Electrical conductivity of liquid and film polymer composites filled with anion-radical salts in the presence of crown ethers

In the example of alkali metal tetracyanoquinodimethanides (M⁺TCQDM), a study has been made of the influence of resonance charge exchange on the conductivity () of polymer composites filled with anion-radical salts. When neutral molecules TCQDM⁰ are introduced into such systems, this leads to an increase in as a result of the lower activation energy of jumps between states TCQDM and TCQDM⁰. The addition of molecules of crown ethers has an analogous effect: They favor the appearance in the polymer matrix (the same as in solution) of TCQDM molecules in different charge states (TCQDM⁰, TCQDM) with migration of the cation within the limits of ternary associates (CE...M⁺...A) that are formed in systems for which the ratio of the crown ether cavity diameter to the cation diameter 1.4. Symbaticity has been found in the dependences of the electrical conductivity of films and the limiting mobility of solutions with the same composition on the parameter .Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 4, pp. 446–452, July–August, 1989.     

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.     

Conducting and insulating salts of phosphiniminium cations with 7,7,8,8-tetracyano-p-quinodimethane (TCNQ)

A new series of cation-TCNQ salts is described: phosphiniminium cations (1) and (2) form 1:2 salts with TCNQ that are organic conductors (σ_rt 0.05–0.15 S cm⁻¹) whereas cations (3) and (4) form insulating 1:1 salts; variable temperature conductivity, magnetic susceptibility and FTir data are described.     

AC and DC percolative conductivity of single wall carbon nanotube polymer composites

The equations needed to correctly interpret both AC and DC conductivity results of single wall carbon nanotube (SWNT) polymer composites and the scaling of these results onto a single master curve are presented. Brief discussions on the factors that determine the critical volume fraction (?_c) and the percolation exponent (t) are also given. The results for a series of SWNT–polyimide composites are presented and the parameters obtained from fitting these results are discussed. The critical volume fraction for electrical percolation of the present composite was about 0.0005. Results obtained from previous work on SWNT (MWNT)–polymer composites and other percolation systems and the modeling (interpretation) of these results are also discussed and compared. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3273–3287, 2005     

Chemical stability and electroconductivity of 7,7,8,8-tetracyanoquinodimethane salts containing polycation polymers

The chemical and electrical stabilities of 7,7,8,8-tetracyanoquinodimethane (TCNQ) salts composed of neutral TCNQ (TCNQ^?), anion radicals of TCNQ(TCNQ^?·), and polycation polymers were studied by measuring their electronic spectra and resistivities (ρ). The results of spectral and chemical analyses confirmed that TCNQ^?· in TCNQ salts was decomposed to α,α-dicyano-p-toluoylcyanide (DTC^?) as the final product by the intermediate formation of TCNQ^? and p-phenylenediamalononitrile (H₂TCNQ) and that H₂O played an important part in the reaction. From these results it was concluded that TCNQ salts are decomposed by two reaction processes: The resistivity of TCNQ salts increases with the decomposition of TCNQ^?·. Studies on electroconductivity of TCNQ salts assume that the change in resistivity arises from the loss of unpaired electrons which become conduction carriers and also from the disintegration of the TCNQ^? and TCNQ^?· complex which forms the conduction path.     

Near-infrared photosensitive composites with electron conductivity

Polymer composite films were prepared on the basis of poly(vinyl ethylal) doped with a low concentration of an anionic polymethine dye that absorbs light in the near IR region and a higher concentration of 2,4,5,7-tetranitro-9-fluorenone or tetrakis(benzylamino)octahydrofullerene organic acceptor. The photoconductivity of the polymer composite films increases on passing to fullerene derivatives. The main reason for this effect is a decrease in the influence of steric factors on intermolecular electronic transitions in the case of the near-spherical structure of acceptor molecules as compared with the planar structure.     

Multi-walled carbon nanotubes coated by multi-layer silica for improving thermal conductivity of polymer composites

Silica has been non-covalently coated on multi-walled carbon nanotubes (MWCNTs) using the sol–gel chemistry, where tetraethoxy silane (TEOS) was used to form an inorganic silica layer immediately next to surface of MWCNTs and octyl triethoxy silane was coated over the TEOS. Transmission electron microscopy (TEM) measurements show that the diameter of MWCNTs increases with increasing the number of coating layer, indicating that the silica has been coated on MWCNTs. Quantitative analysis from thermogravimetric analysis (TG) also indicates that the inorganic and organic silica has been successfully coated on MWCNTs. Further, quantitative analysis found that the amount of silica measured by TG agrees well with the increase of thickness of coated MWCNTs obtained from TEM, indicating that little or no free silica exists in the system. The thermal conductivity of epoxy/MWCNTs composite was studied and the results show that the thermal conductivity of the composite is improved by coating MWCNTs in this manner and increases with increasing the number of coatings.     

