Dispersion Of Graphene Nanosheets Research Articles

Strength-Plasticity Relationship and Intragranular Nanophase Distribution of Hybrid (GNS + SiCnp)/Al Composites Based on Heat Treatment.

The distribution of reinforcements and interfacial bonding state with the metal matrix are crucial factors in achieving excellent comprehensive mechanical properties for aluminum (Al) matrix composites. Normally, after heat treatment, graphene nanosheets (GNSs)/Al composites experience a significant loss of strength. Here, better performance of GNS/Al was explored with a hybrid strategy by introducing 0.9 vol.% silicon carbide nanoparticles (SiCnp) into the composite. Pre-ball milling of Al powders and 0.9 vol.% SiCnp gained Al flakes that provided a large dispersion area for 3.0 vol.% GNS during the shift speed ball milling process, leading to uniformly dispersed GNS for both as-sintered and as-extruded (0.9 vol.% SiCnp + 3.0 vol.% GNS)/Al. High-temperature heat treatment at 600 °C for 60 min was performed on the as-extruded composite, giving rise to intragranular distribution of SiCnp due to recrystallization and grain growth of the Al matrix. Meanwhile, nanoscale Al4C3, which can act as an additional reinforcing nanoparticle, was generated because of an appropriate interfacial reaction between GNS and Al. The intragranular distribution of both nanoparticles improves the Al matrix continuity of composites and plays a key role in ensuring the plasticity of composites. As a result, the work hardening ability of the heat-treated hybrid (0.9 vol.% SiCnp + 3.0 vol.% GNS)/Al composite was well improved, and the tensile elongation increased by 42.7% with little loss of the strength. The present work provides a new strategy in achieving coordination on strength-plasticity of Al matrix composites.

Percolation onset and conductivity of nanocomposites assuming an incomplete dispersion of graphene nanosheets in a polymer matrix.

Herein, stacks of graphene nanosheets resulting from an incomplete dispersion of nanoparticles in polymer graphene nanocomposites are considered. The volume fraction, aspect ratio and conduction of stacks are expressed by the distance between nanosheets (s), thickness of an individual nanosheet (t), nanosheet diameter (D), thickness of the interphase zone (ti) and tunneling length (d). Moreover, the percolation onset, actual filler quantity and portion of networked nanosheets are stated by the stacks of nanosheets, interphase depth and tunneling length. Finally, an advanced model for the conductivity of a graphene-based system is presented using the mentioned terms. The influence of all properties of stacks, tunneling and interphase areas on the percolation onset, portion of percolated nanosheets and conductivity are examined. Furthermore, the tested values of conductivity are applied to confirm the predictability of the model. The larger quantity of thin sheets included in stacks produces a higher conductivity for samples. In addition, a thicker interphase and smaller tunnels can result in higher conductivity. The calculations of conductivity match the tested data at all filler amounts.

Effect of graphene nano-additives on the fatigue limit of fiber-reinforced polymer hybrid composites—A micromechanical modeling procedure

In this article, the effect of graphene nanoadditives on the fatigue limit of unidirectional glass fiber-reinforced polymer (GFRP) composites has been investigated. A micromechanical model based on the crack growth has been used to analyze the fatigue limit response of unidirectional GFRP hybrid composite containing nanoadditives. The influence of different percentages of graphene nanosheets (GNS) and different types of nanofiller dispersion has been investigated by the micromechanical model. The fatigue limit of unidirectional GFRP hybrid composites has been plotted in terms of glass fiber volume fraction, interfacial friction shear stress, interfacial fracture energy and reference length. The fatigue limit of unidirectional composites can be improved by addition of GNS into the polymer matrix of such composite systems. The obtained results on the GNS dispersion type demonstrate that the uniform dispersion of GNS into the polymer matrix increases the fatigue limit of unidirectional GFRP hybrid composites. As the agglomeration density of GNS is low, the fatigue limit of GFRP hybrid composites will be improved more than when the density of agglomeration is high.

