Contribution of conformational change of polymer structure to electrochemomechanical deformation based on polyaniline

The pH dependencies of electrochemomechanical deformation (ECMD) including the cyclic voltammetry and the expansion ratio in conducting polymers, polyaniline (PANI), and poly(o-methoxyaniline) film were studied to elucidate the mechanisms. It was found that the ECMD is governed by the conformational change of polymer structure as well as the insertion of bulky ions in the manner of comparable magnitude. Expansion ratios >20% in the ECMD were demonstrated for the thickness direction of PANI film. The results suggest that the magnitude of ECMD can be improved by choosing the preparation method of films.     

Conducting polymers electromechanical actuators and strain sensors

Electromechanical actuators are being investigated for a wide range of applications in medical, electronics and industrial areas. One attractive application is to incorporate conducting polymer fibre actuators into fabrics for use in prosthetic applications. In this paper, the design of polypyrrole fibre actuators for use in a glove to open and close the human hand (for assisting those with paralysis or hand injuries) is described. The key requirements for this application are the simultaneous generation of 16 mm of contractile movement and 2.9 N of force. Although not critical in the first prototypes, eventually it will also be necessary to produce a rate of movement of around 10 mm sec⁻¹. The effect of the geometry of polypyrrole actuators is examined in this paper and it is shown that a tubular geometry is superior to conventional flat films. Another aspect of the practical use of actuator materials is their control. Fabric strain gauges with polymer actuators is a convenient means for providing feedback control to the actuating element. The fabric strain gauges ideally articulate with fibre actuators to give both the actuating and sensing function in the same fabric structure.     

Redox-induced surface stress of polypyrrole-based actuators

We measure the surface stress induced by electrochemical transformations of a thin conducting polymer film. One side of a micromechanical cantilever-based sensor is covered with an electropolymerized dodecyl benzenesulfonate-doped polypyrrole (PPyDBS) film. The microcantilever serves as both the working electrode (in a conventional three-electrode cell configuration) and as the mechanical transducer for simultaneous, in situ, and real-time measurements of the current and interfacial stress changes. A compressive change in surface stress of about -2 N/m is observed when the conducting polymer is electrochemically switched between its oxidized (PPy+) and neutral (PPy0) state by cyclic voltammetry. The surface stress sensor's response during the anomalous first reductive scan is examined. The effect of long-term cycling on the mechanical transformation ability of PPy(DBS) films in both surfactant and halide-based electrolytes is also discussed. We have identified two main competing origins of surface stress acting on the PPy(DBS)/ gold-coated microcantilever: one purely mechanical due to the volume change of the conducting polymer, and a second charge-induced, owing to the interaction of anions of the supporting electrolyte with the gold surface.     

Electrochemical growth of two-dimensional gold nanostructures on a thin polypyrrole film modified ITO electrode

Two-dimensional gold nanostructures have been fabricated by electrochemical deposition of gold nanoparticles onto indium tin oxide (ITO) glass substrate modified with thin polypyrrole film. By controlling the electrodeposition conditions, gold nanoparticles with dendritic rod, sheet, flower-like (consisting of staggered nanosheets), and pinecone-like structures were generated. The flower-like gold nanoparticles showed high catalytic activity on electrochemical reduction of oxygen, and its activity was measured to be approximately 25 times that of gold pinecones and 10(4) times that of gold nanosheets in terms of gold weight. The pinecone-like nanoparticles can form a compact film with nano-/microscale binary structure like a lotus leaf surface. After modification with n-dodecanethiol, the surface showed superhydrophobic properties with a water contact angle of 153.4 degrees and a tilt angle of 4.4 degrees (5 microL droplet).     

Electrochemically Controlled Ion‐exchange Property of Carbon Nanotubes/Polypyrrole Nanocomposite in Various Electrolyte Solutions

The electrochemically controlled ion‐exchange properties of multi‐wall carbon nanotube (MWNT)/electronically conductive polypyrrole (PPy) polymer composite in the various electrolyte solutions have been investigated. The ion‐exchange behavior, rate and capacity of the electrochemically deposited polypyrrole with and without carbon nanotube (CNT) were compared and characterized using cyclic voltammetry (CV), chronoamperometry (CA), electrochemical quartz crystal microbalance (EQCM), X‐ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). It has been found that the presence of carbon nanotube backbone resulted in improvement in ion‐exchange rate, stability of polypyrrole, and higher anion loading capacity per PPy due to higher surface area, electronic conductivity, porous structure of thin film, and thinner film thickness providing shorter diffusion path. Chronoamperometric studies show that electrically switched anion exchange could be completed more than 10 times faster than pure PPy thin film. The anion selectivity of CNT/PPy film is demonstrated using X‐ray photoelectron spectroscopy (XPS).     

