Conductivity of some semiconducting polyazophenylenes

The electrical conductivity of a series of semiconducting polyazophenylenes was studied as a function of temperature and molecular weight in the temperature range 293–493°K and for molecular weights between 9500 and 62800. The compounds studied included poly-2,4-diminotoluene and poly-2,5-diaminotoluene. The temperature dependence of conductivity obeys the exponential law σ = σ₀ exp {–E_a/kT}. All of the compounds studied show a break in the conductivity curve at a temperature of about 380°K with the slope of the curve greater at temperatures above 380°K. The activation energies E_a determined from the higher slopes are in the range 0.63–0.89 eV, and the corresponding σ₀ values are in the range 10^?4-10° (ohm-cm)^?1. Both E_a and σ₀ show a tendency to increase with increasing molecular weight such that the compensation law was valid. Activation energies and σ₀ values determined from the (smaller) slope below the temperature of the break point showed a tendency to decrease with successive measurements on new samples. This indicates some kind of orientation effect, and conclusions concerning the properties of the material on basis of results below the break point are therefore difficult.     

Dielectric properties of some photo crosslinking acrylate ester copolymers

Photo crosslinking due to the photo polymerization of unsaturated acrylic side-groups attached to copolymers of glycidyl methacrylate and methyl methacrylate (GMA-MMA) by reaction with acrylic acid in the presence of benzoin methyl ether as photolabile initiator has been investigated. The composition of these copolymers based on (GMA-MMA, 30:70) were determined by [¹H] NMR spectroscopy. The reactivity ratios for the GMA-MMA system were determined using the Kelen-Tüdös method.

The dielectric properties of copolymers based on GMA-MMA acrylate ester (30:70) and homopolymers of MMA in combination with different polyfunctional acrylate ester monomers before and after exposure to UV irradiation have been studied in a solid state matrix, over a frequency range of 100 Hz to 50 kHz and at temperatures in the range 20–70°C.     

Dielectric and rheo-optical properties of some ethylene-carbon monoxide copolymers

Studies were made on films of copolymers of ethylene with 0.5 and 1.0 mole-% carbon monoxide. The carbon monoxide appeared negligibly to affect the degree of crystallinity, melting point, morphology, and dynamic mechanical spectra. Infrared dichroism showed that the orientation of the carbonyl groups was comparable with that of the crystalline CH₂ groups and indicated that the carbonyl groups are at least partially within the crystals. This is confirmed by x-ray measurements which indicate an expansion of the a-axis spacing and by an appreciable increase in the height of the α dielectric loss peak which has been assigned to crystalline motion. This α loss peak moves to a lower temperature with increasing carbonyl content, while the γ dielectric loss peak moves to higher temperatures. Activation energies of 25, 35, and 15 kcal/mole for the α, β, and γ peaks, respectively, were independent of carbonyl content and comparable with values for oxidized polyethylene.     

Dielectric properties of some nematic liquid crystals for dynamic scattering displays

The dielectric constants of three room-temperature nematic mixtures suited for dynamic scattering displays are reported. The asymmetrically substituted azoxybenzenes involved exist as two isomers. One isomer has a positive dielectric anisotropy (Δ =

- ?_⊥ > 0), the other a negative one.     

Relaxation properties of some segmented polyurethane-CaCO3 composites. A Dielectric study

Dielectric relaxation in three segmented polyurethane-CaCO₃ composites was investigated between ?70°C and +150°C in the 300 Hz to 100 kHz frequency range. Two of the polymers contained a polyacetal-polyether soft segment, whereas the soft component of the third polymer was polypropylene oxide. The hard segments consisted of 4,4′-diphenyl methane diisocyanate in two cases and toluene-2,4-diisocyanate in the third case. In parallel studies two calorimetric relaxations, designated α and α′, were observed for each sample and were determined to be glass transitions of the soft and hard segments, respectively. In general, the transition temperatures decrease with increasing filler content. High frequency, low temperature permittivities increase while low frequency, high temperature AC conductivities generally decrease with increasing filler content. The shift in the transition temperatures can be explained using the adsorption theory of filler-polymer interactions and the densities of the samples. The interfacial polarization mechanism becomes important only above the α′ transition temperature and below 1 kHz.     

Synthesis and properties of semiconducting aromatic polyquinonediimines

A new class of poly-conjugated polymers has been obtained by condensation of anthraquinones with aromatic diamines in polyphosphoric acid. The polymers are black, intractable powders. Toward obtaining tractable materials, the effect of monomer structure on polymer tractability has been studied. Copolymerizations were also carried out to “soften” these materials. Electrical conductivities in the semiconducting range, 10^?4- 10^?8 (ohm cm)^?1 were observed. Doping with iodine showed small increases.     