Efficient fabrication of poly(vinylidene fluoride)/graphene composite actuators with robust superhydrophobicity and excellent photothermal performance for controllable light-driven motion

The Marangoni effect has garnered significant interest as a promising method for non-contact, remote-controlled actuation. Despite the numerous advantages it offers, the high cost and complex fabrication procedures associated with the technology have limited its widespread application. To address these limitations, an industrialized polymer processing strategy that combines melt blending and hydrophobic modification is proposed for the large-scale and cost-effective production of lightweight poly(vinylidene fluoride)/graphene nanosheets foam with a three-dimensional interconnected network. The foam displays excellent superhydrophobic properties, including a contact angle of 155 ± 2° and a rolling angle of 7 ± 3°. Furthermore, the foam is durable under a variety of conditions, including dynamic impact, high temperatures, acidic and alkaline environments, knife scratching, abrasion damage, and tape peeling. Additionally, the foam displays stable photothermal conversion performance due to the uniform dispersion of graphene nanosheets throughout the polymer matrix. When used as a light-driven actuator, the foam demonstrates the ability to achieve on-demand driving as well as swimming route planning at the water–air interface. The proposed method offers a promising solution for the efficient fabrication of light-driven actuators that are both adapted to practical applications and resistant to external damages.

Bioinspired Micro/Nanostructured Polyethylene/Poly(Ethylene Oxide)/Graphene Films with Robust Superhydrophobicity and Excellent Antireflectivity for Solar-Thermal Power Generation, Thermal Management, and Afterheat Utilization.

The rational utilization and circulation of multiple energy sources is an effective way to address the crises of energy shortages and environmental pollution. Herein, microextrusion compression molding, an industrialized polymer molding technology that combines melt blending and compression molding, is proposed for the mass production of a bioinspired micro/nanostructured polyethylene/poly(ethylene oxide)/graphene (MN-PPG) film. The MN-PPG film exhibits robust shape stability, high storage energy density, and excellent thermal management capability owing to the cocontinuous network formed by poly(ethylene oxide) and the polyethylene matrix. The MN-PPG film has sufficient photothermal property due to the uniformly dispersed graphene nanosheets and the bioinspired surface micro/nanostructures. Interestingly, the MN-PPG film surface exhibits durable superhydrophobicity, acid/alkali resistance, and active deicing performance. Further, a multifunctional energy harvesting and circulation system was established by integrating the MN-PPG film, an LED chip, and a thermoelectric module. The hybrid system produced an open-circuit voltage of 315.4 mV and power output of 2.5 W m-2 under 3 sun irradiation. Furthermore, the afterheat generated by the LED chips at night can be converted into electricity through thermoelectric conversion. The proposed method enables the large-scale fabrication of multifunctional phase change composites for energy harvesting in harsh environments.

Cost-Effective Fabrication of High-Density Polyethylene/Graphene Nanocomposites by an In Situ Exfoliation Method Based on a Series Explosion Effect

As ideal nanofillers, graphene nanosheets (GNS) are widely used to prepare high-performance graphene-reinforced nanocomposites owing to their excellent properties. However, the high manufacturing cost and low production efficiency of GNS severely restrict their large-scale application. Herein, a cost-effective melt blending approach was demonstrated for facilely preparing high-density polyethylene (HDPE)/GNS nanocomposites by using industrial-grade expanded graphite (EG). The exfoliation and dispersion of GNS in the matrix under different processing temperatures and times have been studied. A series explosion effect generated by the synergy of volumetric extensional rheology and free water can violently and fastly exfoliate pristine EG into few-layer GNS. The in situ exfoliation mechanism revealed that the synergistic effect of the explosive forces of free water and the adhesion between HDPE and GNS can destroy the van der Waals forces between the EG sheets during melt blending, thereby realizing ultrafast exfoliation and uniform dispersion of EG in the HDPE matrix. As expected, the HDPE/GNS nanocomposites showed high crystallinity, excellent thermal conductivity, high dielectric constant, and extremely low dielectric loss. This work provides a new idea for facilely fabricating high-performance polymer-based two-dimensional layered nanocomposites.

