Electrochemically instantaneous reduction of conducting polyaniline-coated latex particles dispersed in acidic solution

A cathodic voltammetric wave was observed in an aqueous suspension of mono-dispersed, spherical polyaniline-coated polystyrene particles, whereas no anodic wave was detected. This irreversibility was common to particles with eight different diameters ranging from 0.2 to 7.5 μm. Such irreversibility cannot be found at polyaniline-coated electrodes, and thus is a property of the dispersion of polyaniline latex. The reduction current was controlled by diffusion of dispersed particles. The reduction, being the conversion from the electrical conducting state to the resistive one, should begin at a point of contact between the conducting particle and the electrode in order to be propagated to the whole particle rapidly. In contrast, the oxidation proceeds slowly with the propagation of conducting zone, during which Brownian motion lets the particle detach from the electrode. The number of loaded aniline units per particle, determined by weight analysis, ranged from 6 × 10⁶ (Ø 0.2 μm) to 3 × 10¹¹ (Ø 7.5 μm) and was proportional to 2.9 powers of the particle diameter. The diffusion-controlled current of the cathodic wave was proportional to 2.4 powers of the diameter. The difference in these powers, 0.5, agreed with a theoretical estimation of the diffusion-controlled current, the diffusion coefficient for which was given by the Stokes-Einstein equation.     

Electrochemical preparation of electrically conducting polyurethane/polyaniline composite

Composite films from polyaniline (PANi) and polyurethane (PU), with flexibility and mechanical strength similar to pure PU and conductivity close to pure PANi, have been obtained by electropolymerizing amiline on a PU/Pt electrode in water/acetonitrile/ethylen glycol electrolyte solution. In the composite films, PANi is dispersed, in the form of particulate, inside and on the inner surface of the PU substrates. It is found that the electropolymerization reaction of aniline proceeds much faster in basic solution and composite film as prepared shows higher conductivity than that in acidic solution. PANi in PU/PANi composite film is protonic-acid-doped and is conducting even in case it is electropolymerized in a basic electrolyte solution.     

Electrical currents resulting from reduction/oxidation processes of tested particles on electrodes modified with metal-containing polymer films

Metal-containing films are considered as systems including a multitude of microelectrodes, the role of which is played by metal clusters distributed in both the film interior and film interfaces. In the case of electrode reactions occurring exclusively on the surface of such metal inclusions and the film thickness significantly exceeding clusters’ radii, it is shown that the concentration of species participating in such processes (tested particles, further on) satisfies a diffusion equation complicated with an accompanying electrochemical reaction. By assuming reversibility of the electron transfer processes between polymer fragments, one can arrive at solutions of the derived equation and calculate the corresponding currents resulting from tested particles’ reactions. The role of such factors of inclusion of metal clusters into conducting polymer films, as its density and inhomogeneity is discussed in the context of their influence on the measured currents of reduction/oxidation processes of tested particles. Non-stationary effects that might be observed in cycling voltammetry and potential clamp measurements with electrodes modified by metal-containing films are also analyzed. The performed analysis shows that electrochemical properties of the modified electrodes in question practically coincide with those of the electrodes made of the corresponding metals and immersed into the same solutions.     

Electrochemistry of conductive polymers: 41. Effects of self-assembled monolayers of aminothiophenols on polyaniline films

Effects of self-assembled monolayers (SAMs) of a few different aminothiophenols (ATPs) on growth, morphology, and electrical properties of polyaniline have been studied at gold electrodes employing current sensing atomic force microscopy. The 4-aminothiophenol (4-ATP) SAM showed the best capability of shuttling electrons from the gold electrode to the solution species, and the 4-ATP SAM covered electrode not only showed the best kinetics for the film growth but also produced the film of the highest electrical conductivity. The vertical conductivity of the film ranged from 58 S cm⁻¹ for a film prepared at a bare gold electrode to as high as 148 S cm⁻¹ for a film obtained at the 4-ATP SAM covered electrode. The conductivity was shown to depend on the thickness of the films as well as how they were prepared.     

Self-standing polyaniline film of mono-particle layer

Large, uniform and stable polyaniline (PANI) films were fabricated by ordering and drying polyaniline-coated-polystyrene (PANI-PS) latex microspheres. Particles on a glass substrate were highly ordered, closely packed and formed a two-dimensional lattice structure with the thickness of the diameter of the particle, 3.2 μm. Films fabricated on the substrate were peeled off by the pressure of water to yield the floating film, which could be transferred onto other substrates. One end of the film was connected to the platinum plate electrode while the other end was put in sulfuric acid. The film to which voltage was applied showed color change corresponding to the redox reaction. The voltammogram of the film showed the cathodic and the anodic peaks at 0.20 and 0.35 V versus SCE, respectively, being similar to peaks of electropolymerized PANI films. Films were inserted into tetrahydrofuran to remove the core-polystyrene. The resulting film had similar properties as polyaniline films of PANI-PS latex microspheres.     

