two different constant potentials (0.500 and 0.850 V) with and without Fe3+. Their thickness, roughness, and wettability are measured. The adhesion tendency of Escherichia coli, as a model bacterium, to the four polymers is studied. E. coli shows greater adhesion tendency to the hydrophobic, rough surface of PPy‐DBS, and less adhesion tendency to the smooth and hydrophilic surface of PPy‐PSS. The results facilitate the choice of appropriate electropolymerization conditions to modulate bacterial adhesion. image

Electrochemical Activity and Electrical Properties of Optimized Polypyrrole Coatings on Iron

In this work, electrochemical activity and electrical properties of polypyrrole (PPy) coated iron electrodes have been investigated. PPy film was electrochemically polymerized from sodium salicylate aqueous solution under conditions, which provided an increase of iron corrosion resistance. It was noticed that the pH of the solution and the applied electrode potential range during the study of the polymer properties had an influence on the observed electroactivity of PPy. The electroactivity of PPy was retained in neutral solution when the potential was scanned between −0.6 and 0.3 V. Also the resistance behavior of the synthesized polymer film as a function of the electrode potential during doping/dedoping processes was studied. Determination of the resistance was based on the impedance spectroscopy measurements and was performed in air, in order to avoid the influence of the solution resistance on the resistance of the studied polymer. Depending on the redox properties, the pH of solution and the potential range, different resistances of the polymer film during the doping/dedoping process can be obtained.

Effect of polystyrenesulphonate and electrolyte concentration for electrical properties of polypyrrole film on aluminium alloy using conductive AFM

The electrochemical synthesis of polystyrenesulphonate (PSS) doped polypyrrole (PPy) film onto aluminium alloy (AA 2024-T3) under galvanostatic conditions at current densities of 1 mA cm−2 was studied. In this study, conductive atomic force microscopy (C-AFM) was performed to investigate the electrical properties of PPy film on AA 2024-T3 depending on the concentration of PSS as dopant and nitric acid as electrolyte during electrochemical synthesis. The addition of HNO3 to aqueous electrolyte solution is found to allow the electrochemical synthesis of well adhering homogeneous PPy film in the presence of PSS on AA 2023-T3. The PPy film in the presence of nitric acid alone can be synthesised, although this film showed the poor quality of the electrical properties of PPy film. According to C-AFM, the study confirmed that the conductivity of PPy film is significantly increased with increasing the PSS, nitric acid concentration and electrochemical deposition time.

Influence of ion-exchange on the electrochemical properties of polypyrrole films

Cyclic voltammetry, X-ray microanalysis (EDS), FTIR, and AFM were applied for the systematic examination of the influence of self-exchange and potential stimulated ion-exchange on the electrochemical properties of polypyrrole (PPy) films prepared in the presence of benzene sulfonate (BS), para-toluene sulfonate (pTS), and naphthalene-1, 5-disulfonate (NDS) anions. All electrochemical experiments were carried out in aqueous solutions. It was established that small inorganic anions, like NO3−, Cl−, ClO4− can relatively easily replace an essential part of the sulfonates in PPy/BS and PPy/pTS films simply during a 10min polarization at 0.4V. A single potentiodynamic cycle increases the completeness of the exchange of the anions remarkably. The EDS analysis carried out before and after the anion exchange showed that 5–15% of the sulfonate anions still remain in the PPy films. The ability of the double-charged SO42− anions to replace sulfonate anions is even more pronounced as the exchange process does not need additional electrochemical activation. The quantum chemical model calculations have shown that the interaction of the sulfate anions with charged pyrrole oligomers is essentially stronger compared to other anions under the study.The redox capacitance and the corresponding electrochemical doping level of the redoped PPy films are remarkably higher than those before ion-exchange, showing that the PPy matrix formed in the presence of sulfonate anions does not collapse after ion-exchange and it creates favorable conditions for increased mobility of inorganic anions.

