Undoped Polypyrrole Research Articles

An investigation on the effect of acid dyes as dopants on the electrical conductivity and heat generation of polypyrrole coated polyester fabric

This study investigates the effect of three different acid dyes as dopants on the electrical properties and heat generation of polypyrrole-coated polyester fabric. The polyester fabric was weight reduced by 11 %. Sodium dodecyl sulfate (SDS) was chosen as a reference dopant. Polypyrrole was synthesized on polyester fabric through in-situ chemical polymerization in an oxidation bath containing ferric chloride as oxidant. SEM micrographs showed that the undoped polypyrrole layer is considerably denser with much smaller pores in comparison to the doped ones. It was also revealed that the undoped and SDS doped samples showed the lowest and highest add-on, respectively. Weight reduction of polyester fabric led to a lower electrical resistance irrespective of employing a dopant or not. All the doped polypyrrole-coated weight-reduced polyester fabrics showed a lower resistance than the undoped sample. SDS doped sample enjoyed the lowest electrical resistance, followed by acid red1, acid red 18 and indigo carmine. The SDS doped polypyrrole-coated fabric also showed the highest add-on followed by acid red 1, acid red 18 and indigo carmine. The rise of temperature versus time for the coated samples is exponential, reaching a plateau after about 3 min. Moreover, higher voltages led to higher temperatures. Acid red 1 doped polypyrrole reached the highest temperature (96 °C) at 12 V. In spite of higher electrical resistance, the fabric coated with acid dye doped polypyrrole showed a higher capacity for heat generation than the fabric coated with SDS doped polypyrrole.

Effect of Complex Ceramic Oxide Nanoparticles Addition on the Corrosion Behavior of Stainless Steel in Artificial Sea Water: Physical Chemistry Approach

A novel method of electrochemical synthesis of yttrium aluminum garnet (YAG: Al5Y3O12) is successfully developed in the mixture of YCl3 and AlCl3 aqueous solution. The electrosynthesized YAG are further annealed and characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Ppy/YAG thin film is formed electrochemically on the surface of the stainless steel (SS). The anti-corrosive behavior of polypyrrole films in the presence of YAG nanoparticles synthesized by electropolymerisation on stainless steel (SS) electrodes have been investigated in artificial sea water solutions using potentiodynamic polarization and electrochemical impedance spectroscopy. The undoped polypyrrole synthesized in the presence of YAG nanoparticles coated electrodes offered a noticeable enhancement of protection against corrosion processes. Facile synthesis of YAG and Ppy/YAG nanocomposite and more efficient protection effect of nanocomposite film are main important novelty of the presented work.

Embedding of IrQ(ppy)2 organometallic compounds in polypyrrole conducting polymer for OLED’s applications

Conducting polypyrrole:IrQ(ppy)2 thin films were obtained by electrochemical method which ensure uniform dispersion of the organometallic in the polymer matrix. A thin layer of about 50nm polypyrrole:IrQ(ppy)2 thin films were deposited on the ITO/glass substrate and used for spectroscopic, structural, and electric characterization. The photoluminescence spectrum of polypyrrole:IrQ(ppy)2 have shown the two main emissions of IrQ(ppy)2 at 2.44eV (508nm) and 2eV (620nm) besides of the polypyrrole weak emission centered at 2.55eV (485nm). The electric conductivity of the doped polypyrrole thin layer has almost the same conductivity with the undoped polypyrrole thin film suggesting an homogenous polypyrrole:IrQ(ppy)2 composite which can be used as emissive layer in the OLED’s structures.

Role of dopants on the electro-optic effect in nematic liquid crystals aligned with doped polypyrrole

In order to estimate electro-optical response times, measurements of the transmitted light intensity through positive uniaxial nematic thin films in planar alignment have been performed. Very fast relaxation times were experimentally found for nematic samples aligned with conductive polymers, namely, polypyrrole doped with 5 types of anions having different molecular sizes and geometries. Using undoped polypyrrole alignment layers, slower electro-optical responses were obtained. Given that the improvement in the relaxation times is induced by the presence of the anions in the polypyrrole films, the increasing of the total restoring torque of the nematic molecules to the confining surfaces—responsible for the short relaxation times—is related to the charges accumulated at the nematic-conductive polymer interface.

