Electrical transport properties of the composite of multiwall carbon nanotube–polypyrrole–polyvinyl alcohol below room temperature

We have investigated electrical transport properties of the composite of multiwall carbon nanotubes–polypyrrole–polyvinyl alcohol. Samples are prepared in an in situ chemical oxidative method and they are characterized by X‐ray diffraction, field emission scanning electron microscope to understand their structure and morphology, respectively. Mechanism of electrical transport is done below room temperature (77–300 K) in presence and absence of magnetic field up to 1 T. Samples are following both one dimensional Mott's variable range hopping and tunneling theory. Forward interference model is used to explain the mechanism of magnetic field dependent conductivity. The real part of AC conductivity follows universal dielectric response σ^′ (f) ∞ f^S. The universal dielectric response parameter s varies with temperature according to correlated barrier hopping model. The variation of real part of complex impedance with frequency can be described in terms of Maxwell Wagner effect. The positive variation of AC conductivity can be explained in terms of grain and grain boundary contribution of the samples. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Anomalous electrical transport properties of amorphous carbon films on Si substrates

Amorphous carbon (a-C) films are deposited on n-Si substrates at different temperatures using pulsed laser deposition. Some anomalous current-voltage (I-V) characteristics of the a-C/n-Si are reported. The films deposited at 27 °C have an apparent voltage-induced switch effect, and the value of the switch voltage decreases with increasing temperature. However, the I-V characteristics of the a-C/n-Si deposited at 300 °C and 500 °C are completely different from those deposited at 27 °C. The anomalous I-V characteristics should be of interest for various applications such as field effect devices. In addition, the magnetoresistance (MR) and the resistance of the a-C/n-Si have been studied. Finally, we interpret the anomalous I-V characteristics and MR observed by use of energy band theory.     

Nonlinear surface electrical resistivity of graphite–polyurethane composite films

In this article, we study the surface resistivity of graphite–polyurethane composites using voltage–current characteristics. The evolution of the percolation network of graphite in polyurethane is qualitatively studied using optical micrographs. As expected, the surface resistivity decreases as a function of graphite concentration. In particular, the surface resistivity of the 69% graphite–polyurethane composite is about four orders of magnitude lower than the surface resistivity of the 27% graphite–polyurethane composite. The electrical resistivity of the composite is found to be highly nonlinear with respect to an increasing voltage at a low graphite weight fraction. On the other hand, the nonlinearity is significantly milder at higher weight fractions. The reasons behind the nonlinearity are discussed. Very preliminary studies indicate that very low weight fractions of single wall carbon nanotubes (e.g. 2.5%) are sufficient to generate electrical conductivities comparable to much higher loading fractions (～ 60% and higher) of the heavier graphite particles. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Mechanical properties of silk fibroin–microcrystalline cellulose composite films

Silk fibroin–microcrystalline cellulose (cellulose whisker) composite films with varied compositions were prepared by casting mixed aqueous solution/suspensions of the two components. Silk fibroin was dissolved in 10M LiSCN followed by dialysis; a cellulose whisker suspension was prepared by sulfuric acid hydrolysis of tunicate cellulose. Macroscopically homogeneous films were obtained at all mixing ratios. While the Young's modulus of the composite films showed a linear, additive dependence on the mixing ratio, the tensile strength and ultimate strain showed a maximum at a 70–80% cellulose content, reaching five times those of fibroin‐alone or cellulose‐alone films. At the same mixing ratio, infrared spectra of the composite films showed a shift of the amide I peak from 1654 to 1625 cm^?1, indicating the conformational change of fibroin from a random coil to a β structure (silk II) at the whisker–matrix interface. This change seems to be induced by contact of fibroin molecules with a highly ordered surface of cellulose whisker. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3425–3429, 2002     

Anomalous behavior of the dielectric and electrical properties of polymeric nanodielectric poly(vinyl alcohol)–titanium dioxide films

