Electric conductivity of polymer composites with 7,7,8,8-tetracyanoquinodimethan salts

The electric properties of polymer composites with highly conductive 7,7,8,8-tetracyanoquinodimethan (TCNQ) salts such as quinolinium–TCNQ complex salt (), acridinium–TCNQ complex salt (), and N-methylacridinium–TCNQ complex salt () were studied. Polyacrylonitrile (PAN), poly(N-vinylcarbazole) (PVK), and poly(4-vinylpyridine), (P4VP), etc., were chosen as matrix polymers. The resistivity (ρ) of the was 0.37 Ω cm at the content of 20 wt % in the film. When the content of was increased up to 40 wt%, a phase separation of the needle crystals was observed and the ρ value increased. When was dispersed into PAN or PVK, the separation was also observed and the samples showed low conductivity. The uniform films were obtained in the and systems, but the values of ρ were high because of the degradation of the TCNQ salts. Uniform films with the naked eye were obtained in the and systems, and the values of Ω were 0.37, 1.05, and 3.40 Ω cm, respectively. was stable even when dispersed into P4VP. The properties of the composites were influenced by the combination of the TCNQ salts and the polymers. The uniformity and the stability of the composites were necessary to obtain the high conductive composites.     

Electrical conduction in composites of a TCNQ anion-radical salt in a polymer matrix

The conduction behavior of composites of the anion-radical salt NaTCNQ (sodium 7,7,8,8-tetracyanoquinodimethanide) in poly(vinyl chloride) plasticized by polyurethane has been studied. TCNQ salt-polymer composites that have good moldability and flexibility are characterized by molecular or granular dispersion of the TCNQ salt in a polar polymer matrix. The conduction mode changes from one due to molecularly dispersed sites (CMDS) to one due to granularly dispersed sites (CGDS) with increasing NaTCNQ content. In the CMDS region, the predominant conduction is ionic; TCNQ anion-radicals migrate toward the anode under a dc biasing voltage and a high-resistivity layer is formed near the cathode. The fixation of TCNQ salt at sites in the polymer matrix is believed to be important for the stabilization of electronic conduction under a dc electric field. In the CGDS region, the conduction is electronic and the current-voltage characteristics of the composite are nonohmic, which indicates that carrier generation depends on the Poole-Frenkel effect.     

Interactions of nitrosonium salts with crown ethers

Interactions of nitrosonium tetrafluoroborate and hexafluorophosphate with 18-crown-6, 15-crown-5, and 12-crown-4 in dichloromethane, acetonitrile, and nitromethane have been probed by a combination of proton magnetic resonance spectroscopy, infrared spectroscopy, and conductance measurements. The stoichiometrics of the crown ether-nitrosonium salt complexes were one mole of 18-crown-6 per mole of nitrosonium salt and two moles of 12-crown-4 per mole of nitrosonium salt in all solvents. For 15-crown-5, the one-to-one stoichiometry observed in acetonitrile and nitromethane changed to two moles of crown ether per mole of nitrosonium salt in dichloromethane. The nature of these complexes is discussed. Treatment of a solution of equimolar nitrosonium hexafluorophosphate and 18-crown-6 in dichloromethane with water produced hydronium hexafluorophosphate-18-crown-6 complex.     

Electrical properties of carbon black‐filled polymer composites

This work deals with the dielectric properties of conductive composite materials, which consist of thermoplastic polypropylene (PP) matrix filled with carbon black (CB). The CB concentration was systematically varied in a wide range. Our main interest is focused on the investigation of electrical conductivity mechanism and related percolation phenomena in these materials. To study the electrical and dielectric properties of composites we used broadband ac dielectric relaxation spectroscopy (DRS) techniques in a wide temperature range. By measurements of complex dielectric permittivity, ϵ*, the dependence of ac conductivity, σ_ac, and dc conductivity, σ_dc, on the frequency, the temperature and the concentration of the conductive filler was investigated. The behavior of this system is described by means of percolation theory. The percolation threshold, P_C, value was calculated to be 6.2 wt.% CB. Both, dielectric constant and dc conductivity follow power‐law behavior, yielding values for the critical exponents, which are in good agreement with the theoretical ones. Indications for tunneling effect in the charge carriers transport through the composites are presented. The temperature dependence of dc conductivity gives evidence for the presence of positive temperature coefficient (PTC) effect.     

Complexing of polymer-bound crown ethers with sodium salts in aqueous solution

It has been established that polymer-bound crown ethers L₁ and L₂ are effective sorbents for sodium salts in aqueous solution; the manner in which sodium salts are bound by these ligands differs. Complex compounds of immobilized macrocyclic polyether L₁ with sodium salts have been shown to have the properties of reversible anion exchangers.L. V. Pisarzhevskii Institute of Physical Chemistry, Ukrainian Academy of Sciences, 252028 Kiev. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 87–91, January, 1992.     

