Effect of Processing Parameters on Bonding Performance of a Carbon Fiber/Polyetheretherketone Thermoplastic Composite Prepared by Induction Welding.

Among the various welding techniques used to bond thermoplastic composites, induction welding stands out as a fast, clean, and contact-free process that shortens the welding time and prevents the weight increase of mechanical fastening, such as rivets and bolts. In this study, we manufactured polyetheretherketone (PEEK)-resin-based thermoplastic carbon fiber (CF) composite materials at different automated fiber placement laser powers (3569, 4576, and 5034 W) and investigated their bonding and mechanical characteristics after induction welding. The quality of the composite was evaluating using various techniques, including optical microscopy, C-scanning, and mechanical strength measurements, and a thermal imaging camera was used to monitor the surface temperature of the specimen during its processing. The results revealed that the preparation conditions of the polymer/carbon fiber composites, such as the laser power and surface temperature, significantly affect the quality and performance of the induction-welding-bonded composites. A lower laser power during preparation resulted in weaker bonding between components of the composite and yielded samples with a lower shear stress.

Manufacturing of Carbon Fibers/Polyphenylene Sulfide Composites via Induction-Heating Molding: Morphology, Mechanical Properties, and Flammability.

Conventional thermosetting composites exhibit advantageous mechanical properties owing to the use of an autoclave; however, their wide usage is limited by high production costs and long molding times. In contrast, the fabrication of thermoplastic composites involves out-of-autoclave processes that use press equipment. In particular, induction-heating molding facilitates a quicker thermal cycle, reduced processing time, and improved durability of the thermoplastic polymers; thus, the process cost and production time can be reduced. In this study, carbon fiber/polyphenylene sulfide thermoplastic composites were manufactured using induction-heating molding, and the relationships among the process, structure, and mechanical properties were investigated. The composites were characterized using optical and scanning electron microscopy, an ultrasonic C-scan, and X-ray computed tomography. In addition, the composites were subjected to flammability tests. This study provides novel insights into the optimization of thermoplastic composite manufacturing and thermoset composite curing processes.

A Facile Fabrication of Ordered Mesoporous Carbons Derived from Phenolic Resin and Mesophase Pitch via a Self-Assembly Method.

Ordered and disordered mesoporous structures were synthesized by a self-assembly method using a mixture of phenolic resin and petroleum-based mesophase pitch as the starting materials, amphiphilic triblock copolymer F127 as a soft template, hydrochloric acid as a catalyst, and distilled water as a solvent. Then, mesoporous carbons were obtained via autoclave method at low temperature (60 °C) and then carbonization at a relatively low temperature (600 °C), respectively. X-ray diffraction (XRD), small-angle X-ray scattering (SAXS), and transmission electron microscopy (TEM) analyses revealed that the porous carbons with a mesophase pitch content of approximately 10 wt% showed a highly ordered hexagonal mesostructure with a highly uniform pore size of ca. 5.0 nm. In addition, the mesoporous carbons prepared by self-assembly and low-temperature autoclave methods exhibited the amorphous or crystalline carbon structures with higher specific surface area (SSA) of 756 m2/s and pore volume of 0.63 cm3/g, depending on the synthesis method. As a result, mesoporous carbons having a high SSA were successfully prepared by changing the mixing ratio of mesophase pitch and phenolic resin. The electrochemical properties of as-obtained mesoporous carbon materials were investigated. Further, the OMC-meso-10 electrode delivered the maximum SC of about 241 F/g at an applied current density of 1 A/g, which was higher than those of the MC-10 (~104 F/g) and OMC-20 (~115 F/g).

Hydrothermal Preparation of Ag/TiO2/GO Nanocomposites with Ammonia-Treated Graphene Oxide for Enhanced Conductivity.

In this study, Ag/TiO2/GO nanocomposites were successfully fabricated by a facile hydrothermal method. Nitrogen-doped GO was prepared using ammonia treatment to improve its conductivity. The Ag/TiO2/GO nanocomposites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (DRS), zeta potential, and photoluminescence spectroscopy (PL). A homogeneous dispersion of Ag/TiO2 nanoparticles was shown on the surface of GO. Increasing the nitrogen doping concentration increased hydrophilicity, thereby improving the conductivity of Ag/TiO2/GO nanocomposites.

