The increase of conductivity of ethylene/acetylene copolymers by rolling

Rolling of compact nascent PE/PA copolymer powder allows to increase the dc conductivity of rolled films by two order of magnitudes and to receive the oriented films of good quality with dc conductivity about 10⁻²S/cm.     

Conducting polymers containing in-chain metal centers: electropolymerization of oligothienyl-substituted {M(tpy)2} complexes and in situ conductivity studies, M = Os(II), Ru(II)

The electropolymerization of a series of Ru and Os bis-terpyridine complexes that form rodlike polymers with bithienyl, quaterthienyl, or hexathienyl bridges has been studied. Absorption spectroscopy, scanning electron microscopy, and cyclic voltammetry have been used to characterize the monomers and resulting polymer films. The absolute dc conductivity of the quaterthienyl-bridged {Ru(tpy)2} and {Os(tpy)2} polymers is unusually large and independent of the identity of the metal center at 1.6 x 10(-3) S cm(-1). The maximum conductivity occurs at the formal potential of each redox process, which typically is observed for systems where redox conduction is the dominant charge transport mechanism. Significantly, the dc conductivity of the metal-based redox couple observed in these polymers is 2 orders of magnitude higher thanthat of a comparable nonconjugated system.     

The origin of DC electrical conduction and dielectric relaxation in pristine and doped poly(3‐hexylthiophene) films

We present here the evidence for the origin of dc electrical conduction and dielectric relaxation in pristine and doped poly(3‐hexylthiophene) (P3HT) films. P3HT has been synthesized and purified to obtain pristine P3HT polymer films. P3HT films are chemically doped to make conducting P3HT films with different conductivity level. Temperature (77–350 K) dependent dc conductivity (σ_dc) and dielectric constant (ε′(ω)) measurements on pristine and doped P3HT films have been conducted to evaluate dc and ac electrical conduction parameters. The relaxation frequency (f_R) and static dielectric constant (ε₀) have been estimated from dielectric constant measurements. A correlation between dc electrical conduction and dielectric relaxation data indicates that both dc and ac electrical conductions originate from the same hopping process in this system. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1047–1053, 2010     

Electrical conduction of poly(vinyl alcohol) films

PVA films (30–45 μm thickness) were prepared by casting. dc electrical measurements were done over the temperature range 293–353 K. Two different conduction mechanisms are suggested. The first one is ohmic and extends to 303 K. Above this temperature a space-charge-limited conduction mechanism, with protons as charge carriers, predominates. Dependences of the voltage-reversion current temperature and field were investigated and were attributed to a clean-up effect of charge carriers. The variance in the activation energy, calculated from the conductivity curves and from the mobility curves, led to a discussion of the origin of the charge carriers. No change in conductivity was observed for the PVA films irradiated with UV (of wavelength 365 nm) at 303 K, i.e., PVA is a photostable material under these conditions.     

Dielectric properties of sols of silver nanoparticles capped by alkyl carboxylate ligands

Sols of silver nanoparticles in toluene were studied by broadband dielectric spectroscopy (10⁻³–10⁵ Hz). The frequency dependences of the specific alternating current (ac) conductivity and the complex electric modulus were used to estimate the temperature/frequency intervals of long- and short-range charge transfer occurs, respectively. A considerable increase (by more than 30 °C) in the Vogel temperature T ₀ and the glass transition temperature T _g in sols compared with the pure solvent was found. It can be hypothesized that these cooperative effects reflect the initial stage of the superlattice formation. Although the dielectric characteristics of sols are generally controlled by the conductivity relaxation, the dielectric response was observed in the high-frequency range (1–10³ Hz) at low temperatures (from −50 to +10 °C). This response results from the presence of nanoparticles in solution. It is supposed that the relaxation is caused by the motion of ion impurities on the Ag nanoparticle surface within the carboxylate ligands shell. The dielectric properties of films strongly depend on both the characteristics of nanoparticles and the conditions of the film preparation. Like in sols, the direct current (dc) conductivity and the dielectric response of Ag nanoparticles in films are due to ion impurities.     

