Showing papers on "Conductive polymer published in 2006"

Organic solar cells with carbon nanotube network electrodes

Abstract: We fabricated flexible transparent conducting electrodes by printing films of single-walled carbon nanotube (SWNT) networks on plastic and have demonstrated their use as transparent electrodes for efficient, flexible polymer-fullerene bulk-heterojunction solar cells. The printing method produces relatively smooth, homogeneous films with a transmittance of 85% at 550nm and a sheet resistance (Rs) of 200Ω∕◻. Cells were fabricated on the SWNT/plastic anodes identically to a process optimized for ITO/glass. Efficiencies, 2.5% (AM1.5G), are close to ITO/glass and are affected primarily by Rs. Bending test comparisons with ITO/plastic show the SWNT/plastic electrodes to be far more flexible.

Conducting‐Polymer Nanotubes for Controlled Drug Release

Abstract: The ability to create materials with well-controlled structures on the nanometer length scale is of intense interest for a variety of applications,[1,2] including controlled drug delivery[3] and biomedical devices.[4] Preparing nanoscale objects using self-assembly and templated growth techniques has been described in some recent reviews.[2,5] For example, porous membranes can be used to synthesize desired materials within the pores.[4,6] Conducting polymers are of considerable interest for a variety of biomedical applications.[7] Their response to electrochemical oxidation or reduction can produce a change in conductivity, color,[8,9] and volume.[10] A change in the electronic charge is accompanied by an equivalent change in the ionic charge, which requires mass transport between the polymer and electrolyte.[11] When counterions enter a polymer it expands and when they exit it contracts. The extent of expansion or contraction depends on the number and size of ions exchanged.[12] Electrochemical actuators using conducting polymers based on this principle have been developed by several investigators.[13–15] They can be doped with bioactive drugs, and can be used in actuators such as microfluidic pumps.[16,17] The precisely controlled local release of anti-inflammatory drugs at desired points in time is important for treating the inflammatory response of neural prosthetic devices in the central and peripheral nervous systems.[18] Here we report on a method to prepare conducting-polymer nanotubes that can be used for precisely controlled drug release. The fabrication process involves electrospinning of a biodegradable polymer, into which a drug has been incorporated, followed by electrochemical deposition of a conducting-polymer around the drug-loaded, electrospun biodegradable polymers. The conducting-polymer nanotubes significantly decrease the impedance and increase the charge capacity of the recording electrode sites on microfabricated neural prosthetic devices. The drugs can be released from the nanotubes in a desired fashion by electrical stimulation of the nanotubes; this process presumably proceeds by a local dilation of the tube that then promotes mass transport.

The Origin of the High Conductivity of Poly(3,4-ethylenedioxythiophene)−Poly(styrenesulfonate) (PEDOT−PSS) Plastic Electrodes

Abstract: The development of printed and flexible (opto)electronics requires specific materials for the device's electrodes Those materials must satisfy a combination of properties They must be electrically conducting, transparent, printable, and flexible The conducting polymer poly(3,4-ethylenedioxythiophene)− poly(styrenesulfonate) (PEDOT−PSS) is known as a promising candidate Its conductivity can be increased by 3 orders of magnitude by the secondary dopant diethylene glycol (DEG) This “secondary doping” phenomenon is clarified in a combined photoelectron spectroscopy and scanning probe microscopy investigation PEDOT−PSS appears to form a three-dimensional conducting network explaining the improvement of its electrical property upon addition of DEG Polymer light emitting diodes are successfully fabricated using the transparent plastic PEDOT−PSS electrodes instead of the traditionally used indium tin oxide

