Flexural fatigue behavior of synthesized graphene/carbon-nanofiber/epoxy hybrid nanocomposites

In the present research, effects of adding a combination of synthesized graphene nanosheets and carbon nanofibers (CNFs) on the flexural fatigue behavior of epoxy polymer have been investigated. Graphene nanosheets are synthesized based on a changing magnetic field. The flexural bending fatigue life of 0.5 wt.% of graphene/CNF/epoxy hybrid nanocomposites has been considered at room temperature. The samples were subjected to different displacement amplitudes fatigue loadings. Due to the addition of hybrid nanoparticles, a remarkable improvement in fatigue life of epoxy resin was observed in comparison with results obtained by adding 0.25 wt.% graphene or 0.25 wt.% CNF into the resin. Experimental observations show that at a strength ratio equal to 43% by using 0.5 wt.% of hybrid nanoparticles; 37.3-fold improvement in flexural bending fatigue life of the neat epoxy was observed. While, enhancement of adding only graphene or CNF was 27.4 and 24-fold, respectively.     

Enhanced electrochemical capacitance of polyaniline/graphene hybrid nanosheets with graphene as templates

Polyaniline/graphene nanocomposites (PANi/GR) were prepared via PANi covalent grafting from the surface of GR. The unique structure of hybrid nanosheets was formed with uniform PANi layer coating GR without phase separation appearing when the weight ratio of aniline-to-graphene was 1:1. The unique PANi/GR hybrid nanosheets as electrode material for supercapacitors have a specific capacitance as high as 922 F/g at 10 mV/s and still retain a specific capacitance of 106 F/g at a high scan rate of 1 V/s due to synergistic effect between PANi and GR. The capacitance retention was ∼90% after 1000 cycles, which is much better than that of pure PANi or other PANi nanocomposites. The enhanced capacitive performance of PANi/GR hybrid nanosheets makes them have potential application in developing high performance energy storage devices.     

Ultrasound-assisted fabrication of dispersed two-dimensional copper/reduced graphene oxide nanosheets nanocomposites

Graphene oxide nanosheets (GOS) were employed as template and hydrazine hydrate was used as reductant for GOS and cupric ion. Highly dispersed two-dimensional (2D) copper/reduced graphene oxide nanosheets (Cu/RGOS) nanocomposites were effectively fabricated by ultrasound-assisted electroless copper plating process. Sandwich-like 2D Cu/RGOS nanocomposites consist of uniform Cu layer on the both side of centric RGOS. The Cu layer with thickness of about 60 nm exhibits almost single-crystalline with (1 1 1) preferred crystalline direction and have tight binding with RGOS. The effect of ultrasound on electroless Cu plating includes: accelerating deposition rate, enhancing interfacial bonding and preventing 2D Cu/RGOS nanocomposites from aggregating.     

Combination effect of carbon nanotubes with graphene on intumescent flame-retardant polypropylene nanocomposites

A novel polypropylene (PP) nanocomposite was fabricated by the incorporation of intumescent flame retardant (IFR), carbon nanotubes (CNTs) and graphene into the PP matrix. Results from TEM indicate that IFR, CNTs and exfoliated graphene nanosheets are dispersed finely in the PP matrix, which is supported by the XRD analysis results. Thermogravimetric (TGA) results show that the addition of IFR, CNTs and graphene improved the thermal stability and the char yields of PP. The PP/IFR/CNTs/RGO nanocomposites, filled with 18 wt% IFR, 1 wt% CNTs and 1 wt% graphene, achieve the limiting oxygen index value of 31.4% and UL-94 V0 grade. Cone calorimeter data reveal that combustion behavior, heat release rate peak (PHRR) and average specific extinction area (ASEA) of PP decrease substantially when combination effects of IFR, CNTs and graphene intervene. For the PP/IFR/CNTs/RGO nanocomposites, the PHRR exhibits an 83% reduction and the time of ignition is delayed 40 s compared with neat PP.     

