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Abstract

Graphite's insolubility in conventional solvents is a major obstacle to its utilization. This challenge is typically addressed by chemical modification such as oxidation, followed by reduction. However, pristine graphene possesses superior properties as oxidation and reduction leads to degradation of the graphene. Here we demonstrate the use of an interfacial trapping technique to assemble laterally macroscopic films of pristine graphene that are up to 95% transparent. This is accomplished by modest sonication of natural flake graphite in a water/heptane mixture to form continuous films one to four layers thick at the interface between the two immiscible liquids. Furthermore, the graphene sheets readily climb hydrophilic solid substrates forming a homogeneous thin film. These films are composed of a network of overlapping graphene sheets and shown to have long-range structure with conductivities on the order of 400 S/cm.

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... 10−16 It was shown recently that graphene sheets demonstrate a surface affinity for the high-energy oil−water interface manifested by the spontaneous spreading of the graphene sheets over the interface surface, lowering the total free energy of the system. 17,18 This surfactant-like property of the graphene negates the requirement of using the chemical reduction of graphene oxide or difficult to remove solvents and surfactants for the graphene exfoliation. 12,13,19−22 The simplicity of the approach and ability to substitute the oil phase with a monomeric liquid created a new design platform for grapheneinfused polymeric foams. ...
... 26 The surface activity of the graphene to water−oil and water−styrene interface was confirmed in detailed molecular dynamics simulations. 17,18 In particular, these simulations have shown that there is a free energy barrier which separates graphene sheets at the solvent/solvent interface from their solubilized states in water or oil (monomer) phases. Unfortunately, the high computational cost of these simulations limits them to calculations of the potential of the mean force or aggregation of the individual graphene sheets at the interface. ...
... In Figure 2b, we illustrate how the sheet orientation can change as it departs from the interface. The results of the coarse-grained simulations are in qualitative agreement with the results of the detailed MD simulations of graphene 17,18 and boron nitride 26 systems. ...
Article
We use coarse-grained molecular dynamics simulations to study the formation of composite polymeric foams made by templated polymerization of emulsions stabilized by graphene sheets (G-sheets) acting as 2D surfactants. To demonstrate the affinity of the 2-D sheets to the interface between two immiscible A and B type solvents, we use the potential of the mean force (PMF) calculations. This study shows that the PMF curves converge to the universal form with increasing sheet size. Furthermore, the sheets’ affinity toward the interface diminishes with an increasing degree of substitution of the sites with A-solvent philic groups. The simulations of the emulsion stability show that the final emulsion structure depends on the emulsion composition and degree of modification of the sheets such that for 50% of the sheet site substitution one has inverted emulsion morphology. Composite polymeric foams are obtained by polymerization of the emulsion continuous phase and by removing the solvent minority phase. The mechanical properties of the foams are studied as a function of the sheet size and emulsion composition. In particular, the Young’s modulus of the composite foams monotonically increases with increasing the fraction of the G-sheets in the precursor emulsion. In the limit of small deformations, the stress–strain curves of composite foam deformation show convergence to a universal deformation curve with increasing sheet size. However, this universality breaks down in the limit of large deformations where deformation of the polymeric matrix dominates foam’s elastic response.
... When graphite is introduced to a high energy aqueous/organic interface, it spontaneously exfoliates into graphene sheets to lower the free energy of the system. There is a significant energetic cost to move a sheet of graphene into either liquid phase, which traps the sheets at the interface and prevents them from restacking [10,11]. This solvent interfacial trapping method (SITM) results in single to few layers of overlapping graphene sheets at an aqueous/organic interface without introducing defects, and has been demonstrated with numerous organic solvents including heptane, chloroform, styrene, and butyl acrylate [10,12]. ...
... There is a significant energetic cost to move a sheet of graphene into either liquid phase, which traps the sheets at the interface and prevents them from restacking [10,11]. This solvent interfacial trapping method (SITM) results in single to few layers of overlapping graphene sheets at an aqueous/organic interface without introducing defects, and has been demonstrated with numerous organic solvents including heptane, chloroform, styrene, and butyl acrylate [10,12]. ...
... The spontaneous exfoliation process lowers the interfacial energy of the system, and thus the graphene acts as a surfactant [10,13]. Graphite spreads to cover the surfaces of dispersed droplets in a homogenized system, stabilizing water-in-oil emulsions [12]. ...
Article
Graphene is attractive as a functional 2D surfactant for polymerized high internal phase emulsions (polyHIPEs) due to its remarkable mechanical and electrical properties. We have developed polyHIPEs stabilized by pristine, unoxidized graphene via the spontaneous exfoliation of graphite at high-energy aqueous/organic interfaces. The exfoliated graphene self-assembles into a percolating network and incorporates into the polyHIPE cell walls as verified by TEM. The resulting composites showed compressive strengths of 7.0 MPa at densities of 0.22 g/cm³ and conductivities up to 0.36 S/m. Systematically reducing the concentration of monomer in the oil phase by dilution with a porogenic-acting solvent increased the porosity and lowered the density of the polyHIPEs. Characterization of these composites indicated that graphene’s high compressive strength and modulus was transferred to the polyHIPEs and provided mechanical reinforcement even at low polymer content. SEM showed that the morphology of the polymer changed with decreasing monomer content while the graphene lined cells retained their shape. Moreover, we show that the polyHIPEs contain a continuous graphene percolating network resulting in electrically conductive materials at low graphene loading.
... Exfoliation of graphite to graphene at the oil/water interface has been previously accomplished by using a solvent interface trapping approach. 27 In such a system, water functions as the dispersed phase, filling the microspheres coated by graphene, and oil works as the continuous phase. By use of monomers with vinyl moieties as an oil phase, the graphene-stabilized emulsions can undergo radical polymerizations to form hydrophobic composites with a continuous network of hollow microspheres with a graphene lining. ...
... By use of monomers with vinyl moieties as an oil phase, the graphene-stabilized emulsions can undergo radical polymerizations to form hydrophobic composites with a continuous network of hollow microspheres with a graphene lining. 27 However, to the best of our knowledge, graphite has not been exfoliated to graphene within the hydrophilic hydrogel network until now because of the strong π−π stacking between graphene layers, which is thermodynamically unfavorable. 28 To overcome such strong π−π stacking, we generated a reverse solvent interface trapping approach in which (i) after graphite exfoliates to graphene, it assembles at the water−heptane interfaces to reduce the total free energy of the system, making the exfoliation process thermodynamically favorable; (ii) heptane functions as the dispersed phase, filling the microspheres coated by EG; and (iii) water containing cross-linkable hydrogel serves as the continuous phase. ...
... Such architecture is composed of closely packed microspherical features covered with EG within the hydrogel (Figure 1). 27 Our studies indicate that the reverse solvent trapping approach successfully introduced uniform heterogeneity into the hydrogel via the formation of graphene-lined microspheres. The formation of such microspheres within a G-GMA hydrogel improved its suturability and mechanical properties, without causing any cytotoxicity. ...
... This results in both graphite and graphene being present at the interface. The presence of graphene, and not just graphite, has been shown by TEM images and Raman spectroscopy 36 . Other studies have shown that graphene alone can stabilize emulsions, such as the work of Large et al., where graphite was exfoliated by sonication and used to stabilize water-in-oil emulsions 37 , and the work of Ogilvie et al. who pre-exfoliated with sonication followed by size selection to produce stabilized emulsions with only few layer graphene 38 . ...
... Exfoliating graphite by interfacial trapping relies on graphite not being soluble in either water or oil 36 . The exfoliation is spontaneous and driven by lowering the interfacial energy of oil and water as graphene spreads at the interface 36,40 . ...
... Exfoliating graphite by interfacial trapping relies on graphite not being soluble in either water or oil 36 . The exfoliation is spontaneous and driven by lowering the interfacial energy of oil and water as graphene spreads at the interface 36,40 . Shown in Fig. 1a is a vial containing hexadecane (C16) and water with graphite trapped at the oil/water interface. ...
