Low Graphene Content Research Articles

Flexible composite films with ultrahigh through-plane thermal conductivity yet low graphene content

Graphene-based polymeric composites have become one of the promising thermal interface materials (TIMs) for the high integration electronic devices due to the excellent intrinsic thermal conductivity of graphene. However, the challenges still remain, such as ordered alignment of graphene in elastic polymer and regulation of phonon scattering at graphene/graphene interface. In this study, a vertically oriented graphene framework within a flexible silicone rubber matrix was fabricated by non-solvent induced phase separation (NIPs) coupled with an in in-situ welding technique. The as-prepared film exhibits an outstanding through-plane thermal conductivity of 29.5W/mK at low graphene loading of 7.5 wt%, which indicates an exceptionally high thermal conductivity enhancement per 1 wt% graphene content (specific TCE) over 1950 %/wt%. Furthermore, the composite films demonstrate excellent conformability inherited from the silicone rubber matrix and achieves low contact resistance of 40–70 Kmm2W−1 under various pressure and interfacial conditions. This study contributes to a deeper insight into the development of the high-performance graphene-based polymeric TIMs.

Interfacial engineering in SnO2-embedded graphene anode materials for high performance lithium-ion batteries

Tin dioxide is regarded as an alternative anode material rather than graphite due to its high theoretical specific capacity. Modification with carbon is a typical strategy to mitigate the volume expansion effect of SnO2 during the charge process. Strengthening the interface bonding is crucial for improving the electrochemical performance of SnO2/C composites. Here, SnO2-embedded reduced graphene oxide (rGO) composite with a low graphene content of approximately 5 wt.% was in situ synthesized via a cetyltrimethylammonium bromide (CTAB)-assisted hydrothermal method. The structural integrity of the SnO2/rGO composite is significantly improved by optimizing the Sn–O–C electronic structure with CTAB, resulting a reversible capacity of 598 mAh g−1 after 200 cycles at a current density of 1 A g−1. CTAB-assisted synthesis enhances the rate performance and cyclic stability of tin dioxide/graphene composites, and boosts their application as the anode materials for the next-generation lithium-ion batteries.

Enhancing cutting tool durability: Exploration of Al2O3-SiCw-graphene composites fabricated by SPS for improved mechanical and scratch resistance

This study focuses on the fabrication and characterisation of Al2O3-SiCw-rGO composites sintered by spark plasma sintering (SPS) technique. The research is mainly focused on understanding the impact of varying graphene content (0.5, 1.0 and 1.5 vol %) on nanomechanical properties and scratch resistance. Among the compositions investigated, the composite containing 0.5 vol% graphene showed superior mechanical properties. Specifically, it exhibited a hardness of ∼30 GPa, a fracture toughness of 10.5 MPa m1/2 and a flexural strength of ∼920 MPa. In addition, this composite showed remarkable scratch resistance compared to composites with a higher or lower graphene content. In addition to mechanical properties, the fabricated composites also exhibited high electrical conductivity. This characteristic is especially advantageous for electrical discharge machining (EDM) processes. The high electrical conductivity enables efficient machining of complex shapes by EDM, thereby reducing machining costs while ensuring accuracy and efficiency.

Improving the mechanical performance of low graphene content epoxy nanocomposites: investigation of hybrid and chemically modified nanofillers

Graphene is a promising nanofiller for producing polymer nanocomposites with enhanced mechanical, electrical, thermal, electromechanical, and flame retardancy properties, leading to applications in aerospace, automotive, ballistics, medicine, electronics, and smart materials. Solvent-assisted top-down methods, including mechanical exfoliation of graphite, show great potential for scale-up and mass production of graphene dispersions for use in the fabrication of nanocomposites. However, these approaches can suffer from poor efficiency, which limits the concentrations of graphene/polymer dispersions that can be produced using in situ methods. As such, it is important to find new ways of making more effective use of these low concentrations of graphene nanofillers. Possible approaches include chemical modification of the graphene or finding synergies with other nanofillers to form hybrid nanocomposites. In this work, we demonstrate results that make use of each approach. Specifically, we demonstrate a low-cost and simple method for producing carbon nanotube dispersions and creating hybrid nanocomposites with substantial enhancements to mechanical properties. We also extend the scope of our previously reported semi-in situ exfoliation method by demonstrating its application in the production of a nanocomposite that incorporates chemically modified graphene. The superior mechanical properties exhibited by the nanocomposite are attributed to increased interaction strength between the polymer and nanofiller.

