Morphology,conductivity, and mechanical properties of polypyrrole-containing composites

An electrical-conducting polypropylene/polypyrrole (PP/PPy) composite was prepared by the chemically oxidative modification reaction of pyrrole on the surface of PP particles in suspension. Another type of PP/PPy composite was prepared by mixing the coated PP particles with noncoated PP particles at room temperature. The composites were processed by compression molding or by injection molding. The injection-molded composites exhibited better mechanical properties compared to compression-molded samples, while these composites showed better antistatic behavior and electrical conductivity. The differences in the behavior of the two types of composites were caused by the different structure of the PPy phase, which was studied by hot-stage optical microscopy and X-ray photoelectron spectroscopy (XPS).     

Electrical conductivity of individual polypyrrole microtube

Conducting microtubes (0.4－0.5μm in outer diameter) made of polypyrrole (PPy) doped with p-toluene sulfonic acid (PTSA) were synthesized by a self-assembly method. We report the electrical conductivity of an individual PPy microtube, on which a pair of platinum micro-leads was fabricated by focused ion beam deposition. The measured room-temperature conductivity of the individual PPy microtube was 0.29S/cm, which is comparable to that of template-synthesized PPy micro/nanotubes. The temperature dependence of conductivity of the individual microtube follows the three-dimensional variable-range hopping (3D VRH) model.     

Highly Water‐Dispersible,Highly Conductive,and Biocompatible Polypyrrole‐Coated Silica Particles Stabilized and Doped by Chondroitin Sulfate

Currently available methods to prepare conducting polymers‐coated colloidal substrates for biomedical applications need to be improved because they involve the use of toxic reagents and tend to result in aggregated products with diminished conductivity. The work herein describes for the first time a facile strategy for preparing highly water‐dispersible, highly conductive, and biocompatible polypyrrole‐coated silica core–shell (SiO₂@PPy) particles using only chondroitin sulfate (CS), a biologically derived polymer, as the stabilizer and dopant. The CS preadsorbed onto silica surface serves as a template to control the confined growth of the PPy shell and doping of in situ polymerized PPy shell. The thickness of the PPy shell can be tuned from 8 to 17 nm by varying the CS preadsorbed amount. Increasing the thickness of the adsorbed CS layer can control the deposition of thinner PPy shells on an SiO₂ core surface to provide highly water‐dispersible SiO₂@PPy particles. Moreover, CS‐doped SiO₂@PPy particles exhibit conductivities as high as 5.3 S cm^?1. The conductivity of the particles depends on the PPy mass loading and the doping level of the PPy shell. Furthermore, the SiO₂@PPy particles exhibit good biocompatibility and therefore have potential applications in biomedicine.     

Combination of Fe-Mn based Li-rich cathode materials and conducting-polymer polypyrrole nanowires with high rate capability

The polypyrrole (PPy) nanowires are conducting 1D materials, which can significantly improve the electrical conductivity of the composites. A novel Li_1.26Fe_0.22Mn_0.52O₂ (LFMO) @ PPy nanowire composites were synthesized by simply ultrasonic dispersing LFMO and PPy nanowires in aqueous ethanol. The structure and morphology of pristine LFMO and LFMO@PPy are investigated by XRD, SEM, and TEM. The elemental mapping and FTIR results demonstrate the conductive network of PPy nanowires exists in the composites and the LFMO particles uniformly distribute on the PPy nanowires. LFMO combined with PPy nanowires exhibits better rate capability, higher capacity, coulombic efficiency, and cycleability than the pristine. The rate performance of composites with 10 wt% PPy nanowires shows the discharge capacities of 132.2 mAh/g and 98 mAh/g at 1C and 3C rate after 50 cycles, respectively. Electrochemical impedance spectroscopy test suggests that the conductive PPy nanowires can significantly decrease the charge-transfer resistance of LFMO. The composite with 10 wt% PPy nanowires shows a discharge capacity retention of 71% after 50 cycles at 1C, while the pristine sample only has 50% capacity retention.     