Article
Full-text available
Paper diagnostics are of growing interest due to their low cost and easy accessibility. Conductive inks, necessary for manufacturing the next generation diagnostic devices, currently face challenges such as high cost, high sintering temperatures, or harsh conditions required to remove stabilizers. Here we report an effective, inexpensive, and environmentally friendly approach to graphene ink that is suitable for screen printing onto paper substrates. The ink formulation contains only pristine graphite, water, and non-toxic alkanes formed by an interfacial trapping method in which graphite spontaneously exfoliates to graphene. The result is a viscous graphene stabilized water-in-oil emulsion-based ink. This ink does not require sintering, but drying at 90 °C or brief microwaving can improve the conductivity. The production requires only 40 s of shaking to form the emulsion. The sheet resistance of the ink is approximately 600 Ω/sq at a thickness of less than 6 µm, and the ink can be stabilized by as little as 1 wt% graphite.
... Another approach is the thermodynamically driven spreading of graphite at a water-oil interface [22]. Here graphite is spontaneously exfoliated as the graphene sheets spread and stabilize the high-energy liquid-liquid interface, thus acting as surfactants. ...
... This method is a fundamental departure from previous methods as it does not require the input of mechanical or chemical energy and so does not require stabilizers, sonication, or chemical modification. The thermodynamic driving force for this process has been studied both experimentally and computationally, with theory and experiment appearing to converge [22]. ...
... In the meantime, functional sensing materials play a key role in achieving high-performance sensors, which has been widely exploring for integrating wearable sensing system [3][4][5][6]. Graphene (RGO) is a fascinating two-dimensional material, and diverse forms of RGO are generally studied for various applications, including sensing, catalysis, energy storage, etc. [7][8][9][10][11][12][13][14], especially of RGO nanofilm with better adaptability to complicated environments [15][16][17][18]. Oil-water (O/W) two-phase interface assembly strategy provides a simple, effective, and lowcost fabricated process for preparing RGO nanofilms that are used for blending with a controllable functional group, which would be attractive for further practical sensing application [17]. ...
... Additionally, O/W self-assembly of RGO or PBNPs has been prepared, separately. RGO with large energy gain could overcome effect of thermal energy, and further stably assembled on O/W interface or liquid/solid interface in forming RGO film driven by minimization of interfacial free energy ( Fig. S1a and S1b) [15,18]. On contrast, due to displacement of particles from interface induced by thermal energy, hydrophilic PBNPs with small energy gain could not assemble on O/W interface, but formed oil-in-water emulsions ( Fig. S1c and S1d) [25][26][27]. ...
Article
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Wearable film-based smart biosensors have been developed for real-time biomolecules detection. Particularly, interfacial co-assembly of reduced graphene oxide-prussian blue (PB-RGO) film through electrostatic interaction has been systematically studied by controllable pH values, achieving optimal PB-RGO nanofilms at oil/water (O/W) phase interface driven by minimization of interfacial free energy for wearable biosensors. As a result, as-prepared wearable biosensors of PB-RGO film could be easily woven into fabrics, exhibiting excellent glucose sensing performance in amperometric detection with a sensitivity of 27.78 µA mM⁻¹ cm⁻² and a detection limit of 7.94 μM, as well as impressive mechanical robustness of continuously undergoing thousands of bending or twist. Moreover, integrated wearable smartsensing system could realize remotely real-time detection of biomarkers in actual samples of beverages or human sweat via cellphones. Prospectively, interfacial co-assembly engineering driven by pH-induced electrostatic interaction would provide a simple and efficient approach for acquiring functional graphene composites films, and further fabricate wearable smartsensing devices in health monitoring fields. Graphical abstract
... The graphene film was drawn onto porous GaN when the latter descended into the heptane/DMF interface. This method is known as solvent−interface trapping (SIT) [42]. ...
... The graphene film was drawn onto porous GaN when the latter descended into the heptane/DMF interface. This method is known as solvent-interface trapping (SIT) [42]. ...
Article
Full-text available
This work presents the role of graphene in improving the performance of a porous GaN-based UV photodetector. The porous GaN-based photodetector, with a mean pore diameter of 35 nm, possessed higher UV sensitivity, about 95% better compared to that of the as-received (non-porous) photodetector. In addition, it exhibits a lower magnitude of leakage current at dark ambient, about 70.9 μA, compared to that of the as-received photodetector with 13.7 mA. However, it is also highly resistive in nature due to the corresponding electrochemical process selectively dissolute doped regions. Herein, two types of graphene, derived from CVD and the electrochemical exfoliation (EC) process, were cladded onto the porous GaN region. The formation of a graphene/porous GaN interface, as evident from the decrease in average distance between defects as determined from Raman spectroscopy, infers better charge accumulation and conductance, which significantly improved UV sensing. While the leakage current shows little improvement, the UV sensitivity was greatly enhanced, by about 460% and 420% for CVD and EC cladded samples. The slight difference between types of graphene was attributed to the coverage area on porous GaN, where CVD-grown graphene tends to be continuous while EC-graphene relies on aggregation to form films.
... 36 However, graphene has a strong tendency of reaggregation during deposition, which makes most solution-based methods unsuitable for graphene dispersion produced by liquid exfoliation. 40 Recently, we have reported a novel wettinginduced climbing method to transfer interfacially assembled few-layer graphene to various substrates, achieving fast and large-scale production of ultrathin pristine graphene film. 41 Despite an increasing number of studies conducted on liquid exfoliation of graphene, its use in flexible electronics is limited because of either still-low conductivity 42 or poor transparency. ...
... Once the injected graphene dispersion contacted the water surface, hydrophilic NMP solvent diffused into water, while the remaining PVPmodified graphene nanoplatelets glided along the water surface and then collided, bounded mutually via π−π interactions to assemble into a continuous graphene film owing to NMPdiffusion-induced surface free-energy gradient. 40 The surface tension of the interfacially assembled graphene film was found to be 63.4 mN m −1 using a platinum plate-normal method. 41 Then, a flexible hydrophilic poly(ethylene terephthalate) (PET) with a water contact angle (CA) of about 7°was prewetted with water to form a continuous water film with a surface tension of 72.3 mN m −1 . ...
Article
Full-text available
Graphene has attracted extensive attention for the supply of electrically conductive, optically transparent, and mechanical robust electrodes for flexible optoelectrical devices, as an alternative to commercial indium tin oxide, due to its superior mechanical, electrical, and optical properties. However, conventional chemical vapor deposition is impeded by harsh conditions and complicated processes, and it is still a challenge to fabricate high-performance graphene transparent electrode in a facile and scalable solution-processable route. Herein, a wetting-induced scalable solution-processable approach to fabricate graphene hybrid with conductive ionogel and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), i.e., graphene/ionogel@PEDOT:PSS (G/Ionogel@PEDOT:PSS), for high-performance flexible transparent electrode (FTE) is reported, achieving a low sheet resistance of 30 Ω sq-1 and a high transmittance of 88% at 550 nm. The as-fabricated trinary hybrid FTE as both transparent electrode and electrochromic layer is applied to a compact indium tin oxide (ITO)-free three-layered flexible electrochromic device, showing fast switching response, good electrochromic contrast, and reliable stability. Our work enables a scalable solution-processable approach for the generation of graphene-based FTE and functional devices.
... However, energy-related applications typically require near-pristine graphene, often obtained through mechanical exfoliation of graphite, which presents low yields and consequently inflated costs. Nonetheless, this is rapidly changing, with various potentially up-scalable methods to produce high quality graphene being recently reported in the literature: large-scale graphite exfoliation via a simple stirring process in urea/glycerol [258], one-step solvent interface trapping [259], pulsed laser assisted fabrication of graphene nanosheets in water [260], self-propagating high-temperature synthesis of mesoporous graphene from CO 2 [261], nanoclay-assisted electrochemical exfoliation of pencil cores [262], etc. ...
Article
The growing field of supercapacitors has already gained enough maturity and complexity to be the object of highly specific reviews. This review aims to provide a comprehensive outline of the topic, by presenting the state-of-the-art electrolytes and electrode materials used in supercapacitors as well as the relationship between their intrinsic features and their key performance indicators. This analysis is complemented by numerous examples of recent literature-reported performances of hybrid supercapacitors. To aid comparison, these are listed in tables and shown in plots, organized by type of electrode material and by type of electrolyte. Finally, performance differences between lab scale and commercial scale devices are put in perspective, by exploring, on one hand, the obstacles to the transition from promising lab scale to industrial scale devices and by explaining, on the other hand, the reasons why the same type of electrode material and electrolyte combination often perform more poorly in real-world devices. With this approach, the authors expect to give a useful insight (and a comprehensive snapshot) into the challenges that need to be surpassed to bridge the gap between lab scale and industrial scale devices.