Through Thickness Stress Analysis of GNP/Epoxy Nanocomposites with Low Graphene Content

Through Thickness Stress Analysis of GNP/Epoxy Nanocomposites with Low Graphene Content

A Model for Direct Effect of Graphene on Mechanical Property of Al Matrix Composite

Direct effect of graphene on mechanical property of Al matrix composite has been studied by using molecular dynamic (MD) methods. The models of graphene-reinforced composite are achieved by modeling the sintering system consisting of Al particles and graphene nanosheets (GNSs), while pure Al models are obtained by deleting graphene in the composites. Structural analysis on composites indicate the increment of GNSs can promote the densification of metal matrix, increase the porosity in composite, and restrict the metal grain size. Such analysis is also performed on pure Al models, and the similarity in structure between pure Al and composite models is confirmed by the tiny difference in the nanopores, atomic images, and the number of ordered atoms. Tensile processes on the similar structures with or without graphene reveal that the direct effect of graphene shows an obvious anisotropy, low graphene content may weaken the composite in some directions, while high graphene content can strengthen the composite in more directions. However, the highest content of GNSs just brings a slight increase of 2.7% in tensile strength. The atomic images of crack propagation and the atomic stress confirm that graphene is not efficient in load transfer. Therefore, the direct effect of graphene is believed to play a very small role in strengthening mechanisms.

Enhanced thermal properties of epoxy composites by constructing thermal conduction networks with low content of three-dimensional graphene

Micro/nano electronic devices heat dissipation depends heavily on the thermal interface materials (TIMs). Despite notable progress, it is hard to efficaciously enhance the thermal properties of the hybrid TIMs with high-load additives due to an absence of effective heat transfer routes. Herein, the low content of three-dimensional (3D) graphene with interconnected networks is adopted as the additive to improve the thermal properties of epoxy composite TIMs. The thermal diffusivity and thermal conductivity of the as-prepared hybrids were dramatically improved by constructing thermal conduction networks after adding 3D graphene as fillers. The 3D graphene/epoxy hybrid’s optimal thermal characteristics were observed at 1.5 wt% of 3D graphene content, corresponding to a maximum enhancement of 683%. Besides, heat transfer experiments were further performed to determine the superb heat dissipation potential of the 3D graphene/epoxy hybrids. Moreover, the 3D graphene/epoxy composite TIM was also applied to high-power LED to improve heat dissipation. It effectively reduced the maximum temperature from 79.8 °C to 74.3 °C. These results are beneficial for the better cooling performance of electronic devices and provide useful guidelines for advancing the next-generation TIMs.

Enhancing flame retardancy of polyphenylene sulfide nanocomposite fibers by the synergistic effect of catalytic crosslinking and physical barrier

AbstractProtective clothing with fascinating flame‐retardant features is urgently needed to reduce the large amount of smoke and heat released from combustion during fire protection. In this study, polyphenylene sulfide (PPS) nanocomposite resin with efficient flame retardancy is obtained by mixing a low content of graphene and Fe2O3via a twin screw extruder. Followed by, the PPS/G/Fe2O3fibers are fabricated via melting spinning. The PPS/G/Fe2O3nanocomposite resin with 0.3 wt% of graphene and 1.0 wt% of Fe2O3performs the best during the flame retardant tests, giving a shorter self‐extinguishing time, lower peak heat release rate (22.3 kW/m2), total heat release (11.3 MJ/m2) and total smoke production (1.32 m2) than others. The pyrolysis analysis indicates that a large number of products with fused rings are formed in the residual char layer, which effectively inhibit the release of heat and smoke and thus improve the flame retardancy of PPS nanocomposite resin. In addition, the flame retardant textile weaved with PPS/G/Fe2O3fibers gives a high‐limiting oxygen index (40.1%), zero after‐flame time, no droppings and small damaged length (114 mm in warp and 98 mm in weft direction) during the standard flame retardancy tests provided by a third‐party independent inspection organization. The fabrication of PPS fibers with effective and enhanced synergistic flame retardancy through melting spinning is facile and scalable, providing a promising strategy for advanced protective clothing.

