Multilayer Graphene Sheets Research Articles

Investigation of two different water-dispersed graphene on the performance of graphene/cement paste: Surfactant and superplasticizer effect

• The compressive strength of graphene-based cement paste with 0.1% SP was increased by 82.05%. • Surfactants did not show better performance in the hydration process due to their hydrophilicity. • The optimized concentration of graphite and dispersing agents is determined. • The graphene produced by the superplasticizer has the lowest level of defects. • The microstructure results are in accordance with compressive resistance results. The excellent performance of graphene-based materials to use in concrete has recently attracted the attention of civil engineering researchers. However, the application of graphene faces obstacles due to the high cost of graphene and agglomeration phenomena in cementitious composites. As a result, research into the production of water-dispersed graphene, a combination of graphite and a dispersing agent, is a particularly cost-effective alternative. In this regard, it is essential to select a dispersing agent capable of effectively separating graphene layers while also improving mechanical properties and impermeability. In this study, the influence of two different dispersive agents, surfactant (S) and superplasticizer (SP), on mechanical properties, permeability, and microstructure of cement paste was investigated. SEM, TEM, and Raman spectroscopic analyses demonstrate that multilayer graphene sheets made using superplasticizer have higher quality and fewer defects than surfactant-based sheets. After 3 days of aging, the compressive strength of graphene-containing cement paste with 0.1 % superplasticizer increased by 82.05 % compared to the control paste. On the other hand, a decrease in sorptivity by 54 % compared to the control paste is observed by graphene-containing cement paste with 0.56 g/l surfactant. The microstructure investigation revealed that graphene accelerates the CH and C-S-H productions due to the nucleation effect in the composite cement matrix; however, the effect of SP is more significant than S in cementitious composites. This research suggests that water-dispersed graphene generated by 0.1 % SP and 0.56 S g/l has the potential to be used as an innovative admixture in cement-based composite materials.

Theoretical Model of a Plasmonically Enhanced Tunable Spectrally Selective Infrared Photodetector Based on Intercalation-Doped Nanopatterned Multilayer Graphene.

We showed in past work that nanopatterned monolayer graphene (NPG) can be used for realizing an ultrafast (∼100 ns) and spectrally selective mid-infrared (mid-IR) photodetector based on the photothermoelectric effect and working in the 8-12 μm regime. In later work, we showed that the absorption wavelength of NPG can be extended to the 3-8 μm regime. Further extension to shorter wavelengths would require a smaller nanohole size that is not attainable with current technology. Here, we show by means of a theoretical model that nanopatterned multilayer graphene intercalated with FeCl3 (NPMLG-FeCl3) overcomes this problem by substantially extending the detection wavelength into the range from λ = 1.3 to 3 μm. We present a proof of concept for a spectrally selective infrared (IR) photodetector based on NPMLG-FeCl3 that can operate from λ = 1.3 to 12 μm and beyond. The localized surface plasmons (LSPs) on the graphene sheets in NPMLG-FeCl3 allow for electrostatic tuning of the photodetection wavelength. Most importantly, the LSPs along with an optical cavity increase the absorbance from about N × 2.6% for N-layer graphene-FeCl3 (without patterning) to nearly 100% for NPMLG-FeCl3, where the strong absorbance occurs locally inside the graphene sheets only. Our IR detection scheme relies on the photothermoelectric effect induced by asymmetric patterning of the multilayer graphene (MLG) sheets. The LSPs on the nanopatterned side create hot carriers that give rise to the Seebeck effect at room temperature, achieving a responsivity of V/W, a detectivity of D* = 2.3 × 109 Jones, and an ultrafast response time of the order of 100 ns. Our theoretical results can be used to develop graphene-based photodetection, optical IR communication, IR color displays, and IR spectroscopy over a wide IR range.