One-step polypyrrole coating of self-assembled silver nanoprisms for enhanced stability and Raman scattering

Self-assemblies of silver nanoprisms (AgPRs) having enhanced structural stability and optical properties have been facilely coated with polypyrrole (PPy) via the in situ polymerization of pyrrole monomers that also act as an assembling agent. The assemblies of AgPRs, whose edge lengths and thicknesses are typically 78 and 4 nm, respectively, have been surrounded by a PPy coating of 6 nm. AgPRs are assembled in a side-to-side orientation, and the degree of assembly has been controlled by varying the concentration of trisodium citrate dihydrate, which attaches selectively to the {111} facets of AgPRs. The morphology deformation time of PPy-coated AgPRs in 0.6 mM H₂O₂(aq) is seven times longer than that of PPy-free AgPRs, suggesting that PPy coating prevents the sharp tips of AgPRs from being truncated by oxidizing agents. The SERS effect of highly self-assembled and PPy-coated AgPRs becomes as high as 6.3 due to numerous hot spots generated between nanoprisms. Overall, our fabricated AgPRs assemblies with PPy coating have not only improved structural stability but also enhanced optical properties, extending the practical use of noble-metal nanoprisms for various optical applications.     

Preparation and characterization of multiwall carbon nanotube/polypyrrole coaxial fibrils

Multiwall carbon nanotube (MWNT)/polypyrrole (PPy) fibrils were fabricated by template-free in situ electrochemical deposition of PPy over MWNTs, and characterized by electron microscopy and electrical measurements. Scanning and transmission electron microscopy studies reveal that PPy coating on the surface of nanotube is quite uniform throughout the length, with the possibility of forming unique Y-junctions. Current (I)-voltage (V) characteristics at various temperatures show nonlinearity due to tunneling and hopping contributions to transport across the barriers. AC conductivity measurements (300-4.2 K) show that the onset frequency scales with temperature, and the nanoscale connectivity in MWNT/PPy fibrils decreases with the lowering of temperature.     

Synthesis,characterization, conductivity and sensor application study of polypyrrole/silver doped nickel oxide nanocomposites

Conducting polymer composites of polypyrrole (PPy) and silver doped nickel oxide (Ag-NiO) nanocomposites were synthesised by in situ polymerisation of pyrrole with different contents of Ag-NiO nanoparticles. The formation of nanocomposites were studied by Fourier transform infrared (FTIR) and UV–vis spectroscopy, field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and AC and DC conductivity measurements. The sensitivity of ammonia gas through the nanocomposite was analysed with respect to different contents of nanoparticles. Spectroscopic studies showed the shift in the absorption bands of polymer nanocomposite than that of pure PPy indicating the strong interaction between the nanoparticles and polymer chain. FESEM revealed the uniform dispersion of nanoparticles with spherically shaped metal oxide particles in PPy matrix. The XRD pattern indicated a decrease in amorphous domain of PPy with increase in loading of nanoparticles. The higher thermal stability and glass transition temperature of polymer nanocomposites than that of pure PPy were revealed from the TGA and DSC respectively. The dielectric properties, DC and AC conductivity of nanocomposites were much higher than PPy and these electrical properties increases with the loading of nanoparticles. The nanocomposites showed an enhancement in sensitivity towards ammonia gas detection than PPy.     

Corrosion protection by sonoelectrodeposited organic films on zinc coated steel

A variety of coatings based on electrosynthesized polypyrrole were deposited on zinc coated steel in presence or absence of ultrasound, and studied in terms of corrosion protection. Cr III and Cr VI commercial passivation were used as references. Depth profiling showed a homogeneous deposit for Cr III, while SEM imaging revealed good surface homogeneity for Cr VI layers. These chromium-based passivations ensured good protection against corrosion. Polypyrrole (PPy) was also electrochemically deposited on zinc coated steel with and without high frequency ultrasound irradiation in aqueous sodium tartrate-molybdate solution. Such PPy coatings act as a physical barrier against corrosive species. PPy electrosynthesized in silent conditions exhibits similar properties to Cr VI passivation with respect to corrosion protection. Ultrasound leads to more compact and more homogeneous surface structures for PPy, as well as to more homogeneous distribution of doping molybdate anions within the film. Far better corrosion protection is exhibited for such sonicated films.     