Magnetic properties of lanthanide chalcogenide semiconducting nanoparticles

To understand the importance of the band gap to the magnetic ordering in magnetic semiconductors, we have studied the effect of particle size on the ferromagnetic Curie temperature in semiconducting EuS. We have synthesized capped approximately 20 nm EuS nanoparticles using a single-source precursor, [Eu(S(2)CN(i)()Bu(2))(3)Phen] decomposed in trioctylphosphine. The nanoparticles have been characterized by X-ray powder diffraction, TEM, and magnetic susceptibility measurements as a function of temperature and field. The Curie temperature, based on Arrott plots, is depressed by 1-2 K from the bulk value.     

Dielectric behaviors of some polyvinyl esters

Summary The effects of the bulky side groups on the dielectric high and low temperature absorptions are discussed with respect to the shapes, the magnitudes and the apparent activation energies of the absorptions. To this purpose, the properties of the dielectric absorptions of polyvinyl acetate and polyvinyl benzoate are compared in detail.The asymmetrical shapes of the absorption curves of these polymers can be explained by the characteristic natures of the absorptions in the amorphous linear high polymers, that is, by the fact that the dipoles are combined with each other by the chains in the amorphous solid state. The agreement between the theoretical and the observed curves seems to be satisfactory. The effects of the bulky side groups on the shapes of the absorptions are remarkable in the high frequency side of the absorption curve.The magnitudes of the absorptions of PVAc are larger than those of PVBz, which can be explained by taking account of the difference of the dipole concentrations between these polymers.The attachment of the bulky side groups makes the values of the activation energies increase. The difference of the chemical structures seems to affect more sensitively to the high temperature absorption.

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Zusammenfassung Die Effekte voluminöser Seitengruppen zu den Hoch- und Tieftemperaturabsorptionsmaxima werden hinsichtlich ihrer Form, ihrer Größe und der scheinbaren Aktivierungsenergien diskutiert. Dies geschieht durch einen Vergleich der dielektrischen Eigenschaften von Polyvinylacetat und Polyvinylbenzoat.Die asymmetrische Gestalt der Absorptionsgruppen dieser Polymeren kann durch die charakteristische Art der Absorption für amorphe lineare Hochpolymere erklärt werden, nämlich damit, daß die Dipole durch die Hauptketten im amorphen festen Zustand miteinander verkoppelt sind. Die übereinstimmung zwischen theoretischen und beobachteten Kurven erscheint befriedigend. Die Effekte der großen Seitengruppen auf die Form der Absorption ist auf der Hochfrequenzseite der Absorptionskurve beträchtlich.Die Größen der Absorption für Polyvinylacetat sind stärker als die für Polyvinylbenzoat, erklärbar aus dem Unterschied der Dipolkonzentrationen in beiden Polymeren.Die Festlegung der voluminösen Seitengruppen läßt die Aktivierungsenergie-Werte ansteigen. Unterschiede in den chemischen Strukturen scheinen die Hochtemperaturabsorption empfindlicher zu beeinflussen.

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Department of Applied Chemistry.

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Department of Electronics.

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We express our sincere thanks to Profs.M. Takayanagi andF. Irie of Kyusyu University for their kind supportto this work. We are also indebted to Mr.O. Amano for his experimental works.     

Dielectric properties of emulsions

Summary Dielectric constants of O/W emulsions were measured over a wide range of concentration and at frequencies ranging from 20 cps. to 3 mc. No dielectric dispersion due to the interfacial polarization was observed in the experimental range of frequency, while the electrode polarization was observed below 100 kc. Experimental results were compared with theoretical values for spherical dispersions. It was concluded that the dielectric constants of O/W emulsions were expressed best byBruggeman's equation over the whole range of concentration.

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Zusammenfassung Die DK von ?l/Wasser-Emulsionen wurden über einen weiten Konzentrationsbereich und für Frequenzen zwischen 20 Hz und 3 MHz gemessen. Es war keine dielektrische Dispersion verursacht durch Oberfl?chenpolarisation innerhalb des experimentellen Frequenzbereiches zu beobachten. Dagegen wurde unterhalb 100 kHz Elektrodenpolarisation bemerkbar. Die experimentellen Ergebnisse wurden mit den theoretischen Darstellungen der Misch-DK für Dispersionen mit kugligen Teilchen verglichen. Der Verlauf der DK der ?l/Wasser-Emulsion wird am besten und über den ganzen Konzentrationsbereich durch die Gleichung vonBruggeman dargestellt.

