Electrical conductivity and Raman imaging of double wall carbon nanotubes in a polymer matrix

Raman spectroscopy is used to access the dispersion state of DWNTs in a PEEK polymer matrix. The interaction of the outer tube with the matrix can be determined from the line shape of the Raman G band. This allows us to distinguish regions where the nanotubes are well dispersed and regions where the nanotubes are agglomerated. The percolation threshold of the electrical conductivity of the double wall carbon nanotubes (DWNTs)/PEEK nanocomposites is found to be at 0.2-0.3 wt%. We find a maximum electrical conductivity of 3 × 10⁻² S cm⁻¹ at 2 wt% loading. We detect nanotube weight concentrations as low as 0.16 wt% by Raman spectroscopy using a yellow excitation wavelength. We compare the Raman images with transmission electron microscopy images and electrical conductivity measurements. A statistical method is used to find a quantitative measure of the DWNTs dispersion in the polymer matrix from the Raman images.     

Electrical and mechanical properties of expanded graphite/high density polyethylene nanocomposites

High density polyethylene (HDPE) were filled with expanded graphite particles that have different particle sizes, 5–7 μm (EG5) and 40–55 μm (EG50) in diameter. Nanocomposites were prepared by the melt-mixing technique using EG5 and EG50 at different weight ratios. Transmission Electron Microscopy (TEM) was used to observe the morphology of the nanocomposites. X-ray diffraction patterns of EG5-HDPE and EG50-HDPE nanocomposites were investigated. Tensile tests were carried out to determine tensile strength, Young’s modulus and elongation at break values. The storage modulus and loss modulus were evaluated by Dynamic Mechanical Analysis (DMA). The effect of EG5 and EG50 on electrical conductivity of HDPE was also determined. The tensile strength of HDPE increased 18.7% and 8.5% when 40 wt% EG5 and EG50 was added into HDPE, respectively. The storage modulus of EG5-HDPE and EG50-HDPE is higher compared to that of HDPE. Incorporation of EG5 and EG10 into HDPE also increased the relaxation transition peak of HDPE. The values of electrical conductivity for EG50-HDPE nanocomposites under the same filler content obtained higher in comparison with those for EG5-HDPE nanocomposites.     

High temperature proton exchange membranes prepared from epoxycyclohexylethyltrimethoxysilane and amino trimethylene phosphonic acid as anhydrous proton conductors

High temperature anhydrous proton exchange membranes based on phosphonic acid were prepared from epoxycyclohexylethyltrimethoxysilane (EHTMS) and amino trimethylene phosphonic acid (ATMP) by sol–gel process. The structures and properties of membranes with different phosphonic acid content were extensively characterized by FTIR, TG-DSC and XRD. Their proton conductivity under dry condition was also investigated under different temperature. The results show that the proton conductivity of the prepared membranes strongly depends on temperature, and the proton conductivity ranges from 8.81 × 10⁻⁵ S cm⁻¹ at 20 °C to 4.65 × 10⁻² S cm⁻¹ at 140 °C under anhydrous condition. It indicates that the increasing temperature is favorable for congregating of the grafted–PO₃H₂ and increasing of the proton mobility. In addition, from the results of AFM images, it was confirmed that the continuous distribution of phosphonic acid groups is favorable for the formation of the proton transport channel, which can significantly enhance the proton conductivity of the membranes.     

Preparation and electrical conductivity of SiO2/polypyrrole nanocomposite

In the present study we have chemically polymerized silica/polypyrrole (SiO₂/PPy) nanocomposite in the presence of sodium dodecyl benzene sulfate (SDBS) as dopant and iron chloride (FeCl₃) as oxidant. The SiO₂/PPy nanocomposite presents an electrical conductivity of 32.41 S cm⁻¹ and percolation threshold of 20 wt%. The resulting SiO₂/PPy nanocomposites have been extensively characterized in terms of their molecular structure, particle size, morphology, stability, and electroactivity. These SiO₂/PPy particles have a rather polydisperse morphology. The effects of synthesis parameters such as oxidant, PPy, SDBS, reaction temperature and time, on the electrical conductivity of the nanocomposite have been detailedly optimized. And the conducting nanocomposite presented a good environmental stability.     

