Graphene Nanosheets Content Research Articles

Effect of ball-milling and graphene contents on the mechanical properties and fracture mechanisms of graphene nanosheets reinforced copper matrix composites

Graphene nanosheets (GNSs) reinforced pure copper matrix composites were prepared by ball-milling and hot-press sintering. The morphologies and structures of GNSs-Cu powders were studied after ball-milling for different time. The effects of the GNSs content on the microstructures, mechanical properties and fracture mechanisms of the composites were also investigated. It is indicated that the GNSs are gradually dispersed into the copper matrix with increasing the ball-milling time and a uniform dispersion is achieved after ball-milling for 5 h. When the content of GNSs in the composite is 0.5 wt%, GNSs distribute randomly in the composite and the interface bonding is good which is benefit to enhance the mechanical properties of composite. With increasing the GNSs contents, the aggregation of GNSs in the composite is apparent, which seriously separates the matrix and results in low mechanical properties. The fracture mechanism of the composites changes from ductile to brittle.

Rheological and conductivity percolations of syndiotactic polystyrene composites filled with graphene nanosheets and carbon nanotubes: A comparative study

Two-dimensional graphene nanosheets (GNSs) and one-dimensional carbon nanotubes (CNTs) possess large aspect ratios but different geometries. In this study, syndiotactic polystyrene (sPS) composites reinforced with different contents of GNSs were prepared via a solution coagulation method. The dispersion and microstructure of GNSs in sPS were confirmed via transmission electron microscopy and atomic force microscopy. Rheological and electrical properties of sPS/GNS composites were investigated to reveal the effect of filler concentration, and the results were compared with those of sPS/CNT composites. Percolation scaling laws were applied to the magnitudes of storage modulus and electrical conductivity to determine the threshold concentration and corresponding exponent. The sPS/GNS and sPS/CNT composites possess a similar percolation threshold for melt elasticity and solid conductivity. However, the rheological threshold (∼0.1 vol%) is distinctly lower than the conductivity threshold (∼0.5 vol%) because of the formation of polymer–nanofiller hybrid network. The exponents for rheological and electrical percolations of sPS/GNS composites are determined as 4.12 and 4.71, respectively, which are higher than the corresponding values of 2.64 and 2.87 for sPS/CNT composites. The derived exponents indicate that the 2D GNS-related network is more effective than the 1D CNT-related network for enhancing the melt elasticity and solid conductivity of sPS matrix.

A facile approach for preparation of polystyrene/graphene nanocomposites with ultra-low percolation threshold through an electrostatic assembly process

Improving the dispersion of graphene nanosheets (GN) in a polymer matrix is a critical step in lowering the percolation threshold of nanocomposites. In this paper, an effective method based on an electrostatic assembly process is reported. Polystyrene (PS) latex was first prepared by using hexadecyl trimethyl ammonium bromide (CTAB) as a cationic surfactant, which created positive charges on the surface of the PS micelles. An in situ demulsification process was then conducted by adding negatively charged graphene oxide (GO) particles into the positively charged PS latex. Thus, GO sheets were attached spontaneously to the surfaces of PS particles through electrostatic adsorption. Followed by in situ reduction and hot pressing, the agglomeration of GN was largely prohibited by the PS microspheres and facilitated the formation of GN networks in the PS matrix. The obtained PS/GN nanocomposites exhibited excellent electrical properties with a percolation threshold as low as 0.054 vol.% GN. When the GN content reached 1.53 vol.%, the electrical conductivity was 46.32 S/m and the thermal conductivity 0.47 W/mk. This strategy represents a new environment-friendly pathway, which is also applicable for other polymer matrices, for large-scale production of polymer composites with fully interconnected graphene networks at ultra-low GN content.

Hydrothermal synthesis of graphene nanosheets and its application in electrically conductive adhesives

A highly electrical conductive adhesive based on graphene nanosheets (GNs) was developed. In this study, we prepared highly electrical conductive GNs via a green and efficient method and investigated the influence of graphene materials on the properties of electrically conductive adhesives. Primarily aimed at improving the electrical conductivity properties of electrically conductive adhesives (ECAs), graphene nanosheets was dispersed into an epoxy matrix to play a role as a network for providing a carrier transfer pathway. The results demonstrate that filling graphene nanosheets and microsilver flakes obviously decrease the resistivity of electrically conductive adhesives. Further, with increasing the graphene nanosheets content, resistivity sharply decreases. With a filling ratio up to 0.5% and the filling of 69.5% with microsilver flakes, the lowest resistivity has been reached 5.0×10−5Ωcm.

