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'FRUITCAKE' STRUCTURE IN ORGANIC POLYMERS The field of organic electronics has benefited from the discovery of new semiconducting polymers with molecular backbones that are resilient to twists and bends, meaning [...]

This paper presents results of a preliminary study of feasibility for the application of electroactive polymer (EAP) based actuators to a robotic locomotion system, intended by the European Space Agency (ESA) to operate on the surface of Mars. The system is conceived as an elastic spherical rover, exploiting wind propulsion for surface motion, while adopting an active mechanism for vertical jumping over obstacles. The use of polymeric electromechanical devices is envisaged in order to provide actuation to such a jumping mechanism. Among the available EAP technologies, new contractile linear actuators based on dielectric elastomers are proposed in this study as suitable devices and two potential solutions concerning their use are designed, modeled, and evaluated via numerical simulations. The best solution reveals interesting simulated performances, enabling jumping of obstacle heights corresponding to more than 7% of the diameter of the rover.

Electronic structure calculations on a conjugated polymer chain by Hartree-Fock and density functional theory show a sequence of self-localized states, which stand in contrast to the single self-localized soliton state described by the Su-Schrieffer-Heeger model Hamiltonian. An extended Hubbard model, which treats electron-electron interactions up to second neighbors, is constructed to demonstrate that the additional states arise from a strong band-bending effect due to the presence of localized electric fields of charged solitons. We suggest the optical response of these electronic states may be associated with the near-edge oscillations observed in photo-induced absorption spectra. Our calculations indicate further that in the presence of counterions, the additional localized states continue to exist. Implications regarding soliton mobility and high-resolution ion sensing are briefly discussed. conducting polymer | self localization | soliton

This paper presents an analytical procedure for predicting the shear load-deformation response of concrete filled fiber-reinforced polymer (FRP) composite cylindrical shells with full- and noncomposite behavior. The approach is based on a sectional layered analysis with an iterative algorithm to achieve equilibrium and compatibility conditions of the FRP/concrete system, including the cracked behavior of the FRP-confined concrete, until first-ply failure of the FRP composite. The model follows first order mechanics for the shear behavior of structural members in combination with a smeared shear modulus for cracked concrete and inclusion of extension/shear coupling effects of anisotropic FRP laminates. Comparisons of the analytical response with available experimental data from large- and small-scale tests were found to be in reasonable agreement and corroborated the significant influence of the concrete core and the composite interaction details on the shear load-deformation response. Parametric studies on the influence of concrete properties, axial loads, and FRP laminate design are discussed. DOI: 10.1061/(ASCE)0733-9445(2006) 132:6(949) CE Database subject headings: Cylindrical shells; Fiber reinforced polymers; Composite structures; Composite materials; Shear resistance; Shear deformation.

We have tried to confirm the sign inversion of the photocarrier in regiorandom poly(3-octadecylthiophene), PAT18, by means of the time-of-flight (TOF) method. It was found that the hole mobility decreases with increasing temperature. At the temperature near the solid-liquid phase transition, the hole mobility decreases drastically, and eventually the melting temperature, it was impossible to evaluate the hole mobility from noisy transient photocurrent. On the other hand, transient photocurrents based on electron transport are observed above the melting point. The negative carrier mobility was evaluated in the range from [10.sup.-6] to [10.sup.-5] [cm.sup.2]/Vs, which is comparably the hole mobility at the solid state. Moreover, the electrical conductivity changes drastically at the instant of the solid-liquid phase transition, and transport in the liquid state was not influenced remarkably by applied hydrostatic pressure, which suggests electronic transport and not ionic transport. These facts suggest that the same mechanism, for example interchain hopping limits carrier transport, and the negative carrier is electron. This unique phenomenon is interpreted as modulation of electronic energy state caused by conformational change of the main chain. Index Terms--Conducting polymers, poly(3-alkylthiophene), time-of-flight method, solid-liquid phase transition, sign inversion of photocarriers.

An investigation has been undertaken into the thermal instability of electroactive, cellular polypropylene, in particular concentrating on the interaction between mechanical and electrical properties. A range of mechanical and electrical techniques have been applied including, dynamic mechanical analysis (DMA), thermo mechanical analysis (TMA), thermally stimulated currents (TSC) and admittance spectroscopy. Evidence is presented which indicates that the initial stages of a TSC spectrum is dominated by thickness changes in the foam. Changes in mechanical dimensions correlate well with temperature-induced changes in resonator parameters. Index Terms--Piezoelectricity, electrets, electroactive polymers, cellular polypropylene.

