Assembly Of Graphene Research Articles

Tension-compression asymmetry of the stress-strain behavior of the stacked graphene assembly: Experimental measurement and theoretical interpretation

Two-dimensional (2D) materials as exemplified by graphene have received a bunch of attention for their outstanding properties and enormous application potential. Recently, a macroscopic graphene-based material was fabricated simply by stacking the few-layer graphene flakes. The resulting film, called SGA, exhibits unusual mechanical behavior, which implies the existence of tension-compression asymmetry in its mechanical property. However, direct experimental verification of such unique mechanical property of the SGA remains deficient because of the difficulty in fixturing and applying load on the samples. In this work, we tackle these problems by transferring the SGA film onto a polyethylene (PE) substrate which can elongate and contract in response to the variation of the ambient temperature. Tensile and compressive loads thus can be controllably applied to the SGA samples through the SGA/PE interface by tuning the temperature variation. The stress-strain curves of the SGA, including tensile and compressive, are deduced based on the Stoney equation for thin film-substrate systems, showing the tension-compression asymmetry as expected. Theoretical modeling is carried out and reveals the structural basis of such unique mechanical behavior. This work not only provides a facile yet effective approach to measuring the stress-strain behavior of less-cohesive materials like SGA but also is of great value to the design and applications of SGA and other stacked assemblies of 2D materials in flexible sensors and actuators.

Synthesis of composite of graphene and UO3 composite via one-step solution chemical reaction and its application to UO2-based accident tolerant fuel

In this paper, two kinds of composites constructed by UO3 nanoflakes (which is UO3·yNH3·xH2O, precisely) and different graphene oxide (GO) nanosheets (homemade GO, GO-h, and commercial GO, GO-c) were prepared via solution chemical reaction. The two kinds of GO share similar morphology and possess the same species of functional groups. Nevertheless, GO-h possesses higher oxidization degree and thus could adsorb more uranyl ions, and the corresponding composite shows a much more regular shape: UO3 nanoflakes and GO nanosheets cross each other, which would help overcome the disadvantage of graphene aggregation. As a result, homemade reduced graphene oxide (RGO-h) sheets inside the final UO2 pellets (named as UO2/GO-h) could construct a well-bulit thermally conductive network to enhance its thermal conductivity. However, similar RGO-c network cannot be observed in the UO2/GO-c pellest originated from GO-c. Therefore, only the thermal conductivity of UO2/GO-h pellet acquires a dramatic increase, 37.30% relative to UO2 pellet at 1200 °C, showing that UO2/GO-h possesses great potential for the development of novel UO2-based ATF fuels.

Molecular insight into the reversible dispersion and aggregation of graphene utilizing photo-responsive surfactants

Reversible dispersion and aggregation of graphene with photo-stimuli response have exhibited enormous potential in electrochemical and biomedical fields owing to its green and efficient characteristics. However, the molecular mechanism of photo-controllable dispersibility of graphene is still limited. Herein, the reversible dispersion and aggregation of graphene in the existence of photo-responsive surfactant (2-(4-(4-butylphenyl)diazenylphenoxy) ethyltrimethylammonium bromide, AzoTAB) is investigated by molecular dynamics simulation. Analysis of structural features indicates that the adsorption configurations of trans-AzoTAB and cis-AzoTAB show different evolutions with increasing concentration. At high surfactant concentrations, exceed trans-AzoTAB molecules move away from the graphene surface and generate second adsorption layer, while cis-AzoTAB molecules prefer to lift a benzene ring to obtain an “L-shaped” configuration, which responsible for the larger saturated adsorption capacity of cis-AzoTAB molecules. Subsequently, the potential of mean force (PMF) provides comprehensive direct evidence for the influence of adsorption configurations on the dispersibility of graphene. It is observed that the transition between the π-π stacking structure formed by three trans-AzoTAB layers and the “L-shaped” configuration of cis-AzoTAB molecules can achieve the reversible dispersion and aggregation processes of graphene. Thus, the photoisomerization of AzoTAB triggered by exposure to UV/visible light could be utilized to realize reversible dispersion and aggregation of graphene.