Preparation and properties of electrically conductive PPS/expanded graphite nanocomposites

Nanocomposites based on poly (phenylene sulfide) (PPS) and expanded graphite (EG) or ultrasonicated EG (S-EG) were prepared by melt blending. Morphologies of the nanocomposites were examined using both SEM and TEM. Electrical conductivity and thermal stability of PPS were notably enhanced by the introduction of EG. The percolation threshold values are 1 wt% (S-EG) and 2 wt% (EG) for PPS/S-EG and PPS/EG nanocomposites, respectively. The variation of mechanical strength with the weight fraction of EG and S-EG in the nanocomposites showed somewhat correlation with the threshold filler concentration. The crystallization behavior of PPS matrix in the nanocomposites was investigated using DSC, and the results indicated that the crystallization process was significantly accelerated, leading to an increase in crystallinity.     

Preparation of graphene nanosheets/SnO2 composites by pre-reduction followed by in-situ reduction and their electrochemical performances

The Graphene nanosheets/SnO₂ composites were synthesized using stannous chloride to restore the semi-reduction graphene oxide (SRGO) under a simple hydrothermal reduction procedure. First graphene oxide was pre-reduced by glucose for a certain time to get SRGO, which keeps the good water-solubility of graphite oxide (GO) and has a good conductivity like graphene nanosheets. The higher electrostatic attraction between SRGO and Sn²⁺ makes SnO₂ nanoparticles tightly anchor on the graphene sheets in the hydrothermal reduction process. The formation mechanism of the composite was investigated by SEM, TEM, XRD, AFM and Raman. Moreover, the electrochemical behaviors of the Graphene nanosheets/SnO₂ nanocomposites were studied by cyclic voltammogram, electrical impedance spectroscopy (EIS) and chronopotentiometry. Results showed that the Graphene nanosheets/SnO₂ composites have excellent supercapacitor performances: the specific capacitance reached 368 F g⁻¹ at a current density of 5 mA cm⁻², and the energy density was much improved to 184 Wh kg⁻¹ with a power density of 16 kW kg⁻¹, and capacity retention was more than 95% after cycling 500 cycles with a constant current density of 50 mA cm⁻². The experimental results and the thorough analysis described in this work not only provide a potential electrode material for supercapacitors but also give us a new way to solve the reunification of the graphene sheets.     

Effect of ultrasonication medium on the properties of copper nanoparticle-filled epoxy composite for electrical conductive adhesive (ECA) application

In this study, the relationship of three different media, (air, epoxy fluid, and chloroform solution) on the electrical, mechanical, and thermal properties of 5 vol.% copper nanoparticle (CuNP)-filled epoxy nanocomposite was investigated. Microscopic observation revealed that the CuNP ultrasonicated with chloroform solution exhibited the best filler distribution in the epoxy matrix. It showed high electrical conductivity of 7.65 × 10⁻³ S cm⁻¹ and flexural properties, and low coefficient of thermal expansion (CTE) compared with the other two nanocomposites. However, CuNP prepared by chloroform medium showed inferior thermal property compared with the other two nanocomposites according to thermogravimetric analysis (TGA).     

Impact of ethylene carbonate on ion transport characteristics of PVdF-AgCF3SO3 polymer electrolyte system

The ionic transport in thin film plasticized polymer electrolytes based on polyvinylidene fluoride (PVdF) as the polymer host, silver triflate (AgCF₃SO₃) as salt and ethylene carbonate (EC) as plasticizer prepared by solution casting technique has been reported. Addition of silver triflate has resulted in an increase in the room temperature (298 K) electrical conductivity of the polymer from 10⁻⁶ to 10⁻⁵ S cm⁻¹ whereas incorporation of EC as the plasticizer has further enhanced the conductivity value by an order of magnitude to 10⁻⁴ S cm⁻¹ owing to the possible decrease in crystallinity of the polymer matrix as revealed by the detailed temperature-dependent complex impedance, silver ionic transference number, Fourier transform infrared and X-ray diffraction measurements.     