Processing‐structure‐property relationship of multilayer graphene sheet thermosetting nanocomposites manufactured by calendering

AbstractThe dispersion state of multilayer graphene sheets in polymers has a strong impact on the properties of the nanocomposite, and is driven by the processing parameters of the dispersion method. Herein, multilayer graphene sheet/vinyl ester nanocomposites were manufactured using a three‐roll mill. The roller gaps and number of processing cycles were varied to study their effect on the dispersion state and their relationship with the effective electromechanical properties of the nanocomposites. It was found that reducing the roller gaps and increasing the number of processing cycles yields smaller (up to 7.4 μm in diameter) and more densely packed (up to ~1500 agglomerates/mm2) agglomerates. Nanocomposites manufactured with the three‐roll mill contain agglomerates up to 75% smaller and more densely packed than those manufactured with an ultrasonic tip. Electrical conductivity was higher for moderately‐sized, homogeneously distributed agglomerates (23 μm in diameter) with a high areal density (~920 agglomerates/mm2), while smaller agglomerates reduced electrical conductivity. Smaller agglomerates increased the mechanical properties but decreased the piezoresistive sensitivity. The agglomerate density proved to be a key factor governing the piezoresistive sensitivity, with a lower number of agglomerates per unit area promoting higher gauge factors.

A highly stable potassium-ion battery anode enabled by multilayer graphene sheets embedded with SnTe nanoparticles

Metal telluride is a highly promising anode for alkali-metal ion batteries on account of its high theoretical capacity, distinctive layered structure, and good conductivity. Nonetheless, its application in potassium-ion batteries (PIBs) is restricted by serious structure damage of electrode and sluggish faradic reaction in kinetics stemmed from the intrinsic large ion radius. Herein, a lamellar nanostructure of multilayer graphene sheets embedded with SnTe nanoparticles (SnTe/MGS) is engineered. During the synthesis process, fine monodisperse SnTe nanoparticles and multilayer graphene sheets form a porous network framework together, which effectively buffers the electrode against the pulverization caused by the repeated insertion/extraction of large-sized K+ and provides a wealth of pseudocapacitance storage sites and electronic transmission channels at the meantime. Particularly, both SnTe and MGS possess a layered structure, thus affording more reaction sites for the diffusion behavior. When employed as an anode for PIBs, SnTe/MGS also delivers a high initial reversible capacity of 345.7 mA h g−1 at 0.1 A g−1, prominent long-term stability of 279.4 mA h g−1 at 0.5 A g−1 after 1000 cycles, and desired rate performance of 180.1 mA h g−1 at 2.0 A g−1.

Mechanical Behavior of Blisters Spontaneously Formed by Multilayer 2D Materials

AbstractBlisters can form spontaneously when transferring 2D materials on a substrate because of the small molecules trapped at the interface. Though extensive works have revealed a characteristic aspect ratio of these blisters by neglecting the bending effect of the layer, how the bending comes into play as the layer number increases has not been fully understood. Here, by simply measuring the profiles of blisters formed by transferred multilayer graphene and MoS2 sheets, the variable profiles of blisters and the transition of their characteristic shape from a constant aspect ratio to a constant dome curvature are observed. Taking variable profiles of blisters and different characteristics of the interface into consideration, a theoretical model is established, and the mechanism of such transition is further analytically unveiled. In addition, based on this theory, the bending stiffness of sheets and the adhesion energy between sheets and substrates can be obtained simultaneously. This method is simple but robust, providing a new experimental way to explore the mechanical behavior of 2D material structures.

A simplified elliptical function solution for coupled nonlinear vibration of multilayer graphene sheets

1. Ansari R., Rajabiehfard R., Arash B., 2010, Nonlocal finite element model for vibrations of embedded multi-layered graphene sheets, Computational Materials Science, 49, 4, 831838. CrossRef Google Scholar

A unified size-dependent plate theory for static bending and free vibration analyses of micro- and nano-scale plates based on the consistent couple stress theory

Based on the consistent couple stress theory (CCST), the authors develop a unified formulation of various shear deformation plate theories for static bending and free vibration analyses of simply-supported, micro-/nano-scale plates embedded in an elastic medium. The CCST-based classical plate theory (CPT), first-order shear deformation plate theory (SDPT), and Reddy's refined SDPT, as well as the CCST-based sinusoidal, exponential, and hyperbolic SDPTs can be obtained by assigning specific through-thickness distributions of the shear deformations into the unified formulation, and they are thus included as special cases of the unified consistent couple stress plate theory. The unified CCST-based plate theory is applied to static bending and free vibration analyses of simply-supported, functionally graded microplates (FGMPs) and multilayered graphene sheets (MLGSs) embedded in an elastic medium. The material length scale parameter, aspect ratio, and shear deformation effects on the deformation, stress, and frequency parameters of FGMPs and MLGSs are investigated. It is shown that the solutions for the deformation, the in-plane stress, and the frequency parameters of the FGMPs/MLGSs obtained using the MCST and the CCST are almost identical to each other. The material length scale parameter effects on static bending and free vibration behaviors of the FGMP/MLGS are significant.