Tribological properties and self-lubrication mechanism of in-situ grown graphene reinforced nickel matrix composites in ambient air

In situ synthesis of graphene reinforcements in Ni matrix is a promising strategy to manufacture graphene/Ni composites for advanced lubrication. However, the influence of in situ grown graphene content on the tribological properties and the lubricating mechanisms of the graphene/Ni composites under ambient air are far from clear. According to the dissolution and precipitation of carbon on Ni grain surface, this paper reports a high-quality graphene/Ni self-lubricating composite synthesized by in situ powder metallurgy process. The microstructure and tribological behaviours of the composites with different graphene content are elaborated. It is found that the in situ grown few-layer graphene can induce a significant grain refinement effect and simultaneously achieve excellent anti-friction and wear performances. The lowest friction coefficient and wear rate of 0.254 and 4.385 × 10−5 mm3/(N·m) are obtained by the graphene/Ni composite with 0.6 wt% carbon. In comparison with pure Ni, the friction coefficient and wear rate are reduced by 3.02-fold and 3.44-fold, respectively. The tribological improvements of the presented graphene/Ni composite is related to the high H/E ratio and homogenous dispersion of graphene nanosheets.

Supercritical CO2 microemulsion containing [Emim][Tf2N] coupled jet impact exfoliation of graphene and its application to supercapacitors

Graphene has shown great application prospects as an electrode material for supercapacitors. It is necessary to develop an industrially feasible method to produce a large amount of defect-free graphene. Here, graphite was exfoliated with high quality in a supercritical CO2 (scCO2) microemulsion containing 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Emim][Tf2N]) coupled a self-developed jet impact to produce a dispersion of graphene nanosheets. The height of the graphene was about 70% of 3.5–5.5 nm, and the lateral size was about 70% of 700–1100 nm. After jet impact, the concentration increased by 5–8%, the thickness of the flakes was reduced by about 1 nm, and the lateral size was reduced by about 300 nm. The kinetic calculation proved that the jet impact could achieve the effect of secondary exfoliation. The obtained few-layer graphene could be applied to electrode materials of supercapacitors.

Experimental study on mechanical properties of polypropylene nanocomposites reinforced with a hybrid graphene/PP-g-MA/kenaf fiber by response surface methodology

In this study, the mechanical properties of polypropylene (PP)-based nanocomposites reinforced with graphene nanosheets, kenaf fiber, and polypropylene-grafted maleic anhydride (PP-g-MA) were investigated. Response surface methodology (RSM) based on Box–Behnken design (BBD) was used as the experimental design. The blends fabricated in three levels of parameters include 0, 0.75, and 1.5 wt% graphene nanosheets, 0, 7.5, and 15 wt% kenaf fiber, and 0, 3, and 6 wt% PP-g-MA, prepared by an internal mixer and a hot press machine. The fiber length was 5 mm and was being constant for all samples. Tensile, flexural, and impact tests were conducted to determine the blend properties. The purpose of this research is to achieve the highest mechanical properties of the considered nanocomposite blend. The addition of graphene nanosheets to 1 wt% increased the tensile, flexural, and impact strengths by 16%, 24%, and 19%, respectively, and an addition up to 1.5 wt% reduced them. With further addition of graphene nanosheets until 1.5 wt%, the elastic modulus was increased by 70%. Adding the kenaf fiber up to 15 wt% increased the elastic modulus, tensile, flexural, and impact strength by 24%, 84%, 18%, and 11%, respectively. The addition of PP-g-MA has increased the adhesion, dispersion and compatibility of graphene nanosheets and kenaf fibers with matrix. With 6 wt% PP-g-MA, the tensile strength and elastic modulus were increased by 18% and 75%, respectively. The addition of PP-g-MA to 5 wt% increased the flexural and impact strengths by 10% and 5%, respectively. From the entire experimental data, the optimum values for elastic modulus, as well as, tensile, flexural, and impact strengths in the blends were obtained to be 4 GPa, 33.7896 MPa, 57.6306 MPa, and 100.1421 J/m, respectively. Finally, samples were studied by FE-SEM to check the dispersion of graphene nanosheets, PP-g-MA and kenaf fibers in the polymeric matrix.