The complex dielectric permittivity, alternating‐current electrical conductivity, electric modulus, and impedance spectra of polymeric nanocomposite (PNC) films consisting of a poly(vinyl alcohol) (PVA) matrix dispersed with nanosize particles of titanium dioxide (TiO₂); (i.e., PVA–x wt % TiO₂, where x is 0, 1, 3, or 5) were investigated in the frequency range 20 Hz to 1 MHz at ambient temperature. A detailed analysis of the results showed that the values of the dielectric and electrical parameters of these PNC‐based nanodielectric films varied anomalously with increasing TiO₂ concentration. The temperature‐dependent dielectric characterization of the PVA–3 wt % TiO₂ film revealed that the dielectric polarization at a fixed frequency increased nonlinearly with increasing temperature. The temperature‐dependent electric modulus relaxation time values of the nanodielectric film obeyed Arrhenius behavior. The X‐ray diffraction study confirmed that the crystalline phase of the PVA matrix decreased with increasing TiO₂ concentration; this suggested that the interaction of the TiO₂ nanoparticles caused some destruction of the hydroxyl group dipolar ordering in the hydrogen‐bonded crystalline structure of the pristine PVA matrix. The intensities of the diffraction peaks of the TiO₂ nanofiller were enhanced as its concentration increased in these nanodielectrics; this confirmed the existence of TiO₂ nanoparticles inside the crystalline phases of the PVA matrix. The surface morphology of the films was examined by the study of their scanning electron micrographs. The feasibility of using these flexible polymeric nanodielectric films as electrical insulators and dielectric substrates in low‐power microelectronic devices operated at audio‐ and radio‐frequency electric fields was explored. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44568.     

Spectroscopic,electrical, and relaxor‐like properties of cellulose acetate–erbium (III) chloride composite films

Cellulose acetate thin films doped with erbium (III) chloride (ErCl₃) of different concentrations were prepared by the solution method. The prepared composite films were characterized using scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetric analysis. IR spectral analysis, UV–visible absorption, a.c. conductivity, and dielectric properties were investigated. The studied ErCl₃‐doped samples showed different properties from those of their pure components. SEM micrographs showed that for small dopant concentrations, samples tend to form conducting nanostructures with negligible particle agglomeration. DSC showed a monotonic development of the glass transition temperature by increasing the concentration of dopant material. Variation in the height, shape, and position of the bands in infrared transmission spectra, as well as the glass transition temperatures, indicated a complex interaction with the polymer molecular chains. Thermal stability and thermodynamic parameters were found to be concentration dependent. The electronic transitions’ band gabs and energy tails were calculated from the optical data. The dielectric studies showed that the correlated barrier hopping model was the dominant mechanism of a.c. conductivity. We found that samples with 10% and 20% ErCl₃ exhibited high dielectric constants and have pronounced electrostriction and relaxor‐like properties. Such samples can be used in many applications like electromechanical and thermomechanical transducers. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45220.     

Preparation and electrical properties of metal sulfides–amidoximated PAN composite film

To improve the electrical conductivity of polyacrylonitrile (PAN) film, metallic sulfides and PAN composite film were prepared by the chelating method. Dense PAN film and porous PAN film were prepared by dry process and wet process, respectively. These PAN films were treated to NH₂OH solution to introduce the amidoxime group coordinated with metallic ion. Cu⁺² and Cd⁺² ions were adsorbed to amidoximated PAN films, the sulfur ion was treated with metal-adsorbed PAN films, and thus CuS—and CdS–PAN composite films were prepared. The adsorptive capacity of amidoximated PAN film for the Cu⁺² ion was independent of the morphology of the PAN film, but the adsorptive capacity of the Cd⁺² ion on amidoximated PAN film was dependent on porosity of the polymer. Adsorptive capacity of amidoximated porous PAN film for Cd⁺² was improved about four times than that of amidoximated dense PAN film. The electrical conductivities of CuS–dense and porous PAN composite film were both 10^?1 S/cm in optimum condition, but because of the difference in adsorptive capacity, the electrical conductivities of CdS–dense and CdS–porous PAN composite films were 10^?9 S/cm and 10^?4 S/cm, respectively. Additionally, because CdS was known as a photoconductive material, the photoconductive properties of CdS–porous PAN composite film were investigated.     

