Effect of temperature and moisture on electrical conductivity in polyaniline/polyurethane (PANI/PU) blends

Miscible blend of conductive polyaniline/polyurethane (PANI/PU) showed preferable electrical property at low percolation threshold compared to immiscible blend of PANI/polystyrene-isoprene-copolymer (PANI/SIS) and carbon black/PU composite (CB/PU). The time dependence of the electrical conductivity was investigated with these samples aged under different humidity and temperatures. The electrical conductivity of PANI/PU (11.5/88.5, v/v) decreased with aging time and the morphology changed with time in the coexistence of high moisture and high temperature. After the aging treatment, the film of the miscible blend was re-dissolved and re-cast. The morphology and electrical conductivity were found to recover to the same state as the original film. In addition, the recovery mechanism of the morphology and the conductivity was also proposed here.     

Blends of HCl-doped polyaniline nanoparticles and poly(vinyl chloride) with extremely low percolation threshold — a morphology study

Blends of hydrochloric acid-doped polyaniline (PANI·HCl) nanoparticles and poly(vinyl chloride) (PVC) have been prepared by redispersing sedimented colloidal particles of PANI in tetrahydrofuran solutions of PVC using ultrasound and casting the film from the dispersion. The blends have the characteristics of extremely low percolation threshold at a volume fraction of PANI of 4.02 × 10⁻⁴. The morphology of the blends as revealed by transmission electron microscopy (TEM) of the blend films directly cast on TEM grids is discussed. Above the percolation threshold the dispersed PANI·HCl phase shows a globular network morphology in contrast to the fibrillar network morphology observed earlier for PANI·HCl-poly(vinyl alcohol) blends prepared by the present method.     

Fabrication and percolation behaviour of novel porous conductive polyblends of polyaniline and poly(methyl methacrylate)

The conductive polymer polyaniline is blended with conventional industrial thermoplastics in order to obtain an electrically conductive polymer blend with adequate mechanical properties. Processing these polyblends into foams yields a porous conductive material that exhibits immense application potential such as dynamic separation media and low-density electrostatic discharge protection. In the current study, the morphology of a thermally processable blend consisting of an electrically conductive polyaniline-dodecylbenzene sulfonic acid complex and poly(methyl methacrylate) is explored using a two-phase batch foaming setup. The effect of blend composition and processing parameters on the resulting porous morphology is investigated. The impact of the underlying microstructure and blend composition on the frequency dependent electrical conductivity is elucidated using multiple linear regression and a model is proposed. Finally, dielectric analysis is utilized to experimentally identify the critical dispersion frequency of an unfoamed blend composition near the percolation threshold.     

Preparation and properties of conducting composites of polypyrrole and porous cross-linked polystyrene with and without supercritical carbon dioxide

Composites of polypyrrole (PPy) and porous cross-linked polystyrene (PCPS) were prepared using a two-step batch method proposed by Ruckenstein and Park. However, the solvent employed by Ruckenstein and Park (methanol) in the polymerization step of their method was replaced with supercritical CO₂. For comparison purposes, PPy/PCPS composites were also prepared using no solvent in the polymerization step. Conductivities as high as 10⁻² S cm⁻¹ were obtained, with or without the use of supercritical CO₂. Uniformity of conductivity was determined via surface and bulk conductivity measurements, as well as by a new volume conductivity measurement that provides a measure of spatial (three-dimensional) distribution of the conducting component in the composite.The conductivity of composites prepared with or without the use of supercritical CO₂ conformed to the same percolation behavior with respect to the amount of PPy formed. The percolation threshold in all cases was as low as 4 wt.%. The mechanical strength of the composites was found to be about the same as that of the host PCPS, as was the thermal stability. Therefore, the conductive component did not appear to adversely affect these properties of the host. Finally, the temperature behavior of the conductivity could be correlated with Mott's variable-range hopping (VRH) model for three-dimensional electronic transport.     