Synergetic effect of hexagonal nitride nanopowder and graphene nanosheets on thermal and electrical conductivity of the hBN/GNs/CE resin nanocomposites

In the study, two kinds of nanomaterials [hexagonal nitride nanopowder (hBN) and graphene nanosheets (GNs)] were chosen as resin fillers due to their similar structures and excellent thermal properties. The hBN/CE, GNs/CE and hBN/GNs/CE resin nanocomposites with different hBN and/or GNs contents were prepared by a solution blended method. The structures of hBN and GNs, thermal and electrical conductivities, and thermal properties of the hBN/CE, GNs/CE and hBN/GNs/CE resin nanocomposites were observed with different test instruments. The results showed that the hBN had an analogous structure with GNs. The addition of hBN and GNs in the CE resin made the fractural surfaces of the resin nanocomposites rougher and more fold than that of the pure CE resin. For thermal conductivity, the synergistic effect of the hBN and GNs in the CE resin nanocomposites was better than the hBN or GNs filling the CE resin alone. The thermal diffusivity of GNs was good, meanwhile, the electrical conductivity of GNs was excellent as well. It indicated that the electrical conductivity of the GNs/CE resin nanocomposites was higher than that of the hBN/GNs/CE resin nanocomposites at a given volume contents. The data calculated from the TGA test was roughly corresponding to the experimental hBN and GNs volume content of the hBN/GNs/CE resin nanocomposites.

Morphological features and crystallization behavior of the conductive composites of poly(trimethylene terephthalate)/graphene nanosheets

ABSTRACTPoly(trimethylene terephthalate) (PTT) composites filled with well‐dispersed graphene nanosheets (GNSs) were prepared through a coagulation method. The effects of increased GNS concentration on variations in the structure and properties of the PTT matrix, such as its electrical conductivity, crystallization kinetics, melting behavior, and crystal morphology, were investigated. Several analytical techniques were used, including electrical conductivity measurement, differential scanning calorimetry, Fourier transform infrared spectroscopy, wide‐angle X‐ray diffraction, polarized light microscopy, transmission electron microscopy (TEM), and thermo‐gravimetric analysis (TGA). Electrical conductivity increased from 1.8 × 10−17 S/cm for neat PTT to 0.33 ± 0.23 S/cm for PTT/GNS composites with 2.97 vol % GNS content. Percolation scaling laws were applied, and then threshold concentration and exponent were determined. In the case wherein liquid nitrogen was used to quench the melt, a mesomorphic phase was formed despite the extremely short crystallization time after adding high GNS contents. PTT crystallization rate increased with the gradual addition of GNSs. The enhanced crystallization kinetics was attributed to the high nucleation ability of GNSs to induce epitaxially grown lamellae on their surfaces, as revealed by TEM. PTT nuclei were randomly developed on the GNS surface to form the lamellae. However, crystallinity reached its maximum value near the electrical percolation threshold because the PTT chain mobility was confined after the GNS–GNS network formed. The growth of PTT banded spherulites in the bulk was still observed for composites with high GNS content, and TGA results revealed that the GNS‐filled PTT composites had excellent thermal stability. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43419.

Simultaneous increase in conductivity and phonon scattering in a graphene nanosheets/(Bi2Te3)0.2(Sb2Te3)0.8 thermoelectric nanocomposite

A thermoelectric nanocomposite of Bi0.4Sb1.6Te3 (BiSbTe) incorporated with the graphene nanosheets (GNs) has been synthesized and studied. The reduction of the carrier mobility is much less than the increase of the carrier concentration, resulting in the increase in conductivity at a low graphene nanosheets content. Simultaneously, graphene nanosheets causes 20–30% reduction in thermal conductivity (κ) owing to phonons blocking of nanosheets as well as phase boundaries. As a result, high dimensionless figure of merit (ZT) values of up to 1.29 (300 K) and 1.54 (440 K) are obtained in Bi0.4Sb1.6Te3 incorporated with only 0.3 vol.% and 0.4 vol.% graphene nanosheets, respectively, demonstrating that the thermoelectric performance of the BiSbTe alloy can be improved effectively through incorporation of GNs.

