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.     

Changes During Storage of Electrically Conductive Blends Polyaniline–Poly(Ethylene‐co‐vinyl Acetate)

Abstract

The electrical conductivity behavior of polyaniline–poly(ethylene‐co‐vinyl acetate) (PANI–EVA) blends was variable and dynamic during their storage. It was shown that the apparent concentration of the intrinsically conductive polymer at which a conductivity jump of the blends occurs (Φ _c ) is not a constant value over time. The electrical conductivity of the films of low PANI content (below 2.5 wt.%) increased by several (ca. 5) orders of magnitude. It was found that the PANI phase undergoes a flocculation process subsequently resulting in the formation of conductive pathways and a continuous network. Besides, the shape of percolation curves was found to change during storage of the films. Decreased conductivity deviations were registered for blends of low PANI content (<2.5 wt.%), indicating that an improvement (or decreasing number of defects) of the conductive pathways took place within the bulk of the insulating EVA matrix. These results and observed phenomena are discussed by means of the interfacial model for electrically conductive polymer blends. They supported the dispersion/flocculation phase transition within similar composite materials. The phase separation and conductivity jump are attributed to the interfacial interactions between the polymeric constituents. It was shown that the microstructure of the blends consists of highly ordered PANI paths embedded in the insulating EVA matrix. Long fibrils of PANI and interconnected fractal‐like networks were observed. It was found that the sizes of the PANI domains also varied during storage of the films. Due to the spontaneous flocculation of the primary PANI particles, conductive pathways are formed at extremely low percolation threshold (Φ _c , loading level ca. 5 × 10^?3 wt. fraction). Thus, an important property of the conductive constituent, namely its solid‐state rearrangement, was proved. This PANI self‐organization is also interpreted according to the interfacial model of polymer composites. On the other hand, the competition between self‐organization of the complex of PANI with dodecylbenzenesulfonic acid and crystallization of EVA matrix has resulted in structural changes and formation of continuous conductive networks within the blends, responsible for their significantly increased conductivity.     

Polyaniline-coated coconut fibers: Structure,properties and their use as conductive additives in matrix of polyurethane derived from castor oil

Electrically conducting fibers based on coconut fibers (CF) and polyaniline (PANI) were prepared through in situ oxidative polymerization of aniline (ANI) in the presence of CF using iron (III) chloride hexahydrate (FeCl_3.6H₂O) or ammonium persulfate (APS) as an oxidant. The PANI-coated coconut fibers (CF-PANI) displayed various morphologies, electrical conductivities and percentages of PANI on the CF surface. For both systems, a PANI conductive layer was present on the CF surface, which was responsible for an electrical conductivity of around 1.5 × 10⁻¹ and 1.9 × 10⁻² S cm⁻¹ for composites prepared with FeCl₃.6H₂O and APS, respectively; values that are similar to that of pure PANI. In order to modify the structure and properties of polyurethane derived from castor oil (PU) both CF-PANI and pure PANI were used as conductive additives. The PU/CF-PANI composites exhibited higher electrical conductivity than pure PU and PU/PANI blends. Additionally, the PU/CF-PANI composites showed a variation in electrical resistivity according to the compressive stress applied, indicating that these materials could be applied for pressure-sensitive applications.     