... PS/Graphene Nanocomposites. A water-in-oil emulsion stabilized by graphene was prepared as reported previously 26 and described in the Experimental Section. If neat styrene is used as the oil phase of the emulsion, polymerization results a foam structure with individual spheres in contact with one other as shown in Figure 1A, with higher magnification images showing individual sheets shown in the Supporting Information S2. ...
... PEDOT:PSS has been used in the past for the fabrication of biopotential electrodes because of its mixed nature of conduction. 32 Three layers of PEDOT:PSS ink containing DMSO was screen printed sequentially onto graphene coated textile which corresponds to 2.5 wt % PEDOT:PSS (R s = 5.5 Ω/□). The skin contact impedance from the PEDOT:PSS electrode and PEDOT:PSS−graphene coated electrode is shown in Figure 4c with the composite electrode showing lower impedance than the either PE-DOT:PSS or graphene electrode. ...
Article
Highly conductive, metal-like poly(ethylene terephthalate) (PET) nonwoven fabric was prepared by coating poly(3,4-ethylenedioxythiophene): poly(4-styrene sulfonate) (PEDOT:PSS) containing dimethylsulfoxide (DMSO) onto PET nonwoven fabric previously coated with graphene/graphite. The sheet resistance of the original nonwoven fabric decreases from >80 MΩ/□ to 1.1 Ω/□ after coating with 10.7 wt% graphene and 5.48 wt% PEDOT:PSS with a maximum current at breakdown of 4 A. This sheet resistance is lower than previously reported sheet resistances of fabrics coated with graphene films, PEDOT:PSS films, or PEDOT:PSS coated fabrics from the literature. The effect of temperature on the resistance of graphene/PEDOT:PSS coated fabric has revealed that the resistance decreases with increasing temperature, analogous to semiconductors, with a clear semiconductor-metal transition occurring at 290 K. Finally, a coating of 18 wt% graphene/graphite and 2.5 wt% PEDOT:PSS (Rs =5.5 Ω/□) screen printed on the nonwoven fabric was shown to function as an electrode for electrocardiography without any hydrogel and dry skin conditions. This composite coating finds application in wearable electronics for military and consumer sector.
... Such composite materials have in fact showed advantageous properties: high electrical conductivity, stability, and transparency [44][45][46][47][48]. The creation of a conductive film on a substrate, by drying a nanofluid containing GN, AgNPs and CNT nanoparticles, is quite challenging, requiring innovative solutions to reduce cost and time consumption, the use of toxic chemicals and the complicated process [49,50]. The main obstacle appears to be the tendency of GN, AgNPs and CNT nanoparticles to agglomerate in water, which is caused by their hydrophobic surfaces, used to coat nanoparticles on a substrate by drying a nanofluid. ...
Article
Full-text available
Transparent conductive films are fundamental materials, currently used in several fields. Recently, due to their unique multifunctional properties, composite materials have started to be used in place of fluorine tin oxide and indium tin oxide in transparent conductive electrodes. However, the production of composite materials is still complicated and involves toxic chemicals. Through a simple and environmentally-friendly method, we synthesized new composite materials—conductive, transparent, and flexible films—that can be applied to the production of modern optoelectronic devices. An even dispersion of the nanoparticles was achieved by ultrasound excitation. Moreover, a series of morphological and structural investigations were conducted on the films by scanning and transmission electron microscopy, electrical conductivity, Raman spectroscopy, X-ray diffraction and testing their sheet resistance. The results indicated that the tested composite materials were ideal for film coating. The nanofluids containing multi-walled carbon nanotubes presented the highest electrical conductivity; nevertheless, all the composite nanofluids tended to have relatively high electrical conductivities. The flexible films with composite structures presented lower sheet resistances than those with single structures. Finally, the hybrid materials showed a higher transmittance.
... Assembly of solids at the L/L interface is well-researched and can be traced back to the work of Faraday, 14 yet assembly of graphene at the L/L interface was only first demonstrated in 2009 15 as an approach to generate a highly ordered monolayer film from pre-exfoliated 2D materials. Graphene 16,17 and graphene oxide 18−20 monolayers have been produced at the L/L interface, while graphene-based supercapacitors 21,22 and TMD photoelectrochemical cells 23 have been produced using L/L interfacial films. Nanomaterials have also been prepared at the L/L interface using bottom-up syntheses. ...
Article
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Scalable synthesis of 2D materials is a prerequisite for their commercial exploitation. Here, a novel method of producing nanocrystalline molybdenum disulfide (MoS2) at the liquid-liquid interface is demonstrated by decomposing a molecular precursor (tetrakis(N,N-diethyldithiocarbamato) molybdenum(IV)) in an organic solvent. The decomposition occurs over a few hours at room temperature without stirring or the addition of any surfactants, producing MoS2, which can be isolated onto substrates of choice. The formation of MoS2 at the liquid-liquid interface can be accelerated by the inclusion of hydroxide ions in the aqueous phase, which we propose to act as a catalyst. The precursor concentration was varied to min-imize MoS2 thickness and the organic solvent was chosen to optimize the speed and quality of formation. The kinetics of the MoS2 formation have been investigated and a reaction mechanism has been proposed. The synthesis method is, to the best of our knowledge, the first reported room temperature synthesis of transition metal dichalcogenides, offering a potential solution to scalable 2D material production.
... Grafena memiliki karakteristik yang tidak biasa yaitu memiliki kekuatan 200 kali lebih besar dibandingkan baja dengan tingkat fleksibilitas yang sangat tinggi. Selain itu, grafena juga merupakan bahan konduktor yang sangat baik karena transport elektron yang baik dan juga transparan [1]. ...
... Most literature examples report methods that begin by dispersing the 2D material in one liquid, before adding a second immiscible liquid layer to create the interface. The 2D material in the dispersed phase can be induced to transport to the interface using mechanical means, such as sonication or manual shaking, 16,20,21 or by the addition of a chemical inducing agent. 19,28 There have been few reports of assembly by direct injection of the material to the liquid/liquid interface, as described in this work. ...
Article
Full-text available
Thin films of MoS2 bilayer nanoflakes, which are predominantly a single flake thick and in edge-to-edge contact, have been produced via self-assembled tiling at the planar interface between two immiscible liquids. Films of several square centimeters extent can be produced with total covered area approaching 90 % and over 70 % of the film covered by single flakes without overlap. Films produced through liquid/liquid assembly are shown to produce a lower uncovered area fraction and more uniform thickness when compared with films of similar areal coverage produced by the “top-down” techniques of spin coating and spray coating. Statistical analysis of flake coverage data, measured by AFM, shows that liquid/liquid assembly produces a distinctly different variation in film thickness than conventional “top-down” deposition. This supports the hypothesis that the 2D confinement of liquid/liquid assembly produces more uniform films. Demonstrator field-effect transistors (FETs) manufactured from the films exhibit mobility and on/off current ratios of 0.73 cm² V⁻¹ s⁻¹ and 10⁵ respectively; comparable to FETs of similar layout and CVD-grown or mechanically cleaved single crystal MoS2 channel material. This work demonstrates the use of liquid/liquid interfaces as a useful tool for self-assembly of high performance thin film devices made from dispersions of 2D materials.
... Nowadays, different organic, aqueous and aqueous-organic substances are used for stabilization of the graphene sheets and prevent their agglomeration. Among the liquid media used, the most interesting are the following: imidazole, N,N-dimethylformamide, heptanes, sodium dodecyl sulfate, N,N-dimethyloctylamine, pyridine, hexafluorobenzene, octafluorotoluene and other solvents belonging to a peculiar class of perfluorinated aromatic molecules, N-methylpyrrolidone, o-dichlorobenzene, etc. [16][17][18][19][20][21][22][23][24][25][26][27][28][29]. ...
Article
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N,N-dimethylformamide (DMF) is often used as a liquid medium for the exfoliation of graphene for the further use in a wide range of fields of science and technology: biomedical research,...
