Polymerization and characterization of high conductivity and good adhension polypyrrole films for electromagnetic interference shielding

<正>Polypyrrole(PPy) shows a favorable application in the electromagnetic interference(EMI) shielding due to its good electrical conductivity and outstanding air stability.Conducting PPy films with high conductivity and good adhesion were successfully polymerized on the surface of insulating epoxy resin substrates using chemical polymerization.The factors affecting the properties of PPy films,such as the surface morphology,adhesion between PPy film and substrate,electrical conductivity,EMI shielding effectiveness(SE),were investigated.The adhesion was improved significantly through a three-step surface pretreatment of epoxy resin substrates including removing impurities,roughening,and surface modification with silane coupling agent.An enhancement in the conductivity of PPy films of about one order of magnitude was achieved by adding dopant in FeCl_3 solution.The higher the conductivity,the better the shielding effectiveness.Taking sodium p-toluenesulfonate doped PPy film as example,EMI SE was in the practically useful range of about 30 dB over a wide frequency range from 30 MHz to 1500 MHz.The PPy film samples were characterized by scanning electron microscopy (SEM),infrared spectra(IR),X-ray photoelectron spectroscopy(XPS) and the flange coaxial transmission device.The fourpoint probe method was used to measure conductivity of PPy films.     

Preparation of conductive,flexible and transparent films by in situ deposition of polypyrrole nanoparticles on polyethylene terephthalate

In this study polypyrrole (PPy) nanoparticles were deposited as a thin film on the modified surface of polyethyleneterephthalate (PET) by in situ chemical polymerization in the presence of sodium dodecylsulfate (SDS), sodium dodecylbenzenesulfonate (DBSNa) and mixture of them as the surfactant. The surface of PET was modified by KOH before deposition and was investigated for conductivity and adhesion of PPy nanoparticles to PET. Resulting conductive flexible films were characterized by UV–Vis spectroscopy, fieldemission scanning electron microscopy, contact angle measurements and four-point-probe technique for conductivity. Direct morphological observation (FESEM) and electrical measurements indicated that the morphology, conductivity and the nature of deposited PPy films depend on surfactant, surface modification of PET and monomer concentration. In optimized process condition, uniform conductive films of PPy were obtained with good adhesion to PET.     

New biocompatible polypyrrole-based films with good blood compatibility and high electrical conductivity

A novel O-butyryl chitosan (OBCS)-grafted polypyrrole (PPy) film was described. The immobilization was accomplished by photocrosslinking the OBCS onto PPy films under ultraviolet light irradiation. The surfaces of OBCS-grafted PPy film were characterized by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and electron spectroscopy for chemical analysis (ESCA). The blood compatibility of the OBCS-grafted PPy film was evaluated by platelet-rich plasma (PRP) contacting experiments and protein adsorption experiments in vitro. These results have demonstrated that the surface with immobilized OBCS shows much less platelet adhesive and fibrinogen adsorption compared to the control surface. The bulk conductivity values of PPy films were measured by a modified four-probe method. The composite films have both good blood compatibility and high electrical conductivity that make them suitable for using as potential biomaterials, such as electrically conducting blood vessel and functionally haemocompatible substrate of biosensor used directly in whole blood.     

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.     

Evaluation of the Conductivity of the Polypyrrole Film via Its CC Bonds Stretching on Surface‐Enhanced Raman Spectrum

In this study, the conductivities of various polypyrrole (PPy) films were evaluated via the corresponding surface‐enhanced Raman scattering (SERS) spectrum and X‐ray photoelectron spectroscopy (XPS). The results indicate that the peak position of C?C bonds stretching of PPy obtained from the SERS spectrum shows more exactly both qualitatively and quantitatively representing the conductivity of PPy than the N⁺/N ratio or the doping level obtained from the XPS analysis does. Namely the peak position of C?C bonds stretching of PPy monotone decreases to a lower frequency side with the increase of the conductivity of PPy. Furthermore, a satisfactory correlated equation between them was obtained. On the contrary, neither the N⁺/N ratio nor the doping level can be qualitatively reflective on the corresponding conductivity of PPy.     