Electrical properties of LiBBaTe glass doped with Nd2O3

The dc and ac electrical conductivity of barium tellurite borate glass doped with Nd₂O₃ in the composition 50 B₂O₃- (20-X) BaO- 20TeO₂ 10 LiF or Li₂O where x = 0.5, 1, 1.5 and 2 Nd₂O₃ were measured in the temperature range 303–648 K and in the frequency range 0.1–100 kHz. The dc and ac conductivities values increase, whereas the activation energy of conductivities decreases with increasing Nd₂O₃ content in the glasses containing LiF and by the replacement of LiF by Li₂O the conductivity was found to decrease with addition of Nd₂O₃. The electrical conduction has been observed to be due to small polaron hopping at high temperatures. The frequency dependence of the ac conductivity follows the power law σ_AC (ω) = A ω^s. The frequency exponent (s) values (in the range 0.94 and 0.33) decreases with increasing temperature. The dielectric constant and dielectric loss increased with increasing temperature and decreased with increase in frequency for all glasses studied. In LiF glasses, it is observed that, the values of ?^\ and tan δ are observed to increase with the addition of Nd₂O₃ whereas they decrease in the glasses containing Li₂O. The electrical modulus formalism has been used for studying electrical relaxation behavior in studied glasses. It is for first time that the Nd₂O₃ doped barium tellurite borate glasses have been investigated for dc and ac conductivities and dielectric properties over a wide range of frequency and temperature.     

Study of electrical and dielectric properties of styrene-acrylonitrile/graphite sheets composites

This paper reports the structural, electrical, dielectric and mechanical properties of the Styrene-acrylonitrile (SAN)/graphite sheets (GS) composites. The composites were prepared by in situ polymerization. The variation of electrical conductivity, dielectric constant and ac conductivity as a function of volume fraction of GS was found to follow the power law model. The dielectric constant and dissipation factor of SAN/GS composites increased significantly near the percolation. The frequency dependence of dielectric constant, dissipation factor and ac conductivity was also analyzed. Nearly ohmic behavior of current density with electric field was observed above the percolation threshold. The composite was found to possess the hardness of pure polymer at the threshold value of GS.     

A composite of polyaniline with both conducting and ferromagnetic functions

A composite of polyaniline (PANI) with both conducting and ferromagnetic functions was synthesized by a chemical method proposed by the authors. For the electrical properties, its room-temperature conductivity was measured to be about 10⁻¹ S/cm when doped with 1.0M HCl, and it is independent of the preparation conditions, such as reaction temperature and concentration of FeSO₄ solution. Temperature dependence of the conductivity of the composites at temperature between 77 and 450 K is controlled by thermal activation and dedoping processes, which result in the decrease of conductivity with increase of temperature as T > 320 K. For their magnetic properties, unusual ferromagnetic properties with high saturated magnetization (M₂) and lower coercive force (H_c = 0) were observed. An effect of the preparation conditions on the ferromagnetic properties of composites was observed. The higher the reaction temperature and the concentration of FeSO₄ solution, the higher the saturated magnetization was observed. No hysteresis feature (i.e. H_c = 0) for any PANI composites synthesized in this paper was observed, and this is independent of the preparation conditions. This may be attributed to the nanometer size of the magnetic particles existing in composites. Thus, it suggests that the doping of PANI leads to electrical properties of composites, whereas the nanocrystalline magnetic particles (Fe₃O₄) are responsible for the observed ferromagnetic properties of PANI composites. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2129–2136, 1997     

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.     

Conducting polymers VIII: Optical and electrical conductivity of poly(bis-m-phenylenediaminosulphoxide)

Poly(bis-m-phenylenediaminosulphoxide) (PPDS) was prepared from Michael addition of N,N′-bis-sulphinyl-m-phenylenediamine and m-phenylenediamine. The prepared PPDS was then doped with iodine. PPDS was characterized by FTIR, ¹H-NMR, elemental microanalysis, thermogravimetric analysis (TGA), UV-visible absorption and fluorescence emission spectra. Thermal gravimetric analysis TGA showed that PPDS is thermally stable up to 179 °C. Electronic transitions showed main absorption peak at λ = 340 nm and two emission peaks at 460 and 490 nm. The behavior of both dc and ac electrical conductivities of PPDS were studied. The direct current electrical conductivity (σ_dc) and the alternating current electrical conductivity (σ_ac) were enhanced by the physical doping of I₂ in the polymer matrix. The conduction mechanisms for dc and ac electrical conductivities have been investigated.     