Fabrication and characterization of iron oxide nanoparticles filled polypyrrole nanocomposites

The effect of iron oxide nanoparticle addition on the physicochemical properties of the polypyrrole (PPy) was investigated. In the presence of iron oxide nanoparticles, PPy was observed in the form of discrete nanoparticles, not the usual network structure. PPy showed crystalline structure in the nanocomposites and pure PPy formed without iron oxide nanoparticles. PPy exhibited amorphous structure and nanoparticles were completely etched away in the nanocomposites formed with mechanical stirring over a 7-h reaction. The thermal stability of the PPy in the nanocomposites was enhanced under the thermo-gravimetric analysis (TGA). The electrical conductivity of the nanocomposites increased greatly upon the initial addition (20 wt%) of iron oxide nanoparticles. However, a higher nanoparticle loading (50 wt%) decreased the conductivity as a result of the dominance of the insulating iron oxide nanoparticles. Standard four-probe measurements indicated a three-dimensional variable-range-hopping conductivity mechanism. The magnetic properties of the fabricated nanocomposites were dependent on the particle loading. Ultrasonic stirring was observed to have a favorable effect on the protection of iron oxide nanoparticles from dissolution in acid. A tight polymer structure surrounds the magnetic nanoparticles, as compared to a complete loss of the magnetic iron oxide nanoparticles during conventional mechanical stirring for the micron-sized iron oxide particles filled PPy composite fabrication.     

Selective hydrogenation by polymer-encapsulated platinum nanoparticles prepared by an easy single-step sonochemical synthesis

Polypyrrole-encapsulated platinum nanoparticles (PPy/Pt-NPs) prepared by an easy single-step sonochemical synthesis were used as catalysts for the liquid phase hydrogenation of substituted alkenes in methanol or methanol/water mixtures. Polypyrrole (PPy) coatings on the nanoparticles were able to act as nanoscopic filters for substrates molecules, and consequently substrate selectivity could be controlled in the catalytic processes.     

Preparation of carbon composite from coconut fiber for gas diffusion layer

A natural carbon from coconut fiber is used as a main composite material of gas diffusion layer (GDL) for fuel cell electrode. The composite comprise of polymer (ethylene vinyl acetate and poly ethylene glycol) and carbon in various compositions. The materials are mixed in xylene and printed using casting method. The composite is coated with polytetrafluoro ethylene (PTFE) to achieve hydrophobic requirement as GDL. The electrical properties of composite were measured by using LCR-meter, the porosity was obtained by immersion method, and the hydrophobic properties were observed by measuring its contact angle. The results show the electrical conductivity of GDL prepared corresponds to its carbon content. The electrical conductivity of GDLs is 22.17, 26.89, 35, 43, and 52 S/m for the carbon composition of 65, 70, 75, 80, and 85 %, respectively. The composite of 80 % carbon content and coated with PTFE contains 74 % porosity and has desired hydrophobic properties revealed from its high contact angle, i.e., 120°.     

High temperature oxidation behavior of interconnect coated with LSCF and LSM for solid oxide fuel cell by screen printing

The current study examined the effect of La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) and La_0.7Sr_0.3MnO₃ (LSM) coatings on the electrical properties and oxidation resistance of Crofer22 APU at 800 °C hot air. LSCF and LSM were coated on Crofer22 APU by screen printing and sintered over temperatures ranging from 1000 to 1100 °C in N₂. The coated alloy was first checked for compositions, morphology and interface conditions and then treated in a simulated oxidizing environment at 800 °C for 200 h. After measuring the long-term electrical resistance, the area specific resistance (ASR) at 800 °C for the alloy coated with LSCF was less than its counterpart coated with LSM. This work used LSCF coating as a metallic interconnect to reduce working temperature for the solid oxide fuel cell.     