Electrical,mechanical and thermal properties of polyvinyl chloride composites filled with aluminum powder

In this work, the electrical, mechanical and thermal properties of polyvinyl chloride (PVC) composites filled with different content of aluminum powder varying from 0 to 40 wt.% have been prepared. The dielectric properties of these composites were investigated in the frequency range 100 Hz–100 kHz at temperature range from 30 to 98 °C. The percolation threshold concentration, which is the concentration after which the conductivity increases many orders of magnitude with very little increase in the filler content for PVC/Al composites depends upon the measuring temperature, whether it is below or above the glass transition of the polymer matrix. The highest value of the electrical conductivity, σ, of the composites was found to be in the order of 10⁻⁸ S cm⁻¹, this value recommend such composites to be used in electrostatic dissipation applications as the range of conductivity for such application should be in the range of 10⁻⁵–10⁻⁹ S cm⁻¹.     

Phosphorus-doped bismuth telluride films by electrodeposition

Phosphorus-doped Bi₂Te₃ films were synthesized on a stainless-steel electrode by electrochemical deposition. X-ray diffraction, scanning electron microscopy and transmission electron microscopy confirmed that the films are single-phased Bi₂Te₃ solid solutions with a rhombohedral structure. The as-prepared films exhibit n-type characteristics with the Hall coefficient −1.76E−2 m³ C⁻¹ and the electrical conductivity 280 S cm⁻¹. The thermal conductivity is 0.47 W m⁻¹ K⁻¹, which is as low as one-third of the value observed in the bulk material. The doped P atoms occupy the interstitial positions between the two adjacent Te(1) layers connected by Van der Waals interaction in Bi₂Te₃.     

High-performance conductive materials based on the selective location of carbon black in poly(ether ether ketone)/polyimide matrix

A novel high performance conductive material with excellent comprehensive properties was prepared by melt-blending, and its performances were adjusted by controlling the selective location of carbon black (CB) in poly(ether ether ketone) (PEEK)/thermoplastic polyimide (TPI) matrix. With increasing the CB loadings, the morphology of PEEK/TPI blends changed from sea-island to co-continuous structure, which was owing to the selective location of CB in TPI phase. Notably, with the selective location of CB in the induced co-continuous PEEK/TPI matrix, the electrical percolation threshold was reduced to 5 wt%, which was significantly lower than that of binary PEEK/CB (9 wt%) and TPI/CB (10 wt%) composites. And the electrical conductivity of ternary PEEK/TPI/CB composites was 10⁴ to 10⁶ times higher than that of binary composites at identical 7.5 wt% CB loading, which was attributed to the double percolation effect. Moreover, the incorporation of CB could improve the thermal and mechanical properties effectively.     

Temperature dependent electrical conductivity of CNT–PEEK composites

The effect of temperature on electrical conductivity of nanocomposites consisting of Chemical Vapor Deposition (CVD)-grown multi-walled Carbon Nanotube (MWCNT) and Poly Ether Ether Ketone (PEEK) is presented in this paper. Different weight percentages of carbon nanotubes (CNT) were dispersed in PEEK through shear mixing by calendaring technique in Brabender. Percolation limit of the system was measured and discussed. The resulting nanocomposites were molded into round shaped pieces of 25.4 mm diameter and 1.4 mm thickness. The samples were then heated from room temperature to 140 °C while electrical conductivity is measured. It is found that electrical conductivity increases significantly with the increase in temperature and the rate of increase in conductivity with temperature depends on the content of CNT. The change in electrical conductivity does not follow the same route for heating and cooling cycle, thus resulting in electrical hysteresis.     