Polyanilme-montmorilltonite (PANl-MMT) nanocomposites: Mechanochemical synthesis,structure, thermostability and electrical properties

Polyaniline (PANI)-montmorillonite (MMT) nanocomposites were prepared by direct intercalation of aniline molecules into MMT galleries, followed by in situ mechanochemical polymerization under solvent free conditions. X-rays diffraction, Fourier Transform Infra Red analyses and UV-vis spectroscopy confirmed the successful synthesis of polyaniline chains between the MMT nano-interlayers. On increasing the amount of MMT basal spacing decreased gradually, suggesting less intercalation with decreasing amount of aniline. Scanning electron micrographs demonstrated strong differences between the morphologies of PANI-MMT nanocomposites and those of pure MMT and PANI. DC conductivity was measured in the temperature range from 145 K to 303 K using four probe methods. Temperature dependent DC conductivity of PANI and all the PANI-MMT composites followed 3 dimensional variable range hopping (3D VRH) model. Frequency dependent AC conductivity (σ_AC), dielectric constant (ɛ′) and loss factor (ɛ″) have been measured in the frequency range 10²–10⁶. All these measured quantities; σ_AC, ɛ′ and ɛ″ decreased with the increase in MMT content in the composites at all frequencies. The frequency dependence of σ_AC displayed a low frequency region below 10⁴ Hz with almost constant conductivity, while above this frequency a rapid rise in σ_AC was observed with a power law of frequency dependence with an exponent equal to 0.7. Both real and imaginary parts of the permittivity exhibited a low frequency dispersion which has been attributed to hopping of polarons and bipolarons in PANI and its composites. The thermal stability was checked by thermogravimetric analysis (TGA) and was found to be enhanced due to addition of MMT in the PANI.     

Preparation of polyaniline grafted multiwalled carbon nanotubes and conductive application in polyetherimide

A methodology for improving antistatic property of polyetherimide (PEI) composite using polyaniline (PANI) grafted multi‐walled carbon nanotubes (MWNTs) as conductive medium was proposed. First, the MWNTs grafted with PANI (PANI‐g‐MWNTs) were prepared by in‐situ polymerization in an emulsion system. Subsequently, PANI‐g‐MWNTs were blended with PEI using N‐methyl‐2‐pyrrolidone as solvent. After removing the solvent, the PEI/PANI‐g‐MWNT composite was prepared. As assisted conductive medium, the grafted PANI molecular chains on MWNT surface were dispersed in the PEI matrix to decrease the percolation value of the antistatic composites. The structure and morphology of PANI‐g‐MWNTs were characterized by Fourier transform infrared spectroscopy, transmission electron microscope, thermogravimetric analysis, and X‐ray powder diffraction, respectively. The dispersion of PANI‐g‐MWNTs in PEI matrix was studied by scanning electron microscope. The electrical performance was characterized by highly resistant meter. The volume resistivity of the conductivity percolation threshold was 1.781 × 10^?8 S/cm when the loading of PANI‐g‐MWNTs was 1.0 wt%. The conductivity of PANI‐g‐MWNTs/PEI composites was found to be higher than that of pristine MWNTs/PEI composite. Copyright © 2012 John Wiley & Sons, Ltd.     

Thermoelectrical and optical properties of double wall carbon nanotubes:polyaniline containing boron n‐type organic semiconductors

The electrical conductivity, thermoelectrical, and optical properties of the polyaniline containing boron/double wall carbon nanotubes (CNTs) composites have been investigated. The electrical conductivities of the composites prepared with 1%, 5%, and 8% CNT concentrations at 300 K were found to be 5.31 × 10^?6, 2.72 × 10^?4, and 1.12 × 10^?3 (S/cm), respectively. The thermoelectrical results indicate that all the samples exhibit n‐type electrical conductivity. The optical band gaps of the samples were found to be 3.71 eV for 0% DWNT, 3.32 eV for 1% DWNT, 3.15 eV for 5% DWNT, and 3.12 eV for 8% DWNT. The obtained results suggest that the electrical conductivity of PANI‐B polymer is improved by DWNT doping. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis and characterization of polyaniline/silicon dioxide composites and preparation of conductive films