Relationship Between Functionalized Multi-Walled Carbon Nanotubes and Damping Properties of Multi-Walled Carbon Nanotubes/Carbon Fiber-Reinforced Plastic Composites for Shaft.

The mechanical properties and damping behavior of carbon fiber-reinforced plastic composites with functionalized multi-walled carbon nanotubes were examined. The functionalized multi-walled carbon nanotubes were blended with epoxy resins to prepare multi-walled carbon nanotubes/carbon fiber-reinforced plastic composites. The dispersion properties of functionalized multi-walled carbon nanotubes in epoxy resins were examined using surface free energy. The mechanical properties of functionalized multi-walled carbon nanotubes/carbon fiber-reinforced plastic composites were measured by interlaminar shear strength and torsion strength. The functionalized multi-walled carbon nanotubes/carbon fiber-reinforced plastic composites had superior mechanical properties due to the increase in dispersion properties of functionalized multi-walled carbon nanotubes in epoxy resins. However, the tan delta values of damping behavior, analyzed by dynamic mechanical analysis, varied with the type of functional groups of functionalized multi-walled carbon nanotubes. The composites obtained from functionalized multi-walled carbon nanotubes obtained through spermidine amidation reaction and carbon fiber-reinforced plastic showed excellent tan delta values due to the flexible segments in side chains.

Oxalic acid assisted rapid synthesis of mesoporous NiCo2O4 nanorods as electrode materials with higher energy density and cycle stability for high-performance asymmetric hybrid supercapacitor applications.

In this study, mesoporous nickel cobaltite (NiCo2O4) nanorods as electrode materials for high-performance hybrid supercapacitor were fabricated onto Ni foam by a simple and cost effective oxalic acid (OA) assisted rapid co-precipitation method. The effects of different metal precursors (NCO-Nitrate, NCO-Chloride and NCO-Acetate) on the electrochemical capacitive properties were studied. FE-SEM analysis confirmed that all samples exhibited highly dense mesoporous NiCo2O4 nanorods vertically grown on the surface of Ni foam with excess accessible surfaces and unique sizes and morphologies. The resultant NiCo2O4 nanorod electrodes (for NCO-Nitrate, NCO-Chloride and NCO-Acetate) delivered the maximum specific capacitances of 790, 784, 776 F g-1 at the current density of 1 A g-1 with ultra-high capacitance retention of 82.27, 81.63 and 81.71% even at 20 A g-1 and excellent cyclic stability of 84.25, 83.33 and 83.24% capacitance retention at 5 A g-1 after 5000 cycles. The asymmetric supercapacitor (ASC) device was also sandwiched by using NCO-Nitrate as positive electrode and N-doped graphene hydrogel (NGH) as negative electrode. The fabricated ASC device delivered superior energy density (42.5 W h kg-1) at high power density (746.34 W kg-1) with excellent long cyclic stability (90% initial capacitance retention after 5000 cycles at 5 A g-1).

One-Pot Synthesis of Ag-TiO2/Nitrogen-Doped Graphene Oxide Nanocomposites and Its Photocatalytic Degradation of Methylene Blue.

In this study, we report Ag-TiO2/graphene oxide (GO) nanocomposites prepared by a simple one-pot synthesis using TiO2, AgNO3, and N-doped graphene (NDG). The NDG was synthesized using a microwave-assisted hydrothermal (MHT) method as a function of MHT time. The morphology and structure of Ag-TiO2/GO nanocomposites were characterized by scanning electron microscopy (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), Raman, and Fourier-transform infrared spectroscopy (FTIR). The photocatalytic activity of Ag-TiO2/GO nanocomposites in visible light was explored using the degradation, of methylene blue (MB) dye under the ultraviolet (UV) light. The result showed that Ag-TiO2/GO-3 was very efficient for the degradation of MB with nitrogen doping time. The degradation efficiency of the photocatalytic nanoparticles after 6 h of irradiation was about 80%. Increasing the N-doping time increased their hydrophilicity, thereby improving the photocatalytic performance of Ag-TiO2/GO nanocomposites.

