Variation of the general mixing rule to explore the interphase in the AC electrical conductivity of polypropylene melt-mixed with as-grown carbon nanofiber composites

Estimation of composites conductivity using a general mixing rule

Polyacrylonitrile (PAN) electrospinning in combination with sol–gel method has been a common technique to produce inorganic nanoparticles containing composite carbon nanofibers (CNFs) for diverse applications. To investigate the morphology evolution and crystal transformation of inorganic components along with CNF formation, bioactive glass (BG) containing CNFs (CNF/BG) were prepared by sintering as-spun PAN/precursor composite nanofibers in a nitrogen atmosphere at temperatures of 800, 1000 and 1200 °C. Comprehensive characterizations were performed with TEM, SEM-EDXA and XRD. For samples sintered at 800 °C, numerous BG nanoparticles were observed inside the CNFs and mainly in an amorphous state. With the sintering temperature raised to 1000 °C, a number of spherical BG nanoparticles were detected on the surface of the resulting CNFs, with a crystal structure of wollastonite (β-CaSiO3) polycrystals. When the samples were sintered at 1200 °C, the BG nanoparticles on the surface of CNFs merged into forms with cuboid-like geometry, mainly consisting of pseudowollastonite (Ca3(Si3O9)) single crystals. Based on the geometry evolution and dynamic size distribution function analyses (Ostwald ripening and Smoluchowski equations), it was concluded that the growth of BG nanoparticles conformed to the ripening mechanism at 800 °C and migration–coalescence mechanism at 1200 °C, while the process involved both ripening and migration–coalescence mechanisms at 1000 °C.

Highly conductive, porous RuO2/activated carbon nanofiber composites containing graphene for electrochemical capacitor electrodes

Electrospun fibrous membranes find place in diverse applications like sensors, filters, fuel cell membranes, scaffolds for tissue engineering, organic electronics etc. The objectives of present work are to electrospun polyacrylonitrile (PAN) nanofibers and PAN–CNT nanocomposite nanofibers and convert into carbon nanofiber and carbon-CNT composite nanofiber. The work was divided into two parts, development of nanofibers and composite nanofiber. The PAN nanofibers were produced from 9 wt% PAN solution by electrospinning technique. In another case PAN–CNT composite nanofibers were developed from different concentrations of MWCNTs (1–3 wt%) in 9 wt% PAN solution by electrospinning. Both types of nanofibers were undergone through oxidation, stabilization, carbonization and graphitization. At each stage of processing of carbon and carbon-CNT composite nanofibers were characterized by SEM, AFM, TGA and XRD. It was observed that diameter of nanofiber varies with processing parameters such as applied voltage tip to collector distance, flow rate of solution and polymer concentrations etc. while in case of PAN–CNT composite nanofiber diameter decreases with increasing concentration of CNT in PAN solution. Also with stabilization, carbonization and graphitization diameter of nanofiber decreases. SEM images shows that the minimum fiber diameter in case of 3 wt% of CNT solution because as viscosity increases it reduces the phase separation of PAN and solvent and as a consequence increases in the fiber diameter. AFM images shows that surface of film is irregular which give idea about mat type orientation of fibers. XRD results show that degree of graphitization increases on increasing CNT concentration because of additional stresses exerting on the nanofiber surface in the immediate vicinity of CNTs. TGA results shows wt loss decreases as CNT concentration increases in fibers.