The effect of graphene content and sliding speed on the wear mechanism of nickel–graphene nanocomposites

Nickel–graphene metal matrix composite coatings were fabricated by pulse electrodeposition technique from a Watt's type electrolyte. Effect of the graphene concentration in the electrolyte on the microstructure, microhardness, tribological features of nanocomposite coatings were evaluated in details. Microhardness of the composite coating was measured using a Vicker's microhardness indenter. The surfaces of the samples were characterized by scanning electron microscopy (SEM). Raman spectroscopy, EDS and XRD analysis were used to determine chemical composition and structure of composite coatings. The tribological behavior of the resultant composite coating was tested by a reciprocating ball-on disk method at constant load but varying sliding speeds for determination the wear loss and friction coefficient features against a counterface. The wear and friction variations of the electrodeposited nickel graphene nanocomposite coatings sliding against an M50 steel balls were carried out on a CSM Instrument. The friction and wear properties of the coatings were examined without any lubrication at room temperature in the ambient air. The change in wear mechanisms by changing graphene nanosheets content was also comprehensively studied.

Electrical percolation and crystallization kinetics of semi-crystalline polystyrene composites filled with graphene nanosheets

Syndiotactic polystyrene (sPS) is a semi-crystalline polymer with high melting temperature and good mechanical strength. Composites of sPS filled with different contents of graphene nanosheets (GNS) are prepared by coagulation method. Two types of GNS with different thicknesses (denoted as G1 and G10) are studied to unveil the effect of aspect ratio on electrical conductivity and crystallization kinetics of the composite. Atomic force microscopy and transmission electron microscopy (TEM) show that G1 is a wrinkled sheet with an average thickness of ∼2 nm and that G10 is a smooth flake with a thickness of ∼50 nm; both possess a similar basal dimension of ∼5 μm. The percolation thresholds for electrical conductivity (φc) of the G1-filled and G10-filled composites are 0.46 and 3.84 vol%, respectively. At a given GNS content, the electrical conductivity of the G1-filled composites is higher than that of the G10-filled composites. Both findings are attributed to the larger GNS aspect ratio of G1 compared with G10. The deduced φc of the G1-filled composites is significantly larger than that of GNS-filled amorphous atactic PS composites, indicating that the crystallizability of the matrix has an important influence on formation of GNS networks. Both G1 and G10 nanofillers are found to be good nucleating agents for the heterogeneous nucleation of sPS. Because of its wrinkled surface, G1 is less effective than G10 in inducing sPS crystallization. Compared with 2D sheet-like GNS, 1D CNTs are more effective in enhancing sPS crystallization through surface-induced nucleation as well as the chain-tube wrapping behavior in the sPS/CNT composites.

The effect of type and ratio of reinforcement on the synthesis and characterization Cu-based nanocomposites by flake powder metallurgy

In this study, Cu-based nanocomposites using nanographite, graphene nanosheet and carbon nanotubes have been fabricated by flake powder metallurgy. The objective of using different reinforcement contents is to assess their effect on the microstructure, density, electrical conductivity and hardness of Cu-based nanocomposites. The results show that the average particle size of the prepared Cu-based nanocomposite powders with reinforced 5 wt.% nanographite, graphene nanosheet and Cu-CNT nanocomposite are 97.8, 94.9 and 49.7 μm, respectively. The lowest final density 6.73 g/cm3 for sintered Cu-5 wt.% CNT nanocomposites, while the highest density value was 8.78 g/cm3 for sintered Cu-0.5 wt.% nanografit nanocomposites. For all nanocomposite groups, increasing the reinforcement content from 0.5 to 5 wt.% results in an decrease in hardness values. The electrical conductivity of the Cu-0.5 wt.% graphene nanosheet was approximately 79 IACs, and this value decreased slightly to 62 IACs with increasing graphene nanosheet content.

Effect of graphene nanosheets on the corrosion behavior of Sn–Ag–Cu solders

In this study, the effect of graphene nanosheets (GNSs) on the corrosion resistance of 96.5Sn–3Ag–0.5Cu (SAC) solder at ambient temperature in a 3.5 wt% NaCl solution was investigated using the potentiodynamic polarization method . The corrosion products were analyzed by field emission-scanning electron microscope, energy dispersive spectroscopy , and X-ray diffraction. The results showed that the GNSs affect the anodic polarization behavior of the solders. Adding GNSs enhanced the corrosion resistance of the SAC solder, as GNSs content increased to 0.03 wt%, the corrosion resistance peaked and then declined with further increment in the wt% of the GNSs. Overall, the corrosion resistance of SAC/GNSs was found to be more superior than that of the pure SAC. The mechanism of the corrosion resistance improvement can be explained by the formation of a compact corrosion layer of the GNSs. This provides an inert physical barrier to the initiation and development of corrosion. As the GNSs content further increased (more than 0.03 wt%), the corrosion resistance of the SAC/GNSs solder decreased.