Effect of Silane Coupling Agent on the Creep Behavior and Mechanical Properties of Carbon Fibers/Acrylonitrile Butadiene Rubber Composites.

In this study, we investigated the effect of the silane coupling agent on the relationship between the surface free energy of carbon fibers (CFs) and the mechanical strength of CFs/acrylonitrile butadiene rubber (NBR) composites. Moreover, the creep behavior of the CF/NBR composites at surface energetic point of view were studied. The specific component of the surface free energy of the carbon fibers was found to increase upon grafting of the silane coupling agent, resulting in an increase in the tensile strength of the CF/NBR composites. On the other hand, the compressive creep strength was found to follow a slightly different trend. These results indicate the possible formation of a complex interpenetrating polymer network depending on the molecular size of the organic functional groups of the silane coupling agent.

NiCo2S4 nanosheet-decorated 3D, porous Ni film@Ni wire electrode materials for all solid-state asymmetric supercapacitor applications.

Wire type supercapacitors with high energy and power densities have generated considerable interest in wearable applications. Herein, we report a novel NiCo2S4-decorated 3D, porous Ni film@Ni wire electrode for high performance supercapacitor application. In this work, a facile method is introduced to fabricate a 3D, porous Ni film deposited on a Ni wire as a flexible electrode, followed by decoration with NiCo2S4 as an electroactive material. The fabricated NiCo2S4-decorated 3D, porous Ni film@Ni wire electrode displays a superior performance with an areal and volumetric capacitance of 1.228 F cm-2 and 199.74 F cm-3, respectively, at a current density of 0.2 mA cm-1 with a maximum volumetric energy and power density (EV: 6.935 mW h cm-3; PV: 1.019 W cm-3). Finally, the solid state asymmetric wire type supercapacitor is fabricated using the fabricated NiCo2S4-decorated 3D, porous Ni film@Ni wire as a positive electrode and N-doped reduced graphene oxide (N-rGO) as a negative electrode and this exhibits good areal and volumetric capacitances of CA: 0.12 F cm-2 and CV: 19.57 F cm-2 with a higher rate capability (92%). This asymmetric wire type supercapacitor demonstrates a low leakage current and self-discharge with a maximum volumetric energy (EV: 5.33 mW h cm-3) and power (PV: 855.69 mW cm-3) density.

Hierarchically Assembled Nanofibers Created by a Layer-by-Layer Self-Assembly.

We report the hierarchically assembled nanofibers created by LbL self-assembly depending on the PSS-PAA fraction in the blend solutions and pH during bulid-up of the PAH/(PSS-PAA) multilayer films. The multilayer [(PEI/blend)/(PAH/blend)4] films with ρPAA (PSS-PAA fraction in the blend solutions) = 0.0 in the blend solution exhibited surface morphologies of randomly isolated globular clusters, while at ρPAA = 0.75, worm-like morphologies were observed. Interestingly, the multilayer [(PEI/blend)/(PAH/blend)4 films with ρPAA = 0.9 exhibited unique fibrous morphologies with the diameter of about 50 nm at narrower pH range from 3.5 to 4.2, but also the fiber diameter distribution was narrower. Based on the thickness from the X-ray reflectivity, the thickness of the one bilayer multilayer film seemed to be 8.6 nm. The 3 bilayers multilayer film seemed to be formed as islands with very large roughness. The crystal sizes of the 3 bilayers and 5 bilayers multilayer films were about 71 nm and 123 nm, respectively. The resultant films were characterized using atomic force microscopy (AFM) and real-time in situ X-ray scattering measurements.

Facile Synthesis of Core/Shell-like NiCo2O4-Decorated MWCNTs and its Excellent Electrocatalytic Activity for Methanol Oxidation.