Characterization of interfaces in ZrO 2–carbon nanofiber composite

Fourier transform infrared (FTIR) spectroscopy and wide‐angle X‐ray scattering (WAXS) investigations of isotactic polypropylene (iPP)–vapor‐grown carbon nanofiber (VGCNF) composites containing various amounts of VGCNFs ranging between 0 and 20 wt %. are reported. The FTIR investigations were focused on the regularity bands of iPP. The FTIR data indicated a drop in the isotacticity index as the concentration of nanofibers was increased; this suggested a decrease in the crystallinity. WAXS measurements revealed a dominating α1 phase, with a small admixture of γ phase or mesophase. The loading of the polymeric matrix with carbon nanofibers (CNFs) did not induce significant changes in the morphology of the polymeric matrix. A weak decrease in the size of α crystallites upon loading of CNFs was noticed. The experimental data obtained by FTIR spectroscopy supported the WAXS data. Spectroscopic data (a drop in the isotacticity index as estimated by FTIR spectroscopy and the ratio between the crystalline and total areas of WAXS lines assigned to iPP) failed to confirm the enhancement of the degree of crystallinity of polypropylene upon loading by nanofibers. However, whereas both techniques can identify with a high accuracy vibrations in ordered domains (FTIR spectroscopy) and the crystalline structure, including the lattice parameters and the size of crystallites (WAXS), difficulties in the correct assessment of the baseline and of amorphous components may result in important errors (typically >5%) in the estimation of the degree of crystallinity of the polymeric component. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Surface modification of RuO2 nanoparticles–carbon nanofiber composites for electrochemical capacitors

A properly understanding of how oil mixtures behaves as they flows in a pipeline is a key factor for piping design. Facilities engineers from oil companies currently use commercial pipeline simulators in order to perform pressure and temperature gradients predictions. Nearly all the simulators apply the general mixing rule when they need to calculate the viscosity of a certain oil mixture. As viscosity depends both on molecular characteristics and molecular interaction, and oil is a complex mixture of components, it is not surprising that this rule gives poor results. Besides, non-Newtonian behavior makes things more complex. This paper discusses experimental results of mixing at lab several different oils and measuring their viscosity. Each oil had its own composition and rheological behavior. Some mixtures were prepared in order to reproduce real situations. Once the mixtures viscosities were obtained they were introduced as input data in a commercial pipeline network and nodal analysis software. Then, pressure and temperature gradients were calculated Using the experimental mixture viscosityUsing the general mixing rule viscosity estimated by the software Results showed, in some cases, dramatic differences between the two alternatives. Higher deviations were obtained where the mixtures were composed of crudes of different properties. In order to improve the accuracy other mixing rules were tried and some of them fit better. A proper understanding of crude oil properties seems to be essential for successfully applying complex simulators in pipeline design.

The Discussers would like to congratulate the Author for his contribution to the analysis of response spectra. As mentioned in the Original Paper, engineers often pay little attention to incompatibilities in the histories of ground acceleration, displacement, and velocity. As a result, computed response spectra may exhibit erroneous trends at short and long periods. Different techniques have been proposed to treat the problem, focusing primarily on the initial conditions of the oscillator [5,6,8,9,10,11]. The Author proposes an alternative technique: determining response spectra by combining the incompatible time histories using a 'mixing rule' (Equations (6)-(8) in the Original Paper, which allows for the proper asymptotic behaviour to be obtained at extreme periods. The scope of this discussion is three-fold: (i) to present a simplified version of the method, by applying the Author's idea only to initial conditions; (ii) to discuss a more general mixing rule; (iii) to propose alternative ways for estimating the effective frequency of ground motion. These items are presented to further validate the results provided by the Author and offer additional insight into the derivations presented in the Original Paper.

Composites of carbon nanofibers (CNFs) and nanophase Pt-SnO2 were synthesized using electrospinning followed by carbonization, for use as anode materials in Lithium-ion batteries (LIBs). Composites of CNFs and nanophase Pt-SnO2 (sample B) exhibit the highest capacity (∼621.9 mAh/g at the 50th cycle) and excellent cyclic stability as compared to conventional CNFs and composites of CNFs and nanophase SnO2 (sample A). The result indicates that the improvement in performance of CNFs by the incorporation of nanophase Pt-SnO2 can be explained by the enhancement in electrical conductivity and the increase in the number of electrochemical active sites.