Scalable microfluidic fabrication of vertically aligned two-dimensional nanosheets for superior thermal management.

Two-dimensional (2D) nanosheets have been assembled into various macroscopic structures for wide engineering applications. To fully explore their exceptional thermal, mechanical, and electrical properties, 2D nanosheets must be aligned into highly ordered structures due to their strong structural anisotropy. Structures stacked layer by layer such as films and fibers have been readily assembled from 2D nanosheets due to their planar geometry. However, scalable manufacturing of macroscopic structures with vertically aligned 2D nanosheets remains challenging, given their large lateral size with a thickness of only a few nanometers. Herein, we report a scalable and efficient microfluidics-enabled sheet-aligning process to assemble 2D nanosheets into a large-area film with a highly ordered vertical alignment. By applying microchannels with a high aspect ratio, 2D nanosheets were well aligned vertically under strong channel size confinement and high flow shear stress. A vertically aligned graphene sheet film was obtained and applied to effectively improve the heat transfer of thermal interfacial materials (TIMs). Superior through-plane thermal conductivity of 82.7 W m-1 K-1 at a low graphene content of 11.8 vol% was measured for vertically aligned TIMs. Thus, they demonstrate exceptional thermal management performance for switching power supplies with high reliability.

Spectroscopic investigation of improved corrosion resistance of nickel due to multilayer graphene coating developed with suitably tilted substrate during CVD

The great variability (from remarkable to little) in graphene's ability as a corrosion barrier coating is attributed to the extent of defects and non-uniformity of graphene. This study established the theoretical basis for tailoring the orientation of the metallic substrate with respect to the direction of flow of the incoming precursor gas into the reactor during the chemical vapour deposition (CVD) of uniform graphene film on the substrate. We validated the theoretical basis by demonstration of development of a multilayer graphene coating with considerably improved uniformity and low defect content on a suitably tilted nickel substrate during CVD that provided an effective and durable corrosion resistance to the metal in an aggressive acidic medium. Thorough scanning X-ray photoemission microscopy (SPEM) using synchrotron radiation and Raman spectroscopy enabled the mechanistic understanding of the improved uniformity and low defect content of graphene coating, and their role in considerably improving the corrosion resistance of nickel.

Piezoelectricity enhancement in graphene/polyvinylidene fluoride composites due to graphene-induced α → β crystal phase transition

Piezoelectric polymers represented by polyvinylidene fluoride (PVDF) possess many attractive attributes so they are widely used in electromechanical energy conversion devices. To further enhance the piezoelectric effect of PVDF, graphene and its derivatives have been added. A central issue is how the added graphene improves the piezoelectric properties of the graphene/PVDF composites. Starting from consideration of crystal phase transition from α to β phase in PVDF due to addition of graphene, we first introduce Cauchy’s cumulative probability function to characterize the evolution of β phase as a function of graphene content. Then, by considering the relationship between β phase and the dipole, and between the microscopic dipole moment and the macroscopic piezoelectric coefficient, a theory of piezoelectricity for the composite is obtained. The theory shows that the β phase increases slowly at low graphene content but the increase is very rapid as the graphene concentration approaches the percolation threshold, after which there is no significant growth. The piezoelectric coefficient also increases similarly until the percolation threshold, after which it starts to drop. When the graphene content is 0.11 vol%, the piezoelectric coefficient d33 increases from 22pC/N of pure PVDF to 39.73pC/N of graphene/PVDF composite, which is an 80.5% increase in d33. In addition, this theory is further extended and applied to the other nanoparticle-enhanced piezoelectric polymer composites. This crystal phase transition model serves to fill up the theoretical gap in piezoelectric enhancement in piezoelectric enhancement of PVDF by graphene.