Electrically conducting nylon 6,6–polyaniline short composite fibres synthesised by the solvent coagulation method

Polyaniline (PANI) was blended with nylon 6,6 in concentrated H₂SO₄ and HCl solutions. The solvent coagulation method was utilised to extract short composite fibres of a centimetre in length. A solution of n-butyl acetate, acetone, toluene, 1 μM HCl and chloroform were used as coagulating bath to extract the fibres. The diameters of the fibres ranged from 200 to 300 nm, while the length measured approximately 1 cm, as determined from Scanning Electron Microscopy (SEM). The electrical conductivity varied from 10⁻⁴ to 10⁻² S/cm for different mass fractions of PANI (x_PANI) in the composite fibres. The percolation threshold was reached at x_PANI values between 0.15 and 0.2, and further addition of PANI resulted in saturation of the conductivity of the composite fibre. To observe the effect of MWCNTs on the electrical conductivity of the nylon–PANI fibres, 0.04 g, 0.08 g, 0.4 g and 0.5 g of MWCNTs (1, 2, 10, 12.5 weight percentage, respectively) were added into the nylon–PANI solution and were extracted as fibres in the aforementioned solvents. The electrical conductivity of the short fibres increased by an order of magnitude (0.372 S/cm at 12.5 wt.%) when they were extracted in the presence of the MWCNTs. PANI doped in concentrated HCl exhibited an electrical conductivity of 4.46 S/cm.     

Preparation,FTIR spectroscopic characterization and isothermal stability of differently doped conductive fibers based on polyaniline and polyacrylonitrile

Conductive fibers based on polyaniline (PANI) and polyacrylonitrile (PAN) were obtained by stirring with magnetic bar. This research was conducted to investigate conducting fibers of polyaniline:polyacrylonitrile (PANI:PAN) composite with different weight ratios of aniline in PAN matrix. The fibers were prepared by stirring process. The best conductivity behavior of the fibers was obtained with 5 mL of aniline. The fibers obtained were characterized using Fourier-transform infrared spectra (FTIR), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The variation of electrical conductivity with different type doping agents (HCl, H₂SO₄ and HClO₄) and the stability in terms of DC electrical conductivity retention was studied in an oxidative environment by isothermal characteristics.     

Preparation,FTIR spectroscopic characterization and isothermal stability of differently doped fibrous conducting polymers based on polyaniline and nylon-6,6

The fibrous conducting polymers based on polyaniline and nylon-6,6 are obtained by stirring with magnetic bar. The increase in the ratio of conducting polymer volume in case of such fibers make them attractive materials for potential applications. As it is difficult directly to form fibers of conducting polymers, stirring process is attempted to form fibers of conducting polyaniline and nylon-6,6. In the present paper, the fibrous polyaniline:nylon-6,6 (PANI:Ny-6,6) with different weight percentages (5–20%, w/w) are prepared by stirring process. The fibers obtained are characterized using Fourier-transform infrared spectra (FTIR) and scanning electron microscopy (SEM), the variation of electrical conductivity with different type doping agents 0.1 M (HCl, H₂SO₄ and HClO₄) and the stability in terms of DC electrical conductivity retention was studied in an oxidative environment by isothermal characteristics.     

Conductive fibers from enzymatically synthesized polyaniline

Conducting polyaniline (PANI) fibers have been spun from a water-soluble form of PANI which was enzymatically synthesized. The enzyme, horseradish peroxidase (HRP) was used to polymerize aniline in the presence of sulfonated polystyrene (SPS) to directly form a water-soluble, conducting, PANI/SPS complex which combines moderate electrical conductivity with appreciable processability. The PANI/SPS complex was spun into fibers from aqueous solution using a dry-spinning technique. Thermal studies which included thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and DMA show that the complex has very good thermal stability and a T_g at 150°C. Mechanical properties of the fibers show a tenacity of 0.34 cN/dtex for the as-spun fibers with an increase to 0.56 cN/dtex after thermal stretch alignment. Wide angle X-Ray diffraction shows the presence of two weak peaks at d values of 4.16 Å and 2.95 Å for the drawn fibers, while no crystalline reflections were observed for cast films. The drawn fibers also show an order of magnitude improvement in conductivity. These results show that some degree of fiber orientation and crystallinity may be induced during processing.     