Polypyrrole/carbon nanotube composites: Molecular modeling and experimental investigation as anti-corrosive coating

In this work we present a computational method based on molecular mechanics (MM) and dynamics (MD), to predict mechanical properties of polypyrrole (PPy)/polyaminobenzene sulfonic acid-functionalized single-walled carbon nanotubes (CNT-PABS) and PPy/carboxylic acid-functionalized single-walled carbon nanotubes (CNT-CA) composites. Furthermore, experiments were carried out to assess the anticorrosive features of the PPy film and CNT-PABS and CNT-CA PPy reinforced composite coatings. Computational bulk models of PPy/CNT-PABS and PPy/CNT-CA were implemented at atomistic scale and composite coatings were grown in situ onto carbon steel (OL 48-50) electrodes. PPy, PPy/CNT-PABS and PPy/CNT-CA computational models and films were investigated concerning mechanical properties by using computational tools. The obtained films were assessed experimentally as anticorrosive materials using potentiodynamic measurements, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results clearly confirmed that the CNT-PABS and CNT-CA are properly dispersed in the composite coatings and have beneficial effect on mechanical integrity. Moreover, the anticorrosion protecting ability of the composite coatings is significantly higher than the one characteristic to pure PPy. The Young's moduli generally increased with increasing of CNT content and values ranged from 2.67GPa in the case of pure PPy to 4.15–4.61GPa in the case of PPy/CNT-PABS composite system.In agreement with earlier results from the literature for conducting polymer organic coatings, the higher conductivity of material leads to a more efficient anticorrosion protection capability, our results exhibited an enhance of conducting features even for very low mass of CNT-PABS or CNT-CA loaded in composites coatings therefore, an improvement of anticorrosion protecting ability.

Redoping — A simple way to enhance the redoxcapacity of polypyrrole films

In this work, the beneficial structural properties of polypyrrole (PPy) films formed in the presence of benzenesulfonate (BS) and para-toluenesulfonate ( pTS) were combined with the good mobility of small inorganic anions as chloride by redoping (ion exchange). the combination of voltammetry as the classical method for the determination of redoxcapacity together with the analytical determination of the doping level before and after redoping by X-ray microanalysis (EDS) allow to optimize the redoping process and produce PPy films with high redoxcapacity and stability.

The mechanical and the electrical properties of conducting polypyrrole fibers

The mechanical and the electrical properties of polypyrrole (PPy) fibers and electrochemically deposited PPy films were studied. It was found that the PPy fibers showed a significantly higher strength than the PPy films due to better orientation of the molecular structure. The electrochemically prepared PPy films had a higher electrical conductivity than that of the fibers at high temperature. At low temperature, the PPy fibers showed the higher conductivity. The conductivity results were analyzed in the frame of the three-dimensional variable range hopping model. The results showed that at room temperature the average hopping distance for the fibers was about 4 Å while for the films it increases to about 5.7 Å. This corresponds to about 1 and 2 monomer units in length for the fiber and film samples, respectively.

Impact of the Electrochemical Porosity and Chemical Composition on the Lithium Ion Exchange Behavior of Polypyrroles (ClO4−, TOS−, TFSI−) Prepared Electrochemically in Propylene Carbonate. Comparative EQCM, EIS and CV Studies

Conditions of electrodeposition, i.e. a potential window of the process, addition of water, the current density, and morphology of substrate electrodes (Pt, Pt/TiO(2), Au), were shown to influence strongly ion-exchange properties of polypyrrole (PPy) synthesized in propylene carbonate (PC), doped with ClO(4)(-) or p-toluenesulfonate (TOS(-)). "Electrochemical porosity" and redox activity of PPy films were compared to the characteristics of poly(3,4-ethylenedioxythiophene) (PEDOT). A molecular indicator of the PPy film structure packing was bis(trifluoromethylsulfonyl)imide anion (TFSI(-)). Ion-exchange properties of PPy were found to be almost independent of chemical composition of the polymer, described in the literature as PPy(I), PPy(II), PPy(III). Instead, micro- and nanoscopic morphology of the polymer film and a molecular level packing of the polymer chains as well as the counterion nature are of the foremost importance. The polymer film structure/properties are shown to change upon prolonged redox/ionic stimulations. Lithium exchange between PPy films and contacting phases (PC electrolyte, TiO(2)) proceeds in addition to the anion exchange, the latter being a dominant process under conditions of the reversible electrochemical p-doping of PPy, although diffusion coefficients of PC solvated lithium ions in PPy are higher than diffusion coefficients of perchlorate, p-toluenesulfonate or bis(trifluoromethylsulfonyl)imide anions. The highest flux of Li(+) ions into/out of the PPy phase takes place about -1.0 V vs Ag/Ag(+) which is clearly evidenced by the cathodic/anodic CV peaks. Cation transport phenomena can be analyzed independently from anion transport when observed at a longer time scale (low values of potential scan rate) as each prevails at different redox states of the polymer. However, in a shorter time scale (v > or = 10 mV s(-1)), the opposite fluxes of cations and anions were observed to interfere. Furthermore, a net uptake of propylene carbonate by the as grown PPy film occurs at initial cycles of the cation uptake causing irreversible swelling of the polymer phase. Mechanisms of the redox process and accompanying mass transport involving PPy films were investigated using comparatively three techniques: cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and electrochemical quartz crystal microbalance (EQCM).