Characteristics of the ring stretching of oxidized polypyrrole on the surface-enhanced Raman spectrum

In this study, polypyrrole (PPy) films were electropolymerized under different preparation conditions on rough gold substrates. The peak shown at the higher frequency of the double peaks at about 1329 and 1386 cm^–1 in surface-enhanced Raman scattering of PPy was initially assigned to the ring stretching of oxidized PPy. A systematic study was carried out to confirm this assignment. It was found that the conductivity of PPy was strongly related to and increased with this Raman peak intensity of oxidized PPy. Meanwhile, the normalized relative intensities of this Raman peak for various PPy films are consistent with their corresponding doping levels. Electronic Publication     

ELECTRICALLY CONDUCTIVE COMPOSITE PREPARED BY ELECTROCHEMICAL POLYMERIZATION OF PYRROLE IN POLY-(p- PHENYLENE TEREPHTHALAMIDE) MATRIX

The preparation of PPy/PPTA conductive composite films by electrochemical method is presented.The first step is to cast a thin layer of poly (p-phenylene-terephthalamide) (PPTA) on a slice of Pt working electrode. The second step is to electrochemically polymerize pyrrole on the PPTA/Pt working electrode. Both of the electrical conductivity and the mechanical properties of the PPy/PPTA composite film are better than those of the pure PPy film, and the film has excellent flexibility at low temperature, even in liquid nitrogen.The SEM picture of the cross-section of PPy,/PPTA composite film showed that the two components were well mixed.Cyclic voltammograms of PPy,/PPTA film in aqueous solution showed that the conductive films could be reduced and reoxidized.     

Polypyrrole (PPy) chemical synthesis with xylan in aqueous medium and production of highly conducting PPy/nanofibrillated cellulose films and coatings

Polypyrrole was chemically synthesised by using, for the first time, Birchwood xylan as additive, and ammonium peroxydisulfate (APS) as oxidant. The impact of additive concentration, polymerisation time and reagents concentration on PPy conductivity was studied. It was shown that, once fixed the pyrrole (Py)/APS and Py/xylan optimal ratios, the best conductivities (26 S/cm) were obtained for short polymerisation times (30 min) and increased reactants concentration. Morphological analysis of PPy particles, Py depletion kinetics and oxido-reduction potential measurements of the solutions provided interpretation elements on the impact of the polymerisation time on PPy pellet conductivity. Furthermore, optimised PPy particles obtained with xylan (PPy_x) were mixed with nanofibrillated cellulose (NFC) in order to obtain freestanding films. Their electrical and handling performances were evaluated at increasing PPy weight fraction in the samples. The conductivity mechanism of the most conductive sample (in comparison with a low performing sample) was investigated by measuring the conductivity as a function of temperature (4–350 K) and two transport regimes were identified. Selected formulations were finally used to produce conducting PPy/NFC coatings on non-absorbent (glass) and absorbent (copy paper) substrates. The impact of NFC in the percolation of PPy particles, then in the coating conductivity, was investigated.     

Electropolymerization of polypyrrole, modified with germanium, on a passivated titanium electrode in aqueous nitrate solution: new results on catalytic reduction of protons and dissolved oxygen

Conductive polypyrrole (PPy) films and PPy films containing Ge microparticles were synthesized by anodic oxidation of pyrrole in acidic nitrate solutions using a bare passivated titanium electrode. Well-adhering black PPy films were obtained both under galvanostatic and potentiodynamic polarization. After the formation of the PPy film, during the first anodic cycle, an increase of the anodic deposition current with the number of cycles was observed, revealing the increase of conductivity of the growing film. The variations of the electrode surface area were estimated by impedance spectroscopy measurements. The kinetics of the PPy film formation is controlled by diffusion of the Py monomer in the solution. The diffusion coefficient, estimated by two different methods, was ca. 2×10^–6 cm² s^–1. The reduction rate of oxygen and protons at the Ti/PPy/Ge electrodes depends on how the Ge microparticles are incorporated in the PPy film. Optimum conditions for this incorporation are realized with thin PPy films and high Ge loading. Thermogravimetric analysis shows that the PPy film containing Ge microparticles is more thermally stable than the blank PPy film. Electronic Publication     