Metallic transport in polyaniline

Abstract: Most plastics are good insulators. But conducting polymers also form the basis of a new field of ‘plastic electronics’. Some of these materials show exceptionally high conductivities, almost as high as metals. But their properties deviate from true metallic behaviour in several important ways. Now a conducting plastic with resistivity properties much more like those of true metals has been synthesized. The properties of this polyaniline compound may bring practical plastic electronics a little closer. True metallic conductivity in a much-studied conducting polymer (polyaniline) is demonstrated, but synthesized by a route that minimizes the density of structural defects believed responsible for the earlier deviations from classical metallic behaviour. Despite nearly three decades of materials development, the transport properties in the ‘metallic state’ of the so-called conducting polymers are still not typical of conventional metals1,2,3,4,5,6,7. The hallmark of metallic resistivity—a monotonic decrease in resistivity with temperature—has not been obtained at temperatures over the full range below room temperature; and a frequency dependent conductivity, σ(ω), typical of metals has also not been observed. In contrast, the low-temperature behaviour of ‘metallic’ polymers has, in all previous cases, exhibited an increase in resistivity as temperature is further decreased, as a result of disorder-induced localization of the charge carriers1,2,3,4. This disorder-induced localization also changes the infrared response such that σ(ω) deviates from the prediction of Drude theory5,6,7. Here we report classic metallic transport data obtained from truly metallic polymers. With polyaniline samples prepared using self-stabilized dispersion polymerization8, we find that for samples having room-temperature conductivities in excess of 1,000 S cm-1, the resistivity decreases monotonically as the temperature is lowered down to 5 K, and that the infrared spectra are characteristic of the conventional Drude model even at the lowest frequencies measured.

Chronic neural recordings using silicon microelectrode arrays electrochemically deposited with a poly(3,4-ethylenedioxythiophene) (PEDOT) film

Abstract: Conductive polymer coatings can be used to modify traditional electrode recording sites with the intent of improving the long-term performance of cortical microelectrodes. Conductive polymers can drastically decrease recording site impedance, which in turn is hypothesized to reduce thermal noise and signal loss through shunt pathways. Moreover, conductive polymers can be seeded with agents aimed at promoting neural growth toward the recording sites or minimizing the inherent immune response. The end goal of these efforts is to generate an ideal long-term interface between the recording electrode and surrounding tissue. The goal of this study was to refine a method to electrochemically deposit surfactant-templated ordered poly(3,4-ethylenedioxythiophene) (PEDOT) films on the recording sites of standard 'Michigan' probes and to evaluate the efficacy of these modified sites in recording chronic neural activity. PEDOT-coated site performance was compared to control sites over a six-week evaluation period in terms of impedance spectroscopy, signal-to-noise ratio, number of viable unit potentials recorded and local field potential recordings. PEDOT sites were found to outperform control sites with respect to signal-to-noise ratio and number of viable unit potentials. The benefit of reduced initial impedance, however, was mitigated by the impedance contribution of typical silicon electrode encapsulation. Coating sites with PEDOT also reduced the amount of low-frequency drift evident in local field potential recordings. These findings indicate that electrode sites electrochemically deposited with PEDOT films are suitable for recording neural activity in vivo for extended periods. This study also provided a unique opportunity to monitor how neural recording characteristics develop over the six weeks following implantation.

Hybrid Solar Cells from Regioregular Polythiophene and ZnO Nanoparticles

Abstract: Blends of nanocrystalline zinc oxide nanoparticles (nc-ZnO) and regioregular poly(3-hexylthiophene) (P3HT) processed from solution have been used to construct hybrid polymer–metal oxide bulk-heterojunction solar cells. Thermal annealing of the spin-cast films significantly improves the solar-energy conversion efficiency of these hybrid solar cells to ∼ 0.9 %. Photoluminescence and photoinduced absorption spectroscopy demonstrate that charge-carrier generation is not quantitative, because a fraction of P3HT appears not to be in contact with or in close proximity to ZnO. The coarse morphology of the films, also identified by tapping-mode atomic force microscopy, likely limits the device performance.

Polypyrrole-based conducting polymers and interactions with biological tissues.