Sn4P3 nanoparticles confined in multilayer graphene sheets as a high-performance anode material for potassium-ion batteries

Phosphorus-based anodes are highly promising for potassium-ion batteries (PIBs) because of their large theoretical capacities. Nevertheless, the inferior potassium storage properties caused by the poor electronic conductivity, easy self-aggregation, and huge volumetric changes upon cycling process restrain their practical applications. Now we impregnate Sn4P3 nanoparticles within multilayer graphene sheets (Sn4P3/MGS) as the anode material for PIBs, greatly improving its potassium storage performance. Specifically, the graphene sheets can efficiently suppress the aggregation of Sn4P3 nanoparticles, enhance the electronic conductivity, and sustain the structural integrity. In addition, plenty of Sn4P3 nanoparticles impregnated in MGS offer a large accessible area for the electrolyte, which decreases the diffusion distance for K+ and electrons upon K+ insertion/extraction, resulting in an improved rate capability. Consequently, the optimized Sn4P3/MGS containing 80 wt% Sn4P3 (Sn4P3/MGS-80) exhibits a high reversible capacity of 378.2 and 260.2 mAh g−1 at 0.1 and 1 A g−1, respectively, and still delivers a large capacity retention of 76.6% after the 1000th cycle at 0.5 A g−1.

Sonoelectrochemical exfoliation of graphene in various electrolytic environments and their structural and electrochemical properties

Graphene synthesized via electrochemical exfoliation of graphite is considered to be a simple, fast, and scalable technique. This exfoliation technique leads to the formation of multi-layer graphene sheets with some defects, which is feasible for developing supercapacitor electrodes due to the presence of various pseudocapacitive functionalities. We report the exfoliation of multi-layer graphene via pulse sonication assisted electrochemical exfoliation technique (sonoelectrochemical) and studied the effect of three different aqueous electrolytes having acidic, neutral, and basic properties. The pulse (2/4) of 2 s sonication and 4 s rest time significantly improve the exfoliation process without hindering the electrochemical reaction that takes place on the graphite. The structural quality and functional groups attached to the surface of the exfoliated graphene sheets were evaluated using spectroscopic techniques. The investigation reveals that the nature of electrolyte and intercalation ions highly influences the exfoliation duration, yield, size, and quality of the graphene. The graphene layers exfoliated in sulfuric acid and ammonium sulfate electrolytes possessed many defect sites than those exfoliated in KOH. However, this graphene demonstrated better electrochemical performance than the graphene exfoliated in KOH electrolyte due to the presence of various electroactive defect sites on the surface and edges of the graphene.

Mechanical properties of graphene, defective graphene, multilayer graphene and SiC-graphene composites: A molecular dynamics study

In this article, using molecular dynamics (MD) simulation, several mechanical properties of graphene were calculated for pristine single layer graphene sheet (SLGS), defective SLGS, multilayer graphene sheets (MLGS) without defects and for composites of SiC and graphene. Firstly, the room temperature elastic moduli (Young's, shear and bulk), constants and Poison's ratios were simulated for the above structures and then their properties such as stress vs strain under tensile and compressive loading were simulated within the temperature range of 300K–2000K. The simulations were performed in both zigzag and armchair directions of graphene surface and differences were observed in the mechanical properties. Simulations revealed that the location of defects as well as their type influence the elastic moduli and constants at room temperature and that their tensile and compressive properties vary with temperature. For both MLGS, and SiC-graphene composites, the properties improved with increase in number of continuous graphene layers.