... Most of the organic solvents are highly volatile and evaporate faster, despite lower surface tension compared to water. The evaporation rate of the solvents needs to be properly optimized according to the printing method, otherwise, the ink may clog the nozzle and agglomeration could result through a loss of solvent [65,66]. ...
Article
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As the industry and commercial market move towards the optimization of printing and additive manufacturing, it becomes important to understand how to obtain the most from the materials while maintaining the ability to print complex geometries effectively. Combining such a manufacturing method with advanced carbon materials, such as Graphene, Carbon Nanotubes, and Carbon fibers, with their mechanical and conductive properties, delivers a cutting-edge combination of low-cost conductive products. Through the process of printing the effectiveness of these properties decreases. Thorough optimization is required to determine the idealized ink functional and flow properties to ensure maximum printability and functionalities offered by carbon nanoforms. The optimization of these properties then is limited by the printability. By determining the physical properties of printability and flow properties of the inks, calculated compromises can be made for the ink design. In this review we have discussed the connection between the rheology of carbon-based inks and the methodologies for maintaining the maximum pristine carbon material properties.
... The scalable and cost-effective interface trapping method described by Woltornist et al. 231,232 was useful for realizing fabric from pristine few-layer graphene (FLG)/graphite from natural bulk graphite with enhanced electrical conductivity (EC) and without the need for any additives or surfactants or chemical modification of graphite. Furthermore, sonication of graphite in a water/heptane mixture was carried out to attain continuous films (one to four layers thick) at the interface between two immiscible liquids by reducing the high interfacial energy of the two solvent phases. ...
Article
The voyage of smart textile based wearable technologies first started with the attachment of sensor to fabrics followed by embedding a sensor in the apparel. At present, the garment itself is transformed into a sensor which is a tremendous growth in the field of smart textiles. Wearable applications demand flexible materials that can withstand deformation in order to practically use them in par with conventional textiles. To address this, we explore the potential causes of the enhanced performance of wearable devices realized from the fabrication of carbon nanostructured fibers with the perspectives of graphene, carbon nanotubes and other two-dimensional materials involved in the process. This review highlights a brief introduction of fabrication strategies to form carbon based fibers and the relationship between their properties and characteristics of materials. The likely mechanisms of fiber-based electronic and storage devices, focusing mainly on transistors, nano-generators, solar cells, supercapacitors, battery, sensors and therapeutic devices are also presented. Future perspective of this research field of flexible and wearable electronics are discussed. The present study supplement novel ideas not only for the beginners who are aiming to work in this booming area but also for the researchers actively engaged in the field of fibre based electronics that deals with advanced electronic and wide range of functionalities integrated into textile fibers.
... Considering the graphene production, graphite could be successfully exfoliated in H 2 O/chloroform, H 2 O /n-heptane, H 2 O/DCM and H 2 O/n-octanol biphasic systems. Moreover, based on the liquids' densities these systems allowed choosing where the exfoliated graphite would be preferentially located [57]. The use of ILs for stabilizing these systems was also described [44]. ...
Article
Herein we describe a successful protocol for graphite exfoliation using a biphasic liquid system (water/dichloromethane, DCM) containing ionic liquids (ILs; 1,3-dibenzylimidazolium benzoate- and 1-naphthoate). The use of (surface active) IL and sonication led to stable DCM/water (O/W) emulsion, which enhanced graphene formation, suppressed its re-aggregation and decreased shear/cavitation damage. The O/W emulsion stabilization by the ILs was studied by dynamic light scattering (DLS), whereas their interaction with the graphene sheets were described by Density Functional Theory (DFT) calculations. Moreover, a comprehensive investigation on cavitation-based exfoliation in the O/W systems was performed to assess the importance of operational parameters, including, the type of ultrasound processor, ultrasound power and insonation, and the influence of the exfoliation medium.
... There are many approaches to produce graphene such as chemical exfoliation [12], sonication [13], hydrothermal self-assembly [14], electrochemical synthesis [15], and chemical vapor deposition [16]. Among these approaches, CVD has advantageous for growing high-quality graphene with single or multilayers [17,18]. ...
Article
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Chemical vapor deposition (CVD) is one of the best methods to grow graphene. In this way, there are many methods to produce graphene by liquid and solid precursor. In this research, we grew the graphene using ethanol and cyclohexane as precursors by some of these methods to obtain the best method to enter the precursor to the furnace. We compare the size of graphene domains by these methods and investigate the quality of their products. As the best method, we should keep inert gas into the precursor container to dilute the vapor of the precursor and heat the container to be sure that there is the vapor of precursor in it. Hydrogen should flow from a separate pipeline to the furnace. In this method, the rate of carbon precursor is measurable. Also, the results show that by increasing the growth time, graphene domains grow and become more significant. Also, with increasing the number of carbons in the structure of the precursor, the size of graphene will increase.
Article
This chapter introduces the basics of membranes and reviews the original membranes to the most recent modern membranes. Membrane materials with the appropriate chemical, mechanical, and permeation properties are crucial for high‐performance membranes. In addition, the technology contributes greatly in successfully fabricating this material into a robust, thin, defect‐free membrane and then to package the membrane into an efficient, economical, high‐surface‐area module. The chapter covers the membrane structures, preparation techniques, technology, and modules. In contrast to dense membranes, microporous membranes endow the porous nature. That means membrane materials possess large free volumes and open pores. The chapter illustrates the most important parameters of microporous materials for membrane application. The features of microporous membrane are elucidated from the perspective of pore chemistry because this chemistry plays a central role in membrane separation. The pore properties can be determined using the terms of pore size, configuration, dimensionality, and functionality.
Article
Monolayer particles of two-dimensional (2D) materials represent a scientifically and technologically interesting class of anisotropic particles with colloidal-scale lateral sizes but sub-nanometer thicknesses. This atomic-scale thickness leads to interesting phenomena that can be exploited in next-generation thin-film technologies, and fluid-fluid interfaces provide a potentially scalable platform to confine, assemble, and deposit functional thin-films of 2D materials. However, directly observing how these materials interact and assemble into a given film morphology is experimentally challenging because of their sub-nanometer thicknesses. Here, we demonstrate the ability to directly observe graphene, molybdenum disulfide (MoS2), and hexagonal boron nitride (h-BN) particles at fluid-fluid interfaces using interference reflection microscopy (IRM). Monolayer MoS2 and graphene particles demonstrated >10% optical contrast at an air-water interface, which allowed us to quantitatively analyze in situ images of self-assembled MoS2 particles and to map trajectories of interacting graphene particles. Additionally, the Brownian motion of a graphene particle was tracked and analyzed in the context of passive microrheology theory for 2D particle probes. Our results demonstrate how IRM can be used to obtain quantitative spatiotemporal information regarding the self-assembly and dynamics of 2D materials at fluid-fluid interfaces. It will have a significant impact on our ability to investigate systems of atomically-thin particles at fluid-fluid interfaces, an area that has fundamental scientific importance and materials science applications but has suffered from a lack of direct, in situ observation techniques.
Article
In this work, we have firstly achieved the construction of bismuth oxyiodide (Bi5O7I)/reduced graphene oxide (rGO)/ZnO Z-scheme photoelectrochemical (PEC) system without backward reactions through loading large-area ZnO quantum dots (QDs)/rGO films on Bi5O7I nanosheets. Single-crystal porous Bi5O7I nanosheets with numerous oxygen vacancies (OVs) were firstly fabricated through the calcination of BiOI in reductive glycols. The single-crystal facilitates charge transport, nanoporous structure promotes light absorption and OVs improves charge separation efficiency. As a result, single-crystal porous Bi5O7I nanosheets with OVs exhibited higher PEC performance than other morphologies reported before. Moreover, The PEC activity of Bi5O7I can be further enhanced through loading large-area ZnO QDs/rGO films to construct a pure Z-scheme charge transfer system, which not only achieves efficient separation of electron-hole pairs but also retains its excellent redox ability. To the best of our knowledge, the photocurrent density of Bi5O7I/rGO/ZnO heterostructures is the highest among Bi5O7I-based samples. For comparison, an opposite Z-scheme model has also been built up by replacing Bi5O7I with WO3, in which the photocurrent density decreased conversely. Therefore, it can be known that a pure Z-scheme system without backward reactions can be successfully prepared through loading ZnO QDs/rGO films on photoelectrodes.