Abstract: Polypyrrole (PPy) is a conjugated polymer that displays particular electronic properties including conductivity. In biomedical applications, it is usually electrochemically generated with the incorporation of any anionic species including also negatively charged biological macromolecules such as proteins and polysaccharides to give composite materials. In biomedical research, it has mainly been assessed for its role as a reporting interface in biosensors. However, there is an increasing literature on the application of PPy as a potentially electrically addressable tissue/cell support substrate. Here, we review studies that have considered such PPy based conducting polymers in direct contact with biological tissues and conclude that due to its versatile functional properties, it could contribute to a new generation of biomaterials.

Conducting Polymer‐Based Solid‐State Ion‐Selective Electrodes

Abstract: Conducting polymers, i.e., electroactive conjugated polymers, are useful both as ion-to-electron transducers and as sensing membranes in solid-state ion-selective electrodes. Recent achievements over the last few years have resulted in significant improvements of the analytical performance of solid-contact ion-selective electrodes (solid-contact ISEs) based on conducting polymers as ion-to-electron transducer combined with polymeric ion-selective membranes. A significant amount of research has also been devoted to solid-state ISEs based on conducting polymers as the sensing membrane. This review gives a brief summary of the progress in the area in recent years.

High-voltage asymmetric supercapacitors operating in aqueous electrolyte

Abstract: The performance of supercapacitors based on different materials with pseudocapacitive properties such as several conducting polymers (ECPs), amorphous manganese dioxide (a-MnO2), and activated carbon is reported. Composite electrodes of high resiliency and good electronic conductivity were obtained by mixing the active materials with carbon nanotubes. The various limitations of all the above-mentioned materials, when used as negative and positive electrodes in traditional symmetric systems, are shown. It is demonstrated that a successful application of ECPs and a-MnO2 in supercapacitor technologies is possible only in an asymmetric configuration, i.e. with electrodes of different nature for positive and negative polarizations. Several types of asymmetric capacitors were developed by combining ECPs, a-MnO2, and activated carbon and characterized in aqueous electrolyte by galvanostatic charge–discharge, cyclic voltammetry, and impedance spectroscopy. The best device considering the specific energy and power is the asymmetric supercapacitor using a-MnO2 and poly(3,4-ethylenedioxythiophene) (PEDOT) for the positive and negative electrodes, respectively. It has an operating voltage of 1.8 V, which is attributed to different operating potentials of both electrodes, and good electrochemical stability in neutral aqueous electrolyte. According to the voltage value, the energy density of the asymmetric capacitor at a current density of 250 mA/g is found to be 13.5 W h/kg, which is about ten times more than for a symmetric capacitor based on PEDOT in an aqueous medium. The asymmetric capacitor provides two times higher power than a symmetric capacitor based on activated carbon in organic electrolyte, and is thus extremely promising for the development of environmentally friendly systems.

Syntheses and applications of conducting polymer polyaniline nanofibers

Abstract: Nanofibers with diameters of tens of nanometers appear to be an intrinsic morpho- logical unit that was found to "naturally" form in the early stage of the chemical oxidative polymerization of aniline. In conventional polymerization, nanofibers are subject to second- ary growth of irregularly shaped particles, which leads to the final granular agglomerates. The key to producing pure nanofibers is to suppress secondary growth. Based on this, two methods—interfacial polymerization and rapidly mixed reactions—have been developed that can readily produce pure nanofibers by slightly modifying the conventional chemical syn- thesis of polyaniline without the need for any template or structural directing material. With this nanofiber morphology, the dispersibility and processibility of polyaniline are now much improved. The nanofibers show dramatically enhanced performance over conventional polyaniline applications such as in chemical sensors. They can also serve as a template to grow inorganic/polyaniline nanocomposites that lead to exciting properties such as electrical bistability that can be used for nonvolatile memory devices. Additionally, a novel flash weld- ing technique for the nanofibers has been developed that can be used to make asymmetric polymer membranes, form patterned nanofiber films, and create polymer-based nanocom- posites based on an enhanced photothermal effect observed in these highly conjugated poly- meric nanofibers.