Comparative study of polypyrrole films electrosynthesized in alkaline and acid solutions

The influence of the pH of electropolymerization solutions on the properties of polypyrrole films has been studied using potentiodynamic techniques and faradaic impedance spectroscopy. Scanning electron microscopy (SEM), IR and Raman spectroscopies, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were also used for products characterization. Results indicate that, contrary to what happen with the polymer electrogenerated in acid solutions, the films prepared in alkaline media are stable and present good electrochemical activity in basic solutions. Possible explanations for the observed differences are discussed and it is proposed that the pH of electropolymerization medium directly affects chains organization. Electrosynthesis in solutions of increased basicity results in a more compact and closed polymer structure.

Electrochemical Activity and Corrosion Protection Properties of Doped Polypyrrole Electrodeposited at Pure Aluminium Electrode

ABSTRACT Polypyrrole films were electrodeposited at pure aluminium from aqueous solution of sodium sulphate containing pyrrole and organic compounds as dopants. Substrate-adherent polypyrrole films were obtained by electrochemical oxidation of pyrrole using the potentiodynamic method and cycling the electrode potential from 50 up to 100 cycles on the potential range of 0 ÷ 800 mV. Since the conducting polymers, such as polypyrrole, are electrosynthesized easily at inert electrodes such as gold and platinum, but much more difficult at aluminium electrodes, the surface protective oxide, Al2O3, was removed, as it acts as a barrier inhibiting electron transfer and the polymerization process. The electrochemical properties of polypyrrole films electrosynthesized from aqueous solutions containing sodium dodecylsulphate (SDS) and sodium bis(2-ethylhexyl) sulfosuccinate (AOT) as doping electrolytes were studied by cyclic voltammetry and electrochemical impedance spectroscopy. The results indicate that the mechanism of the redox process is complex and may be governed by the diffusion of the electrolyte. The cyclic voltammograms of polypyrrole film synthesized in solutions having different concentrations of SDS and AOT indicate that the dopant concentration plays a very relevant role in the electrochemical response of the doped polypyrrole films like as: PPY/SDS/aluminium oxide and PPY/AOT/aluminium oxide. The results indicate that the SDS and AOT anions favor redox processes which are faster and more reversible than those associated to usual polypyrrole electrodes. However, the aluminium substrate had a considerable effect on the electrochemical activity of the polypyrrole films and that, because in the presence of pyrrole, anodization of these electrolytes resulted in formation of Al2O3 and PPY layers simultaneously. This is consistent with a galvanic interaction between the polymer and the aluminium substrate, giving rise to oxidation of the aluminium and reduction of the polymer. The corrosion performance of polypyrrole coated aluminium was evaluated by DC polarization and Electrochemical Impedance Spectroscopy. Our results show that the presence of polypyrrole coatings significantly increases the corrosion potential and drastically reduces the corrosion current and corrosion rate of pure aluminium. The corrosion resistance of polypyrrole coated aluminium was higher than of uncoated aluminium.