Highly conducting electrospun polyaniline-polyethylene oxide nanofibrous membranes filled with single-walled carbon nanotubes

Highly conducting nanofibrous composite of well-oriented single-walled carbon nanotubes (SWNTs) in polyaniline (PANI) and polyethylene oxide (PEO) have been fabricated using electrospinning. The room temperature electrical conductivity show nearly four order enhancement with highest (11.9 wt%) loading of SWNT in the PANI–PEO blend. The temperature dependent conductivities are measured in the range of 30–300 K and the results are analyzed by the fluctuation assisted tunneling model.     

Electrical conductivity of α-quinquethiophene/stearic acid Langmuir-Blodgett films doped with iodine

Langmuir-Blodgett multilayer films consisting of 0 – 62 mol% purified α-quinquethiophene (QT) in cadmium stearate-stearic acid (ST) were deposited on glass substrates and characterized by a variety of methods. Exposure of these films to iodine vapor rendered them electrically conductive, the conductivities being strongly dependent on QT concentration and the number of layers deposited. The most conductive samples (≳ 35 mol% QT, ≳ 10 layers) had σ = 0.2 S cm⁻¹. The concentration dependence of the conductivity can be broadly described by the two-site percolation models that take into account the specific chain arrangement and the finite conductivities of both the QT and ST aggregates in the films. Finally, the relevance of the QT-ST system to other conducting materials is discussed.     

Polyaniline nanofibers synthesized in compressed CO2

Polyaniline (PANI) nanofibers were synthesized in compressed liquid carbon dioxide without any template or surfactant. The polymerization of aniline took place at the interface between CO₂ and aqueous solution in a high-pressure stirred reactor. The prepared PANI nanofibers were characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM), electrical conductivity (EC), Fourier-transform infrared (FT-IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and X-ray diffraction (XRD) analyses. The yield of polymerization was high enough to reach 63.04% while maintaining small diameters of the PANI nanofibers. This result is very important for the preparation of the PANI nanofibers because no other previous investigations have achieved both high yield and small diameter of fibers at the same time. Through SEM and TEM analyses, we observed that the PANI nanofibers had diameter range of 30–70 nm and a length range of 0.3–1 μm, which caused them to disperse well in various solvents such as water, ethanol, 2-propanol, m-cresol and toluene. The electrical conductivity of the PANI nanofibers was 4.34 S/cm at 20 °C. The XRD diffraction pattern showed that the PANI nanofibers had crystalline one-dimensional structures, which gave high thermal stabilities as confirmed by TGA.     

Characterization of polyaniline doped with diphenyl phosphate

UV–Vis spectroscopy and conductivity of the polyaniline (PANI) doped with diphenyl phosphate (DPHP), in comparison with that of HCl-doped polyaniline, show that the decrease in polaron delocalization and structural order results from the steric hindrance imparted by the longer chain counter ion. PANI protonated with DPHP is soluble in common organic solvents such as toluene, chloroform, dimethyl sulfoxide, etc. The conductivity of PANI/DPHP pressed pellet (at 25°C, 1.66 S cm⁻¹) increases with temperature from −40°C (1.18 S cm⁻¹) to +140°C (3.07 S cm⁻¹) due to thermal activation, and decreases with temperature from 140 to 180°C (0.25 S cm⁻¹) due to thermal undoping accompanied by the loss of some polarons. The temperature dependence of spin density is consistent with those of conductivity. After the heating scan, the conductivity (0.52 S cm⁻¹) at room temperature reduces to nearly one-third of the original value.     