Preparation and characterization of conducting poly(acryloyl chloride)‐g‐ polypyrrole copolymer

The electroactive copolymer of poly(acryloyl chloride) (PAC) and polypyrrole (PPy) can be synthesized by electrochemical polymerization using a polymer precursor which contains a pyrrole moiety in its side chain. Poly(acryloyl pyrrole) (PAP) was synthesized chemically with acryloyl chloride and potassium pyrrole salt and characterized using FT‐IR and ¹H‐NMR spectroscopy. PAP dissolved in dimethyl formamide (DMF), was spin‐coated on a platinum electrode and polymerized electrochemically in the electrolytic mixture solution consisting of acetonitrile, 0.1 M pyrrole, and 0.1 M lithium perchlorate. Constant potential electrolysis showed that pyrrole groups in the precursor were oxidized to form PPy, that is, they acted as grafting centers at which the PPy grew. Scanning electron microscopy (SEM) results and conductivity measurements supported the formation of the graft copolymer. The morphological feature of PAC‐g‐PPy copolymer films showed homogeneous structure, but that of PAC/PPy composite films showed irregular structure. The maximum conductivity of the final products was about 1 S/cm. Copyright © 2002 John Wiley & Sons, Ltd.     

Influence of polymerization time on the properties of polypyrrole-poly[bis(phenoxyphosphazene)] composites electrogenerated at constant current density

The influence of different polymerization times on the characteristics of films of polypyrrole, PPy, and of composites of polypyrrole-poly[bis(phenoxyphosphazene)], PBPP-PPy, both with p-toluenesulfonic acid (HTSO) as supporting electrolyte and acetonitrile as solvent, has been studied. Films and composites were grown for 10-60 min under galvanostatic control at a current density of 4.2 mA cm⁻². The electrooxidation of the PPy in the films and the composites was controlled by diffusion. With increasing electropolymerization time the specific charge storage capacity of both the films and the composites decreased. PBPP increased the conductivity for all polymerization times, but had almost negligible effect on polimerization efficiency. The specific charge storage capacity and the conductivity increased with PBPP thickness. In contrast, the polymerization efficiency decreased for the thicker composite. The presence of PBPP increased PPy/TSO adhesion to the electrode surface but did not decrease its stability. The influence of the polymerization time on the morphology of films and composites was also studied.     

Synthesis and characterization of conductive polypyrrole grown on the sulfonated surface of polyethylene films

Chemical synthesis of polypyrrole (PPy) was carried out in the presence of FeCl₃ aqueous solution. The grown PPy is fixed on the sulfonated surface of polyethylene (SPE) films, where the sulfonic groups act as counteranions to balance the positive charge of PPy, giving the composite material of PPy–SPE. For reasons of comparison, two types of polyethylene (PE) have been used, low and high densities with different degrees of sulfonation, SD (g/m²), defined as the ratio of weight increase to the area of the two surfaces of the sample. A series of reaction times was used to evaluate the variation of the electrical conductivity, σ (S/cm), of polypyrrole. It was found that σ increases as reaction time increases. To characterize the samples, Fourier transform infrared (FTIR) spectroscopy and conductivity measurements were performed.     