Electrical conductivity and dielectric constant measurements of liquid crystal-gold nanoparticle composites

The behaviour of the anisotropic electrical conductivity of liquid crystal-gold nanoparticle (LC-GNP) composites consisting of a commercially available room temperature nematic compound doped with alkylthiol-capped GNPs has been investigated. The nematic-isotropic transition of the composite decreases nearly linearly with increasing X, the concentration of GNP (in weight %) at a rate of about 1°C /weight %. The inclusion of GNPs increases the electrical conductivity of the system with the value increasing by more than two orders of magnitude for X = 5%. However, the anisotropy in conductivity, defined as the ratio of the conductivity along (σ_∥) and orthogonal (σ_⊥) to the director shows a much smaller but definite decrease as X increases.     

Perfluoroalkylation of benzo crown ethers with sodium perfluoroalkanesulfinates in the presence of oxidant

Using Ce(SO4)2 or Mn(OAc)3 as oxidant, dibenzo crown ethers such as dibenzo-18-crown-6 (1) and dibenzo-24-crown-8 (5) and benzo-12-crown-4 (7) reacted smoothly with sodium perfluoroalkanesulfinates (2a-2e) to give the corresponding perfluoroalkylated products (3,4,6,7) in good yields with two isomers obtained in the case of dibenzo crown ethers. This provides a facile synthesis of perfluoroalkyl-containing crown ethers.     

The electrical conductivity of polymer blends filled with carbon-black

The electrical conductivity of natural rubber/polyethylene blends filled with carbon-black is much higher than those of the individual components at the same loading level. This effect cannot be explained by a higher affinity of carbon-black for one component of the blend.     

Electric conductivity of polymer films filled with magnetic nanoparticles

The conductivity of polymer composites with magnetic nanoparticles (MNP) containing magnetite and other MNP (Ni, Cu–Ni) in the layers and planar cells with Al electrodes is studied. For soluble polymers (polyvinylpyrrolidone and polyvinyl alcohol) containing 1–10 wt % of magnetite MNP, a substantial effect of MNP on surface conductivity is detected over a wide range (from 10^–10 to 10^–3 Ω^–1). It is shown that the addition of magnetite MNP not only results in a considerable change in cell conductivity, but also leads to its partially irreversible variation (by an order of magnitude or more) via minor modifications of the experimental conditions (temperature, electric field). For high-resistance samples with low probabilities of conducting chain formation, temperature current peaks are observed upon moderate heating (up to 350 K). These peaks are similar to the maxima observed upon polymer electret thermodischarges when the charges are captured by the deep centers associated with separate MNP or MNP aggregates. The type and position of the maxima are determined by the characteristics of the polymer matrix. For polyvinylpyrrolidone composites, the maxima are observed some time after heating (the echo effect). With composites based on solventborne polymers (polyalkanesterimides, soluble polyimide) and Ni, Cu–Ni MNP, no change in film conductivity measured electrophotographically is observed, due to the formation of a dielectric coating formed by polymer macromolecules adsorbed on the MNP surface. An explanation based on the possible formation of magnetic aggregates of magnetite MNP and conducting chains is proposed. Magnetic aggregation IPM is proposed as one way of controlling cell conductivity.     

Fluorescent and photo-optical properties of hydrogen-bonded polymer liquid-crystalline composites based on derivatives of stilbazole and crown ethers

New hydrogen-bonded photochromic stilbazole- and crown-ether-containing polymer LC composites are prepared and characterized. A smectic homopolymer with p-oxybenzoic groups, a nematic homopolymer carrying phenylmethoxy benzoate groups, and a nematic copolymer containing p-oxybenzoic and phenylmethoxy benzoate groups are synthesized and used as polymer matrices for these composites. The phase behavior and photo-optical properties of LC composites of various compositions are studied. A marked difference is observed in the fluorescence spectra for hydrogen-stabilized LC mixtures and model mixtures not forming hydrogen bonds. This effect is explained by the reversible transfer of proton of carboxyl groups involved in hydrogen bonding. It is shown that the complexation of crown-ether-containing groups of LC composites with potassium ions leads to a dramatic reduction in the intensity of fluorescence. This phenomenon may be used for creation of a new generation of sensors for metal ions.     

Effect of complexation on electrical conductivity in system consisting of an anion-radical salt and a crown ether

Various experimental methods have been used in a study of the effect of complexation on the electrical conductivity in systems consisting of an anion-radical salt of an alkali metal, a crown ether (CE), and a polar solvent. The electrical conductivity of solutions of M⁺TCQDM (TCQDM = tetracyanoquinodimethane) in the presence of the CE is determined by the ratio () of the radius of the CE cavity to that of the metal ion. The equilibrium constants of the processes taking place in these systems have been determined. It has been established that the electrical conductivity of the systems is determined by the following: a) electrostatic interaction (with = 0–0.8 and > 2); b) formation of complexes {M⁺...CE (with }- 1); c) formation of ternary associates {A...M⁺...CE (with }- 1.4). In the last case, the symmetry of the environment of the M⁺ ion is increased and the potential barrier to the transition of ions between the equilibrium positions is lowered, which is responsible for the observed increase in mobility of the ions in solution.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 2, pp. 188–196, March–April, 1986.     