Electrical and morphological properties of PP and PET conductive polymer fibers

Conductive fibers were obtained using two experimental processes (melt spinning and coating process). In melt spinning process, polyaniline (PANI), polypyrrole (PPy) and graphite were used in order to obtain conductive polypropylene (PP) based fibers with specific electrical and mechanical properties. PANI was treated using dodecylbenzene sulfonic acid (DBSA) to improve the solubility and the dispersion of PANI in xylene. PANI coating on PET yarns were performed by absorption of yarns through PANI solution. The electrical resistance and morphological characteristics of conductive yarns were investigated. These yarns are supposed to be used to create smart clothing, corrosion protection or conductive fabrics for electromagnetic shielding applications.     

Effect of thermal annealing on the electrical conductivity of high-strength bicomponent polymer tapes containing carbon nanofillers

A new concept is described that creates highly oriented multifunctional polymer nanocomposite tapes (or fibres) that combine high stiffness and strength with good electrical properties and a low percolation threshold of conductive nanofillers. The concept is based on a bicomponent construction consisting of a highly oriented polymer core together with conductive polymer composite skins based on a polymer with lower melting temperature than the core. This construction allows for a thermal annealing process that can be applied selectively to the skins to improve their conductivity through a kinetic re-aggregation process while retaining the mechanical properties of the core and hence those of the overall tape or fibre. In the current study this generic concept was applied to bicomponent tapes based on a polypropylene homopolymer core and a multi-wall carbon nanotube or carbon black filled polypropylene copolymer skin. The conductivity of the bicomponent tape containing 5.3 wt.% of MWNTs in its outer skins increased from 1.3E?6 to 1.5 S/cm after annealing while the percolation threshold in the copolymer skins of highly drawn bicomponent tapes could be decreased from 5.3 to 1.1 wt.%. To the best of the authors’ knowledge this is the lowest percolation threshold reported in literature for highly drawn polymer nanocomposites fibres or tapes. In fact, the percolation threshold is as low as 0.1 wt.% when considered on the overall tape as the conductive skins account for only 10% of the total volume of these bicomponent tapes.     

Electrical conductivity and thermoelectric power of polypyrrole with different doping levels

The electrical conductivity and absolute thermoelectric power of the conducting polymer polypyrrole have been measured between approximately 4 K and 350 K. Normally-doped films had a conductivity of 26 Ω⁻¹ cm⁻¹, whilst lightly-doped films had a conductivity of 8 Ω⁻¹ cm⁻¹. The Mott variable-range hopping model for electrical conductivity is obeyed at higher temperatures for both types. The thermoelectric power is approximately linear in temperature, reaching about 5 μV K⁻¹ at 200 K, but is sublinear at higher temperatures and becomes constant above about 300 K. The Kuivalainen model, which explains the reported anomaly between optical and d.c. electrical conductivity, gives a good fit to the experimental data.     

Composite films of nanostructured polyaniline with poly(vinyl alcohol)

The uniform composite films of nanostructured polyaniline (PANI) (e.g. nanotubes or nanorods with 60–80 nm in diameter) were successfully fabricated by blending with water-soluble poly(vinyl alcohol) (PVA) as a matrix. The PANI nanostructures were synthesized by a template-free method in the presence of β-naphthalene sulfonic acid (β-NSA) as a dopant. The molecular structures of PANI–β-NSA and the related composite films were characterized by UV–Vis absorption spectrum, FTIR spectrum and X-ray diffraction. It was found that the electrical, thermal and mechanical properties of the composite films were affected by the content of nanostructured PANI–β-NSA in the PVA matrix. The composite film with 16% PANI–β-NSA showed the following physical properties: room-temperature conductivity is in the range 10⁻² S/cm, tensile strength ∼603 kg/cm², tensile modulus ∼4.36×10⁵ kg/cm² and ultimate elongation ∼80%.     