Pt and Pt–Ru nanoparticles decorated polypyrrole/multiwalled carbon nanotubes and their catalytic activity towards methanol oxidation

Conducting polymer composite films comprised of polypyrrole (PPy) and multiwalled carbon nanotubes (MWCNTs) [PPy–CNT] were synthesized by in situ polymerization of pyrrole on carbon nanotubes in 0.1 M HCl containing (NH₄)S₂O₈ as oxidizing agent over a temperature range of 0–5 °C. Pt nanoparticles are deposited on PPy–CNT composite films by chemical reduction of H₂PtCl₆ using HCHO as reducing agent at pH = 11 [Pt/PPy–CNT]. The presence of MWCNTs leads to higher activity, which might be due to the increase of electrochemically accessible surface areas, electronic conductivity and easier charge-transfer at polymer/electrolyte interfaces allowing higher dispersion and utilization of the deposited Pt nanoparticles. A comparative investigation was carried out using Pt–Ru nanoparticles decorated PPy–CNT composites. Cyclic voltammetry demonstrated that the synthesized Pt–Ru/PPy–CNT catalysts exhibited higher catalytic activity for methanol oxidation than Pt/PPy–CNT catalyst. Such kinds of Pt and Pt–Ru particles deposited on PPy–CNT composite polymer films exhibit excellent catalytic activity and stability towards methanol oxidation, which indicates that the composite films is more promising support material for fuel cell applications.     

Conductive Composite Materials of Polyethylene and Polypyrrole with High Modulus and High Strength

Composite films of polyethylene (PE) and polypyrrole (PPy) were prepared by polymerization of PPy on an ultradrawn polyethylene film with high modulus and high strength in ferric chloride (FeCl₃) aqueous solution. The electrical conductivity of the composite film was found to be related to the polymerization conditions, such as polymerization temperature, polymerization time, the concentration and the oxidation potential of the FeCl₃ solution. Scanning electron microscopy, FTIR and ¹³C NMR spectra were used to elucidate the morphological and structural variations of PPy prepared under different conditions, which lead to the differences in the electrical properties of the resultant composite films. The best electrical conductivity of the composite was about 5.5 S/cm for the film prepared under optimum conditions. The Young's modulus and the tensile strength reached 80 GPa and 3.2 GPa, respectively, which indicated the successful production of a conductive polymer with high strength and high modulus.     

超临界二氧化碳流体环境中导电聚吡咯复合材料的制备

以聚苯乙烯(PS)和锌盐中和的磺化聚苯乙烯(Zn-SPS)膜为基体, 在超临界二氧化碳(SC-CO₂)环境中用化学氧化法原位制备了聚吡咯(PPy)导电复合材料. 由于SC-CO₂对聚合物基体的强溶胀作用, 吡咯分子高效地扩散到基体内部进行聚合而形成导电通路, 得到比传统的水溶液法更高的电导率. 聚合物基体的性质对复合材料的导电性和形貌产生重要影响. 在相同条件下, Zn-SPS/PPy的电导率比PS/PPy高3~4个数量级, 而它们的体积逾渗阈值分别为2.7%和6.2%, 远远低于理论预测值(16%).     

Paper-like free-standing polypyrrole and polypyrrole–LiFePO4 composite films for flexible and bendable rechargeable battery

Highly flexible, paper-like, free-standing polypyrrole and polypyrrole–LiFePO₄ composite films were prepared using the electropolymerization method. The films are soft, lightweight, mechanically robust and highly electrically conductivity. The electrochemical behavior of the free-standing films was examined against lithium counter electrode. The electrochemical performance of the free-standing pure PPy electrode was improved by incorporating the most promising cathode material, LiFePO₄, into the PPy films. The cell with PPy–LiFePO₄ composite film had a higher discharge capacity beyond 50 cycles (80 mA h/g) than that of the cell with pure PPy (60 mA h/g). The free-standing films can be used as electrode materials to satisfy the new market demand for flexible and bendable batteries that are suitable for the various types of design and power needs of soft portable electronic equipment.     