Polyaniline, an electroactive polymer, supports adhesion and proliferation of cardiac myoblasts

Abstract: Conductive polymers, such as polypyrrole, have recently been studied as potential surfaces/matrices for cell- and tissue-culture applications. We have investigated the adhesion and proliferation properties of H9c2 cardiac myoblasts on a conductive polyaniline substrate. Both the non-conductive emeraldine base (PANi) and its conductive salt (E-PANi) forms of polyaniline were found to be biocompatible, viz., allowing for cell attachment and proliferation and, in the case of E-PANi, maintaining electrical conductivity. By comparison to tissue-culture-treated polystyrene (TCP), the initial adhesion of H9c2 cells to both PANi and E-PANi was slightly reduced by 7% (P < 0.05, n = 18). By contrast, the overall rate of cell proliferation on the conductive surfaces, although initially decreased, was similar to control TCP surfaces. After 6 days in culture on the different surfaces, the cells formed confluent monolayers which were morphologically indistinguishable. Furthermore, we observed that E-PANi, when maintained in an aqueous physiologic environment, retained a significant level of electrical conductivity for at least 100 h, even though this conductivity gradually decreased by about 3 orders of magnitude over time. These results demonstrate the potential for using polyaniline as an electroactive polymer in the culture of excitable cells and open the possibility of using this material as an electroactive scaffold for cardiac and/or neuronal tissue engineering applications that require biocompatibility of conductive polymers.

Electrically Controlled Drug Delivery from Biotin-Doped Conductive Polypyrrole

Abstract: An externally controlled, polymeric drug-delivery system potentially allows for release profiles that can be tailored to match physiologic processes. [1] Current implantable electronic delivery systems are not biodegradable and often require additional components, while extended- or controllable-release polymeric systems that have been used do not allow for switchable release profiles. [2,3] Conducting polymers (e.g., polypyrrole (PPy)) offer the possibility of controllable drug administration through electrical stimulation. [4] However, the use of conductive polymers in delivery systems has been restricted due to limitations in the choice of dopant and the molecular weight of the delivered drug. To circumvent these barriers, we have developed a method for attaching molecules to the surface of PPy through biotin–streptavidin coupling. After attachment of the desired molecule to the biotin dopant, drug release is triggered through electrical stimulation. This method provides a novel platform for controlled drug delivery from a conductive polymer substrate. Because of PPy’s beneficial chemical properties and ease of preparation, it is often chosen for biological applications. [5–7] PPy’s favorable biocompatibility also makes it an ideal electroactive polymer for drug-delivery applications. [8–13] Addi

Polypyrrole Conducting Electroactive Polymers: Synthesis and Stability Studies

Abstract: This paper deals with a fundamental review of preparation methods, characterizations, thermal and environmental stabilities and practical applications of polypyrrole (PPy) conducting electroactive polymers. In this article some of the most important factors affecting the electrical, electrochemical, thermal and environmental stabilities of polypyrrole conducting polymers have also been reviewed.

Synthesis, characterization and a.c. conductivity of polypyrrole/Y 2 O 3 composites

Abstract: Conducting polymer composites of polypyrrole/yttrium oxide (PPy/Y2O3) were synthesized byin situ polymerization of pyrrole with Y2O3 using FeCl3 as an oxidant. The Y2O3 is varied in five different weight percentages of PPy in PPy/Y2O3 composites. The synthesized polymer composites are characterized by infrared and X-ray diffraction techniques. The surface morphology of the composite is studied by scanning electron microscopy. The glass transition temperature of the polymer and its composite is discussed by DSC. Electrical conductivity of the compressed pellets depends on the concentration of Y2O3 in PPy. The frequency dependent a.c. conductivity reveals that the Y2O3 concentration in PPy is responsible for the variation of conductivity of the composites. Frequency dependent dielectric constant at room temperature for different composites are due to interfacial space charge (Maxwell Wagner) polarization leading to the large value of dielectric constant. Frequency dependent dielectric loss, as well as variation of dielectric loss as a function of mass percentage of Y2O3 is also presented and discussed.