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Owing to inherent 2D structure, marvelous mechanical, electrical, and thermal properties, graphene has great potential as a macroscopic thin film for surface coating, composite, flexible electrode, and sensor. Nevertheless, the production of large‐area graphene‐based thin film from pristine graphene dispersion is severely impeded by its poor solution processability. In this study, a robust wetting‐induced climbing strategy is reported for transferring the interfacially assembled large‐area ultrathin pristine graphene film. This strategy can quickly convert solvent‐exfoliated pristine graphene dispersion into ultrathin graphene film on various substrates with different materials (glass, metal, plastics, and cloth), shapes (film, fiber, and bulk), and hydrophobic/hydrophilic patterns. It is also applicable to nanoparticles, nanofibers, and other exfoliated 2D nanomaterials for fabricating large‐area ultrathin films. Alternate climbing of different ultrathin nanomaterial films allows a layer‐by‐layer transfer, forming a well‐ordered layered composite film with the integration of multiple pristine nanomaterials at nanometer scale. This powerful strategy would greatly promote the development of solvent‐exfoliated pristine nanomaterials from dispersions to macroscopic thin film materials. A robust wetting‐induced climbing strategy to transfer an interfacially assembled pristine graphene film is developed. This strategy quickly converts a solvent‐exfoliated graphene dispersion into a large‐area ultrathin graphene film on various substrates with different materials, shapes, and hydrophobic/hydrophilic patterns. It is applicable to other solvent‐exfoliated nanomaterials and allows alternate climbing of different ultrathin nanomaterial films, forming layered composite films.
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Confinement of particles to fluid–fluid interfaces provides a unique interaction environment, allowing the directed assembly of particles using lateral capillary forces. The particle laden interfacial layers can be deposited onto a variety of substrates for the fabrication of thin film coatings, designed to have structural or functional properties resulting from the interface‐specific structures. For the fabrication of electrically conducting films and specifically graphene‐based coatings, interfacial deposition techniques could offer a low cost and environmentally favorable alternative to conventional gas phase production methods, with possibly a broader choice of substrates. In this work liquid‐phase electrochemical exfoliation is used to produce platelets of few‐layer graphene from bulk graphite which are directly introduced to the water–air interface. These interfaces are characterized through compression experiments and interfacial shear rheology to probe the mechanical properties of the resulting monolayer films and identify mechanical percolation. Further, in situ measurements of electrical conductivity are integrated as a direct indication of electrical percolation. This directly verifies sufficient film quality as an important characteristic of the deposition process. Once deposited on a solid substrate, these films retain their electrical conductivity. But the mechanical properties of the films allow for facile production of freestanding microporous graphene membranes.
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We use a combination of the coarse-grained molecular dynamics simulations and finite difference method calculations to study electromechanical coupling in composite polymer/graphene foams. In these foams, graphene sheets (G-sheets) cover the surface of the foam cells resulting in a percolating network of graphene sheets. Our simulations have shown that upon uniaxial deformation or under foam swelling conditions, the percolating network of the G-sheets breaks down. This breakdown is manifested as an increase of the foamʼs electrical resistance. The disruption of the graphene networks occurs through crack formation of the Gshells covering the surfaces of the polymeric foam cells. These cracks are responsible for the hysteresis in electromechanical foam properties observed during loading−unloading cycles. In particular, for uniaxial foam deformations, it requires the application of a compressive stress for the foam to retain its initial dimensions. Comparison between uniaxial and swelling foam deformations shows that there is a stronger variation in the foam resistance under uniaxial deformation conditions.
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We present a facile method for the fabrication of ZnO-graphite composite thin films by using the technique of interface exfoliation. Natural graphite and ZnO are trapped at an oil-water interface, resulting in the exfoliation of graphite and formation of a composite. These thin films exhibit photoconductivity in the presence of ultraviolet radiation. The extent of the response and the time scales involved depend on the relative amount of ZnO and graphite, which is determined by fabrication conditions. We focus on using commercially available, non-toxic materials for the entire fabrication route.
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The interfacial adsorption of single-walled carbon nanotubes and few-layer graphene flakes, prepared by solution phase exfoliation, is compared. Strong adsorption of carbon nanotubes was observed at the water/1,2-dichloroethane interface, while a weaker adsorption of the graphene dispersion was seen. Addition of electrolyte to the organic phase was found to have a strong effect on the adsorption of graphene. A simple surface energy model does not fully explain these observations, rather residual charges and their distribution appears to be the key factor behind this difference in adsorptive behaviour. Carbon nanomaterials adsorbed at the liquid-liquid interface can function as bipolar electrodes: a preliminary investigation of the oxidation of the 1,2-dichlorobenzene by metal-modified graphene particles is performed.
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Graphene and its derivatives are popular nanomaterials used worldwide in many technical fields and biomedical applications. Due to such massive use, their anticipated accumulation in the environment is inevitable, with a largely unknown chronic influence on living organisms. Although repeatedly tested in chronic in vivo studies, long-term cell culture experiments that explain the biological response to these nanomaterials are still scarce. In this study, we sought to evaluate the biological responses of established model A549 tumor cells exposed to a non-toxic dose of pristine graphene for eight weeks. Our results demonstrate that the viability of the A549 cells exposed to the tested graphene did not change as well as the rate of their growth and proliferation despite nanoplatelet accumulation inside the cells. In addition, while the enzymatic activity of mitochondrial dehydrogenases moderately increased in exposed cells, their overall mitochondrial damage along with energy production changes was also not detected. Conversely, chronic accumulation of graphene nanoplates in exposed cells was detected, as evidenced by electron microscopy associated with impaired cellular motility.
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For the past ten years, Graphene and graphene oxide has become subject of interest in the research of new material development. However, discoveries and researches about graphene have been conducted for many years before. Graphene is defined as a single layer of atom carbon which has a specific characteristic. It’s very thin but has spectacular strength. The common process to produce single-sheet graphene is thermal or mechanical treatment of Graphene Oxide. Graphene also can be synthesized via some methods such as mechanical exfoliation/intercalation, chemical vapor deposition (CVD) and reduction method include reduction graphene oxide and reduction of other precursors such as glucose, Sic or ethanol. For mechanical exfoliation, using Scotch Tape can produce graphene flakes in μm size by pulling off graphene layers from highly ordered pyrolytic graphite (HOPG). CVD method is also popular, but more expensive than exfoliation. The process occurs at a high temperature. Methane, hydrogen, and a transition metal are used in this method. Almost all synthesis routes using graphite to produce graphene, whereas in our environment many carbon sources can be used to produce graphene, such as charcoal from wood, coconut cell, saw powder and bagasse which will be interesting to study further. Due to its unique properties, graphene can be applied in many fields such as energy, environmental and electronic devices application. In this overview paper, the possible raw materials that can be used to synthesize graphene were explored, the synthesis routes were explained and the applications in many fields were discussed.
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Recently, along with the serious waste polymer issues, the compatibilization and functionalization of immiscible polymers is regarded as a sustainable solution. In this work, for the first time, we explored the role of hexagonal boron nitride (h-BN) as an advanced compatibilizing and functionalizing agent for immiscible polypropylene (PP) and polyethylene (PE) composites through in-situ exfoliation at interface. The exfoliated structure was confirmed by X-ray diffraction and Raman spectra, with its thermodynamics drives in-situ exfoliation mechanism was proposed. The compatibilization effect of h-BN was evidenced by the enhanced tensile strength and Young's modulus of 28.0 MPa and 639.0 MPa of PP/PE/h-BN composite, which are 91.2% and 57.8% higher than PP/PE binary composite. Furthermore, the in-plane thermal conductivity was measured to be 0.87 W/mK at low h-BN loading of 15 wt% which is 2.6 times higher than the reference sample. Benefiting from the in-situ exfoliation, our sample showed the best thermal conductivity reinforcement effect (26.9%/vol%) as compared with the other reports. The heat management performance of our sample had also been revealed. Moreover, an additional experiment was performed to confirm that the concept proposed herein can be a sustainable route for waste polymers recycling. Thus, we believe the inclusion and in-situ exfoliation of h-BN could be a sustainable solution for the value-added recycling of waste polymers.