Thermodynamics, that describes the redox switching of electroactive polymers is examined. During the redox switching of these polymers, the following phenomena occurs, conformatinal changes, income/outcome of solvent molecules with the subsequent changes in the state of swelling and others.

The electroactivity of electrogenerated polypyrrole films is degraded by applying consecutive anodic potential pulses. The charge consumed during each degradation step is calculated by the difference between the degradation ad the control chronoamperograms.

Sound isolation has been achieved using a piezoelectric polymer film connected to a negative capacitance feedback circuit. A curved PVDF film was located in the middle of an acoustic tube and the transmission loss of sound through the film was determined in the audio frequency range. At any chosen frequency, the complete isolation of sound was achieved by adjusting the feedback, i.e. the complex capacitance of the circuit was matched precisely to that of the film. Index Terms--Sound isolation, transmission loss, piezoelectric polymer film, negative capacitance circuit.

Making use of defects modification to P(VDF-TrFE) via either high energy electron irradiation treatment or copolymerizing VDF-TrFE with a small amount of chlorinated monomer to form a random terpolymer, we demonstrate that high electromechanical responses can be realized in P(VDF-TrFE) based polymers. It will be shown that in the stretched and irradiated 68/32 mol% copolymer, a transverse strain of 4.5% and a transverse electromechanical coupling factor [k.sub.31] of 0.65 can be induced under a field of 85 MV/m. In addition, the irradiated copolymer also exhibits a high elastic energy density, ~ 1 J/c[m.sup.3]. For PVDF based terpolymers such as P(VDF-TrFE-CFE) terpolymer (CFE: chiorofluoroethylene), an electrostrictive strain of more than 7% can be obtained. To elucidate the microstructure changes due to the defects modification in P(VDF-TrFE) based polymers, synchrotron X-ray measurement was carried out on the irradiated copolymers and the results show that, the irradiation converts the polar-phase into a non-polar phase. In addition, X-ray date show that the polar-phase can be induced, at the expense of the non-polar phase, by external fields, confirming that the field induced conformation change is responsible for the observed high electromechanical responses. Although the modified PVDF based polymer exhibits the highest room temperature dielectric constant (60 versus below 10), it is still far below those in the inorganic materials. Experimental results show that by using delocalized electrons in conjugated bonds an all-organic composite with a dielectric constant more than 400 can be achieved. As a result, a strain of near 2% with an elastic energy density higher than 0.1 J/c[m.sup.3] can be induced under a low applied field of 13 V/[micro]m. The strain is proportional to the applied field and the composite has an elastic modulus near 1 GPa. Index Terms--Electroactive polymers, relaxor-ferroelectric polymers, high dielectric constant polymers, electrostriction, field effect actuators.

The wrinkled electrode was prepared through in situ deposition of polypyrrole onto the polyurethane elastomer film that was being uniaxially drawn. The bending actuation of the polyurethane film with the wrinkled electrode was improved more than twice that as compared with an unwrinkled one.

Electropolymerized films of the functionalized pyrrole, pentafluorophenyl-3-(pyrrol-1-yl)propionate (PFP), were reacted with a solution-phase nucleophile, ferrocene ethylamine. This reaction was chosen as a model representative of a postdeposition modification of the polymer membrane's properties. For the first time, a nondestructive method for direct chemical analysis of the reaction profile within the electrodeposited polymer membrane after nucleophilic substitution is presented. This was achieved through the application of in situ neutron reflectivity with supplementary analytical information concerning the film's chemical composition obtained from XPS, FT-IR, and electrochemical measurements. The results presented illustrate how, for a partially reacted film resulting from a short reaction time, the extent of reaction with ferrocene ethylamine is not homogeneous throughout the thickness of the film, but occurs predominantly at the polymer/solution interface. We show that the progress of the reaction within the polymer film is limited by the transport of reacting species in the dense regions of the membrane that are furthest from the solution interface. The data do not fit an alternative model in which there is spatially homogeneous progression of the reaction front throughout the bulk of the thin film polymer. Guided by the neutron reflectivity measurements, suitable modifications were made to the electrodeposition method to prepare films whose architecture resulted in faster rates of reaction.