Nonisothermal crystallization behavior and mechanical properties of PEEK/SCF/nano-SiO2 composites

Nonisothermal crystallization of hybrid PEEK composites reinforced with short carbon fibers (SCF) and nano-SiO₂ (1, 1.5 and 2 wt%) was investigated using DSC. Composites were fabricated by melt-mixing process at 400 °C. The Size of the nanoparticles was 13 nm. Samples were cooled from 410 °C to 25 °C with cooling rates of 10, 30, 50 and 70 °C min⁻¹. The onset, peak and end crystallization temperatures were investigated as well as absolute crystallization percentage and crystallization time. Avrami, Ozawa and Ozawa–Avrami equations were fitted to the data in order to investigate the crystallization kinetics. Mechanical behaviors of the composites were examined using nanoindentation and nanoscratching. DSC results revealed that absolute crystallization percentage increases in PEEK/SCF/1%SiO₂ and PEEK/SCF/1.5%SiO₂ samples compared to PEEK/SCF, however it decreases by adding more nano-SiO₂. Ozawa–Avrami is proved to be the best model for describing crystallization behavior of the composites while Avrami equation was suitable for describing a part of the crystallization process. The Avrami and Ozawa–Avrami constants were calculated. Besides, adding SCFs and nano-SiO₂ into PEEK results in a significant decrease in plasticity index, while increases the resistance to plastic deformation of the composite.     

Synthesis of ferrofluid based nanoarchitectured polypyrrole composites and its application for electromagnetic shielding

The monodispersion of magnetic nanoparticles in conducting polymer is the prerequisite to make a high quality composite for tunable electromagnetic interference (EMI) shielding. To meet this challenge, we have designed and synthesized ferrofluid based nanoarchitectured polypyrrole composites containing Fe₃O₄ (8–12 nm) via in situ oxidative polymerization. To tune the microwave signals, polypyrrole composites (PFF) with different monomer/ferrofluid weight ratios have been prepared and characterized in microwave frequency domain. A maximum shielding effectiveness value of SE_A(max) = 20.4 dB (∼99% attenuation) due to the absorption of microwave has been observed in the frequency range of 12.4–18 GHz and attenuation level varied with ferrofluid loading. The electrical conductivity of PFF composite is of the order of 10⁻² S cm⁻¹ order and having superparamagnetic nature with saturation magnetization (M_s) of 5.5 emu g⁻¹. The lightweight PFF composites with high attenuations can provide full control over the atomic structure and are favorable for the practical EMI shielding application for commercial electronic appliances.     

Polyaniline–sodium montmorillonite clay nanocomposites: effect of clay concentration on thermal, structural, and electrical properties

A simple and facile method was used to synthesize polyaniline (PANI) nanocomposites with sodium montmorillonite clay (Na⁺-MMT) using in situ intercalative oxidative polymerization. Aniline was admixed with Na⁺-MMT at various concentrations, keeping the aniline monomer in the reaction mixture constant. The intercalation of PANI into the clay layers was confirmed by X-ray diffraction studies in conjugation with electron microscope techniques and FTIR spectra, particularly by the narrowing of the Si–O stretching vibration band confirmed the interaction between PANI and the clay. The employed route offers the possibility to improve the thermal properties with simultaneously controlled electrical conductivity. Thermal studies show an improved thermal stability of the nanocomposites relative to the pure PANI. Depending on the loading of the clay, the room temperature conductivity values of these nanocomposites varied between 2.0 × 10⁻⁴ and 7.4 × 10⁻⁴ S cm⁻¹, with the maximum at 44 wt% PANI concentration. The decrease of electrical conductivity at high PANI concentration was ascribed to the decrease of the structural ordering of PANI in the nanocomposite.     

Preparation and characterization of the graphene–carbon nanotube/CoFe2O4/polyaniline composite with reticular branch structures

A novel graphene–carbon nanotube (graphene–CNT)/CoFe₂O₄/polyaniline composite with reticular branch structures had been fabricated by in situ chemical polymerization method. The textured structures of the as-prepared composites were characterized by the fourier transform infrared (FTIR) and X-ray diffraction (XRD). The morphology was analyzed by the scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electromagnetic properties were tested by vibrating sample magnetometer and four-probe conductivity tester. The results showed that the graphene–CNT/CoFe₂O₄/polyaniline composite had the unique reticular branch structures. When the mass ratio of the graphene–CNT/CoFe₂O₄ to aniline was 1:3, the magnetic saturation value of the composite achieved 39.6 emu g⁻¹, and the conductivity reached 1.957 S cm⁻¹. Based on the experimental results, a probable formation mechanism for the unique reticular branch structures was proposed.     