Article
Here, we develop a framework for assembly, understanding, and application of functional emulsions stabilized by few-layer pristine two-dimensional (2D) nanosheets. Liquid-exfoliated graphene and MoS2 are demonstrated to stabilize emulsions at ultralow nanosheet volume fractions, approaching the minimum loading achievable with 2D materials. These nanosheet-stabilized emulsions allow controlled droplet deposition free from the coffee ring effect to facilitate single-droplet devices from minute quantities of material or assembly into large-area films with high network conductivity. To broaden the range of compositions and subsequent applications, an understanding of emulsion stability and orientation in terms of surface energy of the three phases is developed. Importantly, this model facilitates determination of the surface energies of the nanosheets themselves and identifies strategies based on surface tension and pH to allow design of emulsion structures. Finally, this approach is used to prepare conductive silicone emulsion composites with a record-low loading level and excellent electromechanical sensitivity. The versatility of these nanosheet-stabilized emulsions illustrates their potential for low-loading composites, thin-film formation and surface energy determination, and the design of functional structures for a range of segregated network applications.
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Graphene papers (GPs) have revolutionized the area of sensors toward low-cost, user-friendly and wearable/portable owning to their unique properties such as scalable production capacity, tunable microstructure, and extraordinary mechanical flexibility. They can be utilized as versatile building blocks by regulating their architectures to enhance various properties like electronic property, thermal conductivity and mechanical strength. Furthermore, thanks to the excellent compatibility, GPs as support materials are able to associate with other materials through various interaction forces to realize specific functionalization. With the impressive performances mentioned above, lots of smart devices like flexible sensors, advanced wearable/stretchable electronics, and high-performance point-of-care analytical devices are continually and rapidly being developed. Herein, this review aims at offering a critical engineering insight from smart architecture of macroscopic GPs to sensor application, with the emphasis on purpose-driven specific dual-mode functionalization (structural functionalization and foreign materials functionalization). We summarize the multiple possibilities to functionalize graphene and its derivative based papers/films/membranes. The sensing application of GPs in human health management, food contaminant inspection, and environmental monitoring is evaluated just before leading to our conclusions and perspectives.
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Advances in synthesis of model 3D colloidal particles with exotic shapes and physical properties have enabled discovery of new 3D colloidal phases not observed in atomic systems, and simulations and quasi-2D studies suggest 2D colloidal systems have an even richer phase behavior. However, a model 2D (one-atom-thick) colloidal system has yet to be experimentally realized because of limitations in solution-phase exfoliation of 2D materials and other 2D particle fabrication technologies. Herein, we use a photolithography-based methodology to fabricate size- and shape-controlled monolayer graphene particles, and then transfer the particles to an air-water interface to study their dynamics and self-assembly in real-time using interference reflection microscopy. Results suggest the graphene particles behave as "hard" 2D colloidal particles, with entropy influencing the self-assembled structures. Additional evidence suggests the stability of the self-assembled structures manifests from the edge-to-edge van der Waals force between 2D particles. We also show graphene discs with diameters up to 50 μm exhibit significant Brownian motion under optical microscopy due to their low mass. This work establishes a facile methodology for creating model experimental systems of colloidal 2D materials, which will have a significant impact on our understanding of fundamental 2D physics. Finally, our results advance our understanding of how physical particle properties affect the interparticle interactions between monolayer 2D materials at fluid-fluid interfaces. This information can be used to guide the development of scalable synthesis techniques (e.g., solution-phase processing) to produce bulk suspensions of 2D materials with desired physical particle properties that can be used as building blocks for creating thin films with desired structures and properties via interfacial film assembly.
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Integrating functional components into graphene film is crucial for taking full advantage of graphene and manufacturing film-based devices. However, most graphene film-based system acts specialized property with complicated fabricated process, limiting further application. Herein, a highly compatible graphene nanofilm, decorated by electroactive Prussian blue (PB) and photoelectric responsive quantum dots (QDs), has been prepared via a simple and effective oil-water (O/W) self-assembly engineering. Interestingly, this graphene film could be transferred on various substrates for flexible application. As a result, PB and QDs have played a synergic effect with reduced graphene oxide (rGO) matrix, respectively, acquiring both excellent electrochemical sensing behaviors and extremely enhanced photocurrent generation compared with pure QDs film under simulated solar light. Furthermore, impressive biosensing performance has been obtained by enzyme-modified PB-rGO-QDs film. Additionally, proposed film-based wearable textile H2O2 sensor possesses high sensitivity of 53.8 µA mM⁻¹ cm⁻², while developed wearable glucose biosensor exhibits good performance, with a sensitivity of 37.24 µA mM⁻¹ cm⁻². Significantly, wearable devices of PB-rGO-QDs films on textile have established flexible bending lifetime over thousands of cycles, accompanying with stable sensor and photoelectronic properties. Prospectively, PB-rGO-QDs films would provide an efficient strategy of multi-components self-assembly for broadening the application of graphene and developing wearable biosensing/photoelectronic devices.
Article
Water-based elastomers (WBEs) are polymeric elastomers in aqueous systems. WBEs have recently continued to gain wide acceptability by both academia and industry due to their remarkable environmental and occupational safety friendly nature, as a non-toxic elastomeric dispersion with low-to-zero volatile organic compound (VOC) emission. However, their inherent poor mechanical and thermal properties remain a drawback to these sets of elastomers. Hence, nano-fillers such as graphene oxide (GO), reduced graphene oxide (rGO) and graphene nanoplatelets (GNPs) are being employed for the reinforcement and enhancement of this set of elastomers. This work is geared towards a critical review and summation of the state-of-the-art developments of graphene enhanced water-based elastomer composites (G-WBEC), including graphene and composite production processes, properties, characterisation techniques and potential commercial applications. The dominant production techniques, such as emulsion mixing and in situ polymerisation processes, which include Pickering emulsion, mini-emulsion and micro-emulsion, as well as ball-milling approach, are systematically evaluated. Details of the account of mechanical properties, electrical conductivity, thermal stability and thermal conductivity enhancements, as well as multifunctional properties of G-WBEC are discussed, with further elaboration on the structure-property relationship effects (such as dispersion and filler-matrix interface) through effective and non-destructive characterisation tools like Raman and XRD, among others. The paper also evaluates details of the current application attempts and potential commercial opportunities for G-WBEC utilisation in aerospace, automotive, oil and gas, biomedicals, textiles, sensors, electronics, solar energy, and thermal management.
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The adsorption of two-dimensional (2-D) graphene oxide (GO) nanosheets at liquid-liquid interfaces has broad technological implications from functional material preparations to oil-water emulsification. Molecular-level understanding of the adsorption thermodynamics and the interfacial behavior is of great significance. Here, the adsorption free energy of GO nanosheets at the water-cyclohexane system was simulated, in which the effect of oxygen-containing groups and deprotonation has been investigated. It was observed that the neutral GO (GO-COOH) has obvious interfacial activity with a reduction of interfacial tension, while the deprotonated GO (GO-COO-) shows a weak interface affinity. There exists an optimal oxidization degree that could cause the best interfacial stability, which is attributed to the balance of interfacial hydrophilic-hydrophobic interactions. The interaction arising from water is the main factor determining interfacial activity. The interfacial morphology and dynamics of GO nanosheets have also been simulated, in which an anisotropic 2-D translation and rotation along the interface were revealed. Our simulation results provide new insight into the adsorption mechanism and dynamics behavior of GO at the oil-water interface.
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Two-dimensional (2D) materials such as graphene, MXenes, and transition-metal dichalcogenides have recently gained substantial attention for their superlative physicochemical properties. Assembling 2D mate-rials into functional composites is of great importance, which could be the key to breakthroughs in emerging technologies and applications.The layer-by-layer assembly technique is a powerful, versatile, facile, and potentially highly scalable processing tool that has successfully been demonstrated to bring unique materials system advantages to various fields such as energy storage, chemical sensors, nanofiltration membranes, and solar cells. The wide range of precursors (e.g., poly-electrolytes) and tuning parameters that facilitate the incorporation of nanostructured materials makes this technique particularly compelling for creating 2D-material-based composites with ordered structure and tunable material properties. In this review, we highlight the exciting works in the field that utilize 2D materials implemented inlayer-by-layer assembled composites. We also discuss the challenges and opportunities toward industrialization of layer-by-layer assembled composites with perspectives on future research directions.