The design and development of an economic and highly active non-precious electrocatalyst for methanol electrooxidation is challenging due to expensiveness of the precursors as well as processes and non-ecofriendliness. In this study, a facile preparation of core-shell-like NiCo2O4 decorated MWCNTs based on a dry synthesis technique was proposed. The synthesized NiCo2O4/MWCNTs were characterized by infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and selected area energy dispersive spectrum. The bimetal oxide nanoparticles with an average size of 6 ± 2 nm were homogeneously distributed onto the surface of the MWCNTs to form a core-shell-like nanostructure. The NiCo2O4/MWCNTs exhibited excellent electrocatalytic activity for the oxidation of methanol in an alkaline solution. The NiCo2O4/MWCNTs exhibited remarkably higher current density of 327 mA/cm(2) and a lower onset potential of 0.128 V in 1.0 M KOH with as high as 5.0 M methanol. The impressive electrocatalytic activity of the NiCo2O4/MWCNTs is promising for development of direct methanol fuel cell based on non-Pt catalysts.

Effects of oxyfluorination on surface and mechanical properties of carbon fiber-reinforced polarized-polypropylene matrix composites.

In this work, oxyfluorination treatments on carbon fiber surfaces were carried out to improve the interfacial adhesion between carbon fibers and polarized-polypropylene (P-PP). The surface properties of oxyfluorinated carbon fibers were characterized using a single fiber contact angle, and X-ray photoelectron spectroscopy. The mechanical properties of the composites were calculated in terms of work of adhesion between fibers and matrices and also measured by a critical stress intensity factor (K(IC)). The K(IC) of oxyfluorinated carbon fibers-reinforced composites showed higher values than those of as-received carbon fibers-reinforced composites. The results showed that the adhesion strength between the carbon fibers and P-PP had significantly increased after the oxyfluorination treatments. As the theoretical and practical comparisons, OF-CF-60s showed the best mechanical interfacial performance due to the good surface free energy. This indicates that oxyfluorination produced highly polar functional groups on the fiber surface, resulting in strong adhesion between carbon fibers and P-PP in this composite system.

Electrochemical characterization of a carbon nanofiber electrode system hybridized with PEDOT-PSS.

In this work, electrochemical properties of a bilayer electrode system prepared from an electrically conducting polymer, poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), PEDOT-PSS coated carbon nanofibers (CNFs), have been investigated. The CNFs were used as supports for the deposition of PEDOT-PSS by a dip-coating technique to yield a bilayer electrode system. Electrodes prepared by such a method were used in supercapacitors operating in acidic (1 M H2SO4) electrolytes. The capacitance values were estimated by voltammetry and galvanostatic techniques with a three-electrode cell configuration. Due to the CNF's graphitic structure and the presence of exterior walls with numerous edges, a high specific surface area and easily accessible electrode/electrolyte interface were obtained, thus yielding good capacitance in the bilayer active materials. The capacitance for PEDOT-PSS coated CNF bilayer electrodes ranged from 80 to 180 F/g and the fabricated materials showed good cycling performance with high stability in aqueous electrolytes. This was probably due to enhanced access to the CNFs, leading to the generation of a double layer and, ultimately, higher values of the capacitance.

Synthesis of mesoporous anatase TiO2 nanotubes by a hydrothermal treatment and their use in solid-state dye-sensitized solar cells.

Mesoporous anatase TiO2 nanotubes (NTs) with the diameter of about 7 12 nm and the length of several hundred nanometers were synthesized by a hydrothermal method on commercial TiO2 particles in NaOH followed by HCI washing. The samples were characterized by X-ray diffraction (XRD), transmitting electron microscopy (TEM), and Brunauer-Emmet-Teller (BET) measurements. The hydrothermal treatment temperature at 130 degrees C was shown to affect not only the extent of particle-to-sheet conversion, and thus the resulting structures of the NTs, but also the anatase-to-rutile transformation. The surface area of the NTs was 200 m2g(-1). This value was much higher in comparison to TiO2 nanoparticles of 50 m2g(-1). It was also found that the NT photoelectrodes had a pronounced impact on the performance of solar cells as compared to nanoparticle ones. This was probably due to lead to a significantly higher specific dye loading and, for certain hydrothermal treatments, resulting in a doubling of the solar cell efficiency (in our case from 2.84% to 4.03% of AM 1.5 conditions).

Preparation and characterization of ACs/TiO2 composite electrodes for improving the specific capacitance of electrochemical double-layer capacitors.