Carbon‐Nanotube‐Reinforced Polyaniline Fibers for High‐Strength Artificial Muscles

Abstract: Actuating materials capable of producing useful movement and forces are recognized as the “missing link” in the development of a wide range of frontier technologies including haptic devices, microelectromechanical systems (MEMS), and even molecular machines. Immediate uses for these materials include an electronic Braille screen, a rehabilitation glove, tremor suppression, and a variable-camber propeller. Most of these applications could be realized with actuators that have equivalent performance to natural skeletal muscle. Although many actuator materials are available, none have the same mix of speed, movement, and force as skeletal muscle. Indeed, the actuator community was challenged to produce a material capable of beating a human in an arm wrestling match. This challenge remains to be met. One class of materials that has received considerable attention as actuators is low-voltage electrochemical systems utilizing conducting polymers and carbon nanotubes. Low-voltage sources are convenient and safe, and power inputs are potentially low. One deficiency of conducting polymers and nanotubes compared with skeletal muscle is their low actuation strains: less than 15 % for conducting polymers and less than 1 % for nanotubes. It has been argued that the low strains can be mechanically amplified (levers, bellows, hinges, etc.) to produce useful movements, but higher forces are needed to operate these amplifiers. In recent studies of the forces and displacements generated from conducting-polymer actuators, it has become obvious that force generation is limited by the breaking strength of the actuator material. Baughman has predicted that the maximum stress generated by an actuator can be estimated as 50 % of the breaking stress, so that for highly drawn polyaniline (PAni) fibers, stresses on the order of 190 MPa should be achievable. However, in practice the breaking stresses of conducting-polymer fibers when immersed in electrolyte and operated electromechanically are significantly lower than their dry-state strengths. The reasons for the loss of strength are not well known, but the limitations on actuator performance are severe. The highest reported stress that can be sustained by conducting polymers during actuator work cycles is in the range 20–34 MPa for polypyrrole (PPy) films. However, the maximum stress that can be sustained by PPy during actuation appears to be very sensitive to the dopant ion and polymerization conditions used, with many studies showing maximum stress values of less than 10 MPa. The low stress generation from conducting polymers, limited by the low breaking strengths, mean that the application of mechanical amplifiers is also very limited. To improve the mechanical performance, we have investigated the use of carbon nanotubes as reinforcing fibers in a polyaniline (PAni) matrix. Previous work has shown that the addition of singlewalled nanotubes (SWNTs) and multi-walled nanotubes (MWNTs) to various polymer matrices have produced significant improvements in strength and stiffness. It has been shown that the modulus of PAni can be increased by up to four times with the addition of small (< 2 %) amounts of nanotubes. Similar improvements in the modulus of actuating polymers may lead to significant increases in the stress generated and work per cycle. Other previous studies have shown that PAni can be wet-spun into continuous fibers and that these may be used as actuators. Isotonic strains of 0.3 % and isometric stresses of 2 MPa were obtained from these fibers when operated in ionic-liquid electrolytes. The aim of the present study was to develop methods for incorporating carbon nanotubes into PAni fibers and to determine the effects on actuator performance at different isotonic loads. A wet-spinning technique was used to prepare the composite fibers. First, the nanotubes (NTs, HiPCO SWNTs from Carbon Nanotechnology, Inc.) were dispersed by sonication for 30 min in a mixture of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA, Aldrich, 99 %) and dichloroacetic acid (DCAA, Merck, 98 %). PAni (Santa Fe Science and Technology, Inc.) and additional AMPSA were then dissolved in the dispersion by high-speed mixing. After degassing, the spinning solution was injected through a narrow outlet using N2 pressure into an acetone coagulation bath. The spun fibers were hand-drawn to approximately five times their original length across a soldering iron wrapped in Teflon tape heated to 100 °C. C O M M U N IC A IO N S