Poly(lactic acid)-based polymer composites with high electric and thermal conductivity and their characterization

Electrically and thermally conductive polymer composites on the basis of biodegradable poly(lactic acid) (PLA) were developed and studied in this work. Pristine single-walled carbon nanotubes (CNTs) and powder of natural graphite (G) were used as fillers in polymer composites. PLA-based composites were prepared by melt-compounding method. The volume resistivity of PLA/CNT composites can be changed by more than ten orders of magnitude compared to that for neat PLA. The thermal conductivity of PLA/G composites can be changed from 0.193 W⋅m⁻¹⋅K⁻¹ (neat PLA) up to 2.73 W⋅m⁻¹⋅K⁻¹. Loading small quantity of CNTs into PLA/G composites increases the thermal conductivity not less than by 40% of magnitude. Besides, all developed PLA-based composites are suitable for processing by injection molding, extrusion or additive manufacturing technology (3D printing).     

Electrolyte conductivity of salts in hexamethylphosphotriamide

Precise conductivity measurements are reported for twenty-two 1:1 salts in hexamethylphosphotriamide at 25°C. The results have been analyzed using the full versions of the equations of Fuoss-Hsia and of Pitts for the conductivity of the free ions. TheK _A andΛ ^∞ values are consistent with strong cation solvation but weak anion solvation by the solvent. Earlier results for salts in related solvents have been reanalyzed for comparative purposes.     

Moisture–absorption,dielectric relaxation,and thermal conductivity studies of polymer composites

In the search for new packaging materials for the electrical/electronics industry, three types of polymer composites have been studied. Silicone/boron nitride powders, polyurethane/alumina powders, and polyurethane/carbon fibers have all been synthesized to study the moisture–absorption kinetics, thermal conductivities, and the dielectric loss spectra under various levels of humidity. The water uptake data indicate that water molecules are absorbed not only by the polymer matrix, but also by the interfaces introduced by the fillers. For all materials, the dielectric relaxation spectroscopy shows the presence of a peak in the 175–200 K range, which is largely due to absorbed water. The silicone/boron nitride samples absorbed the least amount of moisture. Incorporating this result with the thermal conductivity data of the three types of polymer composites, it is concluded that silicone polymers embedded with boron nitride can best serve as the coating for the electronic devices that require heat dissipation and moisture resistance, in addition to electrical insulation. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2259–2265, 1998     

Electric conductivity of TCNQ salts of ionene polymers containing triethylenediammonium or 4,4′-bipyridilium ring

The ionene polymers were prepared by the Menshutkin reaction of α,ω-dibromoalkane (n) with triethylenediamine (TDA) or 4,4′-bipyridil (BP). Resistivities (p) and activation energies of conduction (E_a) were measured for the polymeric 7,7,8,8-tetracyanoquinodimethan (TCNQ) salts with these ionenes. The correlation between the chemical structure of the ionenes and the conductivity was discussed. In the TDA,n-TCNQ complex salts and the BP,n-TCNQ simple salts the salts of the ionenes containing even numbers of CH₂ groups showed higher conductivities than those of the ionenes containing odd numbers of CH₂ groups. The conductivities determined by the narrower interval between the N⁺ cations of the main chains were measured in the simple salts. In the complex salts the conductivities determined by the larger interval were measured. The conformational change of the matrix ionenes affected the arrangement of the TCNQ molecules. The values of p were 79.7 and 12.5 Ω cm, and the values of E_a were 0.122 and 0.063 eV for TDA,4-TCNQ complex salt and BP,5-TCNQ complex salt, respectively.     

Model for thermal conductivity of composites with carbon nanotubes

This paper presents a model for evaluation of effective thermal conductivity for the composites with carbon nanotubes (CNT) having log-normal function of distribution of CNT, with direct effect over depolarization factor. The CNT are considered having cylindrical shape with L/d ratio very high. The model parameters are calculated in function of the data from literature. The influence of volume fraction of reinforced materials, of the aspect ratio of the particles included and of the ratio of the two thermal conductivities is presented.     

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.     

Ion conductivity in ZnO-NaCl composites

High-temperature impedance spectroscopy is used to measure the conductivity of nanocomposites consisting of the NaCl matrix and dispersed ZnO. In the range 500–700°C, a significant increase in the conductivity is found with decreasing ZnO particle size. The results signify that the matrix material interacts with zinc oxide nanoparticles.     