黑碳团簇气溶胶混合生长的红外吸收特性及长波辐射效应

黑碳气溶胶是当前气溶胶辐射强迫评估中最不确定的因子.本文通过构建黑碳的微物理模型,分别模拟了新鲜状态的黑碳气溶胶和混合生长(老化)后被硫酸盐包裹的黑碳气溶胶,利用叠加T矩阵方法计算获得了具有团簇形态和多成分混合的黑碳气溶胶红外吸收特性,通过大气辐射传输模型模拟了黑碳气溶胶的长波辐射强迫,分析了典型理化参数的敏感性.发现黑碳混合生长可以显著增强其大气层顶的长波辐射强迫,最高可达3倍.而且,包裹黑碳的硫酸盐半径越大,将明显增强大气层顶的黑碳长波辐射强迫.这些发现将有助于降低黑碳气溶胶气候效应评估的不确定性.     

Morphological effects of single-layer graphene oxide in the formation of covalently bonded polypyrrole composites using intermediate diisocyanate chemistry

Single-layer graphene oxide (SLGO) possesses carboxylic and hydroxyl groups suitable for reactions with aliphatic or aromatic diisocyanate molecules. TEM analysis reveals that aliphatic diisocyanate molecules caused SLGO to scroll into star-like formations, whereas aromatic diisocyanate molecules retained SGLO in a flat-sheet morphology. TGA confirms the stabilisation of the formed urea and urethane groups on SLGO, but the onset of sheet pyrolysis occurs at a lower temperature due to isocyanate reactions with anhydride and epoxide groups embedded in the sheet. Pendant isocyanate groups act as bridging units to facilitate the attachment of pyrrole molecules, which are then used as anchor sites for the covalent polymerisation of pyrrole to polypyrrole (PPy). The use of FeCl₃ as the polymerisation catalyst generated both covalent and free PPy, but also iron hydroxide nanoparticles were observed decorating the SLGO surface. When using ammonium persulfate as a catalyst and dodecylbenzenesulfonate as a dopant, free PPy could be removed under treatment with solvents to leave a purely covalent system. Discrete regions of SLGO were observed decorated with nanoparticles of PPy along the edge or across the surface of individual sheets. It was found that the flexibility of the SLGO sheet and the type of diisocyanate used directly affected the electrical resistance of the final composite.     

Synthesis and elevated temperature performance of a polypyrrole-sulfur-multi-walled carbon nanotube composite cathode for lithium sulfur batteries

A sulfur-multi-walled carbon nanotube composite (S/MWCNT) was prepared using a two-step procedure of liquid-phase infiltration and melt diffusion. Polypyrrole (PPy) conductive polymer was coated on the surface of the as-prepared S/MWCNT composite by in situ polymerization of pyrrole monomer to obtain PPy/S/MWCNT composite. The composite materials were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The electrochemical performance of the as-prepared cathode material was investigated at 25, 40, and 70 °C at various rates. It was found that temperature has dual effects on the performance of Li/S cells. Increasing the temperature, on one hand, facilitates the lithium ion transport through the cathode and, on the other hand, leads to faster dissolution of active material into the electrolyte. The PPy coating can effectively trap polysulfides in its porous structure, even at elevated temperatures, leading to the improvement of the discharge capacity, the cycle stability, and the coulombic efficiency. The electrochemical impedance spectroscopy (EIS) results reveal that the PPy coating reduces the formation of passive layer on the cathode surface, even at high temperatures, resulting in a better elevated temperature performance. A high reversible capacity of 945 mAh g^?1 was maintained after 50 cycles for the PPy/S/MWCNT composite at 70 °C at a rate of 0.5 C.     

Physical properties,thermal stability,and glass transition temperature of multi-walled carbon nanotube/polypyrrole nanocomposites

Polypyrrole (PPy) was synthesized and doped with 1, 2, 4, and 8?wt.% of functionalized multi-wall carbon nanotubes (MWCNTs) by in situ polymerization. TGA/DTA analysis of nanocomposites revealed an increase in thermal stability by increasing the CNTs wt.%. Measurement of electrical resistivity showed a reduction in the resistivity of the composites at all temperatures. The glass transition temperature (T_g) of the samples was measured using electrical resistivity measurements and showed that by increasing the amount of functionalized MWCNTs in PPy, its T_g was increased. Temperature dependence of resistivity of pressed pure PPy showed that by increasing the pelletization pressure, the T_g increased. Also the hardness of nanocomposites was increased by increasing the MWCNTs wt.%.     