Immobilization of Amino Acids Leucine and Glycine on Polypyrrole for Biosensor Applications: A Density Functional Theory Study

Adsorption based on the immobilization of amino acids, i.e. leucine and glycine, on the surface of undoped polypyrrole (Ppy) is investigated. Calculations are done based on density functional theory using Gaussian03 software and applying GGA with 6-31G(d) basis set and exchange-correlation model of PBE (Perdew, Burke, Ernzerhof) level of theory. The energy of the Ppy doped with amino acids are minimized with respect to the orientation and distance of the amino acids to the Ppy. Neutral leucine carboxyl shows greater binding energy as compared to that other leucine configurations. It has adsorption energy of 0.25 eV at optimum distance of 2.2 A from the surface of Ppy. As for the glycine, the zwitterionic carboxyl exhibits the strongest binding energy among other glycine configurations. It has adsorption energy of 0.76 eV at optimum distance of 1.7 A from the surface of Ppy. The adsorption processes for both amino acids should proceed easily because the activation barriers are either absent or very small.

Hopping and tunneling transport over a wide temperature range in chemically synthesized doped and undoped polypyrrole

Polypyrrole was synthesized by the chemical oxidation method in the presence of phosphoric acid by varying oxidant to monomer molar ratio for the optimization of electrical conductivity. The conductivity in doped polypyrrole reached up to a maximum value of 9.18 S/cm. Granular morphology was observed in chemically synthesized polypyrrole. Neutralization of doped polypyrrole was done with aqueous ammonium hydroxide and three orders of reduced conductivity were obtained in neutral polypyrrole. Doped and undoped samples of polypyrrole were then electrically characterized over a wide temperature range of 10–300 K. The measured electrical conductivity rises with the increase in temperature and shows the semiconducting nature of the material. Strong and weak temperature dependence of conductivity was revealed by undoped and doped polypyrrole samples respectively. An effort has been made to explore the electrical transport in doped and undoped polypyrrole by charge transport models. The experimental data obeys Kivelson’s hopping model in temperature range of 60–300 K and fluctuation assisted tunneling was the dominant conduction mechanism below 60 K.

Chemical synthesis and low temperature electrical transport in polypyrrole doped with sodium bis(2-ethylhexyl) sulfosuccinate

Polypyrrole (PPy) is polymerized by chemical oxidative polymerization in presence of anionic surfactant sodium bis (2-ethylhexyl) sulfosuccinate (DEHS) as the dopant. The electrical conductivity was optimized in terms of oxidant to monomer molar ratio and polymerization yield was measured for these reactions. We have used ammonium persulphate (APS) as the oxidant for polymerization in this series of experiments. The effect of concentration of oxidant on the electrical conductivity is examined. Chemical synthesis of polypyrrole is supported by FTIR spectrum. The electrical conductivity of doped and undoped polypyrrole has been measured in the temperature range of 10–300 K and is found to increase with rise in temperature. Electrical conductivity of PPy was analyzed in the light of various charge transport models. Analysis of the electrical conductivity data reveals that in the temperature range 60–300 K electrical transport is predominantly governed by power law behaviour given by Kivelson model. However in the low temperature range 10–60 K electrical transport is dominated by the fluctuation assisted mechanism.

Chemical reduction method for industrial application of undoped polypyrrole electrodes in lithium-ion batteries

This work describes a new method of chemical reduction of p-doped polypyrrole (Ppy) to make a graphite/Ppy lithium-ion battery. Several reducing agents are analysed (sodium hydrosulfite (Na 2S 2O 4), sodium hydrogensulfite (Na 2S 2O 5), hydroxymethanesulfinic acid monosodium salt (HOCH 2SOONa), sodium borohydride (NaBH 4), formamidinesulfinic acid (H 2NCNHSO 2H), stannous chloride (SnCl 2) and hydrazine (N 2H 4)), obtaining the best results when reducing a Ppy electrode with sodium borohydride (NaBH 4): at least 85% of the polymer electrode can be reduced without significant degradation. To verify the feasibility of the reduction method two lithium-ion batteries with a Ppy cathode have been assembled using different ways (4.5 cm × 1.9 cm electrodes having similar active electrode material (mg cm −2) values and thicknesses to commercial inorganic oxide electrodes). In one of them the doped Ppy electrode is previously electrochemically reduced, applying consecutive potentials steps before the cell assembling; it would be accurate and easy at laboratory scale, but from an industrial point of view it is complicated and not viable. In the second battery the doped Ppy electrode is chemically reduced resulting in a similar charge–discharge characteristic to the electrochemically reduced one. Therefore, the chemical reduction method can be a step forward for using Ppy as cathode in lithium-ion batteries at industry level.

Corrosion performance of conducting polymer coatings applied on mild steel

Conducting polypyrrole electrodes were obtained by galvanostatic electropolymerisation on mild steel electrodes from an aqueous solution. The electrochemical response of the coated electrodes in doped and in undoped state was compared with bare mild steel electrodes. The undoped polypyrrole coated electrode offered a noticeable enhancement of protection against corrosion processes.