On the mechanism of conductivity of ammonium salts

The conductivities of HSO₄^?-doped (NH₄)₂SO₄ (AS) and NH₄H₂PO₄ (ADP) crystals are investigated in the temperature range 25°?180°C. The mobility of the charge carriers (protons) is thermally activated and is expressed in accordance with the relation μ = 0.16 exp(?0.49) eV/kT and μ = 0.80 exp(?0.54 eV/kT)cm² V^?1 sec^?1 for AS and ADP crystals, respectively. Three-stage mechanism of proton transport in the lattice of ammonium salt is suggested: (1) formation of the charge carrier NH₄⁺ + X^? → NH₃ + HX, (2) reorientation of the protonated anion HX → XH, and (3) proton jump to the neighbor anion XH + X^? → X^? + HX. The activation energy for mobility is close to that for dielectric relaxation process, i.e., the only thermally activated stage in the mobility process is reorientation of the protonated anion. This very stage is also the rate-determining in the mobility as it is seen from the comparison of the correlation time for proton diffusion and the dielectric relaxation time. These experimental results are in good agreement with the known proton dynamic data in KDP-type ferroelectric crystals.     

Thermal conductivity epoxy resin composites filled with boron nitride

Boron nitride (BN) micro particles modified by silane coupling agent, γ‐aminopropyl triethoxy silane (KH550), are employed to prepare BN/epoxy resin (EP) thermal conductivity composites. The thermal conductivity coefficient of the composites with 60% mass fraction of modified BN is 1.052 W/mK, five times higher than that of native EP (0.202 W/mK). The mechanical properties of the composites are optimal with 10 wt% BN. The thermal decomposition temperature, dielectric constant, and dielectric loss increase with the addition of BN. For a given BN loading, the surface modification of BN by KH550 exhibits a positive effect on the thermal conductivity and mechanical properties of the BN/EP composites. Copyright © 2011 John Wiley & Sons, Ltd.     

Lignocellulose - polymer composites

Water hyacinth and its mechanical pulps were used as lignocellulose to produce composites together with polystyrene or urea-formaldehyde resins. The bending strength of the composites increased with increasing concentration of the resin. The temperatures of the treatment of water hyacinth to obtain the pulps affect the strength and densities of the composites. This may be attributed to the behavior of lignin at temperatures higher than 135°C. The composites produced using urea-formaldehyde resins showed slight increase in bending strengths compared with those produced using polystyrene, which may be attributed to the ability of formaldehyde to make crosslinks with the free OH groups of cellulose and hemicellulose. Contrary to water hyacinth, the use of ground palm leaves together with 10% urea-formaldehyde resin produced composite with high density and low bending strength, while the ground water hyacinth failed. The pulp from palm leaves when processed into composites using 10% urea-formaldehyde resin show bending and densities affected by its preparation and by the amount of the composite mixture to be pressed. Hence the type of the substrate defined the type of the polymers or resin used to obtain composites with proper mechanical properties. The effect of the pressure used to produce composites from ground palm leaves or their pulp together with polystyrene was investigated. Linear relationships between the bending strength and pressure were obtained, the bending strength and densities increasing with increasing pressure. Thus, the increased pressures enhance mechanical properties of the composites.     

Electrical conductivity of aqueous polymer solutions

 Theoretical equations were proposed to adequately simulate the electrical conductivity behavior of aqueous solutions of both charged and uncharged polymers. The theory, based on the mixture equation of Boned and Peyrelasse, was experimentally verified on poly(acrylic acid) (PAA) in water and poly(ethylene oxide) (PEO) in aqueous electrolyte solutions. The data analysis suggested that both the polymer coils may be depicted as oblate ellipsoids. Subsequently, the semiaxes values of the polymer coils were determined, and they were in good agreement with the results reported in the literature. Received: 25 June 1996 Accepted: 2 October 1996     

Study the electrical conductivity of crosslinked polyester doped with different metal salts

Three crosslinked polymers were prepared via condensation polymerization between triethanolamine and glycerol [(25:75%), (50:50%) and (0:100%) (G:TEA)] with maleic anhydride which produced polymers I, II and III consequently. All the prepared polymers were doped with metal salts (CuCl₂, NiCl₂ and FeCl₂). D.C. conductivity was measured in the temperature range of (298–373 K), the result showed that the electrical conductivity increased several orders of magnitude with increasing temperature, the activation energy decreased with increasing conductivity. A.C. measurement is used to calculate the dielectric constant for the polymers in both pure and doped state.