Nanospherical particles of polypyrrole synthesized and doped by plasma

This work presents the synthesis of nano and meso spherical iodine doped particles of polypyrrole using glow discharges of pyrrole. The synthesis produced polypyrrole powder with the purpose of using the polymers in bioelectric applications. The powder was composed of homogeneous spheres of diameter between 35 and 350 nm, which arranged in agglomerates of several micrometers. A molecular simulation approach of polypyrrole nanoparticles was done considering full networking of 12 pyrrole rings joined in hexagonal arrangements. In those conditions, spherical particles can be obtained with a minimum diameter of approximately 1.4 nm. The inclusion of iodine atoms is difficult in such particles, however as the particles grow, iodine compounds produced in the chemical reactions can be trapped or adhered to the particles. The electric conductivity of polypyrrole powder as a function of relative humidity was in the interval 10⁻⁹-10⁻⁶ S/m.     

Fabrication of polypyrrole micropatterns through microchannel-confined electropolymerization and their electrical conductivities

Creating micropatterns of electrically conductive polymers on solid substrates is important for the low-cost construction of organic microelectronic devices. This work develops a novel strategy for the preparation of large-area polypyrrole (Ppy) micropatterns through area-selected in situ electropolymerization of pyrrole within microchannels. The effects on micropattern formation of electropolymerization procedures such as dynamic potential polymerization (DPP), static potential polymerization (SPP), and constant current polymerization (CCP), the solvent, and the polymerization time were studied systematically. The electrical conductivities of the Ppy micropatterns were measured and compared with a homogeneous Ppy thin film synthesized under the same conditions. Given the straightforward and versatile nature of this method, it is expected to contribute greatly to the convenient fabrication of low-cost organic microelectronic devices.     

Characterization of polypyrrole degradation by the conformational relaxation model

Electrogenerated films of polypyrrole were degraded (overoxidized) by consecutive short anodic polarizations at 900 mV. The degree of degradation was quantified by means of the percentage of anodic voltammetric charge lost after each consecutive degradation processes. The charge consumed to compact 1 mol of polymeric segments (molar compaction charge) was obtained for every degraded state from experimental series of chronoamperograms, as indicated by the electrochemically stimulated conformational relaxation model. The molar magnitude decreases linearly with the change on the degradation percentage indicating the presence of shorter ideal lineal chains on a progressively degraded polymer. The correlation between these magnitudes opens the way to attain new molecular magnitudes of the polymeric chains by electrochemical measurements, as predicted by the model.     

EQCM study of polypyrrole modified electrodes doped with Keggin-type heteropolyanion for cation detection

The incorporation of a Keggin-type heteropolyanion, the phosphotungstate ([PW₁₂O₄₀]³⁻), into polypyrrole has been achieved during the electrochemical preparation of the polymer films in aqueous solution. The redox behaviour of these modified electrodes is described by using cyclic voltammetry (CV) and electrochemical quartz crystal microbalance (EQCM). The data allowed to estimate the doping level that indicates the extent of the heteropolyanion insertion. It is found that the polymer films, in aqueous solution, exhibit sensibility to cations, namely to Na⁺.     

Improvement of the anticorrosion properties of polypyrrole by zinc phosphate pigment incorporation

A commercial zinc phosphate pigment was incorporated into polypyrrole (PPy) matrix during its electrochemical synthesis in order to improve the corrosion protection of polypyrrole on AISI 1010 steel. PPy/zinc phosphate composite films were synthesised in sodium salicylate medium with high current efficiency and containing 10% by weight of zinc and 4% by weight of phosphate. The influence of stirring and concentration of the electrolyte on the degree of pigment incorporation were investigated, as well as polymerisation time and applied current density. The morphology of the films was determined by scanning electron microscopy (SEM) and the distribution of pigment in the polymeric matrix was carried out by X-ray photoelectron spectroscopy (XPS). The PPy and PPy/zinc phosphate films were submitted to salt spray corrosion test, weight loss test and to electrochemical measurements like corrosion potential with time. In all tests, the composite films showed an enhancement in its protective action in comparison with PPy films.     