The focus of this study was to synthesize the inherently conductive polymer polyaniline using an optimized process to prepare polyaniline/silicon dioxide (PANI/SiO₂) composites by in situ polymerization and ex situ solution mixing. PANI and PANI/SiO₂ composite films were prepared by drop‐by‐drop and spin coating methods. The electrical conductivities of HCl doped PANI film and PANI/SiO₂ composite films were measured according to the standard four‐point‐probe technique. The composite films exhibited an increase in electrical conductivity over neat PANI. PANI and PANI/SiO₂ composites were also investigated by spectroscopic methods including UV‐Vis, FT‐IR, and Photoluminescence. UV‐Vis and FT‐IR studies showed that SiO₂ particles affect the quinoid units along the polymer backbone and indicate strong interactions between the SiO₂ particles and the quinoidal sites of PANI (doping effect). The photoluminescence properties of PANI and PANI/SiO₂ composites were studied and the PANI/SiO₂ composites showed increased intensity as compared to neat PANI. The increase of conductivity of PANI/SiO₂ composite may be partially due to the doping or impurity effect of SiO₂ where the silicon dioxides compete with chloride ions. The morphology of particles and films were examined by a scanning electron microscope (SEM). SEM measurements indicated that the SiO₂ were well dispersed and isolated in composite films. Copyright © 2009 John Wiley & Sons, Ltd.     

Structural characterization and dielectric properties of the solid solutions AgPb(Sb,Bi)S3

The new solid solutions AgPbSb_1 − x Bi _x S₃ were prepared by solid state reactions. The phases were characterized by powder X-ray diffractions (XRD), scanning electron microscopy, and thermal analysis. The XRD patterns of different members (x = 0.5, 0.7, 0.8, and 1.0) are consistent with pure phases crystallizing in the cubic PbS-type structure. The electrical characterization was carried out using ac impedance spectroscopy and dc methods. The temperature dependence of the dc conductivity shows typical semiconductor Arrhenius behavior. The impedance measurements were performed in the frequency range of 0.1 Hz to 10 MHz and at the temperature range of 15 °C to 350 °C. The ac conductivity conforms to Jonscher’s universal power law. The frequency dependence of the dielectric permittivity follows the normal dielectric material behavior, and the relaxation is thermally activated. The frequency and temperature dependences of the electrical data are found to follow Summerfield scaling formalism.     

Enhancing dielectric and mechanical behaviors of hybrid polymer nanocomposites based on polystyrene,polyaniline and carbon nanotubes coated with polyaniline

The dielectric and mechanical properties of hybrid polymer nanocomposites of polystyrene/polyaniline/carbon nanotubes coated with polyaniline(PCNTs) have been investigated using impedance analyzer and extensometer. The blends of PS/PANI formed the heterogeneous phase separated morphology in which PCNTs are dispersed uniformly. The incorporation of a small amount of PCNTs into the blend of PS/PANI has remarkably increased the dielectric properties. Similarly, the AC conductivity of PS/PANI is also increased five orders of magnitude from 1.6 × 10~(-10) to 2.0 × 10~(-5) S·cm~(-1) in the hybrid nanocomposites. Such behavior of hybrid nanocomposites is owing to the interfacial polarization occurring due to the presence of multicomponent domains with varying conductivity character of the phases from insulative PS to poor conductor PANI to highly conductive CNTs. Meanwhile, the tensile modulus and tensile strength are also enhanced significantly up to 55% and 160%, respectively, without much loss of ductility for three phase hybrid nanocomposites as compared to the neat PS. Thereby, the hybrid nanocomposites of PS/PANI/_P CNTs become stiffer, stronger and tougher as compared to the neat systems.     