Reduced Drift of CMOS ISFET pH Sensors Using Graphene Sheets

Reduction of drift in Complementary Metal Oxide-Semiconductor (CMOS) Ion-Sensitive Field-Effect Transistor (ISFET) pH sensors is demonstrated using monolayer and multilayer graphene sheets. Graphene blocks the ion penetration in the CMOS passivation layers and provides the physisorption sites needed for electrical double layer formation allowing sensing. With an in-house polymer-assisted graphene transfer (PAGT) process, monolayer and multilayer graphene sheets were manually transferred on top of the sensing membrane of CMOS ISFET sensors on a 2 by 4 mm chip. Experiments with pH buffers on five different chips were performed to extract the average performance parameters of capacitive attenuation, trapped charge, sensitivity, drift and noise. The stretched exponential function, that describes dispersion processes in amorphous solids such as silicon dioxide and silicon nitride, was modified to model the dynamic drift behaviour and analyse the effect of graphene on the performance of the sensors. The results show that on average the graphene coated ISFET sensors experience about 50% reduction in drift amplitude, up to 3 times slower surface modification and perform overall better compared to the plain unmodified devices.

Heat of Decomposition and Fire Retardant Behavior of Polyimide-Graphene Nanocomposites

Polyimide is a high-performance engineering polymer with outstanding thermomechanical properties. Because of its inherent fire-retardant properties, polyimide nanocomposite is an excellent material for packaging electronic devices, and it is an attractive electrode material for batteries and supercapacitors. The fire-retardant behavior of polyimide can be remarkably improved when polyimide is reinforced with multilayered graphene sheets. Differential scanning calorimetry and thermogravimetric analysis were used to study the heat of decomposition and gravimetric decomposition rate, respectively, of polyimide-graphene nanocomposites. Polyimide/graphene nanocomposites containing 10, 20, 30, 40, and 50 wt.% of multilayered graphene sheets were heated at a rate of 10 and 30 °C/min in air and in nitrogen atmosphere, respectively. The rate of mass loss was found to remarkably decrease by up to 198% for nanocomposites containing 50 wt.% of graphene. The enthalpy change resulting from the decomposition of the imide ring was found to decrease by 1166% in nitrogen atmosphere, indicating the outstanding heat-shielding properties of multilayered graphene sheets due to their high thermal conductivity. Graphene sheets are believed to form a continuous carbonaceous char layer that protects the imide ring against decomposition, hence decreasing initial mass loss. The enthalpy changes due to combustion, obtained from differential scanning calorimetry, were used to calculate the theoretical heat release rates, a major parameter in the determination of flammability of polymers. The heat release rate decreased by 62% for composites containing 10 wt.% of graphene compared to the neat polyimide matrix. Polyimide has a relatively lower heat of combustion as compared with graphene. However, graphene significantly decreases the mass loss rates of polyimide. The combined interaction of graphene and polyimide led to an overall decrease in the heat release rate. It is noted that both mass loss rate and heat of combustion are important factors that contribute to the rate of heat released.

SiOx microparticles embedded into 3D wrinkled N, S co-doped multilayer graphene sheets as a high-performance anode for long-life full lithium-ion batteries

Silicon oxide (SiOx) emerges as one of the most promising anodes for lithium-ion batteries (LIBs). However, the severe capacity fading arising from the structural degradation and low electronic conductivity still hinders its practical application. Herein, a novel SiOx anode material is constructed by embedding the SiOx microparticles into the 3D wrinkled multilayer graphene sheets with the heteroatoms of N, S co-doping. The proposed stable 3D conductive architecture can effectively facilitate the electronic and ionic transportation as well as buffer the volume changes of SiOx to maintain the structural integrity during cycling. Moreover, the first principles calculations confirm the synergistic effect of N, S co-doping, which introduces more heteroatomic defects, lowers the band gap and leads to more negative Li adsorption energies to further promote the electron transfer and improve the Li storage capability. Consequently, the fabricated anode material exhibits a high reversible capacity of 1150 mA h g−1 after 500 cycles. When paired with the commercial LiCoO2 cathode, the fabricated full LIB delivers the excellent long-life cycling stability, showing a high reversible capacity of 151 mA h g−1 and a superior energy density up to 501 W h kg−1 after 330 cycles, among the best of the recently reported work.