Paper-like graphene-Ag composite films with enhanced mechanical and electrical properties

In this paper, we have reported that paper-like graphene-Ag composite films could be prepared by a facile and novel chemical reduction method at a large scale. Using ascorbic acid as a reducing agent, graphene oxide films dipped in Ag⁺ aqueous solutions can be easily reduced along with the decoration of different sizes of Ag particles distributed uniformly. The results reveal that the obtained films exhibit improved mechanical properties with the enhancement of tensile strength and Young''s modulus by as high as 82% and 136%, respectively. The electrical properties of graphene-Ag composite films were studied as well, with the sheet resistance of which reaching lower than approximately 600 Ω/□. The graphene-Ag composite films can be expected to find interesting applications in the area of nanoelectronics, sensors, transparent electrodes, supercapacitors, and nanocomposites.     

Structural, electrical and magnetic properties of carbon-nickel composite thin films

Carbon-nickel composite thin films (600 nm thick) were prepared by dc magnetron sputtering of Ni and C at several temperatures (25-800 °C) on oxidized silicon substrates. By transmission electron microscopy it was found that the composite consisted of Ni (or Ni₃C) nanoparticles embedded in a carbon matrix. The metallic nanoparticles were shaped in the form of globular grains or nanowires (of the aspect ratio as high as 1:60 in the sample prepared at 200 °C). The carbon matrix was amorphous, or graphite-like depending on deposition temperature. At low deposition temperatures T_S (25-400 °C) the Ni₃C nanoparticles were of hcp phase. Samples prepared at T_S ? 600 °C contained ferromagnetic fcc Ni nanoparticles. A correlation was found between the structural, electrical and magnetic properties of the composites. To characterise the films, dependences, such as resistivity vs. temperature, current vs. voltage, differential conductivity vs. bias voltage, and magnetoresistivity, were determined. For example, the tunneling effect was found in samples in which the metallic nanoparticles were separated by 2-3 nm thick amorphous carbon. When the metallic nanoparticles were connected by graphite-like carbon regions (having a metallic conductivity, in contrast to a-C), the temperature coefficient of the resistivity became slightly positive. An anisotropic magnetoresistivity of ∼0.1% was found in the sample that contained ferromagnetic columnar fcc Ni. Zero magnetoresistivity was found in the sample in which the metallic nanoparticles were of non-magnetic hcp phase.     

Thermal and electrical properties of nitrile‐containing polyimide/BaTiO3 composite films

Polyimide composite films were prepared by mixing the BaTiO₃ particles into poly(amic acid) solution followed by film casting and thermal imidization under controlled temperature conditions. The poly(amic acid) was synthesized by solution polycondensation reaction of 4,4′‐oxydiphthalic anhydride with 2,6‐bis(4‐aminophenoxy)benzonitrile, using N‐methyl‐2‐pyrrolidone as solvent. The surface of BaTiO₃ particles was modified by treating with an aminosilane coupling agent, 3‐aminopropyltriethoxysilane. Fourier transform infrared spectroscopy, X‐ray diffraction and scanning electron microscopy were used to characterize the structure and properties of the composites. The influence of BaTiO₃ content on the composite film properties was evidenced. The films exhibited good thermal stability having the initial decomposition temperature above 520°C. They had stable dielectric properties over large intervals of temperature and frequency. The dielectric constant and the dielectric loss increased with the increase of BaTiO₃ content. The dynamic mechanical analysis and dielectric spectroscopy revealed subglass transitions γ and β. At higher temperature an α‐relaxation that corresponds to the glass transition and a conductivity process were evidenced. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Structure–property relationships of composite films

Coextruded multifilms of varying chemical composition and structure were studied by the dynamic mechanical technique. The films studied were two- and three-ply combinations of a polyimide (Kapton) and fluorinated ethylene–propylene copolymer (FEP) and four other two-ply polyethylene and modified polyethylene composites: low-density polyethylene (LDPE)–ionomer, rubber-modified high-density polyethylene (HDPE)–ionomer; ethylene–vinyl acetate (EVA) copolymer–LDPE, and EVA-modified HDPE–LDPE. The mechanical spectra of individual film components were also obtained at 110 Hz between ?120° and 120°C (220°C for the Kapton–FEP system). Mechanical relaxations were examined to determine the degree of interaction between adjacent films and correlate them with tensile and ultimate properties of the composite.     