Anomalies and error limits in electrical-conductivity measurements in plasticized transparent poly(vinyl chloride) films

The anomalous behavior of the electrical conductivity of transparent poly(vinyl chloride) films is experimentally studied at field voltages approaching the breakdown threshold, above the threshold, and far below the threshold. The effects of strong nonlinearity, relaxation drifts, and spontaneous reversible transitions between states with high and low electrical conductivities are revealed for the first time in “thick” (20–100 μm) plasticized transparent poly(vinyl chloride) films. When a certain threshold is exceeded, relaxation oscillations in the test sample are generated and their frequency is proportional to the applied voltage. During a “mild” breakdown, the polymer film passes into the high-conductivity state (the current increases by four or more orders of magnitude), which is identical to the states observed during low-voltage transitions. A simple qualitative model explaining the anomalous character of the electrical conductivity of plasticized poly(vinyl chloride) films is advanced.     

Synthesis and characterization of polyaniline-polyvinyl chloride blends doped with sulfamic acid in aqueous tetrahydrofuran

The temperature dependence of direct current (dc) conductivity was studied for various samples of polyaniline-polyvinylchloride (PANI-PVC) blended films. Polyaniline was doped with different concentrations of sulfamic acid in aqueous tetrahydrofuran (THF) and the blended films were prepared by varying the amount of doped PANI relative to a fixed amount of PVC. The dc conductivity of PANI-PVC blended films was measured to determine the effect of sulfamic acid (dopant) in the temperature range (300–400K). The mechanism of conduction is explained by a two-phase model. In order to evaluate the effect of the dopant, conductivity-derived parameters such as the pre-exponential factor (σ _o) and the activation energy (ΔE) were calculated. The structural changes of polyaniline-PVC blended films were characterized by FTIR spectroscopy that explores information about the suitability of the dopant in the chemical doping process.     

Polymer films prepared from aniline in direct-current discharge

Polymer films as organic semiconductors with an intrinsic conductivity of ～10^?11 Ω^?1cm^?1 were prepared from aniline at the cathode in a dc discharge. The conductivity of the films is increased to ～10^?2 Ω^?1cm^?1 by doping with iodine. The chemical structure of the films corresponds to the leucoemeraldine form of polyaniline and includes macromolecules with a high extent of polyconjugation.     

T−12-law of dc conductivity 1N Langmuir films

Measurements of dc conductivity of Cd-stearate multilayer films below room tenperature down to liquid nitrogen temperature have revealed the temperature dependence σ = σ₀ exp(?AT^{?$\text{1}\text{2}$}). This relation, together with the values of σ₀ and A, confirms the theoretical predictions for hopping conduction in a multilayer system associated with interface states.     

Ultrathin transparent conductive films of polymer-modified multiwalled carbon nanotubes

Deposition of multiwalled carbon nanotubes modified by poly(2-vinylpyridine) (CNT-g-P2VP) from aqueous dispersions at low pH is an effective method to prepare homogeneous ultrathin films with a tunable CNTs density. A percolation threshold of 0.25 mug/cm2 and a critical exponent alpha = 1.24 have been found from dc conductivity measurements. The sheet resistance value agrees with the percolation theory for 2D films. According to AFM and electrical measurements, even when only 5% of the surface is covered by CNT-g-P2VPs, the sheet resistance is of the order of 1 MOmega/sq, which indicates that conductivity is imparted by a network of an ultralow density. When the film transmittance decreases down to approximately 70% at 550 nm, the occupied surface area is approximately 15% and sheet resistance falls down to approximately 90 kOmega/sq. These data show that undesired in-plane clustering does not occur upon the dispersion casting of the films and that high-quality networks of CNT-g-P2VPs are built up. The electrosteric stabilization of the CNT-g-P2VP dispersions in water at low pH is at the origin of this desired behavior. Although the multiwalled CNT films prepared in this work are less conductive and less transparent than the SWNTs films, they could find applications, e.g., in touch screens, reflective displays, EMI shielding, and static charge dissipation.     