High hydrogen uptake by a metal-graphene-microporous carbon network

High-surface area carbon nanomaterials are promising candidate as reversible physisorption materials for hydrogen storage in personal transportation vehicles at moderate temperatures and pressures. Metal-incorporated graphitic microporous carbon is considered to be an excellent H2 storage material due to high molecular hydrogen uptake at the micropores coupled with considerable H2 adsorption at the graphitic network. A simple, cost-effective sputtering technique is adopted to fabricate metal-incorporated graphitic microporous carbon film and differential resistance measurements are carried out in H2 ambient to observe the high hydrogen uptake within the samples. Ultrathin amorphous carbon film is irradiated with metal nanoparticles which converts it into graphitic carbon, whereas sputtering plasma acts as dry-etchant to activate it into microporous carbon. Average number of graphene layer formation is observed to be dependent on sputtering parameters (current/voltage/time), which manifest bi-layer to multi-layer graphene sheets. With increase in the graphene layers, hydrogen adsorption also increases due to a four-fold effect - higher molecular hydrogen uptake at the graphene layers, more active sites into the micropores, promotion of molecular dissociation into atomic hydrogen by the metal nanoparticles, followed by adsorption at the active surface sites and the formation of hydrogenated carbon via destruction of the π-bonds.

Electromechanical properties of carbon-nanostructured elastomeric composites measured by digital image correlation

Tensile mechanical and piezoresistive properties of elastomeric (thermoplastic polyurethane) nanocomposites in film form, made of multiwall carbon nanotubes, multilayer graphene sheets and hybrid combinations of both are investigated using digital image correlation (DIC) for strain measurement. For the hybrid materials, the mechanical and piezoresistive responses are dominated by the carbon nanotube network. Comparison between strain measurement conducted using DIC and the crosshead displacement (CHD) of the universal testing machine, indicate that the error in the piezoresistive gage factor (sensitivity) incurred by the use of CHD is proportional to that of the elastic modulus, and it can be as large as 40% for these films. This error incurred when using CHD, could be largely suppressed by proper calibration of the length of the gage section of the tensile coupons, and such a calibration can be conducted based on the average strain fields and elastic modulus measured by DIC.

Paper based pencil drawn multilayer graphene-polyaniline nanofiber electrodes for all-solid-state symmetric supercapacitors with enhanced cyclic stabilities

Graphitic layer of carbon has been deposited on the surface of cellulose paper by simple pencil drawing approach. The edges of exfoliated multilayer graphene sheets formed during pencil drawing on the rough paper surface causes the enhancement of electrochemical capacitance. One step chemical polymerization technique has been adopted to fabricate polyaniline nanofibers on hydrophobic pencil drawn graphitic layer on the cellulose paper. These polyaniline coated pencil drawn paper electrodes were used to fabricate all-solid-state symmetric supercpapcitors with superior performance in comparison to similar pencil drawn paper electrodes without polyaniline. All-solid-state symmetric supercapacitor with paper based multilayer graphene-polyaniline nanofiber electrodes exhibits specific capacitance of 28.37 F g−1, areal capacitance of 93.64 mF cm−2, energy density of 8.32 µW h cm−2, and power density of 39.97 µW cm−2. It also shows excellent cyclic stability with initial increment to a maximum value and then decrease to 91.5 % of the maximum value after 5000 cycles. It is interesting to note that it retains 134.28 % of initial areal capacitance after 5000 cycles.

Effect of well-designed graphene heat conductive channel on the thermal conductivity of C/SiC composites

Poor thermal conductivity, especially in thickness direction, is a major obstacle to extend the service lifetime of C/SiC composite. However, there are few papers focusing on finely designing heat conductive channel but a simply introduction of various modifiers to improve C/SiC thermal conductivity, which leads to less success. Herein, multi-layer graphene sheets were utilized to improve the thermal conductivity of C/SiC composites via an effective method to design graphene heat conductive channels. To determine the role of graphene sheets in improving thermal conductivity, the effect of the different loading fractions of graphene and microstructure of as-prepared composites were systemically investigated. Results revealed that the thermal conductivity of composites increased by 204% with well-designed graphene heat conductive channels. Besides, compared with the porosity, the orderly aligned heat conductive pathways played a more important role in thermal conductivity. This work provides a new and effective method for preparing well-designed heat conductive channels to enhance thermal conductivity of C/SiC.