Influence of the target power on the microstructure and electrical properties of Al-doped ZnO thin films deposited at room temperature

The columnar structure and its formation process have a significant effect on the electrical properties of Al-doped ZnO (AZO) thin film in-situ deposited at room temperature by magnetron sputtering method. The influences of RF power on the formation of the columnar structure and its regular pattern were systematically investigated. The RF power varied from 120 W to 240 W. The best quality AZO sample with the sheet resistance of 6.07 Ω/sq and average transmittance of 83.2% was obtained at 210 W (for 30 min). The analysis of crosses section images indicated that the columnar structure appeared earlier at higher RF power. The thickness at which the columnar structure began to appear didn't fluctuate at a fixed value. Furthermore, high RF power relatively contributed to reduce the thickness. The Drude's model was used for examining the correlation between optical and electrical behaviors, and the theoretical results of electrical properties were well matched with the experimental data. According to the XRD results and XPS analysis, the appearance of Al₂O₃ may exert a significant influence on the deterioration in electrical properties of the sample deposited at 240 W.     

Response of magnetic field and temperature on electrical transport of polyaniline–malic acid nanocomposite

A comprehensive study of the effect of HCl and malic acid on electrical transport properties of polyaniline has been reported. Samples are prepared by chemical oxidative polymerization of aniline. Granular morphology and better thermal stability is obtained. Temperature dependence of dc electrical transport can be explained by Mott's variable range hopping theory. Electrical transport is influenced by magnetic field. POLYM. COMPOS. 37:1042–1048, 2016. © 2014 Society of Plastics Engineers     

Structural,mechanical, and electrical properties of electropolymerized polypyrrole composite films

Electrochemical polymerization of pyrrole in a solution containing dissolved poly(vinyl alcohol) (PVA) produces a homogeneous, free‐standing, flexible, and conductive polymer film. The films were characterized using infrared spectroscopy, wide‐angle X‐ray diffraction analysis, and scanning electron microscopy. The appearance of standard and some new absorption bands for polypyrrole (PPy) and PVA confirms the composite formation. The mechanical properties of conducting PVA + PPy films were studied and found to be improved with respect to the control PPy films. The electrical conductivity of the PVA + PPy films was measured by using standard four‐ and two‐probe methods. The conductivity of the films was found to depend on the pyrrole content. These conducting composites were further used as gas sensors by observing the change in current with respect to ammonia gas. It was observed that the current decreases when these composites were exposed to ammonia gas. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2511–2517, 2001     

Cassava starch–kaolinite composite films. Thermal and mechanical properties related to filler–matrix interactions

The thermal and mechanical properties of cassava starch films are analyzed in relation to the starch–kaolinite interactions. The kaolinite filler induces a lowering of the crystallinity in accordance with an increase plasticization of the starch matrix. The increase of plasticization induces a decrease of the elastic modulus and an increase of the elongation at break. A retardant effect to the starch matrix decomposition is observed. The filler–matrix interface at which the plasticizer infiltration is enhanced and the reduction of starch chain–chain interactions appears as keys of the observed properties changes. POLYM. COMPOS., 36:184–191, 2015. © 2014 Society of Plastics Engineers     

Preparation and properties of conducting arachidic acid/polypyrrole composite langmuir–blodgett films

Electrically conducting arachidic acid/polypyrrole (PPy) composite films were prepared by exposing the arachidic acid LB films containing ferric chloride to pyrrole vapor. The optimum conditions to deposit matrix LB film were the subphase temperature of 23–25°C, pH of 6.0 and ferric chloride concentration of 5.0 × 10⁻⁵ M. The formation of PPy in the arachidic acid matrix LB films was confirmed by UV-visible spectra, FTIR spectra, and scanning electron micrographs. The average thickness of the composite LB films prepared at 0°C was 1525 Å. The composite films prepared at lower temperatures have more uniform surface and exhibit higher electrical conductivity than the films prepared at higher temperatures do. The in-plain conductivity and the transverse conductivity of the composite film were 10⁻³−10⁻² S/cm and 10⁻⁶S/cm, respectively, and, thus, the conductivity anisotropy was about 10³ © 1996 John Wiley & Sons, Inc.     