Synthesis,characterization, and electrochemical and electrical properties of novel mononuclear and binuclear ball-type Zn(II) and Co(II) phthalocyanines substituted with 1a,8b-dihydronaphtho[b]naphthofuro-[3,2-d]furan-7,10-diyl

New mononuclear phthalocyanines [Zn(II) 4 and Co(II) 6] and ball-type bisphthalocyanines [Zn(II) 5 and Co(II) 7] have been synthesized from the corresponding compound 3, which can be obtained from the reaction of 4-nitrophthalonitrile 1 with 1a,8b-dihydronaphtho[b]naphthofuro[3,2-d]furan-7,10-diol 2. The novel compounds have been characterized by elemental analysis, UV/Vis, IR, ¹H NMR and MASS spectroscopy. The electrochemical measurements show the formation of various mixed-valence oxidized and reduced species, due to intramolecular interactions between the two phthalocyanine units in the ball-type binuclear metallophthalocyanines. Detailed studies of the effect of temperature on the electronic properties of the films were investigated by dc conductivity and impedance spectroscopy techniques at temperatures between 290 K and 460 K. Thermally activated conductivity dependence on temperature was observed from the dc measurements. The ac results give a power law behavior in which the frequency exponent decreases with temperature. It was observed that the impedance spectra consist of a curved line at low temperature. These curved lines transform into a full semicircle with increasing temperature.     

Press‐Printed Conductive Carbon Black Nanoparticle Films for Molecular Detection at the Microscale

Carbon black nanoparticle (CBNP) press‐transferred film‐based transducers for the molecular detection at the microscale level were proposed for the first time. Current‐sensing atomic force microscopy (CS‐AFM) revealed that the CBNP films were effectively press‐transferred, retaining their good conductivity. A significant correlation between the morphology and the resistance was observed. The highest resistance was localized at the top of the press‐transferred film protrusions, whereas low values are usually obtained at the deep crevices or grooves. The amount of press‐transferred CBNPs is the key parameter to obtain films with improved conductivity, which is in good agreement with the electrochemical response. In addition, the conductivity of such optimum films was not only Ohmic; in fact, tunneling/hopping contributions were observed, as assessed by CS‐AFM. The CBNP films acted as exclusive electrochemical transducers as evidenced by using two classes of molecules, that is, neurotransmitters and environmental organic contaminants. These results revealed the potential of these CBNP press‐transferred films for providing new options in microfluidics and other related micro‐ and nanochemistry applications.     

Synthesis, characterization and electrical properties of novel mono- and cofacial bisphthalocyanines bridged with four [1a,8b-dihydronaphtho[b]naphthofuro[3,2-d]furan-7,10-diyl] units

Novel mono phthalocyanines and cofacial bisphthalocyanines were synthesized from 4,4′-(1a,8b-dihydronaphtho[b]naphthofuro-[3,2-d]furan-7,10-diyl)bis(oxy)diphthalonitrile 1. The products were characterized by elemental analysis, UV-vis, IR, ¹H NMR and mass spectroscopy. Both the direct current (dc) and alternating current (ac) electrical properties of the product films were investigated as a function of temperature in the frequency range 40-10⁵ Hz. It was observed that the ac response of the films can be represented by the ω^s law. The temperature dependence of dc conductivity showed typical Arrhenius behavior for all compounds.     

SINGLE-ION CONDUCTIVITY IN POLY (LITHIUM PROPIONATE METHYL SILOXANE)

Poly(lithium propionate methyl siloxane )as a single-ion carrier source was synthesized. The crosslinked film showed lower lithium ionic conductivity at room temperature (about 10~(-10) S/cm). However,the lithium ionic conductivity was obviously increased by blending with high polar polymers such as polyethylene oxide, poly (methylsiloxane - co- ethylene oxide) and poly (methylsiloxane- g- ethylene oxide). In the blend system a high conductivity of 10~(-7)-10~(-5) Scm~(-1) at room temperature was obtained and the single-ion conductivity was deeply influenced by the content of the poly (lithium propionate methyl siioxane). The dc ionic conductivity of the flexible crosslinked films is more stable over time.     

Composite Langmuir–Blodgett (LB) films of polyaniline and cadmium stearate

Composite monolayers of cadmium stearate and polyaniline processed with camphor sulphonic acid have been obtained at the air–water interface and subsequently transferred onto substrates as uniform Langmuir–Blodgett multilayers. Pressure–area (Π-A) isotherm studies indicated that polyaniline molecules are not squeezed out of the cadmium stearate matrix during compression or in the compressed state. Monolayer stability is seen to decrease when the polymer content is increased beyond 60% (in weight) which is probably associated with the formation of microaggregates that also affected the monolayer surface potential at large areas per molecule. With increasing amount of polyaniline in the mixture, a transition from Y-type to Z-type deposition has been observed. Transferred multilayer LB films were characterized by UV-vis, FTIR, XRD, surface potential, and dc electrical conductivity measurements. UV-vis results indicated that though the polyaniline was in the doped state in the spreading solution, the transferred films were in the emeraldine base state. FTIR studies revealed that the transferred films mainly contained cadmium stearate salt in addition to polyaniline. XRD results indicated that the stacking order is dependent on the polyaniline content in the composite films, the order was found to decrease upon increasing the polymer amount. The uniformity of transferred films was confirmed by surface potential studies. A possible packing arrangement in these composite Langmuir and Langmuir–Blodgett films has been proposed.     