A Monte Carlo method for analysing the spectral photon emission and extraction efficient of organic light-emitting devices on plastic flexible substrates is described.

This article reviews the research efforts toward the synthesis of polyacetylene from polyene and its impact on the subsequent discovery of conducting polymers and chemical doping. Research describes synthesis of polyethylene thin films by polymerization, its structural and conductivity aspects.

The 'synthetic metal' is an intrinsically conducting polymer exhibiting electrical, electronic, magnetic, and optical properties of a metal and metallic properties of an organic polymer. Research shows that conductivity of the synthetic metals can be increased by doping with a mixture of non-conductive polymers.

This article dwells on the discovery and development of conducting polymers termed the fourth generation of polymers, which include semiconducting and metallic polymers. Research shows that conducting polymers exhibit electrical and optical properties of metals or semiconductors coupled with the mechanical properties of polymers.

Research describing interpenetrating polymer network composites is presented. In particular the results of conductivity measurements showing multiple hopping conduction mechanisms are discussed.

Research is presented describing the development of an array based on a 16 x 16 PVDF ceramic integrated sensor.

A new study investigates the transport properties of polypyrrole-ferric oxide conducting nanocomposites.

Research was conducted to examine the modification of photoluminescent and electroluminescent properties caused by photoirradiation in air of a poly(p-phenylene vinylene) derivative, poly(2-methoxy-5-dodecyloxy-p-phenylene vinylene), and their use in the patterning of the emission from polymer light-emitting device. Results are discussed based on the photoinduced defect creation and scission of main chain due to photo-oxidation.

A new, parameter-free hybrid computational protocol to furnish improved estimates of magnetic properties was used to analyze the structure and spectroscopic properties of tetrathiapentalene and its radical cation. Through a detailed comparison with the well known tetrathiafulvalene molecule, the investigation aimed to understand if tetrathiapentalene could become a new powerful molecular brick in the field of organic metals. Experimental methods and results are discussed.

Research was conducted to examine the crystal structure of the unsubstituted five-ring oligomer, p-bis(p-styrylstyryl)benzene or C38H30, designated (PPV). The similarity between the crystal structure of P5V4 found in the experiment and the generally accepted structural model for PPV makes it very desirable to analyze the optoelectronic characteristics of P5V4 in more detail. The approach will provide a better understanding of the transfer mechanisms for optical and charged excitations in semiconducting organic materials.

A study reports a detailed investigation of the mechanisms contributing to pyroelectricity in the semicrystalline polymer poly(vinylidene fluoride). The study also describes multistep poling procedures which allow for a separate investigation of the contributions to the pyroelectricity from the frozen-in dipole polarization in the amorphous phase, from charges at the amorphous-crystalline interface and from the ferroelectric crystallites.

The ligand 4'-(3,4-dihydroxyphenyl)-2,2':6',2''-terpyridine (L2) is examined to enable a description of the spectroscopic and electrochemical characteristics of its transition-metal complexes to be formed. Results show that for the complexes [M(L(super 2))(sub 2)](super 2+) where (M = Co, Cr, Fe, Ru, Os or Ni), deposits from acetonitrile solution occur at Pt and Gc electrodes at potentials negative of the catechol oxidation peak.

The substituent effects on energy gaps and energy levels in conducting polymers were investigated using density functional theory and NBO analysis. To this end, CH(sub 3-), OH-, NH(sub 2-), CN- and CCH-substituted bithiophenes were analyzed in terms of total charges and pi-electron densities. Experimental results showed that substituents in 3- and 4-positions cause a parallel shift in HOMO and LUMO levels and have no significant effect on HOMO-LUMO gaps.

The conductive quality of the aromatic amine polyaniline (PANI) has potential electronics applications. The stability and electrochemical attributes of PANI make them good materials for organic lightweight batteries and microelectronics. Thus, experiments were conducted to analyze the enzymatic and chemical polymerization of aniline. Aniline samples were analyzed in the presence of the polyelectrolyte template sulfonated polyestrene (SPS). The experiments yielded a a water-soluble, electroactive and conducting PANI/SPS complex.

A study was conducted to analyze the optical characteristics of poly(disilanyleneoligothienylene) and their doping properties. Thin films on polymers were prepared on quartz plates and In-Sn-oxide-coated glass plates supporting a sheet resistance of 10 ohms. Experimental results indicated that photoluminescence was quneched upon C60 doping. Findings also showed that the Stokes shift depended on the number of thienylene rings.