Electrochemistry of Conductive Polymers 37. Nanoscale Monitoring of Electrical Properties during Electrochemical Growth of Polypyrrole and Its Aging

Electrical and morphological properties of polypyrrole (PPy) films were studied during and after their electrochemical growth under various experimental conditions on a nanometer scale using a current-sensing atomic force microscope (CS-AFM). Of acetonitrile (ACN) solutions containing various amounts of water, one that contained 1.0% water produced the best quality films in their electrical and morphological properties in terms of homogeneities. The degree of doping, as well as time evolution of the film structure and its conductivity, of the PPy films was investigated during their growth in water and ACN with 1.0% water by obtaining the current images at a few designated growing stages, and the results were compared. Well-doped, conductive films were obtained from the very early stage during the electrodeposition of PPy in the ACN solution, while the films were poorly doped in water. As the film deposition progressed further in both aqueous and nonaqueous media, the doped areas spread over the whole surface leading to a more homogeneously conducting film. The current-voltage traces were obtained at each growing stage, which showed that the conductivity increases in both media as the PPy grows; the conductivity of the film grown in ACN is much higher than that of the film grown in water at all growing stages. The electrical properties of the PPy film deteriorated gradually upon exposure to air.

Electropolymerization Mechanism and Electrochemical Properties of Polypyrrole Film Doped with a Large Anion

Using the galvanostatic method the polypyrrole films doped with common low molecular weight inorganic anions and with the large surfactant anions were obtained. The electrochemical behaviour of polypyrrole films electrosynthesised in the presence of 1,2 dihydroxybenzenedisulfonic(3,5)acid disodium salt(1,2 DHBSAS)was investigated by cyclic voltammetry. The study has been focused on the evaluation of the effects of electrosynthesis conditions on the electroresponse of the PPY films as well as on the role of the nature of the electrolyte on the doping process and on the interface properties of the polymer electrode.The results indicate that the kinetics of the redox process are mainly governed by diffusion of the cations and anions of the supporting electrolyte(cycling electrolyte), while the large anions remain immobilized in the polymer structure. Therefore, the kinetics of the process can be monitored by changing the nature of the electrolyte and this may allow modulation of the electrical and optical properties of PPY/1,2 DHBSAS film.

Polypyrrole films investigated by electrochemical quartz crystal oscillator and four-probe techniques

Electrochemical quartz crystal oscillator and four-probe techniques were employed to investigate the changes in microrheological properties of polypyrrole (PPy) during electrochemical growth in aqueous electrolyte solutions and the four-probe resistivity with the electrochemically grown PPy films, respectively. PPy films grew elastic at the initial stage and viscoelastic at the later stage in hydrochloric acid solution, while the films remained nearly elastic in the whole range of the thickness examined (8000 Hz) in sulfuric acid solution. Usual negative temperature coefficient of resistivity (TCR) was observed from 77 to 300 K with most PPy samples, but the crossover of TCR with a broad minimum peak near 200 K was found with PPy samples prepared at 0.8 V versus SCE in both hydrochloric acid and sulfuric acid solution.

Electrochemical deposition and properties of polypyrrole films doped with calcion ligands

The properties of polypyrrole (PPy) film doped with calcion (calcichrome) in the process of electrochemical polymerization from aqueous solutions are presented. The properties of the films were inspected using different electrochemical methods, analysis by energy dispersive X-ray analysis and X-ray diffraction. Since the calcion ligands introduced to the PPy film retain the metal-complexing properties known from the aqueous solutions, it is possible to design calcium-sensitive sensors with an anticipated open-circuit response.

Application of thin films of conjugated polymers in novel light‐emitting devices and liquid crystal “light‐valves”

AbstractLight‐emitting electroluminescent diodes and electrochemically‐driven electroluminescent devices involving conjugated polymers are described. The effect on the properties of polypyrrole films (deposited from aqueous polymerizing solutions of pyrrole) caused by the hydrophilicity/hydrophobicity of the substrate surface is utilized by a “microcontact printing” technique to form patterned liquid crystal display devices.