Electrically conducting suspensions formed by polyaniline

Polyaniline was synthesized with the chemical oxidation in the presence of poly(vinylpyrrolidone) as a surfactant for small-sizing polyaniline grains. It was dispersed in glycerin including sulfuric acid to yield electrically conducting solution. Voltammograms of the solution by the two-electrode measurement showed the proportionality of the Ohm's law in the cell voltage from −0.2 to 0.2 V. Voltammograms by the three-electrode measurement in the domain 0.0-1.5 V versus Ag|AgCl were different from the Ohmic law and Faradaic current of polyaniline, because of a mixture of both the contributions. The conductance did not vary with the volume fraction of polyaniline up to 20% and enhanced drastically until 35% with large fluctuation, and then increased proportionally with the volume fraction. This variation was explained in terms of the electric percolation with a threshold at the volume fraction of 20-35%. The mixture with over 45% fraction was actually solid. The suspension was applied to confirming the relation between the Ohmic current at a microelectrode and its diameter. The current showed a linear relation with the electrode diameter with a small intercept of the diameter, of which value corresponded to the size of polyaniline grains.     

Waterborne acrylic–polyaniline nanocomposite as antistatic coating: preparation and characterization

An antistatic and electrically conductive acrylic–polyaniline nanocomposite coating was successfully synthesized by interfacial polymerization of aniline in the presence of acrylic latex. The acrylic latex was prepared through emulsion polymerization, and aniline was polymerized by in situ interfacial polymerization at the interface of acrylic latex/chloroform phase. Fourier transform infrared spectroscopy (FTIR), UV–Vis spectroscopy and CHNS elemental analysis revealed the existence of 6.24 wt% emeraldine salt of polyaniline (PAni) in the dried film of the nanocomposite. Scanning electron microscopy (SEM) confirmed the presence of colloidal polymer particles in the aqueous phase which was confirmed to have some advantages, including prevention of aggregation of particles, dispersibility improvement and enhancement of the PAni nanofibers aspect ratio in the acrylic polymer matrix. According to SEM results, PAni fibers with the length ranging from 12 to 67 µm and diameters between 0.078 and 1 µm, highly dispersed in the acrylic polymer matrix, were successfully synthesized. Thermal, electrical and mechanical properties of the acrylic copolymer were significantly affected by PAni incorporation. The onset degradation temperature in thermogravimetric analysis revealed that the thermal stability of the nanocomposite was improved compared to that of the pure acrylic copolymer. The nanocomposite film showed electrical conductivity of about 0.025 S/cm at room temperature, along with satisfactory mechanical properties, attractive as an antistatic material in coating applications.     

Electrochemical formation of some conducting fibers

A study on the electrochemical grafting of polyaniline onto cotton, silk, and wool fibers was made. These insulating natural fibers became moderately conducting when they were subjected to electrical treatment in the polymerizing solution of aniline in aqueous HBF₄ medium. The weight gain of the fibers increased linearly and electrical resistance decreased with the time of electrolysis. The multiple cycled voltammograms of the solution of aniline in the aqueous solution of HBF₄ at the tip of conducting silk and wool fibers, which functioned as a microelectrode, were successfully recorded. The deep green polyaniline film was deposited on the fiber microelectrodes during electrolysis at +0.85 V vs. an Ag/Ag⁺ electrode. The IR spectra suggest the coordination between the polyaniline and fibers. © 1996 John Wiley & Sons, Inc.     

Growth mechanism and pH-regulation characteristics of composite latex particles prepared from Pickering emulsion polymerization of aniline/ZnO using different hydrophilicities of oil phases

A Pickering emulsion polymerization of aniline, using different hydrophilicities of oil phases, was stabilized by ZnO nanoparticles and performed to synthesize composite latex particles of polyaniline/ZnO. Ammonium peroxydisulfate (APS) was used as an oxidizing agent. The morphologies and growth mechanisms of the resulted composite latex particles were studied. The pH-regulation capacity of the composite latex particles was discussed. When toluene was used as the oil phase, the composite latex particles showed hollow structure, irregular morphology, and hundreds of nanometer in size. It was ascribed to the polymerization of aniline on the interfaces of droplets/water. ZnO nanoparticles, with 50-100 nm in size, acted as surfactants to stabilize the emulsion. When THF was used as an oil phase, the composite latex particles showed spherical morphology and enwrapping ZnO nanoparticles. It was attributed to the homogeneous nucleation of polyaniline in the aqueous phase. ZnO nanoparticles acted as templates for the polyaniline particles. The stability of the Pickering emulsion polymerization was affected by the volume ratio of the oil phase to water. The aqueous solution with pH 3-9 could simply be regulated to about pH 7 by the composite latex particles. It was contributed by the dissolution of ZnO nanoparticles and doping-dedoping of polyaniline in the acidic and alkaline aqueous solutions.     