Electrical behaviour of butyl acrylate/methyl methacrylate copolymer films irradiated with 1.5 MeV electron beam

Electrical conductivity and dielectric parameters of the (BuA/MMA) copolymer films irradiated with 1.5 MeV electron beam (EB) have been studied. The samples were irradiated with different doses of the electron beam: 5, 10, 50, 125 and 200 kGy. The electrical conductivity of the samples was found to decrease as the irradiation dose increases. The temperature dependence of the direct current (dc) conductivity for unirradiated and irradiated samples has been obtained over a temperature range from 293 to 373 K. The activation energy values were calculated for all samples. Moreover, measurements of the dielectric constant, dielectric loss and alternating current (ac) conductivity were performed at a frequency range from 100 Hz to 5 MHz at room temperature. The results indicated that the EB irradiation has formed some traps in the energy gap, which reduce the movement of the charge carriers. Furthermore, a direct proportional relationship between the activation energy and the irradiation dose was estimated in two regions: below and above the glass transition temperature of the polymer. Dipole relaxation was observed in the samples, and the dose effect was found to shift this relaxation towards higher frequencies.     

The effect of magnetic field on conductive films

Conductive paints consisting of nickel powder (conductive material), solvent, and binder polymer were treated in a magnetic field. The efficiency of magnetic treatments on conductivity of coating films was evaluated. The effect of the following factors on conductivity of composite films by magnetic treatment was studied: metal powder concentration, magnetic flow density, time difference between film preparation and magnetic treatment, drying time of paint films, and effect of distance between terminals. Results showed that the volume resistivity of paint films treated magnetically was lower than that for untreated films at each nickel content. Magnetic treatment provided high conductivity even at low magnetic flow density, and conductivity increased with magnetic flow density.     

聚苯胺薄膜的离子束效应

本文采用离子注入掺杂技术，研究了全氧化态聚苯胺薄膜的离子束效应．‘４０ｋＶＫ＋离子束注入后，聚苯胺薄膜的电导率随着剂量的增加而迅速增加．当剂量为１×１０１７Ｋ＋／ｃｍ２时，电导率增加了８个数量级．ＦＴＩＲ光谱图显示了Ｋ＋离子注入使全氧化态聚苯胺中的醌亚胺结构发生还原反应．温差电流法测量表明，离子注入区呈现ｎ型半导体特性．四探针法测量了离子注入掺杂聚苯胺的电导率与温度的关系．本文还对离子注入掺杂全氧化态聚苯胺的导电机制进行了初步探讨．     

Temperature- and humidity-related degradation of conducting polyaniline films

The time dependence of dc conductivity of conducting polyaniline films was measured in relation to temperature and relative humidity of the environment. Optical and structural properties of the samples were checked using Fourier transform infrared (FTIR) spectroscopy.     

Instabilities across the isotropic conductivity point in a nematic phenyl benzoate under AC driving

We characterize the sequence of bifurcations generated by ac fields in a nematic layer held between unidirectionally rubbed ITO electrodes. The material, which possesses a negative dielectric anisotropy epsilona and an inversion temperature for electrical conductivity anisotropy sigmaa, exhibits a monostable tilted alignment near TIN, the isotropic-nematic point. On cooling, an anchoring transition to the homeotropic configuration occurs close to the underlying smectic phase. The field experiments are performed for (i) negative sigmaa and homeotropic alignment, and (ii) weakly positive sigmaa and nearly homeotropic alignment. Under ac driving, the Freedericksz transition is followed by bifurcation into various patterned states. Among them are the striped states that seem to belong to the dielectric regime and localized hybrid instabilities. Very significantly, the patterned instabilities are not excited by dc fields, indicating their possible gradient flexoelectric origin. The Carr-Helfrich mechanism-based theories that take account of flexoelectric terms can explain the observed electroconvective effects only in part.