Enhanced rate performance of polypyrrole-coated sulfur/MWCNT cathode material: a kinetic study by electrochemical impedance spectroscopy

Lithium-sulfur batteries have a poor cyclability and inferior rate capability due to the shuttle effect of lithium polysulfides. To solve these problems, a sulfur-coated MWCNT composite (S/MWCNT) was coated with conductive polypyrrole (PPy) to trap the polysulfides and facilitate charge and lithium ion transport. From the contact angle measurement, it is found that the PPy coating improves the wettability of the S/MWCNT composite. Compared with the bare S/MWCNT composite, the PPy-coated S/MWCNT composite cathode exhibited improved cycle stability and high-rate performance. A reversible discharge capacity of 671 mAh g^?1 was maintained after 50 cycles at 3 C for the PPy-coated composite. The effect of PPy coating on kinetic property was investigated by electrochemical impedance spectroscopy (EIS). The electrolyte resistance, surface film resistance, charge transfer resistance, lithium ion diffusion coefficient, and exchange current density were evaluated from the EIS measurements. The EIS results reveal that the PPy coating increases both Li ion diffusion into the cathode and exchange current density. The as-prepared PPy-coated S/MWCNT composite can be considered to be a promising candidate for high capacity and high-rate performance cathode material.     

Mild steel protection with epoxy top coated polypyrrole and polyaniline in 3.5% NaCl

In this study, the corrosion behaviours of mild steel (MS) samples coated with single epoxy polyamine (MS/E), epoxy polyamine top-coated polypyrrole (MS/PPy/E) and polyaniline (MS/PANI/E) were investigated in 3.5% NaCl solution of pH 8. For this purpose, electrochemical impedance spectroscopy (EIS) and polarisation resistance measurements were utilized when the centres of the electrode surfaces were scratched. It was found that the PPy film reduced the corrosion protection efficiency of the epoxy coating when it was used as the primary film under the epoxy layer. The primary PANI coating was shown to improve significantly the protection efficiency of the epoxy coating against mild steel corrosion. This was related to its healing effect on surface passivation against attack by a corrosive environment along a defect.     

Mathematical Modeling of the Au-Doping Effect on the Radiative Properties of Porous Polymers in Experiments with Laser and Heavy-Ion Beams

We present results of a theoretical study of the radiative opacity characteristics of plasmas produced by indirect heating of porous carbohydrate (CHO) substances (foams) by laser pulses. The plasma targets are created for further interaction with heavy-ion beams. We consider two different foam substances, namely, cellulose triacetate (TAC, C₁₂H₁₆O₈) and TAC with a small admixture of gold. We discuss important features of the theoretical model, known as the ion model (IM) of plasma, which is used to study the radiative opacity characteristics of complex plasma compositions. Also we study the influence of a small admixture of gold on the radiative opacity characteristics and gas-dynamic processes in the plasma.     

Infrared optical constants of aqueous sulfate-nitrate-ammonium multi-component tropospheric aerosols from attenuated total reflectance measurements—Part I: Results and analysis of spectral absorbing features

In this paper, the first part of two, we present new high-spectral-resolution infrared (IR) optical constants for multi-component aqueous solutions composed of ammonium sulfate, ammonium nitrate, sulfuric acid and nitric acid over a range of compositions and temperatures representative of tropospheric conditions and atmospheric aerosols. The optical constants were determined from ATR measurements via a Kramers-Kronig transformation. To accomplish this, we adapted an existing technique for estimating the real index of refraction of aqueous sulfate and nitrate solutions at multiple visible frequencies as a function of concentration and temperature. An approximation of the low-frequency behavior of the ATR spectrum was also used to reduce the error associated with using ATR data of finite frequency range.This paper also provides a brief examination of absorption spectra for analyzed mixtures in relation to their composition and temperature and discusses possible implications. The new optical constants will be of great utility to high-spectral-resolution IR remote sensing as well as radiative balance analysis in climate studies because they will enable researchers for the first time to model the impacts of tropospheric aqueous sulfate-nitrate-ammonium multi-component aerosols, including their mixtures with other important species such as dust or soot.