In this work, the energy storage composite electrodes were prepared by mixing activated carbons (ACs) modified with a nanosize titanium oxide (TiO2) through a means of ultrasonic vibration in ethanol solution for 30 min. We examined the cyclic voltammetry of the composite electrodes in an aqueous electrolyte, 1 M H2SO4. It was found that the specific capacitance of the composite electrodes measured in a range of 0-0.8 V was increased from 100 to 155 F/g compared to carbon electrodes comprised of activated carbon only. This was attributed to a reduction of polarization of the ACs modified by nanosized TiO2.

Electrocatalytic properties of graphite nanofibers-supported platinum catalysts for direct methanol fuel cells.

Graphite nanofibers (GNFs) treated at various temperatures were used as carbon supports to improve the efficiency of PtRu catalysts. The electrochemical properties of the PtRu/GNFs catalysts were then investigated to evaluate their potential for application in DMFCs. The results indicated that the particle size and dispersibility of PtRu in the catalysts were changed by heat treatment, and the electrochemical activity of the catalysts was improved. Consequently, it was found that heat treatments could have an influence on the surface and structural properties of GNFs, resulting in enhancing an electrocatalytic activity of the catalysts for DMFCs.

Surface characteristics of carbon fibers modified by direct oxyfluorination.

The effect of oxyfluorinated conditions on the surface characteristics of carbon fibers was investigated. Infrared (IR) spectroscopy results indicated that the oxyfluorinated carbon fibers showed carboxyl/ester groups (CO) at 1632 cm(-1) and hydroxyl groups (OH) at 3450 cm(-1) and had a higher OH peak intensity than that of the fluorinated ones. X-ray photoelectron spectroscopy (XPS) results for the fibers also showed that oxyfluorination introduced a much higher oxygen concentration onto the fiber surfaces than fluorination with F(2) only. Additionally, contact-angle results showed that the surface was better wetted by following oxyfluorination and that the polarity of the surface was increased by increasing the oxyfluorination temperature.

Influence of surface characteristics of carbon blacks on cure and mechanical behaviors of rubber matrix compoundings.

In this work, the effect of chemical modification on the surface energetics and cure kinetics of carbon blacks (CBs) modified with KOH and C6H6 was investigated by contact angle and rheometer measurements, respectively. Also, the resulting mechanical properties of the CBs/styrene-butadiene composites were studied in terms of tensile and dynamic mechanical analysis. As experimental results, the polar basic and nonpolar chemical treatments showed an increase of the London dispersive component (gamma(S)(L)) of gamma(S) of the CBs without significantly changing the surface properties and microstructures that resulted from the deaggregation of microstructures and decrease of the swollen weight of the sample in the equilibrium state. Also, it was clearly revealed that the increase of gamma(S) of the CBs could largely affect the vulcanization and mechanical properties of the composites, resulting from the increase in gamma(S)(L) of the CBs. These results were evident that the mechanical properties of the composites were controlled more by the gamma(S)(L) of gamma(S) than by the specific (or polar) component (gamma(S)(SP)), including electron acceptor and donor parameters on CB surfaces in an organic matrix composite system.

Influence of atmospheric plasma on physicochemical properties of vapor-grown graphite nanofibers.

Vapor-grown graphite nanofibers (GNFs) were modified by plasma treatments using low-pressure plasmas with different gases (Ar gas only and/or Ar/O2 gases), flow rates, pressures, and powers. Surface characterizations and morphologies of the GNFs after plasma treatment were investigated by X-ray photoelectron spectroscopy (XPS), contact angle, titration, and transmission electron microscopy (TEM) measurements. Also, the investigation of thermomechanical behavior and impact strengths of the GNFs/epoxy composites was performed by dynamic-mechanical thermal analysis (DMTA) and Izod impact testing, respectively. The plasma treatment of the fibers changed the surface morphologies by forming a layer with a thickness on the order of 1 nm, mainly consisting of oxygen functional groups such as hydroxyl, carbonyl, and carboxyl groups. After functionalization of the complete surfaces, further plasma treatment did not enhance the superficial oxygen content but slightly changed the portions of the functional groups. Also, the composites with plasma-treated GNFs showed an increase in T(g) and impact strength compared to the composites containing the same amount of plasma-untreated GNFs.