Formation of stable passive film on stainless steel by electrochemical deposition of polypyrrole

Stable passive film has been formed on 304 stainless steel during the electrochemical deposition of polypyrrole (PPy) from sulfuric acid solution. The stability of passive film under PPy increases with aging in H₂SO₄ and this film has much higher resistance to pitting than that formed by anodic polarization under the same condition of aging. XPS studies indicate that the content of chromium components in the oxides under PPy layer is about twice that of the anodically formed passive film with larger value of the ratio Cr₂O₃/Cr(OH)₃. Higher content of iron with a ratio of Fe²⁺/Fe³⁺ more than unity is also observed with a considerable lower hydration and sulfate content in the oxides under PPy layer. It is suggested that sulfate ion is consumed as a dopant in the formation of PPy film and the oxidation of stainless steel is achieved under the environment of lower concentration of water and sulfate molecules. This may result in the enhancement of formation of corrosion-resisting oxides rather than hydroxides and sulfates.     

Water/ionic liquid/organic three-phase interfacial synthesis of coral-like polypyrrole toward enhanced electrochemical capacitance

Two interfacial synthesis strategies are proposed to synthesize polypyrrole samples for electrochemical capacitors (ECs). In contrast to water/organic two-phase route, unique water/ionic liquid (IL)/organic three-phase interface strategy is first performed to prepare coral-like polypyrrole with even better electrochemical capacitance, where 1-Ethyl-3-methylimidazolium tetrafluoroborate IL, as a “buffering zone”, is set between the water and organic phases to control the morphology and micro-structure of the polypyrrole phase during polymerization. The polypyrrole synthesized by three-phase interfacial route owns more ordered structure, less charge transfer resistance and better electronic conductivity, compared with two-phase method, and delivers larger specific capacitance, higher rate performance and better electrochemical stability at large current densities in 3 M KCl aqueous electrolyte.     

Hybrid nanostructure of polypyrrole and porous silicon prepared by galvanostatic technique

Nanostructured porous silicon (PS) layer is prepared in a lightly doped p-type substrate (with pores < 5 nm) and used as a working electrode to deposit conducting polypyrrole (PPy) by the electrochemical oxidative polymerization technique in an organic liquid phase. Three distinguishable stages of PPy deposition are observed and recorded under constant applied current: nucleation of polymer at the pore bottom, unidirectional growth of PPy inside the pores, and polymerization outside the PS surface. The hybrid nanostrucutre of PS/PPy shows a significant improvement of electrical conductivity as opposed to the unmodified PS layer. The improved conductivity is observed in spite of the formation of insulating layer of silicon oxides as detected by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) measurements. Systematic study of fabrication and characterization of this organic-inorganic heterosystem, quantification of the PPy in the PS matrix, and the mechanism of filling the nanopores with polymer are presented and thoroughly discussed.     

The corrosion protection of mild steel by single layered polypyrrole and multilayered polypyrrole/poly(5-amino-1-naphthol) coatings

Electrochemical synthesis of polypyrrole (PPy) and top coat of poly(5-amino-1-naphthol) (PANAP) on PPy films from oxalic acid solution was achieved on mild steel (MS) by cyclic voltammetry technique. The morphology and the structure of the films were investigated by scanning electron microscopy (SEM). The corrosion performance of this multilayer coating and single PPy coating were investigated in 3.5% NaCl solution by using open circuit potential (E_ocp)–time curves, polarization curves and electrochemical impedance spectroscopy (EIS). It was found that the multilayer PPy/PANAP coating could provide much better protection than single PPy coating for corrosion of MS. It was observed that corrosion performance of coatings was increasing with immersion period. This was explained by auto-undoping properties of PPy coatings during immersion in corrosive solution. The improved corrosion performance in the presence of PANAP top coat on PPy was explained by increase in barrier effect of bilayer films.     

Effect of surface treatment of pigment particles with polypyrrole and polyaniline phosphate on their corrosion inhibiting properties in organic coatings

The effect of pigment particle surface treatment with conductive polymers on the corrosion inhibiting properties of organic paints was investigated. Mixed oxides possessing the spinel and perovskite structures were synthesised for the study. Natural graphite and pigments based on ferric oxide and silicate were studied. Coating materials based on a water-based epoxy resin were prepared for the investigation of the corrosion protection properties of the pigments, the surfaces of which had been provided with a conductive polymer layer. Laboratory corrosion tests were applied to the paint films. A commercial corrosion protection pigment, based on modified zinc phosphate, served as the corrosion protection efficiency standard. Polyaniline phosphate was found preferable to polypyrrole as the modifying agent of the pigment surface regarding the pigment's corrosion inhibiting efficiency. Surface treatment with the conductive polymers is also beneficial to the mechanical properties of the paint.     