Oxidation of organic sulfur compounds with hydrogen peroxide in the presence of crown ethers

Hydrogen peroxide oxidizes methyl phenyl sulfide and benzothiophene in the presence of crown ethers to the corresponding sulfoxides and sulfones. The oxidation is retarded by amino acids. UV and NMR spectroscopies show that, at the initial stage of oxidation, complexation occurs between crown ether, hydrogen peroxide, and sulfide, as well as between crown ether and amino acid.     

碲化镉纳米晶与聚合物复合研究进展

综述了近年来半导体纳米晶CdTe/聚合物复合材料在电致发光器件和复合发光材料方面的研究和应用进展情况,详细介绍了CdTe与水溶性高分子,非水溶性高分子以及生物大分子的复合情况,并展望了其发展前景。     

Structure-electrical properties relationships of polymer composites filled with Fe-powder

Structure-properties relationships of composite materials, consisting of a polymer matrix and metal inclusions, is very important for designing new materials with desirable properties. In the present work the electrical and dielectric properties of several composites, consisting of a polymer matrix and iron (Fe) particles as filler, were investigated. Broadband dielectric relaxation spectroscopy measurements were carried out. The electrical behaviour of the composites is described in terms of the percolation theory. Percolation threshold values were calculated and the values of the dielectric permittivity critical exponent were found in good agreement with the theoretical ones. The influence of using different polymer matrices on the physical properties of the composites was also of particular interest. The results were related to the microstructure of the composites and a schematic model was proposed.     

Photo-optical properties of polymer composites based on stretched porous polyethylene filled with photoactive cholesteric liquid crystal

A new type of polymer-liquid crystal composite with photovariable dichroism and birefringence is described. Porous stretched polyethylene films were used as polymer matrices. To induce a cholesteric phase in a commercial nematic host, a chiral photochromic dopant based on sorbide and cinnamic acid capable of E-Z isomerization under UV irradiation was used. A merocianine-type substance was selected as a dichroic dye. Introduction of a dye-doped cholesteric mixture with a helical pitch higher than ∼300 nm to polymer film led to an almost complete transition from a cholesteric to an oriented nematic phase, as well as to an increase in birefringence and the appearance of dichroism. Decrease of the helical pitch by increasing in the chiral dopant concentration in the liquid crystal-polymer composite results in a reduction of the dichroism values. UV irradiation of polymer composite leading to an isomerization of the chiral dopant and helix untwisting induces a noticeable gradual growth of dichroism and birefringence. These new composites can be considered as promising materials for optical applications.     

取代芳基重氧盐及其冠醚配合物的XPS研究

本文用XOS 研究了十四种芳基重氮盐及其与18-c-6(1)和二苯并-24-c-8(2)的配合物.结果表明, 重氮盐中α-N1s 结合能的化学移大小与R有关. 重氮盐与冠醚以β-N向醚氧提供电子(β-N→O)而配位的, 而醚氧O1s 结合能降低多少似可反映配合物的稳定性.     

Study of substituted aryldiazonium salts and their crown ethers complexes by XPS

The complexes of fourteen substituted aryldiazonium salts RC₆H₄N₂+BF₄^? (R?H, p-CH₃, p-NO₂, p-I, p-Cl, p-F, m-Br, m-Cl. m-CH₃, o-CH₃, o-OCH₃, o-NO₂, o-Br, o-Cl) with crown ethers 18-C-6 (1) and dibenzo-24-c-8 (2) have been studied by XPS. The results show that the chemical shifts of α-N1s and β-N1s of substituted aryldiazonium salts are closely related to the induction and conjugation effects of R groups. It is interesting to note that charge transfer(β-N→O) take place upon complexation of substituted aryldiazonium salts with crown ethers. Therefore the decrease of binding energy of crown ether oxygen may be used as a measurement of the stabilities of these complexes.     

Photochemistry of iminium salts in the presence of N-electron donating alcohols and ethers

Irradiation of 2-phenyl and 2-isobutenyl-1-pyrrolinium salts in solutions of alcohols and ethers containing α-hydrogens leads to production of addition products. In addition, alcohols and ethers having low ionization potentials and α-hydrogens serve as efficient quenchers of fluorescence from 2-phenyl-1-pyrrolinium salts. Deuterium isotope effects on fluorescence quenching rate constants appear to implicate electron transfer mechanisms in photoaddition and quenching pathways.