Synthesis of polypyrrole films for the development of ammonia sensor

In the present investigation, we have synthesized a polypyrrole films by chemical polymerization technique for the development of ammonia sensor. The polypyrrole films were synthesized in an aqueous acidic medium on glass substrate with mild oxidation of ferric chloride at temperature 29°C. The concentrations (molar) of monomer (pyrrole), oxidant (ferric chloride), and dopant (polyvinyl sulfonate) have been optimized for the uniform and porous surface morphology of the synthesized polypyrrole film. The synthesized films were characterized by scanning electron microscopy, ultraviolet‐visible, and Fourier transforms infrared spectroscopy. Ammonia gas sensing behavior of polypyrrole films was studied by using indigenously developed gas sensing chamber. The synthesized polypyrrole film with optimized process parameters shows excellent and reproducible response to low concentration (100 ppm) of ammonia gas. Copyright © 2007 John Wiley & Sons, Ltd.     

Tunable wetting mechanism of polypyrrole surfaces and low-voltage droplet manipulation via redox

This paper presents the experimental results and analyses on a controlled manipulation of liquid droplets upon local reduction and oxidation (redox) of a smart polymer-dodecylbenzenesulfonate doped polypyrrole (PPy(DBS)). The electrochemically tunable wetting property of PPy(DBS) permitted liquid droplet manipulation at very low voltages (-0.9 to 0.6 V). A dichloromethane (DCM) droplet was flattened upon PPy(DBS) reduction. It was found that the surface tension gradient across the droplet contact line induced Marangoni stress, which caused this deformation. Further observation of PPy(DBS)'s color change upon the redox process confirmed that the surface tension gradient was the driving force for the droplet shape change.     

Detection of DNA hybridization by ABEI electrochemiluminescence in DNA-chip compatible assembly

The electrochemiluminescence (ECL) of a luminol derivate (ABEI) generated both by a carbon electrode and a polypyrrole-coated carbon electrode was examined. It was found that the polypyrrole film (ppy) did not inhibit the ECL. After that, ABEI anchored on a single stranded DNA target (ODNt) has been used for the ECL detection of the hybridization between a complementary single stranded DNA probe (ODNp) covalently linked to a polypyrrole support and the ODNt. The ECL detection has been performed using a DNA sensor having a low surface concentration of ODNp probes, constituted of a polypyrrole copolymer electrosynthesized from a pyrrole-ODNp/pyrrole monomer ratio of 1/20,000.     

Photoelectrodes based on acceptor–donor assemblies in functionalized polypyrrole films

The capability to act as molecular photoelectrodes under visible light irradiation of optically transparent electrodes (ITO) modified by thin films of polypyrrole containing several kind of electron acceptor–donor assemblies has been examined. Photolysis of electrodes coated by thin films of polypyrrole substituted by a reversible electron donor (phenothiazine) in the presence of an irreversible electron acceptor (tropylium cation) in acetonitrile gives weak photocurrents. In contrast, appreciable photocurrents can be obtained using a symmetrical arrangement; viologen as reversible electron acceptor, benzilate anion as irreversible donor. The photoresponses result from the photo-induced charge separation of the charge transfer complexes created in the film. The measured photocurrents are markedly larger (up to five times), with films of polypyrrole substituted by a reversible electron acceptor (viologen) covalently linked with a donor (phenothiazine, triphenylamine or benzidine) than with the unimolecular immobilized system in similar experimental conditions. The greater efficiency of these materials is attributed to the formation of an intramolecular charge transfer complex occurring inside films between the two molecular entities. Markedly weaker photocurrents are obtained with polypyrrole films based on bilayers of the two independent components than those with the unimolecular design, while films based on copolymers arrangements give moderately weaker photoresponses.     

Preparation and characterization of electrostrictive polyurethane films with conductive polymer electrodes

All-polymer electrostrictive soft films were developed for the first time by depositing conductive polymer (polypyrrole) directly on both sides of solution-cast electrostrictive polyurethane elastomer films. The final composite films are flexible with strong adhesion between the polyurethane film and the conductive polymer electrode. The conductivity (sheet resistivity ∼1000 Ω/□), of the polymer electrode is appropriate for its intended use. The compatible interface between the polypyrrole electrode polymer and the electrostrictive polyurethane significantly improves the acoustic and optical transparency of these composite films, compared with using a metal electrode film. The all-polymer films also exhibit comparable dielectric properties to gold-electroded polyurethane films in the temperature range from −40^°C to +80^°C. The temperature range covers the soft segment glass transition temperature of the polyurethane elastomers, which is about −20^°C. The films also show large electric field induced strain responses which are dependent on film thickness and measurement frequency. The electrostrictive characteristics in the all-polymer films show similarities to those of the films with gold electrodes under identical measurement conditions. © 1998 John Wiley & Sons, Ltd.     