Optimized deposition and characterization of nanocrystalline magnesium indium oxide thin films for opto-electronic applications

Transparent conducting magnesium indium oxide films (MgIn₂O₄) were deposited on to quartz substrates without a buffer layer at an optimized deposition temperature of 450 °C to achieve high transmittance in the visible spectral range and electrical conductivity in the low temperature region. Magnesium ions are distributed over the tetrahedral and octahedral sites of the inverted spinel structure with preferential orientation along (3 1 1) Miller plane. The possible mechanism that promotes conductivity in this system is the charge transfer between the resident divalent (Mg²⁺) and trivalent (In³⁺) cations in addition to the available oxygen vacancies in the lattice. A room temperature electrical conductivity of 1.5 × 10⁻⁵ S cm⁻¹ and an average transmittance >75% have been achieved. Hall measurements showed n-type conductivity with electron mobility value 0.95 × 10⁻² cm² V⁻¹ s⁻¹ and carrier concentration 2.7 × 10¹⁹ cm⁻³. Smoothness of the film surface observed through atomic force microscope measurements favors this material for gas sensing and opto-electronic device development.     

Nano iron oxide (Fe2O3)/carbon black electrodes as electrode material for electrochemical capacitors: Effect of the nanoparticles dispersion quality

In the present study, nano Fe₂O₃/carbon black electrodes are proposed for electrochemical capacitors and the effect of nanoparticles dispersion quality on the surface morphology, nature and electrochemical properties of the electrodes are investigated. Mechanical pressing is accompanied by different mixing (mechanical and sonication) processes to prepare the electrode. Electrochemical properties of the produced nanocomposites are studied using cyclic voltammetry and electrochemical impedance spectroscopy tests in 2 M KCl electrolyte. Scanning electron microscopy is used to characterize the microstructure and the nature of the nanoparticles on the nanocomposites produced. Results obtained show that the sonicated and unsonicated 10:80:10 (CB:Fe₂O₃:PTFE) electrodes have specific capacitance of 22.02 and 22.35 F g⁻¹ respectively, at scan rate of 10 mV s⁻¹. Sonication process breaks the agglomerated particles and disperses them on the electrode surface, uniformly. This increases the specific surface area and the electrical resistance of the electrodes. The sonicated electrodes show a higher charge separation capability at electrolyte/electrode interfaces, lower ratio of outer to total charge (q_O*/q_T*) of 0.13 and lower current response at end potentials. Energy density was increased after the sonication process from 0.686 to 1.498 (Wh kg⁻¹). Charge/discharge cycling results confirmed that the uniform dispersion of active material on the electrode surface postpones the electrolyte decomposition and improves the electrical conductivity during cycling.     

Wide gap p-type degenerate semiconductor: Mg-doped LaCuOSe

Hole transport and optical properties were investigated on undoped and Mg-doped LaCuOS_1−xSe_x (x=0-1) epitaxial films. Both electrical conductivity and Hall mobility were found to increase monotonously with increasing Se content in the films. The increase in Hall mobility is considered to be associated with the increase in valence band dispersion. Mg ion doping increased hole concentrations in the undoped films by an order of magnitude to ∼2×10²⁰ cm⁻³, while Mg doping reduced mobility to merely half that of undoped films. The results suggest that hole scattering due to Mg impurity ions is suppressed by natural modulation doping originating from the layered structure of LaCuOS_1−xSe_x. Hole concentrations showed no temperature dependence, indicating degenerate conduction. The largest value for conductivity, 140 S cm⁻¹, was obtained with Mg-doped LaCuOSe epitaxial film. Accompanying characteristics included moderately high optical transparency in the visible region and blue photoluminescence.