Reduced graphene oxide as an adhesion enhancer of fusion-bonded epoxy coatings

Alternative coating technologies based on advances in polymer engineering have been continuously developed to face the always present challenges of wear in metal surfaces. Fusion-bonded epoxy (FBE), an epoxy-based powder coating, has been widely used in some sectors due to its quick and easy application and the reduction of waste material. FBE is a high-performance composite with approximately 30 wt% microparticles, and the challenge addressed herein is to improve the coating properties by adding a low content of graphene. In this work, new coatings based on FBE and thermally reduced graphene oxide (rGO) were developed and prepared by two different processes: in one case, highly thermally stable and low functionalized graphene (rGO-tre with 4.6 % oxygenated groups) and in the other case, highly exfoliated and more functionalized graphene (rGO-tr with 9.8 % oxygenated groups). FBE/rGO-tr and FBE/rGO-tre nanocomposites were produced in concentrations of 0.1, 0.3, 0.5 and 1.0 wt% in a planetary ball mill. The coated steel plates were heated in a conventional oven at 204 °C, and the curing of the material was confirmed by using differential scanning calorimetry (DSC) analysis. The addition of rGO-tr (1.0 wt%) and rGO-tre (0.5 wt%) improved the adhesion of the nanocomposite coating in the wet test by 104 % and 95 %, respectively, when compared with neat FBE coatings. Small gains in abrasion and hardness were also observed. In addition to the tendency to reduce indentation (micro and nano), it was possible to observe a better recovery of the FBE with the addition of rGO-tr and rGO-tre after the deformation carried out by the tip. The integration of graphene nanofillers of different grades in a ternary composite with silicate microparticles and epoxy powder was successfully achieved, and the adhesion, abrasion and hardness benefit from the synergy between micro- and nanofillers.

Near-Infrared-Light-Assisted Self-Healing Graphene-Thermopolyurethane Composite Films

Graphene-thermopolyurethane (G-TPU) composite films were fabricated and the effects of the TPU initial concentration, characteristics of TPU, and graphene loading on the electrical, mechanical, thermal, infrared thermal response and near-infrared-light-assisted self-healing properties of the composite films were investigated in detail. The experimental results demonstrate that the comprehensive performances of the composite film are related to the initial concentration of the TPU solution and the characteristics of the TPU and the graphene loading. The composite film prepared from TPU solution with low initial concentration can have conductivity under the condition of low graphene content. However, the composite film prepared with appropriate initial concentration of TPU solution and high graphene loading is conducive to obtain high conductivity. After 60 s of near-infrared illumination, the temperature of the composite film first increases and then decreases with the increase in graphene loading until it reaches saturation. The near-infrared light thermal response of the composite film with high graphene loading is related to the initial concentration of TPU solution, while the near-IR thermal response of the composite film with low graphene loading is independent of the initial concentration of TPU. The surface micro-cracks of the composite film almost disappeared after 10 min of near-infrared illumination. The resistance of the conductive composite film increases after healed. The composite film prepared with low melting point TPU is more favorable to obtain high near-IR thermal self-healing efficiency.

Mechanically strong, stiff, and yet ductile AlSi7Mg/graphene composites by laser metal deposition additive manufacturing

Laser metal deposition (LMD) with a coaxial powder feeding technology has been applied to fabricate pure aluminum alloy (AlSi7Mg) and low oxidation graphene aluminum matrix (LOG-Al) composites with low oxidation graphene (LOG) contents of 0.05 wt % and 0.1 wt % after the powder was prepared by wet ball milling. The LOG-Al composites showed improvements in all properties including hardness, tensile strength, ductility, modulus of elasticity and yield strength with the increase of LOG addition contents. The microstructures and fracture surfaces of the composites were observed and the results of TEM, HRTEM, optical microscope, EBSD, XRD spectra, Raman spectra, Vickers hardness, tensile properties were analyzed. The effects of wet ball milling, the addition of low oxidation graphene and its contents and LMD process on microstructure formation and resulting mechanical properties were discussed.