Isothermal crystallization of syndiotactic polystyrene induced by graphene nanosheets and carbon nanotubes: a comparative study

Composites of sPS filled with different contents of graphene nanosheets (GNS) are prepared by coagulation method. Two types of GNS with different thicknesses (denoted as G1 and G10) are studied to unveil the effect of aspect ratio on the crystallization kinetics of the composite. Atomic force microscopy and transmission electron microscopy (TEM) show that G1 is a wrinkled sheet with an average thickness of ~2 nm and that G10 is a smooth flake with a thickness of ~50 nm; both possess a basal dimension of ~5 μm. TEM studies on the melt-quenched composites reveal that G1 has a more uniform dispersion in the sPS matrix than G10. Short lamellae of sPS are observed in the G10-filled composites with GNS content higher than 0.5 wt.%. The results of wide-angle X-ray diffraction show that the produced sPS crystallites are in β form under severe cooling conditions in liquid N2. Regardless of the GNS content and type, the glass transition and equilibrium melting temperature of the sPS matrix are unchanged at ~96 and ~290 °C, respectively. Both G1 and G10 nanofillers are good nucleating agents for the heterogeneous nucleation of sPS. With increasing GNS loading, the isothermal crystallization rate of sPS increases. G10 is more effective than G1 in inducing sPS crystallization despite the higher concentration required to form the GNS network. Compared with 1D CNT nanofiller, 2D GNS is less effective in enhancing sPS crystallization through surface-induced nucleation because of the geometrical difference between the two materials.

Effect of Oxidation Condition on the Synthesis of Graphene Nanosheets and the Electrical Properties of Poly (Trimethylene Terephthalate) Composites Prepared Using these Nanosheets

Graphene nanosheets (GNSs) with different oxygen contents crucially affect the performance of polymer composites. In this study, we compared GNSs prepared from graphite oxide (GO) using three different concentrations of potassium permanganate and thermal reduction of GO at 1050 °C. The structural properties of GO and GNSs were investigated by Fourier transform infrared spectroscopy and Raman spectroscopy. Moreover, an effective coagulation method was used to prepare poly (trimethylene terephthalate) (PTT) composites filled with well-dispersed GNSs by selecting suitable solvents for solution blending. The electrical properties of PTT/GNSs were investigated to reveal the effect of oxygen content of GNSs.

Mechanical, electrical, and thermal properties of graphene nanosheet/aluminum nitride composites

Graphene nanosheet (GNS)/aluminum nitride (AlN) composites were prepared by hot-pressing and effects of GNSs on their microstructural, mechanical, thermal, and electrical properties were investigated. At 1.49vol% GNSs content, the fracture toughness (5.09MPam1/2) and flexural strength (441MPa) of the composite were significantly increased by 30.17% and 17.28%, respectively, compared to monolithic AlN. The electrical conductivity of the composites was effectively enhanced with the addition of GNSs, and showed a typical percolation behavior with a low percolation threshold of 2.50±0.4vol%. The thermal conductivity of the composites decreased with the addition of GNSs.

Microstructural Modification of NiAl Layered Double Hydroxide Electrodes by Adding Graphene Nanosheets and Their Capacitative Property

NiAl layered double hydroxide (LDH) composite electrodes containing various contents of graphene nanosheets (GNS) were prepared by a hydrothermal method. The micro‐structure and morphological properties were examined by FE‐SEM, FE‐TEM, XRD, and FTIR. Electrochemical analysis was also carried out by cyclic voltammetry, impedance, and cycle life measurement. The as‐prepared composite that contained 500 mg of graphene (denoted as NiAl/G‐50) achieved the highest specific capacitance of 1147 F/g among the various NiAl LDH/GNS composites. Besides, the NiAl LDH/GNS composite exhibited the lower diffusion resistance, improved rate capability, and good cyclic stability (83% of initial capacitance after 2000 cycles). Considering the morphological data and the improved capacitative properties together, we concluded the synthesized NiAl LDH/GNS composites would be a promising electrode material for supercapacitors.