Polymer Nanofibers and Nanotubes: Charge Transport and Device Applications

Abstract: A critical analysis of recent advances in the synthesis and electrical characterization of nanofibers and nanotubes made of different conjugated polymers is presented. The applicability of various theoretical models is considered in order to explain results on transport in conducting polymer nanofibers and nanotubes. The relationship between these results and the one-dimensional (1D) nature of the conjugated polymers is discussed in light of theories for tunneling in 1D conductors (e.g., Luttinger liquid, Wigner crystal). The prospects for nanoelectronic applications of polymer fibers and tubes as wires, nanoscale field-effect transistors (nanoFETs), and in other applications are analyzed.

Conjugated Polymers : Theory, Synthesis, Properties, and Characterization

Abstract: THEORY OF CONJUGATED POLYMERS On the Transport, Optical, and Self-Assembly Properties of p-Conjugated Materials: A Combined Theoretical/Experimental Insight David Beljonne, Jerome Cornil, Veaceslav Coropceanu, Demetrio A. da Silva Filho, Victor Geskin, Roberto Lazzaroni, Philippe Leclere, and Jean-Luc Bredas Theoretical Studies of Electron-Lattice Dynamics in Organic System Sven Stafstrom SYNTHESIS AND CLASSES OF CONJUGATED POLYMERS Helical Polyacetylene Synthesized in Chiral Nematic Liquid Crystal Kazuo Akagi Synthesis and Properties of Poly(arylene vinylene)s Andrew C. Grimsdale and Andrew B. Holmes Blue-Emitting Poly(para-Phenylene)-Type Polymers Emil Joachim Wolfgang List and Ullrich Scherf Poly(paraPhenyleneethynylene)s and Poly(aryleneethynylene)s: Materials with a Bright Future Uwe H.F. Bunz Polyaniline Nanofibers: Synthesis, Properties, and Applications Jiaxing Huang and Richard B. Kaner Recent Advances in Polypyrrole Seung Hyun Cho, Ki Tae Song, and Jun Young Lee Regioregular Polythiophenes Malika Jeffries-El and Richard D. McCullough Poly(3,4-Ethylenedioxythiophene)-Scientific Importance, Remarkable Properties, and Applications Stephan Kirchmeyer, Knud Reuter, and Jill C. Simpson Thienothiophenes: From Monomers to Polymers Gregory A. Sotzing, Venkataramanan Seshadri, and Francis J. Waller Low Bandgap Conducting Polymers Seth C. Rasmussen and Martin Pomerantz Advanced Functional Polythiophenes Based on Tailored Precursors Philippe Blanchard, Philippe Leriche, Pierre Frere, and Jean Roncali Structure-Property Relationships and Applications of Conjugated Polyelectrolytes Kirk S. Schanze and Xiaoyong Zhao PROPERTIES AND CHARACTERIZATION OF CONJUGATED POLYMERS Insulator-Metal Transition and Metallic State in Conducting Polymers Arthur J. Epstein One-Dimensional Charge Transport in Conducting Polymer Nanofibers A.N. Aleshin and Y.W. Park Structure Studies of p- and s-Conjugated Polymers Michael J. Winokur Electrochemistry of Conducting Polymers P. Audebert and Fabien Miomandre Internal Fields and Electrode Interfaces in Organic Semiconductor Devices: Noninvasive Investigations via Electroabsorption Thomas M. Brown and Franco Cacialli Electrochromism of Conjugated Conducting Polymers Aubrey L. Dyer and John R. Reynolds Photoelectron Spectroscopy of Conjugated Polymers M.P. de Jong, G. Greczynski, W. Osikowicz, R. Friedlein, X. Crispin, M. Fahlman, and W.R. Salaneck Ultrafast Electron Dynamics and Laser Action in p-Conjugated Semiconductors Z. Valy Vardeny and O. Korovyanko

Electrospun polyacrylonitrile/poly(methyl methacrylate)-derived turbostratic carbon micro-/nanotubes