Effect of ammonia on the temperature‐dependent conductivity and thermopower of polypyrrole

We report the first measurements of the effect of ammonia gas on the temperature dependence of the conductivity and thermoelectric power of polypyrrole films. Our data are for samples of very different conductivities, extending down to a temperature of 200 K for low‐conductivity polypyrrole gas sensors, and down to 4.2 K for more highly‐conducting PPy(PF₆) samples. We demonstrate that (except for the most metallic case) our polypyrrole samples show greater sensitivity to ammonia as the temperature is lowered (i.e. the fractional reduction in conductivity is greater at lower temperatures). Remanent decreases in conductivity are present after the removal of ammonia for higher pressure exposures, and remanent increases in the metal‐like thermoelectric power for the PPy(PF₆) for samples grown at higher temperatures. Our results indicate that the mechanism of this conductivity decrease in PPy(PF₆) is that ammonia causes a reduction in the size of metallic regions as disordered barrier regions are thickened. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1331–1338, 2006     

Electronic conductivity of pyrrole and aniline thin films polymerized by plasma

In this article, we present a study of the influence of temperature and humidity on the electric conductivity of polyaniline and polypyrrole thin films doped with iodine and synthesized by plasma (PAn/I and PPy/I, respectively). The polymers presented the characteristic ohmic conduction mechanism via electrons; however, the conductivity was much lower than that presented by the polymers obtained by traditional chemical oxidation. We submitted the polymers to heating–cooling cycles to study the temperature dependence of the conductivity. During the heating stage of the cycles, the electric conductivity of PPy/I showed a strong dependence on the humidity content. However, during the cooling step, the plots of conductivity, as a function of the inverse temperature of PPy/I and PAn/I, showed typical Arrhenius behavior. The activation energy of PPy/I had an average value of 1.1 ± 0.1 eV and was independent of the reaction time, whereas PAn/I presented a more complex behavior with activation energies that depended on the reaction time and the regional crystallinity induced in the heating step of the cycles. All the activation energies were below 2 eV, which places them in the semiconductor regime. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3247–3255, 2000     

Surface reactivity of polypyrrole/iron-oxide nanoparticles: electrochemical and CS-AFM investigations

Composite materials based on iron-oxide nanoparticles (magnetite, hematite, and maghemite) and tetraoxalate-doped polypyrrole (PPy) were electrochemically generated from aqueous solutions. Their composition was determined using electrochemical quartz crystal microbalance experiments. The oxide percentage in mass was found to vary from 17 to 27% depending on the oxide identity. They were all shown to be fascinating candidates as protective materials against corrosion of iron and carbon steel materials although maghemite-nanoparticle-loaded polypyrrole films offer the best performances. An anionic surfactant (sodium dodecylsulfate) was added to the electrodeposition solution to avoid the formation of clusters. These anions were also shown to improve the conductivity of the resulting PPy films, while the presence of oxide nanoparticles tends to decrease this same surface conductivity. On the other hand, the correlation between the morphology and the local conductivity appears to be more obvious in the absence of anionic surfactants than in their presence. This aspect is discussed although it still needs further investigation. Contribution to the International Workshop on Electrochemistry of Electroactive Materials (WEEM-2006), Repino, Russia, 24–29 June 2006.     

Fabrication and Properties of Conducting Polypyrrole/SWNT‐PABS Composite Films and Nanotubes

We report the electropolymerization and characterization of polypyrrole films doped with poly(m‐aminobenzene sulfonic acid (PABS) functionalized single‐walled nanotubes (SWNT) (PPy/SWNT‐PABS). The negatively charged water‐soluble SWNT‐PABS served as anionic dopant during the electropolymerization to synthesize PPy/SWNT‐PABS composite films. The synthetic, morphological and electrical properties of PPy/SWNT‐PABS films and chloride doped polypyrrole (PPy/Cl) films were compared. Characterization was performed by cyclic voltammetry, atomic force microscopy (AFM), scanning electron microscopy (SEM) and Raman spectroscopy. SEM and AFM images revealed that the incorporation of SWNT‐PABS significantly altered the morphology of the PPy. Cyclic voltammetry showed improved electrochemical properties of PPy/SWNT‐PABS films as compared to PPy/Cl films. Raman Spectroscopy confirmed the presence of SWNT‐PABS within composite films. Field effect transistor (FET) and electrical characterization studies show that the incorporation of the SWNT‐PABS increased the electronic performance of PPy/SWNT‐PABS films when compared to PPy/Cl films. Finally, we fabricated PPy/SWNT‐PABS nanotubes which may lead to potential applications to sensors and other electronic devices.