A study was conducted to analyze the enhanced electrical features of rigid-rod polymer supporting electroactive triarylamino moieties. Various triarylamino fractions were used to synthesize copolymers and homopolymers. Experimental results indicated that changes in film color increased optical absorbance. Findings also showed temporal stabilities for the conductivity. In addition, there was no new electronic state produced by iodine doping.

The spatial distributions of individual polymers in multicomponent modified electrodes are determined using neutron reflectivity. A probe of the buried polymer/polymer interfaces reveals that both bilayers has electropolymerized poly(2,2'-bithiopene) as an inner, mediating layer. The outer layer is comprised of either electropolymerized polypyrrole or electroprecipitated polyxylylviologen. Neutron reflectivity data demonstrate that the very different current-potential behaviors of these devices is a consequence of the fabrication method and the consequent polymer/polymer interfacial structure. A composite structure is observed for the polybithiophene/polypyrrole film, while polybithiophene/polyxylylviologen forms a film consisting of segregated polymer layers.

The electrochemically stimulated conformational relaxation treatment has been proven to be valid for describing theoretically anodic coulovoltametric responses of conducting polymers. Congruent experimental and theoretical curves were obtained from experimental variables representing departure potential, sweep rate, temperature and electrolyte concentration. The oxidation of a compacted polypyrrole film under conformational relaxation control and diffusional full completion does not erase a deep structural memory and promotes the appearance of a hysteresis cycle.

Picosecond and femtosecond dynamic studies of photogenerated ion pairs in the photoconducting polymer poly-N-epoxypropylcarbazole (PEPCz) were performed. The experiments were conducted to measure the polarized transient absorption spectra and kinetics of films and solutions of PEPCz. Strong absorption bands estimated at 4.8,4.2 and 3.6 eV were observed. The speedy formation of a carbazolyl cation radical and electron acceptor anion was attributed to the photoexcitation of a weak electron donor-acceptor complex. Moreover, a limited hole transfer was observed after photoexcitation.

Ultrathin films were formed by self-assembling trioctylphosphine oxide, capped n-type 20-40 angstrom diameter CdSe nanoparticles and 1,6-hexadecanethiol onto p-doped semiconducting polymers, poly(3-methylthiophene) and poly(pyrrole). The semiconducting polymers have been layered onto derivatized conducting substrates. The ultrathin films were characterized by absorption and emission spectroscopy, transmission electron microscopy, scanning force microscopy, X-ray photoelectron spectroscopy, and by electrochemical measurements.

XPS provides answers to two significant issues that arise in studying electroactive polymers. First, what fraction of possible charge centers participates in the redox process? Second, what are the relative partition coefficients of two counterions that compete as charge-compensating counterions? To answer both these questions, we emersed (or immersed) poly(vinylferrocene) films from (or into) supporting electrolytes while maintaining potential control to govern the electrochemical history of the electroactive film. We found that all ferrocene units in the surface of a poly(vinylferrocene) film deposited on gold can be oxidized when the counterion is perchlorate, tetrafluoroborate, hexafluorophosphate, tosylate, or 1,5-naphthalenedisuffonate. In answering the second question, no internal standard was needed: the concentration ratios of the two competing ions in both water and polymer phases were used as the experimental variables. For the completely oxidized ferricinium film, we found that the partition coefficient of perchlorate ions is 67% of that of fluoroborate ions.

The doping of polyaniline emeraldine base films by sulfonated fullerene and dendrimers with multiple -(O)SO3H groups is investigated. The doping of sulfonated dendrimers yields conductivities of up to ca. 10 S/cm. Materials doped with hydrogenated fullerenol exhibited metallic characteristics with room temperature conductivities of up to 100 S/cm, which is about six order of magnitude higher than the that for conducting polymers doped with fullerene.

Ab initio computations are presented for various electronic and structural properties of doped polypyrroles, simulated as three-dimensional periodic arrangements of infinite chains with one chlorine (Cl) atom or molecule added per unit cell. Technical features of the method used for the calculations are given. Results indicate that the oxidation efficiency of the Cl2 molecule is generally less than that of separate chlorine atoms at the same concentration. Furthermore, the concentration of the doping agent is inversely proportional to localization effects.