Stable polyaniline dispersions prepared in nonaqueous medium: synthesis and characterization

Peroxodisulfate-induced polymerization of aniline at 10°C in acidic (HCl) nonaqueous medium using dimethyl sulfoxide (DMSO) as the solvent, readily produced polyaniline (PANI) in a stable dispersion form. The stability of the dispersion of PANI in the nonaqueous (DMSO) medium is much enhanced when the same is synthesized in the presence of a support polymer, poly(vinyl alcohol) (PVA) dissolved in the solvent. Results of studies on HCl-doped PANI prepared in DMSO medium by UV–VIS and FTIR spectroscopy support that the doped PANI so obtained is structurally similar to that of doped PANI prepared likewise in acidic aqueous medium. PANI and PANI–PVA composite as prepared in DMSO medium and the relevant isolated dry products were further characterized thermally, employing differential scanning calorimetry (DSC) and thermogravimetry (TG) and morphologically, employing transmission electron microscopy (TEM). HCl-doped PANI prepared separately in DMSO and aqueous media shows electrical conductivity values of 1.07 and 12.0 S cm⁻¹, respectively, the polymer prepared in nonaqueous medium (DMSO) being measurably poorer in electrical conductivity,     

Electrical conductivity and dielectric response of poly(vinylidene fluoride)–graphite nanoplatelet composites

Poly(vinylidene fluoride)/graphite nanoplatelets (PVDF/GNP) composites were fabricated using solution mixing followed by compression molding. The electric conducting and dielectric behavior of such nanocomposites were determined over a wide frequency range from 10² to 10⁷. The results showed that the electrical behavior of PVDF/GNP nanocomposites can be well described by the percolation theory. Both conductivity and dielectric constant were found to be greatly enhanced at the percolation threshold. A large dielectric constant of 173 and low loss tangent of 0.65 were observed in the PVDF/2.5 wt% GNP nanocomposite at 1 kHz. Moreover, dynamic mechanical analysis was also used to characterize the relaxations of polymers in PVDF/GNP nanocomposites. Dielectric and mechanical relaxations of PVDF/GNP nanocomposites showed strong dependence with frequency and temperature. The activation energy for glass transition determined from mechanical relaxation is considerably higher than that evaluated from the dielectric analysis. This resulted from different operating mechanisms for dielectric and mechanical relaxation processes.     

Electro-conductive composite fibers by melt spinning of polypropylene/polyamide/carbon nanotubes

In this study, the blends of polypropylene/polyamide with carbon nanotubes (CNTs) have been prepared and melt spun to as-spun and drawn fibers. Thermal analysis showed that increasing the polyamide content, decreased the degree of crystallinity in the blends. Characterization of fibers showed that both conductivity and tensile strength have been improved by increasing the amount of polyamide in the blends as well as the melt blending temperature; furthermore, the morphology, electrical and mechanical properties of the blends were significantly influenced by adding 1 phr compatibilizer to the blend. The comparison between as-spun fibers and drawn fibers proved that although mechanical properties were improved after drawing, the electrical conductivity was decreased from the order of E?02 to E?06 (S/cm), due to applied draw-ratio of three.     

Water-borne conductive polyaniline doped by acidic phosphate ester containing polysilsesquioxane precursor

Acidic phosphate ester (APES) bearing polysilsesquioxane precursor was prepared employing the ring-opening reaction of (3-glycidoxypropyl)trimethoxysilane (GPTMS) with acidic phosphate monoester carrying long hydrophilic tail. Doped with APES, polyaniline emeraldine base (PANI) was successfully dissolved or dispersed in water, and a free-standing film with electrical conductivity as high as 0.05 S/cm was available. The obtained film showed water-resistance due to the confinement from inorganic networks of amorphous polysilsesquioxane characterized by ²⁹Si-MAS NMR spectrum. When the conductive film was soaked in water for 14 days, its electrical conductivity showed a little decline at the first stage of 6 days, and a considerably long platform existed at the following stage. However, for the film without polysilsesquioxane network, the electrical conductivity showed a sharp decline, and the film was broken into pieces for only 1 day soaking. Covalently linked with inorganic network of polysilsesquioxane by POC bond, thermal stability of the conductive polyaniline was also improved compared with that of the conductive hybrid film from physical blending.