The growth of polypyrrole films on electrodes

The kinetics of growth of polypyrrole films deposited onto electrode surfaces from aqueous solutions of pyrrole have been investigated. The rate-determining step for the growth of the film is the oxidation of pyrrole units or oligomers and their incorporation at the end of polymer chains. In spite of the positive potential imposed on the electrode during electrodeposition, polypyrrole remains essentially in its neutral state during growth and exhibits conductivities which are several orders of magnitude lower than those of already grown films. It is shown that the rate of film growth is limited by the low conductivity of the growing film, which was evaluated from potentiostatic current transients recorded during electrodeposition of polypyrrole.     

吡咯在HOPG上电聚合机理的ECSTM现场观测

电聚吡咯过程机理的研究,多年来由于仪器的限制仅限于从间接的方式获得证据,为了得到溶液中真实的电聚吡咯过程信息,我们用自制的ECSTM仪器首次对电聚吡咯成膜的全过程跟踪观测,得到了有意义的结果。 1 实验条件 ECSTM仪器是本实验室在中科院北京电子显微镜实验室制造的STM基础上     

Preconcentration and Determination of Metal Species at Polypyrrole Modified Glassy Carbon Electrodes

Metal species can be extracted/preconcentrated onto electropolymerized polypyrrole film electrodes without deliberate incorporation of chemically active counterions. Silver species preconcentrated on polypyrrole film can be determined electrochemically. The effects of polypyrrole film coverage, electropolymerization conditions,solution composition and the presence of other species have been investigated. Experimental results showed that the anodic peak current for incorporated silver species was proportional to silver concentration in solution in the range from 2 to 150 μM. The detection limit was estimated to be about 0.2 \μM (20 ppb). Most of the metal ions studied, including Ni, Cd, Pb, Zn and Fe, did not show obvious interference on the determination. Cu and Hg were also extracted onto polypyrrole film electrodes. Polypyrrole film electrodes were reuseable. The mechanism involved in the preconcentration was also investigated.     

The effect of casting solvent on the material properties of poly(γ-methyl-D-glutamate)

The effect of casting solvent on the material properties of poly(γ-methyl-D -glutamate), PMDG, was investigated. The specific solvents used were chloroform, trifluoroacetic acid, dichloroacetic acid, methylene chloride, hexafluoroisopropanol, and tetrachloroethane. The different nature of these solvents controlled the degree of α, β, or random coil contents of the final film. The effect of the morphology on material properties induced by the respective solvents was investigated by dynamic mechanical measurements of the dry films, stress strain behavior of both wet and dry films as well as by wide-angle x-ray diffraction, small-angle light scattering, and optical microscopy. Infrared spectroscopy was used to help determine α or β content. It was found that the casting solvent has considerable influence on material behavior and morphology. These differences are reflected in both the dynamical mechanical (small strain) and stress–strain (large strain) measurements as well as the x-ray scattering and optical microscopy. It was noted by light scattering that all films gave rise to anisotropic rod scattering with the exception of the β film cast from trifluoroacetic acid. This latter film appeared to be optically isotropic.     

Enhancement of response by incorporation of platinum microparticles into a polypyrrole-glucose oxidase electrode

Platinum was incorporated into a polypyrrole/glucose oxidase electrode by immersion in a hexachloroplatinate(IV) solution after electrochemical oxidation of the polypyrrole film; dispersed platinum was then formed by electrochemical reduction. The platinized electrode reproducibly yielded a response to glucose (20 mM) which was typically about 40% higher than that obtained in the absence of platinum microparticles in the polypyrrole/glucose oxidase film.     

Incorporation of ferrocene into polypyrrole films via an ionic adduct with boron trifluoride

1-(Ferrocenyl)ethanol has been immobilized within polypyrrole films during their electrochemical deposition, or following their deposition, via its adduct with boron trifluoride. Dissociation of H⁺ from this adduct, formed in a solution of boron trifluoride diethyl ether (BFEE) in acetonitrile, produces an anion that can act as a counterion for oxidized polypyrrole. Its subsequent hydrolysis produces a polypyrrole film containing neutral 1-(ferrocenyl)ethanol which was found to be strongly retained. In addition to producing a novel type of polypyrrole–ferrocene composite, this work provides clear evidence to support the efficacy of this methodology for the incorporation of neutral species within conducting polymer films.     