Graphene nanosheet- and flake carbonyl iron particle-filled epoxy–silicone composites as thin–thickness and wide-bandwidth microwave absorber

An epoxy–silicone matrix filled with both graphene nanosheets (GNs) and flake carbonyl iron (FCI) particles was prepared, and the influence of GNs and/or FCI particle content on the electromagnetic and microwave-absorbing properties was investigated in the frequency range of 2–18GHz. Thin–thickness, broadband absorption microwave absorbers with homogeneously dispersed GNs and FCI particles were obtained. The values and frequency dependencies of the electromagnetic properties of such absorbers can be adjusted by simply changing the content of GNs and/or FCI particles. These changes led to an apparent improvement of impedance matching and then significantly improved the microwave absorptions. Reflection loss values exceeding −6dB (>74.9% absorption) can be obtained in the frequency range of 5.4–18GHz with a thickness of 0.9mm.

Mechanical properties and toughening mechanisms of epoxy/graphene nanocomposites

Abstract Because of extraordinary physical, chemical and mechanical properties, graphene nanosheets (GNS) are suitable fillers for optimizing the properties of different polymers. In this research, the effect of GNS content (up to 1 wt.%) on tensile and flexural properties, morphology of fracture surface, and toughening mechanism of epoxy were investigated. Results of mechanical tests showed a peak for tensile and flexural strength of samples with 0.1 wt.% GNS such that the tensile and flexural strength improved by 13% and 3.3%, respectively. The Young’s modulus and flexural modulus increased linearly with GNS content, although the behavior of the Young’s modulus was more remarkable. Morphological investigations confirmed this behavior because the GNS dispersion in the epoxy matrix was uniform at lower contents and agglomerated at higher contents. Finally, microscopical observation showed that the major toughening mechanism of graphene-epoxy nanocomposites was crack path deflection, which changed the mirror fracture surface of the pure epoxy to rough surface.

Effect of graphene nanosheets on the mechanical, electrical, and rheological properties of polyamide 6/acrylonitrile–butadiene–styrene blends

Polyamide 6 (PA6) and acrylonitrile butadiene styrene blend reinforced by graphene nanosheets (GNs) nanocomposites were prepared by batch system followed by hot compression to get samples for different tests. A low amounts of graphene were used (1, 2, 3, 4 wt%), with this selected loading range, the mechanical properties (Young's modulus) have increased linearly with GNs contents. However, it is observed stability in the tensile strength. The electrical and rheological properties are well characterized and have shown that the evolution of the properties runs through a threshold loading charge. The results are related to the blends morphology, and SEM images showed selective preferential localization in the polyamide 6 phase. Moreover, the presence of GNs in the blends has reduced the surface tension between the two polymers. POLYM. COMPOS. 37:998–1006, 2016. © 2014 Society of Plastics Engineers

Effect of Graphene on the Fire and Mechanical Performances of Glass Fiber-Reinforced Polyamide 6 Composites Containing Aluminum Hypophosphite

The effect of graphene nanosheets (GNS) on the fire and mechanical performances of glass fiber-reinforced polyamide 6 composites containing aluminum hypophosphite (GFPA6) was investigated. Results indicated that the introduction of GNS played little role in improving the thermal stability and fire retardancy of the GFPA6 composite, but exhibited visible anti-dripping phenomenon performance. With the addition of GNS, the mechanical properties of the composite are obviously increased. When the content of GNS was 1 wt.%, the composite had the optimized mechanical properties with tensile strength of 52 Mpa, bending strength of 66 Mpa, and impact strength of 15 KJ/m2, respectively.

Effect of graphene nanosheets content on the morphology and electrochemical performance of LiFePO4 particles in lithium ion batteries

Few layers graphene nanosheets (GS) are obtained by the reduction of graphite oxide (GO) via Lithium aluminium tetrahydride (LiAlH4) and Phosphorus tribromide (PBr3) as the deoxidizer. The LiFePO4/GS composite is prepared using a solution phase method followed by a calcination process with only 2h at 600°C. The effect of the GS content in LiFePO4/GS on the morphology and electrochemical performance of LiFePO4 particles is extensively investigated. Results show that the optimized amount of GS in LiFePO4/GS is 5%. The primary particle size of LiFePO4/5%GS is 100∼150nm which are wrapped and connected homogeneously and loosely by GS with ∼4 layers. The GS can restrict the growth of LiFePO4 particle and construct an effective conductive network LiFePO4/GS composite, which all can enhance the conductivity of LiFePO4 particle. The LiFePO4/5%GS composite delivers a capacity of 155.4mAhg−1 at 0.2C, which is much higher than pure LiFePO4 (125.3mAhg−1). Even at high rate of 5C, a specific capacity of 124.3mAhg−1 is achievable, with no obvious capacity fading after 100 cycles.