Spreading GO nanosheets-coated nickel foam decorated by NiCo2O4/NiCo2S4 nanoarrays for high-performance supercapacitor electrodes

Porous nickel foam (NF) is often wrapped by reduced graphene oxide (rGO) for loading active nanomaterials. To clarify the influence of the dispersion of graphene nanosheets in NF framework on the electrochemical performance, herein, spreading GO nanosheets-coated NF (NF@sGO) is developed via negative pressure immersion method, in which, GO sheets spreading on the macropores adjust the pore structure and enlarge the supporting surface of NF framework. Compared to the NF@rGO prepared by hydrothermal method, NF@sGO scaffold exhibits a high capacitance for the pseudocapacitance contributed by GO. Acting as a porous scaffold for growing NiCo2O4 nanoneedles, the NF@sGO/NiCo2O4 composite delivers a specific capacitance of 2522 F g−1 (1135 C g−1) at 1 A g−1, much higher than that of the control sample NF@rGO/NiCo2O4. To further improve the electrochemical performance of NF@sGO/NiCo2O4, thin NiCo2S4 nanosheets are decorated on NiCo2O4 nanoneedles. Optimized NF@sGO/NiCo2O4/NiCo2S4-0.02 sample delivers a maximum specific capacitance of 2980 F g−1 (1341 C g−1) at 1 A g−1 and a superior long-term cycling stability. The performances of NF@sGO/NiCo2O4 and NF@sGO/NiCo2O4/NiCo2S4-0.02 are both higher than existing composites. The superior electrochemical performance is attributed to the combination of novel NF@sGO scaffold and NiCo2O4 nanoneedles or optimized NiCo2O4/NiCo2S4 hybrid nanostructures. In view of the easy preparation and superior performance, NF@sGO scaffold has a promising prospect for preparing high-performance integrated electrodes.

Experimental analysis of mechanical properties of graphene/kenaf/basalt reinforced hybrid nanocomposites using response surface methodology

In this study, the flexural strength and elastic modulus of polypropylene-based nanocomposites reinforced with graphene nanosheets, basalt, and kenaf fiber were investigated. Response surface methodology based on Box–Behnken design was used as the experimental design. The blends fabricated in three levels of parameters include 0, 0.75, and 1.5 wt% graphene nanosheets, 0, 7.5, and 15 wt% basalt fibers, and 0, 7.5, and 15 wt% kenaf, prepared by an internal mixer and a hot press machine. The fiber length was 5 mm and was being constant for all samples. Flexural and tensile tests were conducted to determine the blend properties. The addition of graphene nanosheets to 0.75 wt% increased the flexural strength by 12% and a graphene addition up to 1.5 wt% reduced flexural strength by 6%. The addition of graphene nanosheets to 1.5 wt% increased the elastic modulus by 37%. The addition of basalt fiber up to 15 wt% increased the flexural strength and elastic modulus by 13% and 61%, respectively. The addition of kenaf fiber up to 15 wt% increased the flexural strength by 18% and the elastic modulus by 46%. Finally, samples were studied by field emission scanning electron microscopy to check the dispersion of graphene nanosheets, basalt, and kenaf fibers in the polymeric matrix.

Graphene nanosheets homogeneously incorporated in polyurethane sponge for the elimination of water-soluble organic dyes

Highly dispersed graphene nanosheets (GNS) are directly integrated into polyurethane sponge for the very first time. Individual GNS with an average thickness of 5 nm were uniformly encapsulated in polyurethane sponge (PUF). Highly durable, flexible, hydrophilic GNS/PUF demonstrated excellent organic dye absorption properties. For a detailed study, we selected typical water-soluble organic dyes such as methylene blue (MB), ethidium bromide (EtBr), eosin Y (EY). The adsorption behavior follows the Langmuir isotherm model indicating strong monolayer chemisorption. Adsorption capacity (μmol/g) of GNS while using in GNS/PUF is 586.8 (MB), 843.1 (EtBr), and 813.3 (EY). Thermodynamic study on the adsorption with three organic dyes using GNS/PUF revealed that the process was spontaneous and exothermic in nature.Additionally, the rate of adsorption is higher and follow the pseudo-second-order kinetic model. The detailed pH-dependent study showed that cationic dyes' adsorption increases with an increase in pH, and anionic dyes follow the opposite trend. The overall results show that the new adsorbent has highly suitable for practical application.