3D architecture reduced graphene oxide-MoS2 composite: Preparation and excellent electromagnetic wave absorption performance

High-performance electromagnetic absorbers with wide absorption band, strong absorption and lightweight are necessary for industry and military application. To obtain the desired materials, two-dimensional (2D) atomic layers structure nanosheets, such as graphene and graphene-like, were adopted due to its unique structure and properties. Here, 3D architecture reduced graphene oxide-molybdenum disulfide (RGO-MoS₂) composite was prepared by one-pot hydrothermal reaction. MoS₂ generated on graphene oxide intercalation through hydrothermal process and rGO is obtained in the meanwhile. 3D architecture RGO-MoS₂ composite can effectively prevent two-dimensional nanosheets re-stacked and can be applied in electromagnetic wave absorption field. In this paper, composites consist of RGO and various MoS₂ were prepared and their electromagnetic performances were investigated for the first time. Maximum absorption bandwidth (R_L < −10 dB) is 5.92 GHz with thickness of 2.5 mm. We may reasonably conclude that RGO-MoS₂ composite can serve as excellent light-weight electromagnetic wave absorbers and can be widely used in practice.     

Graphene-enhanced microwave absorption properties of Fe3O4/SiO2 nanorods

Fe₃O₄/SiO₂/graphene composite composed of Fe₃O₄/SiO₂ core–shell nanorods and graphene nanosheets were synthesized by a facile wet chemical method. Structure and morphology studies reveal that the Fe₃O₄/SiO₂ nanorods with porous structure and large aspect ratio are densely wrapped by the graphene nanosheets. By changing the graphene content, the electromagnetic properties of the Fe₃O₄/SiO₂/graphene composite can be well tuned. When the weight ratio of Fe₃O₄/SiO₂ to graphene reaches an appropriate value, excellent microwave absorption performance is achieved due to the large electromagnetic losses and good impedance matching. The Fe₃O₄/SiO₂/graphene composite with graphene content of 5 wt.% shows the minimum reflection loss of −27.1 dB at 12.2 GHz when the coating layer thickness is only 1.5 mm.     

Hybrid nanocomposites for mid-range ballistic protection

This paper focuses on ballistic tests of a new class of composite materials, i.e. hybrid nanocomposites. The two hybrid nanocomposites studied are fiber glass/epoxy/nanoclay and fiber glass/epoxy/nanographite. The fiber glass used is a plain weave 200 g/m², while the nanoclay is an organically modified montmorillonite ceramic (Nanomer I30E). The expandable graphite used to generate the graphene nanosheets was from Graftech (grade 160-80N). Ballistic tests were performed considering two types of ammunition, i.e. 38 caliber and 9 mm full metal jacketed. The results showed that for a 38 revolver projectile a 5 mm thick nanocomposite with additional 5 mm nanoclay layer was able to absorb the energy efficiently. A 9 mm projectile, with speed of 380 m/s, was stopped by a two plates (5 mm each) arrangement with elastic deformation of the second plate less than 18 mm. The energies during the ballistic tests ranged from 316 to 576 J.     

Investigation of the effect of nanoclay and processing parameters on the tensile strength and hardness of injection molded Acrylonitrile Butadiene Styrene–organoclay nanocomposites

Polymer–clay nanocomposites have attracted considerable interest over recent years due to their dramatic improved mechanical properties. In the present study, compatibility of Acrylonitrile Butadiene Styrene (ABS) and organically modified montmorillonite nanoclay (Cloisite 30B) and composition capability of them are investigated. Polymethylmethacrylate (PMMA) in varying amount (0, 2, and 4 wt%) is used as the compatibilizer. In order to produce nanocomposite parts, the material is first compounded using a twin-screw extruder and then injected into a mold. The effect of the nanoclay percentage and processing parameters on the tensile strength and hardness of nanocomposite parts is also explored using Taguchi Design of Experiments method. Nanoclay content (in three levels: 0, 2 and 4 wt%), melt temperature (in three levels: 190, 200 and 210 °C), holding pressure (in three levels: 80, 105 and 130 MPa) and holding pressure time (in three levels: 1, 2.5 and 4 s) are considered as the variable parameters. Moreover, distribution of nanoclay layers is analyzed using Wide Angle X-ray Diffraction (XRD) test. XRD results displayed that with the presence of PMMA, nanoclay in ABS matrix is compounded in more exfoliated and less intercalated dispersion mode. Adding PMMA also leads to a remarkable increase in the fluidity of the melt during injection molding process. Results also illustrated that nanocomposites with medium loading level (i.e. 2%) of nanoclay have the highest tensile strength, while the highest hardness number belongs to nanocomposites with 4 wt% nanoclay. Obtained results also indicated that injection temperature has the most important effect on tensile strength and hardness of ABS–clay nanocomposites.     