Sensitization effect in doped and undoped state of polypyrrole by methylene blue in solid state electrochemical cells

Methylene blue (MB) at small concentration is used as a photosensitizer in the solid state photoelectrochemical cells fabricated using doped and undoped polypyrrole (Ppy) coated electrodes sandwiched with solid polymer electrolyte (SPE) viz. polyvinylalcohol (PVA) doped with phosphoric acid. Different sensitization effects are observed for the same polymer–dye combination. MB sensitizes Ppy in doped state more efficiently as compared to undoped state of the polymer. The actual placement of the energy levels of dye with respect to polymer and ease with which polymer transports photogenerated charge carriers without recombination are observed to be important in such sensitization processes and governs the overall process.

Electrical conductivity response of polypyrrole to acetone vapor: effect of dopant anions and interaction mechanisms

The chemically prepared undoped polypyrrole (PPy) and the PPy doped with seven dopant anions, at a dopant to monomer molar ratio of 1/12, were used as chemical sensors to detect acetone vapor. The negative changes in specific conductivity, Δ σ, of PPys upon exposed to acetone vapor were observed. The magnitudes of Δ σ depend critically on the type of the dopants which induces different properties amongst doped PPys. For the sulfonate doped PPy, Δ σ depends exponentially on the doping level (N +/N) and on the initial specific conductivity. It also depends linearly on the proportions of the bipolaron species and of the order aggregation of PPy. However, it depends inversely on the proportion of the imine-like nitrogen defect (N). An environmental scanning electron microscope and an X-ray diffractometer, for instances, were used to investigate the interaction between PPy and acetone molecules. The swelling or the disordering effect, the hydrogen-bonding formation, and the reduction of charge carrier species are suggested to be the mechanisms causing the PPy conductivity changes when exposed to acetone vapor.

Structural and mechanical degradation of polypyrrole films due to aqueous media and heat treatment and the subsequent redoping characteristics

Polypyrrole films doped with p-toluenesulfonate and poly(4-styrenesulfonate) anions were synthesized electrochemically. These films were treated with water and dilute NaOH solution for varying periods of time. The films do not lose the anions readily when treated with water. In NaOH, dedoping occurs rapidly, either via migration of the toluenesulfonate anions out of the film or the neutralization of the poly(4-styrenesulfonate) anions. The undoped polypyrrole is very susceptible to ring oxidation resulting in C(SINGLE BOND)O and C(DOUBLE BOND)O groups. Severe deterioration of the mechanical properties of the film also results upon prolonged exposure to NaOH. The effects of heat on the polypyrrole doping level, structure, and mechanical properties were investigated. The results from redoping experiments suggest that unless the dedoping process by NaOH is carried out rapidly, the redoped films will have significantly lower doping levels and conductivities than the pristine films © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 519–526, 1997

Effect of the Composition of Polypyrrole Substrate on the Electrodeposition of Copper and Nickel

Electrodeposition of copper and nickel on a variety of substrates including conductive polymer films with two different compositions has been studied. The enhancement of the copper and nickel electrodeposition rate was observed for composite polypyrrole films with cation‐exchange properties in comparison to undoped polypyrrole films with anion‐exchange properties. Significant enhancement of the nickel electrodeposition rate on both types of conductive polymer vs. the bare gold electrode was also found. An explanation of these effects is presented. An electrochemical quartz crystal microbalance (EQCM) with 10 MHz AT‐cut piezoelectrodes was used in this study. Use of the EQCM technique allowed for simultaneous monitoring of voltamperometric and resonance frequency vs. potential or time characteristics. The thickness of electropolymerized polypyrrole films as well as the amounts of electrodeposited metals were controlled by monitoring the EQCM resonant frequency. The nucleation density has been determined from scanning electron microscope experiments.

Photoelectron Spectra of Polypyrrole: The Effect of the Ambient Atmosphere to the Spectra

Abstract Ultraviolet and X-ray photoelectron spectra of carefully prepared undoped as well as doped polypyrrole have been measured. Reliable UPS of undoped polypyrrole must be the first one in spite of its popularity, because of its instability in the air. Our UPS were compared with those of presumably polymerized pyrrole by X-ray irradiation and other reported results. We examined the validity of these spectra and we found the deformation of the UPS caused by air exposure of the undoped film. A comparison of our UPS with theoretical calculation gave 1.40 Å as an estimated bond distance between α,α′ carbon atoms. Both Cls and Nls XPS were asymmetric and consisted of a few peak components, which was not dependent on doping. Their peak envelopes varied with its historical back ground. While the Cls peak envelopes were not deformed so seriously by air exposure, the Nls envelopes were affected by slight air exposure as were observed in the UPS.