Multiscale modelling of graphene sheet and its application in laminated composites

Multiscale modeling strategy development of graphene and its composites is of critical importance in engineering and technological applications. In this work, we systematically developed a chirality preserved coarse-grained graphene model and the corresponding potential, TersoffCG(16–1). The robustness of this potential is verified through structural and mechanical characterization analysis comparison between coarse-grained and all-atomistic models. The Lennard-Jones potential is emphasized to adjust the interlayer properties of the interlayer distance and binding energy. Furthermore, in-plane properties of multilayer graphene assembly tensile and monolayer graphene crack, and out-of-plane properties of nanoindentation are fully analyzed. The copper/graphene nanocomposite tensile test indicated that the coarse-grained graphene model is compatible with the copper matrix. Our efficient and portable coarse-grained graphene model successfully reproduced the architectural parameters, elastic, fracture, and interlayer adhesion properties of graphene sheets compare with the reported experiment and theoretical results, which can serve as an effective strategy to research more hybrid composite systems.

A simple and direct SPR platform combining three-in-one multifunctional peptides for ultra-sensitive detection of PD-L1 exosomes

Exosomes are lipid-bilayer-enclosed extracellular vehicles (EVs) derived from all cells and circulating in the blood. Identification of cancer specific exosomes in body fluids has shown great potential for cancer diagnostics. The low concentration in blood and likely to deplete their native character on the solid surface makes it difficult to measure it in real time sensitively. Here we describe a strategy to detect PD-L1 exosomes through graphene modified gold chip using a multifunctional peptide (M-Pep, SS-IMVTESSDYSSY-KK-FHYQRDTPKSYN) as a recognition supermolecule. Graphene assembly, antifouling and PD-L1 specific binding domains in the M-Pep enhanced the inclusion affinities between the graphene and supermolecules and ensure keeping its recognition properties efficiently. The fabricated direct-real-time SPR sensor based on M-Pep shows a good sensitivity for the detection of PD-L1 exosomes. Own to its simple, convenient and effective, this M-Pep based SPR sensor provides a useful platform to facilitate clinical investigations of exosomes for noninvasive disease diagnoses. This approach may serve as a potential non-invasive diagnostic and screening tool to detect cancer biomarker and facilitate possible curative therapy.

Atomistic Insights on the Rheological Property of Polycaprolactone Composites with the Addition of Graphene

AbstractTo facilitate the biomedical applications of biocomposites, researchers have used different types of fillers to enhance their mechanical properties. However, the addition of fillers not only changes the mechanical performance of the biocomposites, but also affects their printability, that is, their rheological properties. With the aid of atomistic simulations, this work investigates the influence of graphene size and aggregation on the rheological properties of polycaprolactone (PCL) composites. For the same weight ratio, increasing the graphene size causes the viscosity of the PCL composite to increase until a threshold edge length equal to PCL's average radius of gyration. After this threshold value, the viscosity decreases with increasing edge length. The PCL composite with multilayered graphene exhibits a lower viscosity compared with its counterpart with monolayer graphene. Specifically, the addition of graphene is shown to augment the shear‐thinning effect. The findings in this work provide a fundamental understanding of the rheological property of PCL composites with the addition of 2D nanofillers, which shed light on the ink design for bioprinting.

A Meta-Analysis of Conductive and Strong Carbon Nanotube Materials.

A study of 1304 data points collated over 266 papers statistically evaluates the relationships between carbon nanotube (CNT) material characteristics, including: electrical, mechanical, and thermal properties; ampacity; density; purity; microstructure alignment; molecular dimensions and graphitic perfection; and doping. Compared to conductive polymers and graphitic intercalation compounds, which have exceeded the electrical conductivity of copper, CNT materials are currently one-sixth of copper's conductivity, mechanically on-par with synthetic or carbon fibers, and exceed all the other materials in terms of a multifunctional metric. Doped, aligned few-wall CNTs (FWCNTs) are the most superior CNT category; from this, the acid-spun fiber subset are the most conductive, and the subset of fibers directly spun from floating catalyst chemical vapor deposition are strongest on a weight basis. The thermal conductivity of multiwall CNT material rivals that of FWCNT materials. Ampacity follows a diameter-dependent power-law from nanometer to millimeter scales. Undoped, aligned FWCNT material reaches the intrinsic conductivity of CNT bundles and single-crystal graphite, illustrating an intrinsic limit requiring doping for copper-level conductivities. Comparing an assembly of CNTs (forming mesoscopic bundles, then macroscopic material) to an assembly of graphene (forming single-crystal graphite crystallites, then carbon fiber), the ≈1 µm room-temperature, phonon-limited mean-free-path shared between graphene, metallic CNTs, and activated semiconducting CNTs is highlighted, deemphasizing all metallic helicities for CNT power transmission applications.