Investigation of SPR and electrochemical detection of antigen with polypyrrole functionalized by biotinylated single-chain antibody: A review

An electrochemical label-free immunosensor based on a biotinylated single-chain variable fragment (Sc-Fv) antibody immobilized on copolypyrrole film is described. An efficient immunosensor device formed by immobilization of a biotinylated single-chain antibody on an electropolymerized copolymer film of polypyrrole using biotin/streptavidin system has been demonstrated for the first time. The response of the biosensor toward antigen detection was monitored by surface plasmon resonance (SPR) and electrochemical analysis of the polypyrrole response by differential pulse voltammetry (DPV). The composition of the copolymer formed from a mixture of pyrrole (py) as spacer and a pyrrole bearing a N-hydroxyphthalimidyl ester group on its 3-position (pyNHP), acting as agent linker for biomolecule immobilization, was optimized for an efficient immunosensor device. The ratio of py:pyNHP for copolymer formation was studied with respect to the antibody immobilization and antigen detection. SPR was employed to monitor in real time the electropolymerization process as well as the step-by-step construction of the biosensor. FT-IR demonstrates the chemical copolymer composition and the efficiency of the covalent attachment of biomolecules. The film morphology was analyzed by electron scanning microscopy (SEM).Results show that a well organized layer is obtained after Sc-Fv antibody immobilization thanks to the copolymer composition defined with optimized pyrrole and functionalized pyrrole leading to high and intense redox signal of the polypyrrole layer obtained by the DPV method. Detection of specific antigen was demonstrated by both SPR and DPV, and a low concentration of 1 pg mL⁻¹ was detected by measuring the variation of the redox signal of polypyrrole.     

Electrocatalytic Reactions by an Iron Porphyrin/Polypyrrole Modified Electrode Monitored by Electrochemical Quartz Crystal Microbalance

Electropolymerization of pyrrole in aqueous solution is monitored by electrochemical quartz crystal microbalance (EQCM) during potential scan. The film formation process on the electrode is reflected by the frequency decrease for the quartz oscillator as a function of time. The film growth rate is greatly enhanced in the presence of iron(III) meso-tetrakis(3-sulfonatomesityl)porphyrin, which carries 3- of charge. The metalloporphyrin is trapped and remains intact in the polypyrrole films. The ion transport property through the iron porphyrin/polypyrrole film is the reverse of that for pure polypyrrole. Electroreduction of dioxygen and electrooxidation of alkenes are parallel to those in the solution state.     

Electrochemistry of Polypyrrole Films in Aqueous Solutions: The Character of the Bond between the Anion and the Polymer Matrix

Mechanisms of the formation and doping of polypyrrole films and their behavior in aqueous media are studied by voltammetry, chronoamperometry, and other methods combined with IR spectroscopy and the tracer technique. The last two methods reveal that pyrrole molecules in acid media form complexes with protons and anions, and that a strong interaction occurs in a polypyrrole film between links of polypyrrole chains and anions, leading to a change in their structure. The obtained data are used to propose a mechanism for the synthesis of polypyrrole films, which includes the discharge of a complex of protonated pyrrole with the anion yielding radical cations, which induce the growth and development of polypyrrole chains. It is stressed that the incorporation of anions into a film (doping) occurs in the course of its formation during the discharge and partial destruction of the pyrrole complexes with the anion.     

All-organic actuator fabricated with single wall carbon nanotube electrodes

Compliant electrodes to replace conventional metal electrodes have been required for many actuators to relieve the constraint on the electroactive layer. Many conducting polymers have been proposed for the alternative electrodes, but they still have a problem of poor thermal stability. This article reports a novel all- organic actuator with single wall carbon nanotube (SWCNT) films as an alternative electrode. The SWCNT film was obtained by filtering a SWCNT solution through an anodized alumina membrane. The conductivity of the SWCNT film was about 280 S/cm. The performance of the SWCNT film electrode was characterized by measuring the dielectric properties of NASA Langley Research Center – Electroactive Polymer (LaRC-EAP) sandwiched by the SWCNT electrodes over a broad range of temperature (from 25 to 280 °C) and frequency (from 1 kHz to 1 MHz). The all-organic actuator with the SWCNT electrodes showed a larger electric field-induced strain than that with metal electrodes, under identical measurement conditions. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2532–2538, 2008