In situ fabrication and characterization of cobalt ferrite nanorods/graphene composites

Cobalt ferrite nanorods/graphene composites were prepared by a one-step hydrothermal process using NaHSO₃ as the reducing agent and 1-propyl-3-hexadecylimidazolium bromide as the structure growth-directing template. The reduction of graphene oxide and the in situ formation of cobalt ferrite nanorods were accomplished in a one-step reaction. The structure and morphology of as-obtained composites were characterized by field emission scanning electron microscopy, transmission electron microscopy, high resolution transmission electron microscopy, atomic force microscope, X-ray diffractometer, Fourier transform infrared spectra, X-ray photoelectron spectroscopy and Raman spectroscopy. Uniform rod-like cobalt ferrites with diameters of about 100 nm and length of about 800 nm were homogeneously distributed on the graphene sheets. The hybrid materials showed a saturation magnetization of 42.5 emu/g and coercivity of 495.1 Oe at room temperature. The electromagnetic parameters were measured using a vector network analyzer. A minimum reflection loss (RL) of − 25.8 dB was observed at 16.1 GHz for the cobalt ferrite nanorods/graphene composites with a thickness of 2 mm, and the effective absorption frequency (RL < − 10 dB) ranged from 13.5 to 18.0 GHz. The composites exhibited better absorbing properties than the cobalt ferrite nanorods and the mixture of cobalt ferrite nanorods and graphene.     

Diazonium functionalization of graphene nanosheets and impact response of aniline modified graphene/bismaleimide nanocomposites

For developing high performance of graphene-based nanocomposites, dispersibility of graphene sheets in matrices and interfacial interaction are challenging due to the strong tendency of agglomeration and surface inertia of graphene. Here we report an efficient way to functionalize graphene nanosheets with aniline groups on their surfaces, to attain the functionalized graphene nanosheets (FGS) by diazonium treatment following reduction of graphene oxide with hydrazine hydrate. Two kinds of nanocomposites based on diallyl bisphenol A modified bismaleimide (BMI-BA) resin which was filled with functionalized graphene and reduced graphene oxide nanosheets were prepared, and the FGS were linked with BMI resin by chemical bonds. The FGS/BMI-BA composite at a loading of 0.3 wt% revealed a 39% increase in impact strength and a slightly improvement in flexural strength, and the resulting composite remains stable at high temperature. This work provides more possibilities for incorporation of graphene into polymer matrices and an efficient method to toughening the BMI resin.     

A facile assembly of polyimide/graphene core–shell structured nanocomposites with both high electrical and thermal conductivities

Polyimide/reduced graphene oxide (PI/r-GO) core–shell structured microspheres were fabricated by in-situ reduction of graphene oxide (GO), which was coated on the surface of PI microspheres via hydrogen bonding and π–π stacking interaction. The highly ordered 3D core–shell structure of PI/r-GO microspheres with graphene shell thickness of 3 nm was well characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM) and Raman spectra. The glass transition temperature (T_g) of PI/r-GO microspheres was slightly increased because of the interaction of r-GO and PI matrix while the temperature at 5% weight loss (T_5%) of PI/r-GO microspheres was decreased due to the side effect of reductant hydrazine hydrate. The PI/r-GO nanocomposites exhibited highly electrical conductivity with percolation threshold of 0.15 vol% and ultimate conductivity of 1.4 × 10⁻² S/m. Besides, the thermal conductivity of PI/r-GO nanocomposites with 2% weight content of r-GO could reach up to 0.26 W/m K.     

Microwave absorbing behavior of metal dispersed TiO2 nanocomposites

Metal dispersed TiO₂ nanocomposites were prepared by milling process. The microwave absorbing characteristics of the prepared nanocomposites with epoxy were studied in the 8.2–12.4 GHz frequency range for the microwave absorption application. The measured relative complex permittivity of metal dispersed nanocomposite-epoxy indicates higher values in comparison to the pure TiO₂-epoxy nanocomposite. The Reflection loss (RL) values were calculated for thickness from 0.1 to 2.2 mm with an interval of 0.1 mm and the maximum value of RL found for TiO₂-epoxy nanocomposite was −4.96 dB at 10.21 GHz frequency for 2.0 mm thickness. Whereas, RL value is improved to a maximum value of −13.67 dB at 10.13 GHz with Al dispersion (1.8 mm thickness) and −7.24 dB at 10.38 GHz with Ni dispersion (1.3 mm thickness). This study suggests the effectiveness metal particles dispersion for the development of thin microwave absorbers as well as increasing the level of RL.     