Ultrasensitive Immunosensor Based on Langmuir-Blodgett Deposited Ordered Graphene Assemblies for Dengue Detection.

In this manuscript partially reduced graphene oxide (RGO) nanosheet-based electrodes have been utilized for quantification of the NS1 protein and subsequently for dengue detection. NS1 is the biomarker found circulating in the body of dengue-infected persons on or after first day of the appearance of disease symptoms. Graphene oxide (GO) has been synthesized using a modified Hummer's method, and its ordered nanostructured films have been electrophoretically deposited on indium tin oxide (ITO)-coated glass substrates using Langmuir-Blodgett (LB) deposition. Deposited LB films of GO have been reduced with hydrazine vapors to obtain RGO-coated ITO electrodes. NS1 antibodies have been grafted onto the ordered thin films using covalent linking, and the bioelectrodes have been utilized for the specific detection of NS1 antigen. The electrochemical performance of the fabricated bioelectrodes for NS1 antigen detection has been explored in standard and spiked sera samples. The limit of detection for the standard samples and spiked serum samples is found to be 0.069 ng mL-1 and 0.081 ng mL-1, respectively, with a sensitivity of 8.41 and 36.75 Ω per ng mL, respectively, in the detection range of 101 to 107 ng mL-1.

In Situ Investigation of the Motion Behavior of Graphene on Liquid Copper.

The in situ investigation of the dynamic growth process and novel assembly phenomena of graphene on liquid copper (Cu) is of great significance to deeply understand the special behavior of graphene and self‐assembly mechanism. Here, the direct observation of the graphene growth and motion behavior on liquid Cu via in situ imaging is reported. Evidence of graphene movement on liquid Cu is offered and it is demonstrated that the translation and rotation behaviors of graphene are affected by the surface condition of liquid Cu. The self‐assembly process of graphene array is also revealed by capturing the dynamic changes of graphene in real‐time. Further analysis highlights the importance of surface energy of liquid Cu and the interaction between graphene building blocks during the self‐assembling process. The growth parameters are also investigated to flexibly control the assembly configuration of graphene arrays. This work provides an insight into the mechanism of graphene motion and assembly behavior that can be used to guide the controllable manipulation of 2D materials and on‐demand fabrication assembly structures with desired properties.

Preparation and tribological characteristics of graphene/triangular copper nanoplate composites as grease additive

PurposeThis study aims to the preparation and tribological characteristics of graphene/triangular copper nanoplate composites (abbreviated as GN/Cu nanoplates) as grease additive and clarifies the growth mechanism and tribological mechanism of GN/Cu nanoplates by different analysis methods. In this paper, it is expected to alleviate the problems of easy aggregation and poor dispersion stability of graphene in lubricants and provide theoretical support for the application of graphene and its composites in the tribology field.Design/methodology/approachIn this study, the GN/Cu nanoplates have been successfully prepared by the electrostatic self-assembly method. The structural characteristics of GN/Cu nanoplates were analyzed via transmission electron microscopy and X-ray diffraction. Then the tribological properties of GN/Cu nanoplates were investigated under different loads with SRV-IV [Schwingung, Reibung, Verschleiß (German); oscillating, friction, wear (English translation)] tribotester. White-light interferometry was applied to quantify the wear loss of the disk. The element chemical state on worn surfaces was analyzed by an X-ray photoelectron spectroscope to clarify the tribological mechanism of graphene composites.FindingsThe electrostatic force between the negative charge of graphene and the positive charge of triangular copper nanoplates promotes the self-assembly of GN/Cu nanoplates. With the addition of GN/Cu nanoplates, the wear loss and average friction coefficient under the load of 200 N have been decreased by 72.6% and 18.3%, respectively. It is concluded that the combined action of graphene deposition film and the copper melting film formed on the worn surface could effectively improve the antiwear ability and friction reduction performance of the grease.Originality/valueThis manuscript fulfills a new approach for the preparation of GN/Cu nanoplates. At the same time, its tribological properties and mechanism as a lubricating additive were studied which provide theoretical support for the application of graphene and its composites in the tribology field.

In Situ Growth of Novel Graphene Nanostructures in Reduced Graphene Oxide Microspherical Assembly with Restacking-Resistance and Inter-Particle Contacts for Energy Storage Devices.