The electric conductivity and Seebeck coefficient in air-stable conducting polymers polypyrrole and polyaniline were measured at various doping levels. Results indicate a general correlation that the electrical conductivity logarithm varies linearly with the Seebeck doping coefficient. The unexpected correlation was found reduce thermoelectric efficiency and is not advisable for thermoelectric applications.

Although in principle semiconductor-metal (Schottky) diodes should be tunable by changing the work function of the metal, such flexibility cannot be achieved in a single device and in practice is often limited by interfacial states that cause Fermi-level pinning. A tunable diode is reported based on a hybrid inorganic-organic, n-indium phosphide|poly(pyrrole)|nonaqueous electrolyte architecture. By electrochemically manipulating the work function of the conjugated polymer poly(pyrrole), the turn-on voltage (more precisely, the forward bias potential required to pass a particular current) of the diode can be continuously and actively tuned by more than 0.6 volt. The work highlights a distinguishing feature of conjugated polymers relative to more traditional semiconductor materials, namely, the ability of dopant ions to permeate conjugated polymers, thereby enabling electrochemical manipulation., The current-voltage (I-V) characteristics of an inorganic semiconductor (IS)|metal Schottky diode are largely determined by the potential barrier height [Φ.sub.b] at the interface. Small barrier heights yield ohmic contacts, and [...]

Samples of polypyrrole, poly(N-methyl pyrrole-pyrrole), and poly(N-methyl pyrrole) with varying BF4 concentrations are subjected to tests to determine the relationship between the dielectric constant, electron spin resonance and dc conductivity of the said materials. Results indicate that the Mott's variable range hopping model is applicable in the said study as seen from parameters such as the average hopping distance and the average hopping energy.

This paper describes a computer-aided design study for a large (5000 kg/hr) single-screw melt extruder processing 0.2 MFI LDPE using a quasi 2D steady-state non-Newtonian flow and heat transfer model that takes into account screw conduction. The effect of different screw materials has also been investigated.

Scanning probe microscopy research on electrical microcontacts in the nanometer range shows that a TiB2 microcontact can sustain a maximum voltage of approximately 0.1-1 volts before melting. The contact reacts to atomic force microscope current and its own current-voltage characteristics. Current-voltage characteristics and voltage at constant current characteristics were measured as a function of the contact position.

The effect of oxygen on the potential of electrodes coated with a thin layer of various conducting polymers and immersed in aqueous neutral buffer solution has been studied. A theoretical equation describing the dependence of the potential on the concentration of oxygen has been derived and shown to be in conformity with the experimental results for polyaniline, polypyrrole, and poly-(3-methylthiophene). The theory is based on the formation of charge-transfer complexes between oxygen molecule and the reduced (undoped) form of conducting polymer.

Molecular research shows that oxygen and the conjugated polymer poly(3-alkylthiophenes) bond together as a weak charge transfer complex which shows maximum absorption in the spectrum's visible area. Ionization potential and physical structure has a direct influence over charge transfer and extent of equilibrium constant. Further research is required to ascertain whether charge transfer is positively influenced by a polymer with lower ionization potential.

A new family of conducting polymers was developed by modifying first- to fifth-generation poly(amidoamine) dendrimers with cationically substituted naphthalene diimides. The dendrimers, which were reduced with sodium dithionite in water or formamide into thin films, demonstrated humidity-dependent electronic and isotropic conductivity of as high as 18 S/cm. at 90% relative humidity.

The thermal diffusivity of conducting polypyrrole films were measured utilizing the photoacoustic method in an open photoacoustic cell configuration. The samples were produced by electrochemical deposition from solutions of pyrrole dissolved in 0.08 M p-toluene sulfonic acid and their thicknesses varied from 50 to 125 microns. The thermal diffusivity was observed to be very much affected by the synthesis conditions.

Gain narrowing in optically pumped thin films, both neat and undiluted, of luminescent conjugated polymers with different molecular structures was demonstrated. These results indicate that the polymers studied have large cross sections for stimulated emission, that population inversion can be achieved at low pump energies, and that the emitted photons travel distances greater than the gain length within the gain medium. The use of simple waveguide structures is sufficient to cause low gain narrowing thresholds in submicrometer-thick films., Many conjugated polymers are luminescent materials with emission that is shifted sufficiently far from the absorption edge that self-absorption is minimal. Because of the large joint density of states associated [...]