Reduced graphene oxide coated polyurethane composite foams as flexible strain sensors for large deformation

Combining graphene composite with three-dimensional structure is an effective strategy to avoid the agglomeration of graphene nanosheets and significantly enhances the properties of composite at low graphene content. In this work, reduced graphene oxide coated polyurethane composite foams (RPFs) with different pore sizes were prepared by a simple and economical self-assembly method. The RPFs are found to have good structural integrity and excellent flexibility, with a remarkable ability to withstand large deformation of 90% and 3 orders of magnitude decrease of electrical resistance. The RPF composite with higher density and smaller pore size exhibits better elasticity and responsive piezoresistivity. The resistance-time curves of RPFs in compression and bending modes exhibits a quick response of loading and release procedures by 0.10 s and 0.74 s in compression, 1.14 s and 0.91 s in bending, respectively, showing a good potential application of flexible and highly sensitive strain sensors for large deformation.

Electrical conductivity and hydrophobicity of graphene oxide-modified carbon nanofibers

Graphene oxide-modified carbon nanofibers were prepared by electrospinning and the effect of the amount of graphene additive and carbonization temperature on the physical and chemical properties of graphene/carbon nanofiber composites was investigated. Results showed that the conductivity of graphene-modified nanofibers increased with graphene content. The conductivity of the composite containing 5 wt% of graphene (0.39S/cm) was 2.2 times higher than that of the pure fiber (0.19S/cm). The conductivity also increased with carbonization temperature. The low graphene content allows to preserve the mechanical properties of graphene/carbon nanofiber composites. The graphene/carbon nanocomposite fibers obtained in this work were found to have excellent chemical stability, mechanical strength, and hydrophobic properties. In view of the overall enhancement in physical properties upon addition of even low amounts of graphene, these composites are advantageous in future industrial applications.

Microstructure and Fracture Mechanism Investigation of Porous Silicon Nitride-Zirconia-Graphene Composite Using Multi-Scale and In-Situ Microscopy.

Silicon nitride–zirconia–graphene composites with high graphene content (5 wt.% and 30 wt.%) were sintered by gas pressure sintering (GPS). The effect of the multilayer graphene (MLG) content on microstructure and fracture mechanism is investigated by multi-scale and in-situ microscopy. Multi-scale microscopy confirms that the phases disperse evenly in the microstructure without obvious agglomeration. The MLG flakes well dispersed between ceramic matrix grains slow down the phase transformation from α to β-Si3N4, subsequent needle-like growth of β-Si3N4 rods and the densification due to the reduction in sintering additives particularly in the case with 30 wt.% MLG. The size distribution of Si3N4 phase shifts towards a larger size range with the increase in graphene content from 5 to 30 wt.%, while a higher graphene content (30 wt.%) hinders the growth of the ZrO2 phase. The composite with 30 wt.% MLG has a porosity of 47%, the one with 5 wt.% exhibits a porosity of approximately 30%. Both Si3N4/MLG composites show potential resistance to contact or indentation damage. Crack initiation and propagation, densification of the porous microstructure, and shift of ceramic phases are observed using in-situ transmission electron microscopy. The crack propagates through the ceramic/MLG interface and through both the ceramic and the non-ceramic components in the composite with low graphene content. However, the crack prefers to bypass ceramic phases in the composite with 30 wt.% MLG.