Separation of tryptophan enantiomers with polypyrrole electrode column by potential-induced technique

Polypyrrole (PPy), synthesized by chemical oxidation in the presence of l-tryptophan (l-Trp) as template molecules, was packed into a porous ceramic column as the conductive stationary phase to fabricate an electrode column which can be regarded as a working electrode of a three-electrode system from an electrochemical point of view. The electric potential of this column can be easily controlled by a potentiostat. l-Trp anions were ejected from the PPy backbone after overoxidation of PPy, and thus cavities complementary to l-Trp were left in the stationary phase. When the solution containing l- or d-Trp was pumped through the column packed with imprinted overoxidized polypyrrole (oPPy), a negative potential was applied on the electrode column for re-binding Trp enantiomers. The novel electrode column offers an excellent chiral selectivity for l-Trp over d-Trp as the result of stereochemistry, and it also displays satisfactory selectivity for tyrosine (Tyr) enantiomers which is analogous to Trp in structure. The advantage of this method proposed over previously reported is that the separation of amino acids enantiomers can be performed in a high efficiency by controlling the potential applied on the electrode column.     

Electrochemical properties of polypyrrole/sulfonted SEBS composite nanofibers prepared by electrospinning

The electrochemical behavior of electrospun polypyrrole (PPy)/sulfonated-poly(styrene-ethylene-butylenes-styrene) (S-SEBS) composite nanofibers was investigated, compared to PPy/poly(styrene-ethylene-butylenes-styrene) (SEBS) fibers prepared by a casting method. The electrospun PPy/S-SEBS (E-PSS) fibers were about 300 nm in average diameter, while PPy/SEBS composite (C-PS) prepared by a casting method showed the granular macroporous structure. The effect by both electrospinning and sulfonation results in higher electrochemical capacity due to the increase of doping level, high electrical conductivity, low interfacial resistance, and high reversibility by easy intercalation of Li ion. In addition, sulfonated SEBS induces higher elongation force to jet in the processing of electrospinning due to the role of dopant.     

Shape-controlled synthesis of monodispersed beta-gallium oxide crystals by a simple precipitation technique

Uniformly sized and monodispersed β-Ga₂O₃ crystalline micro-rods and ellipsoids have been successfully synthesized through a facile direct precipitation technique, respectively, using Ga(NO₃)₃ and NH₄OH solution as starting materials. The as-prepared particles were characterized by XRD, FESEM equipped with EDS, TEM equipped with SAED, TG-DSC and Laser diffraction particle size analyzer, respectively. The results showed that the obtained β-Ga₂O₃ particles with a narrow particle size distribution were assembled with single crystalline β-Ga₂O₃ nano-sheets with the thickness of 100 nm. Furthermore, the reaction parameters including aging temperature, the molar concentration of Ga³⁺ and pH value had an essential effect on the morphology and size of the particles. Ostwald ripening and oriented attachment growth mechanism of the uniformly hierarchical β-Ga₂O₃ crystals were proposed. Finally, the target fabricated by using the as-prepared β-Ga₂O₃ particles as the raw materials exhibited a density as high as 6.01 g/cm³, showing potential applications in the high-quality thin film formed by magnetron sputtering for optoelectronic devices.     

Corrosion protection of mild steel by polypyrrole phosphate composite coating

Electrodeposition of polypyrrole phosphate (PPy–P) on mild steel (ST₁₂) was achieved in oxalic acid medium using cyclic voltammetry (CV) technique. Adherent and homogeneous PPy–P films were obtained. The corrosion behavior of mild steel with phosphate (PPy–P) coatings in 3.5% NaCl solutions was investigated through potentiodynamic polarization technique, open circuit potential–time curves, and electrochemical impedance spectroscopy (EIS). Based on a physical model for the corrosion of mild steel composite, the Zview (II) software was applied to the EIS to estimate the parameters of the proposed equivalent circuit. It was found that the PPy–P coatings could provide much better protection than PPy. The effect of phosphate on the morphology and structure of the passive film was investigated by scanning electron microscopy and electron dispersion X-ray analysis (EDX). The results reveal that the PPy–P coated electrode provided a noticeable enhancement of protection against corrosion process.     

Inhibition of corrosion of mild steel by homopolymer and bilayer coatings of polyaniline and polypyrrole

Homopolymers and bilayers of polyaniline (PAni) and polypyrrole (PPy) coatings have been electropolymerized on mild steel by potentiodynamic synthesis technique in aqueous oxalic acid solutions. Characterization of coatings was carried out by cyclic voltammetry. Corrosion behavior of the polymer coated mild steel electrodes was investigated using linear anodic potentiodynamic polarization, Tafel test and electrochemical impedance spectroscopy (EIS) techniques in various aqueous corrosive solutions. Corrosion test results clearly showed that PPy and PAni/PPy bilayer coatings served as a stable host matrix on mild steel against corrosion. However, bilayers of PAni and PPy did not exhibit good combined properties of each polymer, unlike expected. PPy exhibited the best corrosion resistance among all coatings.     

