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The influence of carbon nanofibers (CNFs) on carbon fiber (CF) reinforced polymer (CFRP) is investigated in this study. A program is developed to generate the finite element model (FEM) for the nanocomposites. The randomness of both CNFs and CF in CFRP is considered. The effects of volume fraction of CNFs and CFs, as well as interfacial strength are analyzed numerically. The improvement in strength and toughness of composites under different loading conditions is investigated. It shows that CNFs lead the redistribution of stress in the matrix, which releases stress concentration between CFs and polymer and increases the initial damage threshold. [ABSTRACT FROM AUTHOR]

The paper presents the results of experimental studies in the scope of formation of bulky aluminum based composite materials (CM) with carbon nanofibers (CNF), including the research methods of hot extrusion and rolling. Extrusion manufacture of bulky composite materials contributes to obtain billets with a minimum compression degree (λ = 1.5). To reduce shear deformations and formation of pores in extruded billet, the extrusion process modes were selected experimentally. In the course of further rolling operation, mechanical properties increase twice and inhomogeneity is compensated after significant compression of the extrusion billets, and the shear deformations are reduced in full volume of the material. Bulky materials gain high hardness, wear resistance and strength. The economically alloyed composite material has feasible prospects to be applicable in lightweight structures for aviation and automobile industries. [ABSTRACT FROM AUTHOR]

The aim of this study was to research the effect of carbon nanofiber (CNF), the microballoon (MB) volume fraction and its density on both the vibration properties and impact behavior of carbon nanofiber – reinforced syntactic foam. Twelve different types of syntactic foam were produced with two different CNF contents, two different MB densities and two different MB volume fractions. Neat epoxy, syntactic foams with and without carbon nanofiber were manufactured for characterization by comparing each other in terms of mechanical and dynamic properties. With the free vibration tests, natural frequencies and damping ratios were investigated. Besides vibrations tests, low-velocity impact and tensile tests were conducted on the syntactic foams. Analyses of the results were performed on the effect of the volume fraction of additives and MB density on the vibration, impact and tensile behavior of the syntactic foams. In addition, SEM was used to understand the microstructure of the samples tested. Vibration results presented that the presence of carbon nanofiber enhanced strength but was not effective on damping, while low-velocity impact, and tensile test results also demonstrated the same trend. [ABSTRACT FROM AUTHOR]

Activated carbon nanofibers (CNFs) were derived from electrospun nanofibers with subsequent heat treatment. They were characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. The applicability of activated CNFs for preconcentration and determination of organophosphorus pesticides (OPPs) was investigated by high-performance liquid chromatography with diode array detector (HPLC-DAD). Some important parameters influencing the extraction efficiency, such as amount of sorbent, pH, flow rate and amount of salt, were investigated by response surface method (RSM). The obtained results showed that this analytical method will be useful for the analysis of OPPs in tap water with high precision and accuracy. [ABSTRACT FROM AUTHOR]

This article presents the fabrication and characterization of poly dimethylsiloxane/carbon nanofiber (CNF)-based nanocomposites. Although silica and carbon nanoparticles have been traditionally used to reinforce mechanical properties in PDMS matrix nanocomposites, this article focuses on understanding their impacts on electrical and thermal properties. By adjusting both the silica and CNF concentrations, 12 different nanocomposite formulations were studied, and the thermal and electrical properties of these materials were experimentally characterized. The developed nanocomposites were prepared using a solvent-assisted method providing uniform dispersion of the CNFs in the polymer matrix. Scanning electron microscopy was employed to determine the dispersion of the CNFs at different length scales. The thermal properties, such as thermal stability and thermal diffusivity, of the developed nanocomposites were studied using thermogravimetirc and laser flash techniques. Furthermore, the electrical volume conductivity of each type of nanocomposite was tested using the four-probe method to eliminate the effects of contact electrical resistance during measurement. Experimental results showed that both CNFs and silica were able to impact on the overall properties of the synthesized PDMS/CNF nanocomposites. The developed nanocomposites have the potential to be applied to the development of new load sensors in the future. [ABSTRACT FROM AUTHOR]

The present work reported on the use of graphene oxide (GO) as effective dispersant to isolate different carbon allotropes. The nature of its chemical structure which consists of hydrophobic and hydrophilic components enables GO to behave as surfactant, paving routes for dissolution of graphitic materials and achieving surfactant free all-carbon solutions. Two additional carboneous materials under the family of fullerene (carbon nanofiber—CNF) and graphite (graphene nanoplatelets—GnP) were introduced within the present study to form a new GO based hybrid complexes on top of the commonly investigated carbon nanotube (CNT) based GO hybrid. Investigation on GO stability with respect to particle size and zeta potential measurements showed that the strength of its dispersibility was highly dependent on its morphological size and less affected by the pH. Rheological study revealed that GO shear–strain relationship is highly sensitive to the particle size. The GO viscosity experienced dramatic changes from Newtonian toward shear thinning behaviors as the particle size increases. Thermal conductivity measurement highlighted as high as 8% increase in magnitude with the addition of CNT, CNF, and GnP carbon constituents, indicating that the enhancement may be attributed to the much efficient thermal transport along the conducting path of pristine carbon allotropes. [ABSTRACT FROM PUBLISHER]