Natural rubber composites with different contents of 1 wt%, 3 wt%, 5 wt%, 10 wt%, and 20 wt% vapor-grown carbon nanofibers were synthesized using a solvent casting method. The morphology, electrical conductivity, dielectric property, and electromagnetic interference shielding effectiveness of natural rubber/vapor-grown carbon nanofiber composites at room temperature were investigated. The scanning electron microscopy image showed there was an even dispersion of vapor-grown carbon nanofibers in natural rubber. The electrical conductivity increased with the increase in vapor-grown carbon nanofiber content. The percolation threshold of natural rubber/vapor-grown carbon nanofiber composites was about 4.9 wt% according to the power law. The dielectric property of natural rubber/vapor-grown carbon nanofiber composites had frequency dependence and increased along with the addition of vapor-grown carbon nanofibers. The electromagnetic interference shielding effectiveness in X-band microwave frequency of natural rubber/20 wt% vapor-grown carbon nanofiber composite with 1 mm thickness was 12.8 dB.

Rational Fabrication and Improved Lithium Ion Battery Performances of Carbon Nanofibers Incorporated with α-Fe2O3 Hollow Nanoballs

Porous nanocomposites are prepared by electrospinning blended polyacrylonitrile, copper acetate and mutiwalled carbon nanotube in N, N-dimethylformamide. The electrospun nanofiber webs are oxidatively stabilized and then carbonized resulting in composite carbon nanofibers. The study reveals that composite nanofibers with relatively smooth surface morphology are successfully prepared. X-ray diffraction is used to confirm the presence of Cu in carbon nanofibers. The carbon nanofibers with CNTs have better thermal stability and higher electrical conductivity. The Brunauer-Emmett-Teller analysis reveals that C/Cu/CNTs nanocomposites with mesopores possess larger specific surface area and narrower pore size distribution than that of C/Cu nanofibers. The electrochemical properties are investigated by cyclic voltammetry and galvanostatic charge-discharge tests. The nanocomposite with 0.5 wt.% CNT loading exhibits an energy density of 2 Whkg−1, power density of 1916 Wkg−1, a specific capacitance of about 225 Fg−1 at a current density of 2 Ag−1 and its capacitance decreased to 78 % of its initial value after 3,000 cycles.

Graphene, carbon nanotubes (CNT), and carbon nanofibers (CNF) are the most studied nanocarbonaceous fillers for polymer-based composite fabrication due to their excellent overall properties. The combination of thermoplastic elastomers with excellent mechanical properties (e.g., styrene-b-(ethylene-co-butylene)-b-styrene (SEBS)) and conductive nanofillers such as those mentioned previously opens the way to the preparation of multifunctional materials for large-strain (up to 10% or even above) sensor applications. This work reports on the influence of different nanofillers (CNT, CNF, and graphene) on the properties of a SEBS matrix. It is shown that the overall properties of the composites depend on filler type and content, with special influence on the electrical properties. CNT/SEBS composites presented a percolation threshold near 1 wt.% filler content, whereas CNF and graphene-based composites showed a percolation threshold above 5 wt.%. Maximum strain remained similar for most filler types and contents, except for the largest filler contents (1 wt.% or more) in graphene (G)/SEBS composites, showing a reduction from 600% for SEBS to 150% for 5G/SEBS. Electromechanical properties of CNT/SEBS composite for strains up to 10% showed a gauge factor (GF) varying from 2 to 2.5 for different applied strains. The electrical conductivity of the G and CNF composites at up to 5 wt.% filler content was not suitable for the development of piezoresistive sensing materials. We performed thermal ageing at 120 °C for 1, 24, and 72 h for SEBS and its composites with 5 wt.% nanofiller content in order to evaluate the stability of the material properties for high-temperature applications. The mechanical, thermal, and chemical properties of SEBS and the composites were identical to those of pristine composites, but the electrical conductivity decreased by near one order of magnitude and the GF decreased to values between 0.5 and 1 in aged CNT/SEBS composites. Thus, the materials can still be used as large-deformation sensors, but the reduction of both electrical and electromechanical response has to be considered.

Effect of mechanical stretching on electrical conductivity and positive temperature coefficient characteristics of poly(vinylidene fluoride)/carbon nanofiber composites prepared by non-solvent precipitation