Graphene is extensively investigated for various energy storage systems. However, the very low density (<0.01 g cm-3 ) of graphene nanosheets has hindered its further applications. To solve this issue, a controlled assembly of 2D graphene building blocks should be developed into graphene microspheres with high packing density, and restacking of graphene should be prevented to ensure an electrochemically accessible surface area during the assembly. Furthermore, graphene microspheres should have multiple 1D external conductive architecture to promote contacts with the neighbors. This study reports in situ growth of novel graphene nanostructures in reduced graphene oxide microspherical assembly (denoted as GT/GnS@rGB) with restacking resistance and interparticle contacts, for electrochemical energy storage. The GT/GnS@rGB showed high gravimetric (231.8 F g-1 ) and volumetric (181.5 F cm-3 ) capacitances at 0.2 A g-1 in organic electrolyte with excellent rate capabilities of 94.3% (@ 0.2 vs 10 Ag-1 ). Furthermore, GT/GnS@rGB exhibited excellent cycling stability (96.1% of the initial capacitance after 100 000 charge/discharge cycles at 2 A g-1 ). As demonstrated in the electrochemical evaluation as electrode materials for electrical double-layer capacitors, unique structural and textural features of the GT/GnS@rGB would be beneficial in the use of graphene assembly for energy storage applications.

Engineered Electrode Structure for High‐Performance 3D‐Printed All‐Solid‐State Flexible Microsupercapacitors

A method to prepare graphene-carbon black composite ink for 3D printing electrodes of microsupercapacitors is developed by Lei Li and co-workers, article number 2100357. The carbon black (cartoon child) works as pillar to tailor graphene sheets space in electrode structure, relieving graphene aggregation issue. The tailored-structure of electrode facilitates electron (pupple ball) and electrolyte ion (red ball) transport, boosting the electrochemical performance of microsupercapacitors.

3D percolation modeling for predicting the thermal conductivity of graphene-polymer composites

Graphene-based polymer composites exhibit a microstructure formed by aggregates within a matrix with enhanced thermal conductivity. We develop a percolation-based computational method, based on the multiple runnings of the shortest path iteratively for ellipsoidal particles to predict the thermal conductivity of such composites across stochastically-developed channels. We analyze the role of the shape and the aspect ratio of the flakes and we predict the onset of percolation based on the density and particle dimensions. Consequently, we complement and verify the conductivity trends via our experiments by inclusion of graphene aggregates and fabrication of graphene-polymer composites. The analytical development and the numerical simulations are successfully verified with the experiments, where the prediction could explain the role of larger set of particle geometry and density. Such percolation-based quantification is very useful for the effective utilization and optimization of the equivalent shape of the graphene flakes and their distribution across the composite during the preparation process and application.

Highly Reduced Graphene Assembly Film as Current Collector for Lithium Ion Batteries

Highly Reduced Graphene Assembly Film as Current Collector for Lithium Ion Batteries

Promotion of Color-Changing Luminescent Hydrogels from Thermo to Electrical Responsiveness toward Biomimetic Skin Applications.

The active color-changing ability of many living species has inspired scientists to replicate the optical property into soft wet and tissue-like hydrogel materials. However, the color-changing processes of most reported examples are controlled by the traditional stimuli (e.g., pH, temperature, and ions), which may suffer from the residual chemical product accumulation, and have difficulty in achieving local control and integration into the commercial robots, especially when applied as biomimetic skins. Herein, inspired by the nervous (bioelectricity) control of skin color change in cephalopods, we present an electrically powered multicolor fluorescent hydrogel system with asymmetric configuration that couples thermoresponsive fluorescent hydrogel with stacked graphene assembly (SGA)-based conductive paper through luminous paint as the middle layer. Owing to the highly controllable electrical stimulus in terms of amplitude and duration, the Joule heat supplied by SGA film can be regulated locally and in real time, leading to precise and local emission color control at low voltage. It also avoids the addition of any chemicals. Furthermore, the electrically powered color-changing hydrogel system can be conveniently integrated into the commercial robots as biomimetic skins that help them achieve desirable camouflage, display, or alarming functions.

Graphene's Role in Emerging Trends of Capacitive Energy Storage.

Technological breakthroughs in energy storage are being driven by the development of next-generation supercapacitors with favorable features besides high-power density and cycling stability. In this innovation, graphene and its derived materials play an active role. Here, the research status of graphene supercapacitors is analyzed. Recent progress is outlined in graphene assembly, exfoliation, and processing techniques. In addition, electrochemical and electrical attributes that are increasingly valued in next-generation supercapacitors are highlighted along with a summary of the latest research addressing chemical modification of graphene and its derivatives for future supercapacitors. The challenges and solutions discussed in the review hopefully will shed light on the commercialization of graphene and a broader genre of 2D materials in energy storage applications.