Self-assembly of the surfactant mixtures on graphene in the presence of electrolyte: a molecular simulation study

The insolubility of graphene nanosheets in aqueous media has been a limitation for the practical applications of this unique material. The non-covalent functionalization of graphene with mixed surfactants is an effective procedure for preparation of stable graphene dispersions. Physical adsorption of surfactants onto graphene surfaces is a significant stage in the dispersion of graphene nanosheets in the aqueous environment. Studies have shown that the presence of electrolyte greatly affects the adsorption process of pure surfactants on solid surfaces. Examination of mixed surfactants adsorption on graphene in the presence of electrolyte will help to better understand the mechanism of molecular interactions between the graphene nanosheets and mixed surfactants. Therefore, in this study, we used molecular dynamics simulations to investigate the adsorption of mixed surfactants on graphene in the presence of electrolyte and to study the morphology of assemblies formed from mixed surfactants on graphene. We investigate the effects of electrolyte concentration and surface coverage of surfactants' mixture on the adsorption process and structural changes in the assemblies formed on graphene nanosheets. We have found that increasing the ionic strength of electrolyte reinforces stretching of surfactants adsorbed on graphene toward the aqueous phase, and this leads to a clear volume expansion in the structure of graphene-surfactant mixture hemi-spherical micelles. In fact, screening effect of electrolyte ions on electrostatic repulsion between charged head-groups made molecules approach each other, leading to a more compact assembly of surfactants on graphene surface. As hemi-spherical micelles of mixed surfactants-graphene expanded, the steric repulsion between these micelles also increased, which in turn, inhibited the re-aggregation of graphene sheets covered with surfactants.

Expandable polystyrene without any embedded blowing agent

In this research, in-situ suspension polymerization of styrene in the presence of graphene, without any blowing agent, was investigated. Steam used in the expansion process of graphene-filled expandable polystyrene (GEPS). The dispersed graphene nano-sheets in the polystyrene matrix may absorb water in high temperatures, which evaporates by lowering the pressure and expansion precedes. The effects of graphene type and loading and steam temperature on the expansion ratio evaluated. Scanning electron microscopy (SEM) used to reveal the cross-section morphologies before and after expansion. The effect of graphene on the polymerization kinetics evaluated by differential scanning calorimetry (DSC). The results showed that by increasing the graphene loading, the rate of polymerization decreased, and the expansion ratio increased. The highest expansion ratio of about 4.8 was for particles containing 0.4% of graphene. Therefore, it was shown that by using graphene as a dispersed phase, polystyrene particles expanded without any organic blowing agents. Here, the idea of expandable polymers without any embedded blowing agent is introduced, which eliminates the release of volatile organic compounds and makes the process environmentally friendly.

Photocatalytic degradation of methylene blue using three-dimensional porous graphene-titania microparticles under UV light

Porous graphene and graphene-silica microparticles containing titania nanoparticles were synthesized by emulsion-assisted self-assembly for the photocatalytic decomposition of methylene blue in an aqueous medium. After the mixed dispersion of graphene nanosheets and titania nanoparticles with or without silicic acid was prepared, the complex fluid was emulsified in a continuous oil phase to form tiny droplets that act as micro-reactors for the synthesis of porous photocatalytic particles, the morphology of which was three-dimensional spherical shapes with a number of irregular-shaped macropores. The three dimensional conductive graphene scaffolds greatly enhanced the photocatalytic activity of the porous particles due to the suppression of the recombination of electron-hole pairs generated from titania under UV light irradiation, and adsorption of dye molecules on graphene-silica scaffolds caused rapid removal of aqueous contaminants. Unlike previous reports, the kinetics of the photocatalytic decomposition reaction could not be explained by Langmuir-Hinshelwood kinetics, but the experimental data could be fitted well by the second- or third-order kinetics. This indicates that the removal rate of the pollutant could be enhanced by the supporting material. The removal efficiency of methylene blue was estimated as more than 95% when sufficient amount of the photocatalytic particles was used, implying that application to water treatment process will be possible.