Abstract: Nanotubes have great potential for applications in a rapidly increasing range of fields: catalysis, medicine, pharmacy, pheromone-release systems for crop protection, sensorics, and photonics. This is due to their high anisotropy, huge specific surface area that enhances reactivity, high rate of adsorption, and efficiency of transport processes both within and across the nanotube walls. Electrospinning is a process that produces continuous polymer fibers through the action of an external electric field imposed on a polymer solution (for a review of this process see previous publications). To manufacture nanotubes, two fundamentally different approaches have been reported: self-assembly and template-based methods. In the TUFT (tubes by fiber templates) process, electrospun nanofibers themselves are used as templates to produce nanotubes. The template-based TUFT process for nanotube production consists of three stages: i) the electrospinning of template nanofibers, ii) shell deposition via chemical or physical vapor deposition (CVD or PVD, respectively), and iii) core removal by thermal or chemical means. Recently, a new technique was introduced that allows the co-electrospinning of polymer solutions from a spinneret containing two coaxial capillaries. Using this technique, coelectrospinning of immiscible and miscible pairs of polymer solutions produced nanofibers with core/shell structures. This technique was then used to co-electrospin conjugated polymer nanofibers and to make the PCL/gelatin (PCL: poly(e-caprolactone)) core/shell structure that holds great potential for controlled drug delivery and as a scaffold for tissue engineering. It was possible to co-electrospin almost non-spinnable polymers such as the conducting polymer polyaniline (PAni). Using this same co-electrospinning technique, ceramic sol–gel precursors were added to the shell solutions to create ceramic nanotubes. The core material—a heavy mineral oil—was later extracted with octane. The aim of the present work is to produce hollow carbon nanotubes by co-electrospinning two polymer solutions. The process was carried out in two stages. In the first stage, use was made of the non-solvent effect on one of the polymers to facilitate the creation of a solid interface between the nanofiber’s core and shell. In the second stage, the nanofibers were subjected to heat treatment to degrade the core polymer and carbonize the polymer shell. Figure 1 shows a typical pattern of the co-electrospinning process close to the core/shell spinneret. The core-polymer capillary protrudes 0.3 to 1 mm below the shell capillary. As

Oxidative Chemical Vapor Deposition of Electrically Conducting Poly(3,4-ethylenedioxythiophene) Films

Abstract: An oxidative chemical vapor deposition (CVD) process is presented as an alternative to conventional solution-based processing of poly(3,4-ethylenedioxythiophene) (PEDOT) thin films. This solventless technique yields PEDOT with higher conductivities and conformally coats fibers and other high area morphologies, important for enhancing efficiencies in some organic electronic devices. The CVD method eliminates corrosive poly(styrenesulfonate) that is used to disperse PEDOT in an aqueous suspension for solution-based processing. A mechanistic approach is presented that favors the deposition of the conjugated, conducting form of PEDOT. We achieved conductivities as high as 105 S/cm and demonstrated films about 100 nm thick that do not crack upon bending and are more than 84% transparent to visible light. The compatibility of oxidative CVD deposition of PEDOT is demonstrated on silicon, glass, plastic, and paper substrates.

Synthesis of metal (Fe or Pd)/alloy (Fe–Pd)‐nanoparticles‐embedded multiwall carbon nanotube/sulfonated polyaniline composites by γ irradiation