Electrospun polyacrylonitrile (PAN) nanofibers were pre-oxidized under 1, 2, and 3 wt% of KMnO4aqueous solutions. Scanning electron microscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, X-ray diffraction and Raman spectroscopy were used to study the effect of KMnO4concentration on the structures and properties of PAN-based heat stabilized and carbonized electrospun nanofiber mats. In FT-IR spectra of the preoxidized samples a new peak at 2340 cm−1designated to MnO4–C=N conjugation was revealed. Chemical modification by KMnO4was used to decrease the average diameter, increase the Bragg spacing, and decrease the preferred orientation and the crystal size. According to the Raman spectra, the bandwidths of the G mode became wider in the cases of preoxidized samples, while the G mode intensities belonging to the crystalline regions were decreased. According to the TGA studies, the weight losses in the preoxidized samples were severe due to the permanganate attack. [ABSTRACT FROM PUBLISHER]

Electrospun carbon nanofibers (ECNFs) have many qualities that make them attractive for applications in various fields of technology. For many applications, it is necessary to modify the surface of CNFs by chemical functionalization. Here, a systematic functionalization of polyacrylonitrile (PAN)-based ECNFs by oxidation in concentrated nitric acid was examined. The effects of oxidation on the microstructural, electrical, and mechanical characteristics have been studied. The Fourier transform infrared spectroscopy results revealed the time-dependent functionalization of ECNFs. However, according to the scanning electron microscopy, there was no considerable change in the surface morphology of CNFs due to functionalization. The microstructures as well as electrical and mechanical properties were severely dependent on oxidation duration according to X-ray diffraction and Raman spectroscopies as well as conductivity and mechanical strength measurements, respectively. Increase in oxidation duration led to more structural disorders and noticeable decrease in electrical conductivity and mechanical strength. [ABSTRACT FROM AUTHOR]

Carbon naonfibers (CNFs) were heat-treated in a spark plasma sintering (SPS) system with vacuum condition at 1500°C with various uniaxial pressures. The microstructural evolutions of CNFs under both high temperature and additional pressure were investigated by scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. It is proposed that the high temperature is contributing to the formation of high ordered and large crystalline graphitic layers, while applied pressure is in favor of cutting down the CNFs to shorter ones and coalescing them to form micro-sized graphitic sheets. Our results propose that the SPS is an efficient route to explore the materials’ structural conversions at high pressure and high temperature. [ABSTRACT FROM AUTHOR]

A novel electrochemically-based biosensor was developed for the determination of hydrazine by modifying a glassy carbon electrode with an aqueous dispersion of carboxylic group-functionalized carbon nanofiber/chitosan solution, and then absorbing hemoglobin on the surface of chitosan-carbon nanofibers. Nafion was used to coat the hemoglobin membrane. The interactions of hemoglobin and the nafion/chitosan-carbon nanofibers were investigated by ultraviolet-visible absorption, infrared, and circular dichroism spectroscopies. The results indicated that the native structure of hemoglobin was retained post-immobilization. The circular dichroism results showed that the α-helical structure of hemoglobin was preserved though a small change was observed in the presence of the nafion/chitosan-carbon nanofibers. The modified nanofibers were further characterized by scanning electron microscopy, electron impendence spectroscopy, and cyclic voltammetry. The electrocatalytic mechanism of hemoglobin to the oxidation of hydrazine was investigated and an irreversible diffusion-controlled electrode process was obtained. The electron transfer rate constant (ks), transfer coefficient (α), and Michaelis–Menten constant (Km) were also evaluated. The peak current of the catalytic oxidation was linear with hydrazine concentration from 3.722 × 10−5to 1.601 × 10−3molar with a correlation coefficient of 0.995. The detection limit was estimated to be 2.7 micromoles per liter. The sensitivity, stability, and reproducibility of the nafion/hemoglobin/chitosan-carbon nanofiber/glassy carbon electrode for the oxidation of hydrazine were also investigated. [ABSTRACT FROM AUTHOR]

Ultra-high-performance concrete (UHPC) incorporates a relatively large volume fraction of very dense cementitious binder with microscale fibers. The dense binder in UHPC can effectively interact with nano- and microscale reinforcement, which offers the promise to overcome the brittleness of UHPC. Nanoscale reinforcement can act synergistically with microscale fibers by providing reinforcing action of a finer scale, and also by improving the bond and pullout behavior of microscale fibers. Carbon nanofiber (CNF) and polyvinyl alcohol (PVA) fiber were used as nanoand microscale reinforcement, respectively, in UHPC. An optimization experimental program was conducted in order to identify the optimum dosages of CNF and PVA fiber for realizing balanced gains in flexural strength, energy absorption capacity, ductility, impact resistance, abrasion resistance, and compressive strength of UHPC without compromising the fresh mix workability. Experimental results indicated that significant and balanced gains in the UHPC performance characteristics could be realized when a relatively low volume fraction of CNF (0.047 vol.% of concrete) is used in combination with a moderate volume fraction of PVA fibers (0.37 vol.% of concrete). [ABSTRACT FROM AUTHOR]