Controlled-fabrication,morphology formation mechanism of TiO2-B nanobelts with NiO-doping

The NiO/TiO₂-B hybrid nanomaterials were synthesized by a hydrothermal process and subsequently a uniform precipitation-method. The phase and morphology of the NiO/TiO₂-B hybrid nanomaterials can be controlled to be either nanoparticles or nanosheets by varying the experimental conditions, e.g., the reaction time, the concentration of Ni(NO₃)₂·6H₂O, and the precipitants. We systematically studied the mechanism of morphology evolution which is mainly affected by the reaction conditions. It is found that the NiO nanosheets are intensively and perpendicularly aggregated on the TiO₂-B nanobelts. The mechanisms of the nanosheets growth and the formation of NiO/TiO₂-B hybrid nanomaterials were discussed based on their morphology evolution processes. The NiO/TiO₂-B hybrid nanomaterials deliver a high discharge capacity of 395 mAh g^− 1 and 96.2% capacity retentions over 50 cycles, implying excellent cycling stability with reversible capacity which is 7.8% higher than that of isolated TiO₂-B nanobelts. This excellent electrochemical performance of the morphology-controlled NiO/TiO₂-B hybrid nanomaterials has a significant potential for lithium-ion battery application.     

Enhanced microwave absorption properties of flake-shaped FePCB metallic glass/graphene composites

A novel kind of composite absorber, i.e. FePCB/graphene composite, with excellent microwave absorption properties was successfully fabricated by a simple and scalable ball milling method. After being milled, the FePCB particles displayed flaky morphology with large aspect ratio. The complex permittivity and permeability of the flaky FePCB distinctly increased compared with those before milling. Furthermore, with the introduction of graphene, the flaky FePCB/graphene composite exhibited excellent microwave absorption performance with strong absorption and wide absorption band. In particular, for FePCB/graphene composite with an absorber thickness of 2 mm, the reflection loss (RL) reached a minimum of −45.3 dB at 12.6 GHz and the effective absorption bandwidth (RL < −10 dB) covered 5.4 GHz. The enhanced microwave absorption performance of the FePCB/graphene composite was attributed to the high magnetic loss and improved impedance matching which were closely related to the flake-shaped FePCB particles and the introduction of graphene sheets.     

Lepidocrocite-like ferrititanate nanosheets and their full exfoliation with quaternary ammonium compounds

Efficient methods for the synthesis of layered structure nanomaterials (nanosheets), their complete exfoliation (delamination) into the layers of atomic thickness and design of organic–inorganic nanohybrids present important stages toward development of improved polymer-based nanocomposites and pillared heterostructures with potential application in purification technologies such as photocatalysis. A rapid and efficient exfoliation process of protonated layered ferrititanates with lepidocrocite-like structure and formation of organic–inorganic nanohybrids is performed starting from the nanosheets composed of only a few host layers and nanometric lateral dimensions using quaternary ammonium compounds. These nanosheets are initially synthesized from a highly abundant precursor through an alkaline hydrothermal route. We demonstrated that dimethyldioctadecylammonium cations strongly interact with the exfoliated single host layers (0.75 nm thick) providing thermal stability (~ 500 °C) to the as-prepared organic–inorganic nanohybrid over the temperature range commonly applied for the processing of thermoplastic nanocomposites.     

Durability of GFRP nanocomposites subjected to hygrothermal ageing

This paper presents long term durability prediction of 0–5 wt.% nanoclay/vinylester/glass fibre nanocomposites based on their tensile strength retention in accelerated hygrothermal ageing using Arrhenius rate model. The specimens were exposed to 30 °C, 50 °C and 60 °C and 95% relative humidity for 75 days and tested for tensile strength retention as a function of duration of exposure. The predicted tensile strength retentions for one year of ageing of vinylester/glass at 30 °C, 50 °C and 60 °C using Arrhenius rate model were 59%, 48% and 43% respectively. The corresponding strength retentions predicted for 4 wt.% nanoclay/vinylester/glass were 81.1%, 77.9% and 76.4%. Strength retentions for ten years were predicted using the analytical model to assess their long-term performance.     