Roughening for Strengthening and Toughening in Monolayer Carbon Based Composites.

Three-dimensional (3D) aggregation of graphene is dramatically weak and brittle due primarily to the prevailing interlayer van der Waals interaction. In this report, motivated by the recent success in synthesis of monolayer amorphous carbon (MAC) sheets, we demonstrate that outstanding strength and large plastic-like strain can be achieved in layered 3D MAC composites. Both surface roughening and the ultracompliant nature of MACs count for the high strength and gradual failure in 3D MAC. Such properties are not seen when intact graphene or multiple stacked MACs are used as building blocks for 3D composites. This work demonstrates a counterintuitive mechanism that surface roughening due to initial defects and low rigidity may help to realize superb mechanical properties in 3D aggregation of monolayer carbon.

Engineered Electrode Structure for High‐Performance 3D‐Printed All‐Solid‐State Flexible Microsupercapacitors

Graphene aggregation is the major issue limiting its electrochemical performance when used as electrode material for microsupercapacitors (MSCs) with the interdigitated architecture. Solving this issue boosts the device's electrochemical performance, especially the areal energy density, facilitating its applications in advanced miniaturized electronic systems. Herein, a facile method to prepare the graphene−carbon black composite ink for the direct 3D printing of electrodes of MSCs is developed. Carbon black present in the composite ink tailors the graphene sheets space in the electrode structure during the 3D printing process, relieving the graphene aggregation issue. The MSCs show great improved electrochemical performance with a high areal energy density (2.49 μWh cm−2), high power density (0.25 mW cm−2), promising cycling stability, and good mechanical flexibility. The method developed herein paves a way to prepare high‐performance, all‐solid‐state flexible MSCs in a scalable process.

Auxetic behavior of a novel graphene assembly model

Graphene assembly, e.g. graphene aerogel, is an open-cell porous material with randomly distributed graphene sheets and voids. In this study, we propose a method to generate the 3D graphene assembly models which can reasonably display the structural properties of graphene aerogel. Our 3D graphene assembly models are firstly established by a Voronoi construction method that is usually used to build the polycrystalline materials. The optimization and relaxation are then conducted to obtain 3D graphene assembly with proper structures by using molecular dynamics (MD) simulations. In order to explore the mechanical properties of graphene assembly, the tensile and compressive tests are carried out by MD simulations. The results show that the 3D graphene assembly reveals auxetic behavior under compression while it has positive Poisson’s ratio under tension. We also find that the Poisson’s ratios are specifically related to the grain sizes and mass densities. Furthermore, from our simulation the stress–strain relations for the compressive tests and tensile tests are also obtained. The compressive Young’s modulus, tensile Young’s modulus, compressive strength and tensile strength are found to follow the power law relation to the mass density with the exponential factors of 2.31756, 2.33005, 2.6243 and 1.5084, respectively.

Electrically powered repeatable air explosions using microtubular graphene assemblies

Controllable rapid expansion and activation of gases is important for a variety of applications, including combustion engines, thrusters, actuators, catalysis, and sensors. Typically, the activation of macroscopic gas volumes is based on ultra-fast chemical reactions, which require fuel and are irreversible. An “electrically powered explosion”, i.e., the rapid increase in temperature of a macroscopic relevant gas volume induced by an electrical power pulse, is a feasible repeatable and clean alternative, providing adaptable non-chemical power on demand. Till now, the fundamental problem was to find an efficient transducer material that converts electrical energy into an immediate temperature increase of a sufficient gas volume. To overcome these limitations, we developed electrically powered repeatable air explosions (EPRAE) based on free-standing graphene layers of nanoscale thickness in the form of microtubes that are interconnected to a macroscopic framework. These low-density and highly permeable graphene foams are characterized by heat capacities comparable to air. The EPRAE process facilitates cyclic heating of cm3-sized air volumes to several 100 °C for more than 100,000 cycles, heating rates beyond 300,000 K s−1 and repetition rates of several Hz. It enables pneumatic actuators with the highest observed output power densities (>40 kW kg−1) and strains ∼100%, as well as tunable microfluidic pumps, gas flowmeters, thermophones, and micro-thrusters.