Investigation of the effectiveness of graphene/polyvinyl alcohol on the mechanical and electrical properties of cement composites

Smart cement-based composites provide indispensable support for the intellectualization of a concrete structure. Graphene and its composites have been the focus of research in recent years. However, the application of graphene in smart cement-based concrete is still rare, which is probably due to the poor compatibility between graphene and the cement matrix, the high preparation cost of graphene and the complex construction process of the composites. Moreover, existing smart cement-based composites have poor ductility, so their self-sensing range of the ultimate tensile strain is much smaller than that of the compressive strain. In contrast, it is very important to monitor the tensile strain and detect cracks in concrete structures. Additionally, it is necessary to improve the ductility of smart cement-based composites. Therefore, in this study, a graphene/polyvinyl alcohol (PVA) dispersion is prepared by one-step liquid-shear exfoliation at a relatively low cost when compared to commercial graphene products; the dispersion can not only substitute for water but also can be directly used in the cement-based composite material for casting. The mechanical, electrical and piezoelectric properties of the as-prepared graphene/PVA hybrid modified cement with a low graphene content can be comparable with the cement materials using commercial graphene. Thus, graphene/PVA hybrid modified cement could be a potential candidate for structural health monitoring material.

Grain refinement induced friction reduction and anti-wear performances of electrodeposited graphene/Ni composites with low content reduced graphene oxide

Graphene and its derivatives have attained a considerable amount of popularity as effective reinforcements in the electrodeposited nickel (Ni) matrix composites for lubrication. However, the composites suffer from certain challenges, such as the agglomeration of graphene nanosheets in the electrodeposition process and the uncertain role of graphene on the friction reduction and wear resistance during sliding. By using a polyvinylpyrrolidone assisted reduction method to improve the dispersity of reduced graphene oxide (RGO) in the electrolyte, we prepare the bulk RGO/Ni composites with different RGO adding amount and perform a complete research on the tribological behaviours. Our work reveals that although an extremely low amount of RGO nanosheets (carbon content below 0.018%) have been incorporated into the Ni matrix, it induces significant grain refinement and friction reduction effects. Compared with the RGO-free Ni deposit, the friction coefficient and wear rate of the composite is reduced by 25.6% and 27.5%, respectively. The improved tribological properties are ascribed to the fine-grain strengthening effect and the formation of a continuous easy-shear nickel oxide film on the contact surface. This finding offers a new view on the wear mechanism of graphene/Ni composites with low graphene content, for which the fine-grain strengthening rather than the formation of carbon-rich transfer layer will dominate the lubricating and anti-wear performances.

Microstructure and mechanical properties of Cu-graphene composites produced by two high pressure torsion procedures

True bulk nanostructured composites promising for a wide range of applications however being difficult to produce using established engineering techniques. Most of previous works aimed to design of Cu graphene composite used the approach of high temperature sintering inevitably associated with growth of Cu grains. Another advantageous approach of composites consolidation allowing to avoid heating of the sample is shear deformation under high pressure that has been earlier used for Al – graphene composite. Our work reports the first attempt of Al-graphene composite consolidation by means of is high pressure torsion (HPT). Two-step processing by constrained and non-constrained HPT was applied to produce bulk Cu-graphene composite with nanoscaled Cu grains laminated by graphene. After the constrained HPT high and low graphene content layers were interspersed in the microstructure. The second step of not-constrained HPT led to the refinement of graphene agglomerates to the range of 10 nm and Cu grains to the range of 100 nm with quite uniform distribution of graphene, preserving the equiaxial shape of the grains seldom in case of the composite structure. The process significantly increased microhardness of Cu-graphene composite from 1450 to 1900 MPa in the edge region after consolidation with even more pronounced increase from 1900 to 2950 after following constrained HPT. However, infusion of graphene resulted in a prominent decrease of both ductility from 15 to 4% and strength of the material. Brittle failure with low value of critical fracture stress should be related to the role of graphene as an obstacle for the dislocation movement. The dynamic recrystallization in the Cu-graphene composite during severe plastic deformation by not-constrained HPT suggests also that dispersed graphene may play role in the dislocation sinking at the micro-grains boundaries. The obtained results contribute to figuring out the major issues of Cu and graphene interaction under pressure and can be helpful in validation of prospective research plan in this field.