Preparation of diamond like carbon thin films above room temperature and their properties

Diamond like carbon (DLC) thin films were deposited on p-type silicon (p-Si), quartz and ITO substrates by microwave (MW) surface-wave plasma (SWP) chemical vapor deposition (CVD) at different substrate temperatures (RT ∼ 300 °C). Argon (Ar: 200 sccm) was used as carrier gas while acetylene (C₂H₂: 20 sccm) and nitrogen (N: 5 sccm) were used as plasma source. Analytical methods such as X-ray photoelectron spectroscopy (XPS), FT-IR and UV–visible spectroscopy were employed to investigate the structural and optical properties of the DLC thin films respectively. FT-IR spectra show the structural modification of the DLC thin films with substrate temperatures showing the distinct peak around 3350 cm^− 1 wave number; which may corresponds to the sp² C–H bond. Tauc optical gap and film thickness both decreased with increasing substrate temperature. The peaks of XPS core level C 1 s spectra of the DLC thin films shifted towards lower binding energy with substrate temperature. We also got the small photoconductivity action of the film deposited at 300 °C on ITO substrate.     

Magnetic field alignment and electrical properties of solution cast PET-carbon nanotube composite films

Single-wall carbon nanotubes (SWNTs) were dispersed in a polyethylene terephthalate (PET) matrix by solution blending and then cast onto a glass substrate to create flexible films. Various SWNT loading concentrations were implemented (0.5, 1.0, and 3.0 wt%), and the processing method was repeated to produce films in the presence of magnetic fields (3.0 and 9.4 T). Alignment of the SWNTs in the PET matrix was characterized by Raman spectroscopy. Impedance spectroscopy was utilized to study the electrical behavior of the nanocomposites. It was concluded that SWNT concentration and dispersion are the key variables for improving electrical conductivity, while alignment plays a secondary role. Interestingly, it appears that a magnetic field may prove to be a novel method for improving the dispersion of unmodified SWNTs by disrupting van der Waals interactions.     

Starch–recycled gelatin composite films produced by extrusion: Physical and mechanical properties

This article describes using recycled gelatin in production of blends of starch (Manihot esculenta Crantz). Films were produced by extrusion using varying percentages of recycled gelatin (2.5, 5, 7.5, 10, 12.5, and 15% relative to the starch weight), plasticized with glycerol (20 wt % relative to the starch weight), and then characterized. The morphology results showed films with a cohesive matrix and no phase separation. The crystallinity analysis showed that the extrusion process eliminated crystalline zones of the granules and produced low‐crystallinity films. The addition of recycled gelatin caused an increased thermal stability and significantly increased the mechanical strength and solubility in water of the films. It also accelerated the biodegradation process. It was concluded that the process of recycling and reprocessing did not affect the properties of gelatin, even as it has significantly influenced the properties of the films. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46254.     

Study on preparation and properties of PVA‐SA‐PHB‐AC composite carrier for microorganism immobilization

Polyvinyl alcohol(PVA) bead crosslinked with boric acid has been widely utilized as a microorganism immobilization carrier. However, it has some disadvantages such as drastic cell viability loss, small adsorption capacity and mass transfer limitation. To improve upon these drawbacks, a new method to prepare PVA composite pieces with the addition of activated carbon (AC) and poly‐3‐hydroxybutyrate(PHB) was explored through a combination of freezing/thawing and the boric acid method and by using Tween‐80 to improve the mass transfer performance of hydrophobic organics. m‐Cresol and pyrene were used as representative compounds with benzene ring structures to model hydrophilic and hydrophobic organics in order to test the performance of PVA pieces. The results showed that, compared with the boric acid method alone, a combination of freezing/thawing and the boric acid method led to a decrease in total organic carbon(TOC) loss from 0.315 g g^?1 to 0.033 g g^?1 and increased the oxygen uptake rate(OUR) of microorganisms from 0.03 mg L^?1·min^?1 to 0.22 mg L^?1 min^?1. The m‐cresol equilibrium adsorption amount of the PVA‐SA(sodium alginate)‐PHB‐AC piece was 2.80 times that of the PVA‐SA piece. The diffusion coefficient of pyrene in the PVA‐SA‐PHB‐AC piece increased from 0.53×10^?9 m² min^?1 to 2.30×10^?9 m² min^?1 with increasing concentrations of Tween‐80 from 1000 mg L^?1 to 5000 mg L^?1. The PVA‐SA‐PHB‐AC composite carrier demonstrated great scope for immobilizing microorganisms for practical wastewater bio‐treatment. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39837.