Abstract: Composites of multiwall carbon nanotubes (MWCNTs) and sulfonated polyaniline (SPAN) were prepared through the oxidative polymerization of a mixture of aniline, 2,5-diaminobenzene sulfonic acid, and MWCNTs. Fe, Pd, or Fe–Pd alloy nanoparticles were embedded into the MWCNT–SPAN matrix by the reduction of Fe, Pd, or a mixture of Fe and Pd ions with γ radiation. Sulfonic acid groups and the emeraldine form of backbone units in SPAN served as the source for the reduction of the metal ions in the presence of γ radiation. The existence of metallic/alloy particles in the MWCNT–SPAN matrix was further ascertained through characterization by high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, thermogravimetric analysis, and conductivity measurements. HRTEM pictures clearly revealed the existence of Fe, Pd, and Fe–Pd nanoparticles of various sizes in the MWCNT–SPAN matrices. There were changes in the electronic properties of the MWCNT–SPAN–M composites due to the interaction between the metal nanoparticles and MWCNT–SPAN. Metal-nanoparticle-loaded MWCNT–SPAN composites (MWCNT–SPAN–M; M = Fe, Pd, or Fe–Pd alloy) showed better thermal stability than the pristine polymers. The conductivity of the MWCNT–SPAN–M composites was approximately 1.5 S cm−1, which was much higher than that of SPAN (2.46 × 10−4 S cm−1). Metal/alloy-nanoparticle-embedded, MWCNT-based composite materials are expected to find applications in molecular electronics and other fields. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3355–3364, 2006

Redox-Active Polypyrrole: Toward Polymer-Based Batteries

Abstract: One of the most important challenges in energy research is the development of an energy-storage device that can deliver electricity for longer periods of time at higher power demand. A governing principle, as illustrated in Ragone plots of energy density (ED) versus power density (PD), is that the deliverable energy stored in a device decreases with an increasing demand for power or current. At high power demands, the inefficiency of a device (i.e., loss of energy) is due to limitations involving the mass transfer of ions or sluggish reaction kinetics, or ionic or electric resistance involved within materials or at interfaces between different phases or materials. Batteries and electric double-layer capacitors (EDLCs) are both ends of a wide spectrum of devices used to deliver power. Batteries are based on faradaic reactions (e.g., electrochemical reduction and oxidation); EDLCs are based on nonfaradaic reactions (e.g., charging and discharging the electric double layer). Batteries are known for their high ED but low PD (ED = 20–100 W h kg and PD = 50–200 W kg), whereas ultracapacitors are the opposite (ED = 1–10 W h kg and PD = 1000–2000 W kg). The faradaic reactions on which batteries are based enable high EDs but charge-transfer reactions (e.g., from Li to LiCoOx) that accompany a phase change (e.g., from ions in electrolyte to solid) are kinetically slow processes, making batteries inappropriate for applications that require high PDs. In contrast, the non-faradaic processes (i.e., charging) on which EDLCs are based involve the formation of an electric double layer at the interface between the electrolyte and the porous electrodes. This process is fast and facile, making EDLCs ideal for applications that require high PDs. We describe herein a device for storing energy, the performance parameters of which reside between a rechargeable battery and an ultracapacitor. This system consists of two electrodes coated with polypyrrole (pPy) doped with different redox-active compounds: indigo carmine (IC) or 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) (Fig. 1). The resulting redox-active conducting polymers (pPy[IC] and pPy[ABTS]) form the basis of a battery that depends on the faradaic reactions of the redox-active dopants. This feature is uniquely different from batteries or electrochemical capacitors that depend solely on redox reactions or doping/dedoping of conducting polymers. The battery consisting of pPy[IC]  pPy[ABTS] shows significant enhancement in performance at high PDs (e.g., ED = 8 W h kg at PD = 10 to 10 W kg). This enhanced performance derives from a combination of merits found in batteries and EDLCs. The principle of energy storage is based on faradaic processes of redoxactive dopants (battery-like) but the electrochemical reactions are surface confined without diffusion of the electroactive materials. Instead, the counterions in the electrolyte neutralize the charge on the electrode (EDLC-like). The porous structure of the conducting polymer provides an electrode with high surface area and enables counterions to access the redoxactive dopants. In addition, the polymer matrix provides an environment that is conductive, leading to enhanced electron transfer between the base electrodes and the electroactive dopants. The cationic charge that develops in pPy during the electropolymerization of pyrrole requires an influx of anions from the electrolyte to maintain charge neutrality. Because the C O M M U N IC A TI O N S