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Molybdenum disulfide (MoS2) is considered a promising material in energy storage systems, and is thus drawing considerable attention. However, the relatively low conductivity of bulk MoS2 has been a threat for practical applications. This study developed a simple and scalable fabrication method of few-layer MoS2 sheets embedded in a nanoporous graphene film (NGF) as a high capacitance active material. Transfer of MoS2/NGF onto a flexible substrate followed by plotter cutting produced a highly efficient micro-supercapacitor with superior flexibility, mechanical stability, and great potential for applications in wearable electronics. Notably, MoS2/NGF-based mSC revealed a high volumetric capacitance of 55 F cm-3 and 82.2% of capacitance retention after 20,000 cycles, which are superior to the reported data for solid-state micro-supercapacitors. With these performances, the flexible MoS2/NGF mSC exhibited an ultrahigh energy density of 7.64 mWh cm−3 and power density of 9.96 W cm−3 in a H3PO4 gel polymer electrolyte. The high volumetric capacitance and energy/power densities of MoS2/NGF as micro-supercapacitor electrodes are due to direct growth of ultra-thin MoS2 onto the interconnected 3D nanoporous graphene film with extended active sites and good conductivity. The MoS2/NGF mSC integrated on the skin efficiently powered a light emitting diode and strain sensors. This work suggests a meaningful way to realize film type MoS2 active materials in flexible micro-supercapacitors for wearable applications.
Article
Polymer dielectrics play an important role in modern electric power systems because of their ultrahigh power density, low cost, and lightweight. Current high-k polymers represented by poly(vinylidene fluoride) (PVDF) based ferroelectric polymers suffer from the high energy loss as well as the low temperature level. To overcome the conduction induced high loss, in present work, a BN thin layer fabricated from an oil-water self-assembly method is transferred on poly(vinylidene fluoride-chlorotrifluoroethyelen) (P(VDF-CTFE)) films. The BN layer with high bandgap may significantly depress the dielectric loss of polymer films, and reduce the charge injection in the films at both elevated temperature and electric field. That is responsible for the dramatically increased breakdown strength, energy density, discharge efficiency and even temperature level of P(VDF-CTFE). The optimized sample (c.a. BP-3) possesses a high energy density of 12.95 J/cm³ at 525 MV/m at ambient temperature. At 80 °C, BP-3 sample has an energy density of 6.38 J/cm³, which is nearly 8 times that of pristine P(VDF-CTFE) (0.78 J/cm³). This work offers a promising strategy to improve the breakdown strength and the dielectric performance of polymeric dielectrics.
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The versatile surface chemistry of MXenes affords a simple way by which the surface of MXene nanosheets can be modified. Here, by selectively grafting polystyrene onto one side of MXene nanosheets, a new amphiphilic surfactant nanomaterial, termed Janus MXene nanosheets (JMNs) or MXene nanosheet surfactants, is designed and synthesized. The prepared JMNs can be dispersed in either water or oil, and can spontaneously assemble at the water–oil interface to reduce the interfacial tension, making a promising solid surfactant to stabilize emulsions. Macroscopic assemblies of JMNs can also be easily prepared by interfacial assembly. Using creamed emulsions as templates, a lightweight, isotropic MXene aerogel is produced in one-step freeze-drying, where the matrix comprises the anchored PS and the pore structure is commensurate with the parent emulsion.
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Ion partitioning and behavior in electrolyte solutions plays an important role in drug delivery and therapeutics, protein folding, materials science, filtration and energy applications such as supercapacitors. Here we show that the segregation of ions in solutions also plays an important role in the exfoliation of natural flake graphite to pristine graphene. Polarizable anions such as iodide and acetate segregate to the interfacial region of the aqueous phase during solvent interfacial trapping exfoliation of graphene. Ordered water layers and accumulated charges near the graphene surface aid in separating graphene sheets from bulk graphite while, more importantly, reducing the reversibility of the exfoliation event. The observed phenomenon not only results in the improved stability of graphene stabilized emulsions, but also a low cost and environmentally friendly way of enhancing the production of graphene is offered.
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The fundamental colloidal properties of pristine graphene flakes remain incompletely understood, with conflicting reports about their chemical character, hindering potential applications that could exploit the extraordinary electronic, thermal, and mechanical properties of graphene. Here, the true amphipathic nature of pristine graphene flakes is demonstrated through wet‐chemistry testing, optical microscopy, electron microscopy, and density functional theory, molecular dynamics, and Monte Carlo calculations, and it is shown how this fact paves the way for the formation of ultrastable water/oil emulsions. In contrast to commonly used graphene oxide flakes, pristine graphene flakes possess well‐defined hydrophobic and hydrophilic regions: the basal plane and edges, respectively, the interplay of which allows small flakes to be utilized as stabilizers with an amphipathic strength that depends on the edge‐to‐surface ratio. The interactions between flakes can be also controlled by varying the oil‐to‐water ratio. In addition, it is predicted that graphene flakes can be efficiently used as a new‐generation stabilizer that is active under high pressure, high temperature, and in saline solutions, greatly enhancing the efficiency and functionality of applications based on this material.
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Two-dimensional (2D) nanomaterials have attracted interest from the scientific community due to their unique properties. The production of these materials has been carried out by diverse methodologies, the liquid phase exfoliation being the most promising one due to its simplicity and potential scalability. The use of several stabilizers allows to obtain dispersions of these 2D nanomaterials in solvents with low boiling points. Herein we describe a general exfoliation method for different 2D materials employing a biphasic water/dichloromethane system and two different (poly)aromatic hydrocarbons (PAHs). This method allows us to obtain dispersions of the exfoliated 2D materials with high concentrations in the organic solvent. Due to the low boiling point of dichloromethane, and therefore its easy removal, the obtained dispersions can be employed as additives for different composites. We corroborate that the exfoliation efficiency is improved due to the π-π and van der Waals interactions between the PAHs and the layers of the 2D materials.
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Spontaneously exfoliated pristine graphene is used as a surfactant to template the formation of electrically conductive filters for the adsorption of an organic dye from water. In contrast to other reported graphene-based adsorption materials, our system provides a continuous approach to water treatment rather than a batch approach, and uses pristine graphene instead of the more costly and environmentally challenging graphene oxide. The use of self-assembled graphene also results in our filters being electrically conductive, providing a convenient route to clean the filters by resistive heating. An investigation of the mechanism of formation and filtration by these filters, templated by self-assembled two-dimensional pristine graphene, is presented. The thermodynamically driven exfoliation of natural flake graphite at a high-energy monomer/water interface produces water-in-oil emulsions stabilized by a thin layer of overlapping graphene sheets. Subsequent polymerization of the continuous monomer phase produces polymer foams with cells lined by graphene. With a combination of acoustic spectroscopy and electron microscopy, the effects of graphite concentration and temperature are studied, as is the correlation between droplet size and the size of the cells in the final polymer foam.
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The interfacial assembly of graphene oxide (GO) at the water/oil interface was investigated using pendant drop tensiometry as a function of the pH, GO size and concentration, and the molecular weight of the polymer ligands. It was found that the smaller the lateral dimension of GO sheets, the more rapidly the interfacial tension decreased, and the lower was the interfacial tension between oil and water is. The differences in the rates at which the interfacial tension decreased is related to the diffusion of the GO to the interface, the presentation of the GO at the interface, the degree of functionalization relative to the surface area, and the in-plane motion of the GO to accommodate the arrival of more GO at the interface to effectively cover the interface. The solid-like film formed at the interface had a modulus that increased with decreasing lateral GO dimensions.
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As with CNTs, graphene has been studied exhaustively from a theoretical, experimental, and application’s point of view since the renewed impetus for its study following the seminal work of Geim and Novoselov [462]. And as with CNTs, applications studied have spanned a very wide field. The applications below are representative and no means exhaustive: Sensors Energy devices, including batteries Electronics and electrical conductors Displays and transparent films Drug delivery and biomedical Specialized applications Miscellaneous applications
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The outstanding electrical, mechanical and chemical properties of graphene make it attractive for applications in flexible electronics. However, efforts to make transparent conducting films from graphene have been hampered by the lack of efficient methods for the synthesis, transfer and doping of graphene at the scale and quality required for applications. Here, we report the roll-to-roll production and wet-chemical doping of predominantly monolayer 30-inch graphene films grown by chemical vapour deposition onto flexible copper substrates. The films have sheet resistances as low as approximately 125 ohms square(-1) with 97.4% optical transmittance, and exhibit the half-integer quantum Hall effect, indicating their high quality. We further use layer-by-layer stacking to fabricate a doped four-layer film and measure its sheet resistance at values as low as approximately 30 ohms square(-1) at approximately 90% transparency, which is superior to commercial transparent electrodes such as indium tin oxides. Graphene electrodes were incorporated into a fully functional touch-screen panel device capable of withstanding high strain.