High Performance Na-O2 Batteries and Printed Microsupercapacitors Based on Water-Processable, Biomolecule-Assisted Anodic Graphene.

Integrated approaches that expedite the production and processing of graphene into useful structures and devices, particularly through simple and environmentally friendly strategies, are highly desirable in the efforts to implement this two-dimensional material in state-of-the-art electrochemical energy storage technologies. Here, we introduce natural nucleotides (e.g., adenosine monophosphate) as bifunctional agents for the electrochemical exfoliation and dispersion of graphene nanosheets in water. Acting both as exfoliating electrolytes and colloidal stabilizers, these biomolecules facilitated access to aqueous graphene bio-inks that could be readily processed into aerogels and inkjet-printed interdigitated patterns. Na-O2 batteries assembled with the graphene-derived aerogels as the cathode and a glyme-based electrolyte exhibited a full discharge capacity of ∼3.8 mAh cm–2 at a current density of 0.2 mA cm–2. Moreover, shallow cycling experiments (0.5 mAh cm–2) boasted a capacity retention of 94% after 50 cycles, which outperformed the cycle life of prior graphene-based cathodes for this type of battery. The positive effect of the nucleotide-adsorbed nanosheets on the battery performance is discussed and related to the presence of the phosphate group in these biomolecules. Microsupercapacitors made from the interdigitated graphene patterns as the electrodes also displayed a competitive performance, affording areal and volumetric energy densities of 0.03 μWh cm–2 and 1.2 mWh cm–3 at power densities of 0.003 mW cm–2 and 0.1 W cm–3, respectively. Taken together, by offering a green and straightforward route to different types of functional graphene-based materials, the present results are expected to ease the development of novel energy storage technologies that exploit the attractions of graphene.

Investigating the Microstructure and Mechanical Properties of Aluminum-Matrix Reinforced-Graphene Nanosheet Composites Fabricated by Mechanical Milling and Equal-Channel Angular Pressing

Layered-graphene reinforced-metal matrix nanocomposites with excellent mechanical properties and low density are a new class of advanced materials for a broad range of applications. A facile three-step approach based on ultra-sonication for dispersion of graphene nanosheets (GNSs), ball milling for Al-powder mixing with different weight percentages of GNSs, and equal-channel angular pressing for powders’ consolidation at 200 °C was applied for nanocomposite fabrication. The Raman analysis revealed that the GNSs in the sample with 0.25 wt.% GNSs were exfoliated by the creation of some defects and disordering. X-ray diffraction and microstructural analysis confirmed that the interaction of the GNSs and the matrix was almost mechanical, interfacial bonding. The density test demonstrated that all samples except the 1 wt.% GNSs were fully densified due to the formation of microvoids, which were observed in the scanning electron microscope analysis. Investigation of the mechanical properties showed that by using Al powders with commercial purity, the 0.25 wt.% GNS sample possessed the maximum hardness, ultimate shear strength, and uniform normal displacement in comparison with the other samples. The highest mechanical properties were observed in the 0.25 wt.% GNSs composite, resulting from the embedding of exfoliated GNSs between Al powders, excellent mechanical bonding, and grain refinement. In contrast, agglomerated GNSs and the existence of microvoids caused deterioration of the mechanical properties in the 1 wt.% GNSs sample.