Interfacial thermal conductance between multi-layer graphene sheets and solid/liquid octadecane: A molecular dynamics study

Mixtures of paraffin and carbon nanofillers have promising potential for thermal storage, as paraffin (the matrix) possesses high latent heat and the nanofillers compensate for the low thermal conductivity (TC) of paraffin. Understanding thermal transport in these materials is essential for practical applications, as weak thermal transport hinders fast charge/discharge of thermal energy. Here, we use non-equilibrium molecular dynamics (NEMD) simulations to study the interfacial thermal conductance (ITC) between graphene sheets and octadecane (C18H38) matrix under the limiting conditions of the sheets being parallel or perpendicular to the direction of the imposed heat flux. The results show that the systems containing thin graphene layers exhibit higher values of ITC. This study captures the asymptotic saturation of thermal conductance for the liquid phase of the perpendicular structure. Besides, given the greater number of structured layers of paraffin upon phase change, the ITC for the solid paraffin-graphene system is higher than the conductance of the liquid paraffin-graphene interface. We use the Pearson correlation coefficients of the vibrational power spectrum (VPS) of interfacing materials to explain the orders of magnitude variations of the observed ITC.

Li intercalation into multilayer graphene with controlled defect densities

We studied the influence of defect density in multilayer graphene sheets on the intercalation of Li ions by means of x-ray photoelectron spectroscopy. The multilayer graphene was prepared by chemical vapor deposition on Ni substrates. The deposition of Li at room temperature results in immediate intercalation, while additional annealing at 300 °C partially removes Li from the sample surface. We found that varying the defect density over several orders of magnitude does not influence the intercalation process. We propose that the edges of the graphene flakes are the dominant sites that facilitate Li intercalation in multilayer graphene.

Tribological Performance of Graphite Nanoplatelets Reinforced Al and Al/Al2O3 Self-Lubricating Composites.

In the present work, the effect of graphite nanoplatelets (GNPs) on tribological properties of the aluminum (Al), and Al/alumina (Al2O3) composite are studied. GNPs are multilayer graphene sheets which were used as a solid lubricant material. Two sets of composites, Al/GNPs and Al/GNPs/Al2O3 with varying amounts of reinforcements, were synthesized by powder metallurgy that involves cold compaction followed by hot compaction. The hardness of the composites increased with the addition of GNPs and Al2O3. The Al/GNPs composite with 1 wt.% of GNPs (Al/1GNPs) showed a 20% increase in hardness whereas Al/GNPs/ Al2O3 composite with 1 wt.% GNPs and 2 wt.% Al2O3 (Al/1GNPs/2Al2O3) showed 27% increases in hardness compared to the pure Al. The coefficient of friction measured at 20 N was observed to be 22% and 53% lesser for Al/1GNPs and Al/1GNPs/2Al2O3, respectively, compared to corresponding alloys without graphene Al. The X-ray diffraction and scanning electron microscopy analysis revealed the presence of GNPs at the worn surface after the tribology tests. The wear rate was also reduced significantly. In comparison with pure Al, the Al/1GNPs and Al/1GNPs/2Al2O3 composites resulted in 5- and 20-times lesser wear rate, respectively. The addition of Al2O3 caused reduction in wear rate due to higher hardness and load carrying ability, whereas composites with more than 1 wt.% GNPs showed higher wear rate due to lower hardness and higher porosity. The Al/1GNPs/2Al2O3 composite exhibited the least coefficient of friction (0.2–0.25) and wear rate (1 × 10−6–4 × 10−6 mm3/N.m) compared to other GNPs and Al2O3 reinforced Al composites. The worn surfaces were further analyzed to understand the wear mechanism by Raman spectroscopy, transmission electron microscopy, and x-ray diffraction to detect the Al4C3 phase formation, chemical bonding, and defect formation in graphene.