EQCM studies on polypyrrole in aqueous solutions

Electrochemical quartz crystal microbalance (EQCM) studies revealed that the electrochemical properties of polypyrrole (PPY) in aqueous solutions are greatly dependent on the solution pH. A PPY film immersed in an aqueous KCl solution shows redox processes which involve not only anion transport but also cation transport if the solution pH is greater than 3–4, whereas at lower pH values only anion transport prevails as has been widely recognized. It has been found from comparative studies using poly( N-methylpyrrole) that protonation and deprotonation at nitrogen atoms of PPY play a key role in the observed pH-dependent electrochemical behavior. Deprotonated PPY allows transient incorporation of hydrated cations upon reduction in weak alkaline aqueous solutions, followed by slow ejection of the incorporated cations when conventional electrolytes such as KCl and NaClO 4 are used, but not in NH 4Cl solution. Discussion on the cation transport in PPY is made in terms of deprotonation and protonation of nitrogen atoms of pyrrole subunits in PPY.

An electrochemical acid concentration system using conducting polymer electrodes

The proton permeability of polyanion-doped polypyrrole membranes was studied by measuring the ionic currents flowing across the membranes and the amounts of protons transferred. By utilizing the proton permeability and redox properties of polypyrrole films, an acid concentration system was constructed using polypyrrole membrane electrodes. The acid concentration was achieved by repeating redox reactions of the polypyrrole membrane electrodes in a specially designed electrochemical cell. As a result of the redox reactions, protons were transferred through the membrane electrodes, without causing chemical and physical changes in the polypyrrole films, by applying a d.c. voltage of 0.8 V.

Electrochemical properties of polypyrrole films polymerized in the presence of Methylene Blue

The electrochemical properties of polypyrrole (PPy) electropolymerized in 0.1 M KCl solution containing Methylene Blue (MB) are investigated. It is found that a large amount of Methylene Blue is incorporated in the film during the electropolymerization process, which indicates that the Methylene Blue cation plays a role in the film formation process. In strong acidic medium, two redox processes are observed in cyclic voltammograms of the film, corresponding to the redox couples of PPy and MB, respectively. The redox potential of the incorporated MB depends on the pH of the electrolyte solutions and a highly stable and reversible cyclic voltammogram is obtained at pH values lower than 2.0. In neutral or alkaline medium, the redox waves of MB are overlapped by the waves of PPy and the electrochemical behaviour of the film is similar to that of normal PPy films doped with chloride. However, a more pronounced relaxation behaviour of the film is obtained and a logarithmic law for the shifts of the anodic peak parameters as a function of waiting time in the insulating state is observed. Electrochemical impedance spectra clearly show two charge transfer processes in the film. the electroactivity of the polymer films is also investigated with respect to the ionic nature of the electrolytes. The results indicate that the redox process of MB is mediated by PPy and can only occur when PPy is in its oxidized state.

Direct measurements of bipolaron-band development in doped polypyrrole with inverse photoemission.

Inverse-photoemission spectroscopy has been used to investigate dopant-dependent electronic properties of polypyrrole (PPy) films doped with ${\mathrm{BF}}_{4}^{\mathrm{\ensuremath{-}}}$ (tetrafluoroborate) or (PSS${)}^{\mathrm{\ensuremath{-}}}$ [poly(4-styrenesulfonate)]. The results show that the bonding and antibonding bipolaron bands appear at \ensuremath{\sim}1.0 and \ensuremath{\sim}2.6 eV above the valence-band maximum for heavily doped PPy films (\ensuremath{\sim}1 dopant per 3 pyrrole units). The bandwidth of each of these bipolaron bands is \ensuremath{\sim}0.4 eV and the band gap for heavily doped films is \ensuremath{\sim}3.6 eV. The bipolaron bands move toward the band edges and the gap shrinks with decreasing dopant concentration. Annealing of heavily doped films at 300 \ifmmode^\circ\else\textdegree\fi{}C leads to dopant loss from the surface. This effect is less pronounced for the larger polymeric anions such as (PSS${)}^{\mathrm{\ensuremath{-}}}$ than for the smaller counterions such as ${\mathrm{BF}}_{4}^{\mathrm{\ensuremath{-}}}$, suggesting that the former is more stable or has a greater thermal activation energy for bipolaron dissociation into single polarons.