Thermo-sensitive poly(N-vinylcaprolactam-co-acetoacetoxyethyl methacrylate) microgels. 3. Incorporation of polypyrrole by selective microgel swelling in ethanol-water mixtures

Behaviour of temperature-sensitive core-shell VCL/AAEM microgels has been studied in binary alcohol/water mixtures. Amount of alcohol in binary mixture influences strongly the swelling and thermo-sensitive properties of microgels. Alcohol induces swelling of VCL-rich microgel shell leading to larger dimensions of microgel particles and larger surface area. Under these conditions pyrrole polymerization was carried out, and the influence of pyrrole concentration, oxidant nature and temperature on morphology and properties of composite particles was investigated. Contrary to the polymerization in water medium, this selective swelling method gives possibility to increase three times loaded polypyrrole amount and maintain the stability of the colloidal system. It was found that in case when persulfate was applied as oxidant it is possible to vary effectively the particle size of composite microgels by changing the ethanol concentration in water. Contrary, when FeCl₃ was used as oxidant formation of secondary particles was detected leading to dispersions with bimodal particle size distribution. The conductivity of the composite particles was much higher if polypyrrole synthesis was carried out in pure water.     

Predicting the shape of organic crystals grown from polar solvents

A method for predicting the shape of organic crystals grown from polar solvents is presented. The model is an improvement of the recent method developed by Winn and Doherty (A.I.Ch.E. Journal 44 (1998) 2501) for predicting the shape of organic crystals grown from solvents in which the energy of adhesion at the interfaces is dominated by dispersive forces (e.g., non-polar solvents). The principal characteristic of the new method is that it can account for the role of hydrogen donor and hydrogen acceptor atoms in forming strong bonds at the interface. This technique is a first step towards predicting the shapes of organic crystals grown from polar solvents, and has been applied successfully to predict the shape of adipic acid grown from water, and succinic acid grown from water and from propanol.     

Study of polaron and bipolaron states in polypyrrole by in situ Raman spectroelectrochemistry

The transitions from the reduced-polaron-bipolaron states of polypyrrole (ppy) were analyzed by in situ Raman spectroelectrochemistry. The distinct vibrational modes presented by the polymer in different oxidation levels were assigned to specific signatures of polaron and bipolaron states. As the polymer was oxidized from the neutral state, an intermediary phase featuring vibrational bands from both the benzoid (reduced) and the quinoid (oxidized) forms were observed. This intermediary phase was correlated to the polaron state. The results were compared with previous ESR data that confirm the presence of polaron and bipolaron states in the potential region where the vibrational modes of these phases were identified.     

Electrically conductive coatings of nickel and polypyrrole/poly(2-methoxyaniline-5-sulfonic acid) on nylon Lycra textiles

Woven nylon Lycra^® has been coated with finely-divided electroless nickel-phosphorus, polypyrrole and electroless nickel/polypyrrole to produce flexible and electrically conductive textiles. The coated textiles were tested for their electrochemical activity, electrical resistivity and resistivity in response to mechanical strain. Pre-dyeing the textile with poly(2-methoxyaniline-5-sulfonic acid) (PMAS) prior to electroless metallization by electroless nickel and via chemical polymerization of polypyrrole was found to be beneficial in enhancing the resultant coating as well as stabilizing surface resistance responses when exposed to a wide range of strain. The mass gain due to the nickel coating was found to increase linearly with deposition time. The surface resistivity of the coated textile was found to decrease at longer nickel deposition times.     

Characterisation and corrosion studies of steel electrodes covered by polypyrrole/phosphotungstate using Electrochemical Impedance Spectroscopy

Polypyrrole/PW₁₂O₄₀³⁻ hybrid material was electrosynthesised on carbon steel electrodes in acetonitrile medium. The coatings obtained were characterised by Electrochemical Impedance Spectroscopy (EIS). On free-standing polypyrrole films the electrical response was mainly due to ion–ion charge transfer resistance, with a value of 175 Ω cm². A value of 2 × 10⁻⁵ S/cm was determined for the hybrid material conductivity. A charge transfer resistance about 7000 Ω cm² was obtained due to steel/oxide interface. Corrosion tests showed an important improvement in the protection against corrosion when the carbon steel electrodes were coated by these polymeric films.