In situ electropolymerised silica-polyaniline core-shell structures: Electrode modification and enzyme biosensor enhancement

Micro- and nanostructured electrode interfaces have the potential to exhibit improved performance characteristics. Here, we illustrate the interaction of an electropolymerised polyaniline film with silica microparticles on glassy carbon electrodes. It was found that the polyaniline grew preferentially around the silica particles rather than on the underlying electrode surface. This was found to be due to the adsorption of aniline monomers onto the silica surface, followed by in situ electropolymerisation. The thickness of the PANI layer could be controlled through the adjustment of polymerisation time from several to many tens of nanometres.In conjunction with immobilisation of the enzyme, horseradish peroxidase (HRP), the electrocatalytic reduction of hydrogen peroxide was found to be enhanced under certain conditions over polymer films grown in the absence of silica particles. It is believed that this may be due to the special structure of the silica-PANI core-shell particles. Silica particles coated with a nanofilm of PANI appear to adsorb HRP more effectively, while also increasing the active electrode surface area.     

Reduction of hexavalent chromium using polyaniline films. Effect of film thickness, potential and flow velocity on the reaction rate and polymer stability

Reduction of very toxic hexavalent chromium (Cr(VI)) to its trivalent state (Cr(III)) is necessary to facilitate the treatment of wastewater by precipitation or adsorption. The present study proposes the use of thin films of polyaniline on a conducting substrate for this purpose. The reduction rate of hexavalent chromium and the degree of degradation of the polyaniline film were studied as a function of the solution flow velocity, applied potential and film thickness. The reduction rate was significantly affected by the flow velocity, while the film thickness was observed to have little effect. The potential had no effect on the reduction rate within the range studied. The current efficiency was 100% in all experiments and no significant degradation of polyaniline was observed.     

Warburg type impedance in thin layer unsupported electrochemical cells containing associated salts

The Warburg type impedances in thin layer unsupported electrochemical cells containing associated salts where the electrode reaction is kinetically reversible and the equilibrium between the associated neutral species and charge carriers is fast, are derived using the approach based on bulk electroneutrality. The extension of the approach to cells with slow electrode reactions where the use of the Nernst equation is not allowed, is also demonstrated by using the Butler-Volmer equation.     

Polythiophene, polyaniline and polypyrrole electrodes modified by electrodeposition of Pt and Pt+Pb for formic acid electrooxidation

The electrosynthesis of polythiophene (PTh), polyaniline (PANI) and polypyrrole (PPy) films modified by dispersion of Pt or Pt+Pb and its employment in the electrocatalytic oxidation of HCOOH are studied and compared. The influence of parameters such as polymer film thickness, the number of dispersed Pt particles, the amount of Pb deposited and the presence of Pb2+ in the electrolyte on the electrooxidation of HCOOH is investigated. Electrode systems including the polymer and a mixture of Pt and Pb particles show a better electrocatalytic activity than electrodes having a polymer–Pt combination or bulk Pt electrodes. Furthermore, during the electrooxidation of HCOOH using polymer–(Pt+Pb) electrodes the presence of fewer poisoning species is observed, indicating that the role of Pb in these electrode systems is in agreement with the Pb adatom effect observed when bulk Pt electrodes are used. However, the presence of Pb(ii) in the electrolyte is not required for the PTh–(Pt+Pb) electrode system and, in addition, a better electrocatalytic effect is obtained in this case. With application of an appropriate E/t program the activity is unchanged over a long time.     

All electrochemical synthesis of polyaniline/silica sol–gel materials

A potentiostatic method has been employed to obtain silica layers on the surface of glassy carbon electrodes from a precursor sol–gel solution. The silica-modified electrodes were then used as a porous matrix for the electrochemical growth of conducting polyaniline. As a result, the overall synthesis of an organic–inorganic nanohybrid material has been achieved only by electrochemical methods. The growth of polyaniline is, in the first step, confined inside the silica matrix and appears to be controlled by the diffusion of aniline monomer units. Later, once the polyaniline fibers have reached enough length, emerge out of the template and the growth kinetics becomes comparable to that for polyaniline synthesized on a bare electrode. The silica matrix has a positive effect on the electrical capacitance of Pani since the polymer chains grow dispersed and the collapse between them is minimized.     