Wet‐spinning and carbonization of graphene/PAN‐based fibers: Toward improving the properties of carbon fibers

ABSTRACTGraphene/polyacrylonitrile (PAN)‐based composite fibers, as monofilaments, multifilaments, and yarns, were prepared through a facile solution mixing and wet‐spinning method. The PAN‐based (PANb) precursor was synthesized via reversible addition–fragmentation chain transfer polymerization with N‐isopropylacrylamide as a comonomer. Following wet‐spinning, the PANb yarns were carbonized at 900 °C. Scanning electron microscopy images confirmed the presence of a homogenous dispersion of graphene nanosheets inside the polymer matrix. It has been shown that the addition of graphene not only enhanced the thermal and mechanical properties of the PANb fibers, but also improved their graphitic structure after heat treatment. Tensile strength and Young's modulus of the PANb yarns were increased by 28 and 20%, respectively, on addition of 0.5 wt % graphene. Raman spectra demonstrated improvement in the graphitic structure of the carbonized yarns even at low graphene content. These graphene/ PANb fibers show potential as a suitable precursor for the development of next generation carbon fibers. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47932.

Nano Graphene-Reinforced Bio-nanocomposites Based on NR/PLA: The Morphological, Thermal and Rheological Perspective

Bio-based graphene-reinforced thermoplastic elastomers (TPE) based on natural rubber (NR), and poly lactic acid (PLA) were successfully prepared via melt blending. The effect of graphene nanosheets (GNS) content and coupling agent were investigated on morphological, thermal and rheological properties of the PLA/NR/GNS bio-nanocomposites. More stable morphology of uniformly dispersed NR phase in the continuous PLA matrix with a relatively narrower diameter-size distribution was achieved in the presence of a compatibilizer. Moreover, transmission electron micrographs showed more improved dispersion of GNS with predominantly exfoliated morphology in the case of ENR-compatibilized PLA/NR/GNS bio-nanocomposites. Crystallization/melting studies revealed that, as the GNS content increased, the cold-crystallization peak, melting peak and glass-to-rubber transition temperature values shifted to higher temperatures and the crystallinities of blends slightly decreased (about 7%) which might be attributed to the reduction of polymeric segments mobility by the restricting effect of GNS. Dynamical mechanical investigation showed that the storage modulus (E′) increased about 25% by the introduction of GNS due to the inherent stiffness of GNS and the occurrence of compatibility in the PLA/NR blend in the presence of ENR. The presence of ENR shifted the $$ T_{g} $$ of the NR phase and the PLA matrix towards each other which is a characteristic of higher miscibility and compatibility. The thermogravimetry (TGA) and derivative thermogravimetry (DTG) curves revealed higher thermal stability of the compatibilized-PLA/NR blends due to the enhanced interfacial adhesion and the homogenous dispersion of GNSs as direct effects of the presence of ENR. Rheological studies indicated that the formation of the effective GNS-polymer networks by the presence of ENR increased the storage modulus (G′) and complex viscosity (η*) value due to the effectiveness of the GNS in taking loads and restricted molecular motion, respectively.

An Approach to the Uniform Dispersion of Graphene Nanosheets in Powder Metallurgy Nickel-Based Superalloy.

In this paper, a wet-chemical based method was adopted to acquire the uniform dispersion of graphene nanosheets (GNSs) in a powder metallurgy nickel-based superalloy (FGH96) to fabricate a new GNSs reinforced FGH96 metal matrix composite. The surface of the FGH96 powder was modified using a hydrophilic surfactant named polyvinyl alcohol (PVA), which has good wettability and strong hydrogen bonding between the –OH groups of PVA and oxygen groups of GNSs such as –COOH, –CHO, and –OH. It was shown that the GNSs displayed much better dispersion uniformity on the PVA modified FGH96 powder than the unmodified one. The existence of PVA improved the adsorptive capacity of the GNSs attached on the powder surface and prevented the agglomeration in the following thermal preparation process. Consequently, the micro-hardness of PVA modified composite with 0.1 wt.% GNSs reached 497.9 HV, 3.4% higher than the unmodified FGH96 alloy. Therefore, this preparation process could act as the foundation of a common strategy for the fabrication of GNSs in metal matrix composites with good dispersion uniformity, which may have great potential application in aerospace applications.