纤维状填料/HDPE复合体系的导电渗流与流变渗流行为的关系

研究了纤维状导电材料不锈钢纤维(SSF)填充高密度聚乙烯(HDPE)导电复合体系的导电渗流与流变渗流行为之间的关系,并与颗粒状导电颗粒炭黑(CB)/HDPE导电复合体系进行了比较.发现当SSF含量极低(0.3vol%)时,SSF/HDPE体系即发生导电渗流现象,且导电渗流转变区域极窄;而仅当SSF含量达到4.8vol%时,该复合体系才表现出流变渗流现象,这一结果与CB/HDPE体系及纳米级导电纤维填充体系截然不同.此外,通过正温度系数效应的研究发现SSF形成的导电通路稳定性高于CB/HDPE体系.我们认为,SSF/HDPE体系呈现的这些特点均与SSF较大的直径及长径比且其导电通路及流变渗流网络的形成机理不同有关.     

Poly(phenylene sulfide) magnetic composites. I. Relations of percolation between rheology,electrical, and magnetic properties

Poly(phenylene sulfide)/ferrosoferric oxide composites (PPS/Fe₃O₄) with various loading levels were prepared by melt compounding. The microstructure of composites was investigated using SEM and XRD. The rheological, electrical and magnetic properties were characterized respectively by the parallel plate rheometer, high resistance meter, and magnetometer. The results reveal that the Fe₃O₄ particles are well dispersed in the PPS matrix due to their nice affinity, which results in a weak strain overshoot at large amplitude oscillatory level. Both the rheological and the electrical responses of the composites show a typical percolation behavior. But the rheological percolation presents lower threshold (< 40 wt %) than that of electrical percolation (～ 50 wt %), which is attributed to the difference structure of the percolation network. The magnetic response, however, shows good linear relation with Fe₃O₄ loadings, indicating that the physical percolation has little influence on the magnetic properties. This is mainly due to the yielded long‐range magnetic interactions among Fe₃O₄ particles in the applied field, which are far stronger than those nonmagnetic physical interactions accounting for percolation. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 233–243, 2008     

Electrical transport properties of an organic semiconductor on polyaniline doped by boric acid

The electrical conductivity, thermoelectric power, and dielectric properties of polyaniline doped by boric acid (PANI‐B) have been investigated. The room temperature electrical conductivity of PANI‐B was found to be 1.02 × 10^?4 S cm^?1. The thermoelectric power factor for the polymer was found to be 0.64 µW m^?1 K^?2. The optical band gap of the PANI‐B was determined by optical absorption method, and the PANI‐B has a direct optical band gap of 3.71 eV. The alternating charge transport mechanism of the polymer is based on the correlated barrier hopping (CBH) model. The imaginary part of the dielectric modulus for the PANI‐B suggests a temperature dependent dielectric relaxation mechanism. Electrical conductivity and thermoelectric power results indicate that the PANI‐B is an organic semiconductor with thermally activated conduction mechanism. Copyright © 2008 John Wiley & Sons, Ltd.     

Characterization and electrical transport properties of polyaniline and multiwall carbon nanotube composites

Polyaniline/multiwalled carbon nanotube (PANI/MWNT) composites were prepared by in situ polymerization. Scanning electron microscope, X‐ray diffraction, Fourier transform infrared, Uv‐Visible spectroscopy, Fluorescence spectrophotometry were done to characterize the PANI/MWNT composites. Thermal stability was measured by thermogravimetry analysis. The thermal stability of PANI/MWNT composites becomes higher than PANI. Electrical transport properties of different PANI/MWNT composites were investigated in the temperature range 77 ≤ T ≤ 300 K with and without magnetic field up to 1 T. The dc resistivity of PANI/MWNT composites shows different behavior compared to the sample without MWNT. The room temperature dc magnetoconductivity of the samples is negative; however, its sign changes to positive by lowering the temperature, which has been explained by hopping type charge transport. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1767–1775, 2010     

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