Conductive hybrid film from polyaniline and polyurethane-silica

In order to improve the mechanical performance and water resistance of water-borne conducting polyaniline film, conducting polyaniline/polyurethane-silica hybrid film was prepared in aqueous solution employing silanol-terminated polyurethane and methyltriethoxysilane as sol-gel precursors. The hybrid film showed surface resistivity of 10⁸ Ω even though the conducting polyaniline loading was only 10 wt% (or 1.5 wt% of polyaniline), and the mechanical performance as well as water resistance was significantly improved, making it suitable for antistatic application. Therefore, a practical route to water-borne processing of conducting polyaniline is disclosed.     

Spectroscopic and electrochemical study of hybrids containing conductive polymers and carbon nanotubes

We report the preparation and characterization of hybrid materials from conducting polymers and single walled carbon nanotubes. Electrochemical polymerization yields nanotubes wrapped by conducting polymers - polyaniline, polycarbazole and melanin (i.e., polydopamine). The materials were characterized by ultraviolet-visible-near infrared, infrared, Raman and impedance spectroscopy. We found that wrapping the nanotubes with polymers can decrease the impedance of such composite electrode and increase the rate of electron transfer from the electrolyte to the electrode. From the attenuation of in-plane vibrations in the infrared spectra and the bathochromically shifted polaron band, we infer that the strongest interaction occurs between polyaniline and the nanotube surface.     

Theory of porous electrodes—XII. The negative plate of the lead-acid battery

Partial differential equations describing the transport of mass and electricity in the pores of the negative electrode of a lead-acid battery were derived. The theory is based on exact transport equations and on the assumption that the electrode potential is governed by the Nernst equation. Volume changes in both phases are taken into account. Numerical solutions depend on the product of electrode thickness times current density and on the initial porosity. Differences between the negative and positive plates are discussed.     

Fabrication and properties of solution processed all polymer thin‐film ferroelectric device

A ferroelectric device, making use of a flexible plastic, polyethylenterephtalate (PET), as a substrate was fabricated by all solution processes. PET was globally coated by a conducting polymer, poly(3,4‐ethylenedioxythiophene) poly(styrenesulfonate) acid (PEDOT/PSSH), which is used as bottom electrode. The ferroelectric copolymer, poly(vinylidenefluoride–trifluoroethylene) (PVDF–TrFE), thin film was deposited by spin‐coating process from solution. The top electrode, polyaniline, was coated by solution process as well. The ferroelectric properties were measured on this all solution processed all polymer ferroelectric thin‐film devices. A square and symmetric hysteresis loop was observed with high‐polarization level at 15‐V drive voltage on a all polymer device with 700 Å (PVDF–TrFE) film. The relatively inexpensive conducting polyaniline electrode is functional well and therefore is a good candidate as electrode material for ferroelectric polymer thin‐film device. The remnant polarization P_r was 8.5 μC/cm² before the fatigue. The ferroelectric degradation starts after 1 × 10³ times of switching and decreases to 4.9 μC/cm² after 1 × 10⁵ times of switching. The pulse polarization test shows switching take places as fast as a few micro seconds to reach 90% of the saturated polarization. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

导电聚苯胺／丁苯吡胶乳复合聚合物

以丁苯吡胶乳（ＰＳＢＲＬ）为稳定剂，苯胺（Ａｎ）进行氧化聚合，制得的导电ＰＡｎ／ＰＳＢＲＬ复合聚合物可直接浇铸成膜，亦可经破乳后用其沉淀物经热压成膜。氧化聚合条件：［ＨＣｌ］＝１．４ｍｏｌ／Ｌ，［Ａｎ］＝０．５ｍｏｌ／Ｌ，［氧化剂］＝０．２５ｍｏｌ／Ｌ。胶膜性质：当该复合聚合物中ＰＡｎ含量约为５０％时，电导率可达５×１０２Ｓ／ｍ左右，拉伸强度约１３ＭＰａ，扯断伸长率为５３％，在空气气氛中贮存２８ｄ电导率基本不变。     

Formation of transparent conducting films based on core‐shell latices: Influence of the polypyrrole shell thickness

Transparent conducting latex films have been prepared from core‐shell latices. The latex particles have a poly(butyl methacrylate) (PBMA) core of about 700 nm and a very thin polypyrrole (PPy) shell. We have studied the film formation of latices with 1, 2, and 4 wt % PPy and compared this with the film formation of the pure PBMA latex. The film formation process was studied by transparency measurements, atomic force microscopy surface flattening, and transmission electron microscopy on ultrathin sections of films after various annealing times at 120°C. It is demonstrated that highly transparent (>90%) and antistatic films can be produced using these latices. The presence of a polypyrrole shell around the PBMA latex particle seriously hinders the deformation of the particles. The amount of polypyrrole, and thus the shell thickness, is the determining factor for the speed of film formation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 900–909, 2001