     

Dielectric relaxation in some polyacrylate solutions

The dielectric constant ?′ and loss factor ?″ of poly(butyl acrylate), poly(butyl methacrylate), and poly(isobutyl methacrylate) solutions are reported in the frequency region of 1 kHz to 24.42 GHz at four different temperatures of 27, 40, 50, and 60°C. Cole–Cole plots are plotted to obtain the distribution parameter and relaxation time. The activation energies are evaluated assuming dielectric relaxation to be a rate process in these solutions. A possible relaxation mechanism is discussed.     

Dielectric behavior of some aromatic polyimide films

Aromatic polyimides were prepared by polycondensation reaction of two aromatic diamines, such as 4,4′-diaminodiphenylmethane (DDM) and 3,3′-dimethyl-4,4′-diaminodiphenylmethane (MDDM), with aromatic dianhydrides, such as 4,4′-isopropylidene-diphenoxy-bis(phthalic anhydride) (6HDA), benzophenonetetracarboxylic dianhydride (BTDA) and hexafluoroisopropylidene-bis (phthalic anhydride) (6FDA). These polymers are soluble in polar aprotic solvents and can be cast into thin films from such solutions. The polyimides show high thermal stability, with decomposition temperature being above 430 °C in air, and high glass transition temperature being in the range of 200–287 °C. The free standing films, having the thickness of tens of micrometers, exhibited good mechanical and electrical insulating properties. The dielectric constant, molecular mobility and AC conductivity of thin films prepared from these polymers were investigated in detailed. The study of their dielectric behavior evidenced low dielectric constant values, in the range of 2.88–3.48 at 1 Hz at room temperature, and three relaxation processes (γ,β₁ and β₂) were observed at sub-glass temperatures for polyimides based on 6HDA and 6FDA and only two (γ and β) relaxations were detected for polyimides based on BTDA. The cooperativity of the molecular motions associated with the relaxation processes was discussed.     

Synthesis and optoelectronic properties of novel benzodifuran semiconducting polymers

Two new semiconducting polymers poly{4,8‐bis(4‐decylphenylethynyl)benzo[1,2‐b:4,5‐b′]difuran} ( P1 ) and poly {4,8‐bis(4‐decylphenylethynyl)benzo[1,2‐b:4,5‐b′]difuran‐alt‐4,8‐bis(4‐decylphenylethynyl)benzo[1,2‐b:4,5‐b′]dithiophene} ( P2 ) have been synthesized. These polymers were tested in bulk heterojunction solar cells yielding power conversion efficiencies of 1.19% for P1 and 0.79% for P2 . The surface morphology of the solar cell devices indicated that both the polymers display a granular morphology with smoother films displaying higher power conversion efficiencies. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Dielectric properties of moist cellulose

The dielectric constant ?′ and the dielectric loss ?″ for cellulose fiber were measured over a frequency band 0.2 to 10 Mc/sec and a temperature range from ?20 to 80°C. Also, the variation of the dielectric behavior with relative humidity was measured at 25°C. From these data, both the specific resistivity R_s and the dissociation energy U₀ were calculated. The results showed that the dielectric constant increased with frequency and temperature. This may be due to the increase in the rotation and the polarization of the flexible part in the fiber. The variation of the dielectric loss with temperature showed a maximum absorption corresponding to the β-relaxation. For the moist fiber, it is found that as the relative humidity increases, the dielectric constant and the dielectric loss increase. This increase may be due to the presence of polar water molecules, to the freeing of the polar groups, and to the freeing of the ions in the fiber molecule as well as to the increase in the number of OH^? and H⁺ ions resulting from the ionization of water. A relation between the dielectric constant and resistivity at different humidities is represented graphically. From this relation, it is found that the dissociation energy is equal to 0.318 × 10^?12 and 5.46 × 10^?12 erg below and above 52% RH, respectively.     

Electrical transport properties of semiconducting lithium molybdate glass nanocomposites

We have reported the formation of lithium molybdate glass nanocomposites embedded with lithium molybdate nanophases from the x-ray diffraction and transmission electron microscopic studies. We have investigated the dc electrical conductivity in a wide temperature range for these glass nanocomposites, which exhibit semiconducting behavior. We have analyzed the dc electrical data in the light of polaronic conduction models of Mott and Schnakenberg. We have also studied ac electrical conductivity of these glass nanocomposites in wide temperature and frequency ranges. The experimental ac results have been analyzed with reference to various theoretical models based on quantum-mechanical tunneling and hopping over the barrier. We have observed that the temperature dependence of the dc conductivity is consistent with the polaronic hopping models, while the temperature and frequency dependence of the ac conductivity is consistent with the polaronic tunneling models.