Fabrication and characterization of functionally graded Al–SiC nanocomposite by using a novel multistep friction stir processing

Functionally graded materials are one of the most promising candidates among advanced materials. However, some challenges still exist in its fabrication methods. The current study aims to produce functionally-graded bulk Al–SiC nanocomposites by a novel multistep friction stir processing (FSP) for the first time. The SiC nanoparticles were packed into a groove on the 6061 aluminum plate and FSP was performed by using a tool with pin length of 6 mm. Subsequently, FSP was reapplied on another groove by using a tool with a shorter pin length of 3.2 mm. The desirable distribution of SiC nanoparticles in the matrix was confirmed by scanning electron and atomic force microscopes. The composition of graded sample was changed continuously from 18 to 0 wt% SiC along the thickness. Accordingly, the microhardness profile showed a maximum of 160 Hv in the enriched zone which is 3.2 times higher than the hardness of the particle-depleted zone. However, a constant hardness value of 135 Hv was obtained along the thickness of homogenous sample which is 15% lower than that of superficial layer in graded sample. Moreover, the hardness values were linearly correlated with the inverse of interparticle spacing.     

Thermal and rheological properties of highly concentrated PET composites with ferrite nanoparticles

Ferrite nanoparticles were introduced into poly(ethylene terephthalate) (PET) in a melt state at 270 °C upto 20 wt%, and the thermal and rheological properties of the nanocomposites were investigated. The introduction of ferrite nanoparticles increased a little the crystallization temperature (T_c) of PET by ca. 3 °C, while it had little effect on the melting temperature (T_m). In addition, it increased both heat of crystallization (ΔH_c) and heat of fusion (ΔH_m) with ferrite content. PET nanocomposites with ferrite 5 wt% and above exhibited an increased thermal stability and a two-stage degradation. The dynamic viscosity of PET nanocomposites was increased with ferrite content. However, ferrite loading of 5 wt% and above produced a high degree of shear thinning leading to even lower viscosity in a high frequency range than that of pure PET. The nanocomposites gave a non-zero positive value of yield stress, which was notably increased particularly from 5 wt% loading. In the Cole–Cole plot, at contents 1 wt% and above, ferrite nanoparticles caused the deviation from the master curve and a reduced slope. In addition, the relaxation time was increased with ferrite content and an increasing degree was more notable at a lower frequency.     

Boiling heat transfer from a horizontal flat plate in a pool of liquid hydrogen

Heat transfer from a flat plate facing upward immersed in a liquid hydrogen pool was measured for the pressures from atmospheric to 1.1 MPa. The flat plate heater used was 10 mm in width, 100 mm in length and 0.1 mm in thickness. Critical heat fluxes (CHFs) in saturated boiling increased with the increase in pressure up to around 0.3 MPa and then decreased with further pressure increase. The CHFs under subcooled condition at each pressure increased with the increase in sub-cooling. Discussions were made on the experimental results by comparing with those of the other cryogenic liquids and also the Kutateladze’s equations under saturated and subcooled conditions. The experimental CHFs were much smaller than the Kutateladze’s equation for higher pressure up to critical. The heater surface temperature was found to reach the critical temperature before the occurrence of hydrodynamic instability and jump to the film boiling regime at the lower heat flux in the higher pressure range. It was suggested that the CHFs are determined not by the heat flux but by the temperature in the higher pressure range.     

Facile synthesis and microwave absorbability of C@Ni–NiO core–shell hybrid solid sphere and multi-shelled NiO hollow sphere

We reported the preparation of C@Ni–NiO core–shell hybrid solid spheres or multi-shelled NiO hollow spheres by combining a facile hydrothermal route with a calcination process in H₂ or air atmosphere, respectively. The synthesized C@Ni–NiO core–shell solid spheres with diameters of approximately 2–6 μm were in fact built from dense NiO nanoparticles coated by random two-dimensional metal Ni nanosheets without any visible pores. The multi-shelled NiO hollow spheres were built from particle-like ligaments and there are a lot of pores with size of several nanometers on the surface. Combined Raman spectra with X-ray photoelectron spectra (XPS), it suggested that the defects in the samples play a limited role in the dielectric loss. Compared with the other samples, the permeability of the samples calcined in H₂ and air was increased slightly and the natural resonance frequency shifted to higher frequency (7, 11 and 14 GHz, respectively), leading to an enhancement of microwave absorption property. For the sample calcined in H₂, an optimal reflection loss less than − 10 was obtained at 7 GHz with a matching thickness of 5.0 mm. Our study demonstrated the potential application of C@Ni–NiO core–shell hybrid solid sphere or multi-shelled NiO hollow sphere as a more efficient electromagnetic (EM) wave absorber.