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If they could be easily exfoliated, layered materials would become a diverse source of two-dimensional crystals whose properties would be useful in applications ranging from electronics to energy storage. We show that layered compounds such as MoS2, WS2, MoSe2, MoTe2, TaSe2, NbSe2, NiTe2, BN, and Bi2Te3 can be efficiently dispersed in common solvents and can be deposited as individual flakes or formed into films. Electron microscopy strongly suggests that the material is exfoliated into individual layers. By blending this material with suspensions of other nanomaterials or polymer solutions, we can prepare hybrid dispersions or composites, which can be cast into films. We show that WS2 and MoS2 effectively reinforce polymers, whereas WS2/carbon nanotube hybrid films have high conductivity, leading to promising thermoelectric properties.
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The richness of optical and electronic properties of graphene attracts enormous interest. Graphene has high mobility and optical transparency, in addition to flexibility, robustness and environmental stability. So far, the main focus has been on fundamental physics and electronic devices. However, we believe its true potential to be in photonics and optoelectronics, where the combination of its unique optical and electronic properties can be fully exploited, even in the absence of a bandgap, and the linear dispersion of the Dirac electrons enables ultra-wide-band tunability. The rise of graphene in photonics and optoelectronics is shown by several recent results, ranging from solar cells and light emitting devices, to touch screens, photodetectors and ultrafast lasers. Here we review the state of the art in this emerging field.
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The excellent electrical, optical and mechanical properties of graphene have driven the search to find methods for its large-scale production, but established procedures (such as mechanical exfoliation or chemical vapour deposition) are not ideal for the manufacture of processable graphene sheets. An alternative method is the reduction of graphene oxide, a material that shares the same atomically thin structural framework as graphene, but bears oxygen-containing functional groups. Here we use molecular dynamics simulations to study the atomistic structure of progressively reduced graphene oxide. The chemical changes of oxygen-containing functional groups on the annealing of graphene oxide are elucidated and the simulations reveal the formation of highly stable carbonyl and ether groups that hinder its complete reduction to graphene. The calculations are supported by infrared and X-ray photoelectron spectroscopy measurements. Finally, more effective reduction treatments to improve the reduction of graphene oxide are proposed.
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Graphene has been attracting great interest because of its distinctive band structure and physical properties. Today, graphene is limited to small sizes because it is produced mostly by exfoliating graphite. We grew large-area graphene films of the order of centimeters on copper substrates by chemical vapor deposition using methane. The films are predominantly single-layer graphene, with a small percentage (less than 5%) of the area having few layers, and are continuous across copper surface steps and grain boundaries. The low solubility of carbon in copper appears to help make this growth process self-limiting. We also developed graphene film transfer processes to arbitrary substrates, and dual-gated field-effect transistors fabricated on silicon/silicon dioxide substrates showed electron mobilities as high as 4050 square centimeters per volt per second at room temperature.
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Fully exploiting the properties of graphene will require a method for the mass production of this remarkable material. Two main routes are possible: large-scale growth or large-scale exfoliation. Here, we demonstrate graphene dispersions with concentrations up to approximately 0.01 mg ml(-1), produced by dispersion and exfoliation of graphite in organic solvents such as N-methyl-pyrrolidone. This is possible because the energy required to exfoliate graphene is balanced by the solvent-graphene interaction for solvents whose surface energies match that of graphene. We confirm the presence of individual graphene sheets by Raman spectroscopy, transmission electron microscopy and electron diffraction. Our method results in a monolayer yield of approximately 1 wt%, which could potentially be improved to 7-12 wt% with further processing. The absence of defects or oxides is confirmed by X-ray photoelectron, infrared and Raman spectroscopies. We are able to produce semi-transparent conducting films and conducting composites. Solution processing of graphene opens up a range of potential large-area applications, from device and sensor fabrication to liquid-phase chemistry.
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Graphene sheets--one-atom-thick two-dimensional layers of sp2-bonded carbon--are predicted to have a range of unusual properties. Their thermal conductivity and mechanical stiffness may rival the remarkable in-plane values for graphite (approximately 3,000 W m(-1) K(-1) and 1,060 GPa, respectively); their fracture strength should be comparable to that of carbon nanotubes for similar types of defects; and recent studies have shown that individual graphene sheets have extraordinary electronic transport properties. One possible route to harnessing these properties for applications would be to incorporate graphene sheets in a composite material. The manufacturing of such composites requires not only that graphene sheets be produced on a sufficient scale but that they also be incorporated, and homogeneously distributed, into various matrices. Graphite, inexpensive and available in large quantity, unfortunately does not readily exfoliate to yield individual graphene sheets. Here we present a general approach for the preparation of graphene-polymer composites via complete exfoliation of graphite and molecular-level dispersion of individual, chemically modified graphene sheets within polymer hosts. A polystyrene-graphene composite formed by this route exhibits a percolation threshold of approximately 0.1 volume per cent for room-temperature electrical conductivity, the lowest reported value for any carbon-based composite except for those involving carbon nanotubes; at only 1 volume per cent, this composite has a conductivity of approximately 0.1 S m(-1), sufficient for many electrical applications. Our bottom-up chemical approach of tuning the graphene sheet properties provides a path to a broad new class of graphene-based materials and their use in a variety of applications.
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Hey ho, let's GO: Graphene oxide platelets can be self-assembled into highly ordered, mechanically flexible carbon films with tunable porous morphologies. Further nitrogen doping enhanced the electrical properties and supercapacitor performances of the carbon-based assemblies, and provided chemical functionalization.
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The outstanding electrical, mechanical and chemical properties of graphene make it attractive for applications in flexible electronics. However, efforts to make transparent conducting films from graphene have been hampered by the lack of efficient methods for the synthesis, transfer and doping of graphene at the scale and quality required for applications. Here, we report the roll-to-roll production and wet-chemical doping of predominantly monolayer 30-inch graphene films grown by chemical vapour deposition onto flexible copper substrates. The films have sheet resistances as low as approximately 125 ohms square(-1) with 97.4% optical transmittance, and exhibit the half-integer quantum Hall effect, indicating their high quality. We further use layer-by-layer stacking to fabricate a doped four-layer film and measure its sheet resistance at values as low as approximately 30 ohms square(-1) at approximately 90% transparency, which is superior to commercial transparent electrodes such as indium tin oxides. Graphene electrodes were incorporated into a fully functional touch-screen panel device capable of withstanding high strain.
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Graphite oxide sheet, now called graphene oxide (GO), is the product of chemical exfoliation of graphite and has been known for more than a century. GO has been largely viewed as hydrophilic, presumably due to its excellent colloidal stability in water. Here we report that GO is an amphiphile with hydrophilic edges and a more hydrophobic basal plane. GO can act like a surfactant, as measured by its ability to adsorb on interfaces and lower the surface or interfacial tension. Since the degree of ionization of the edge -COOH groups is affected by pH, GO's amphiphilicity can be tuned by pH. In addition, size-dependent amphiphilicity of GO sheets is observed. Since each GO sheet is a single molecule as well as a colloidal particle, the molecule-colloid duality makes it behave like both a molecular and a colloidal surfactant. For example, GO is capable of creating highly stable Pickering emulsions of organic solvents like solid particles. It can also act as a molecular dispersing agent to process insoluble materials such as graphite and carbon nanotubes in water. The ease of its conversion to chemically modified graphene could enable new opportunities in solution processing of functional materials.
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Graphene oxide (GO) is a promising precursor for preparing graphene-based composites and electronics applications. Like graphene, GO is essentially one-atom thick but can be as wide as tens of micrometers, resulting in a unique type of material building block, characterized by two very different length scales. Due to this highly anisotropic structure, the collective material properties are highly dependent on how these sheets are assembled. Therefore, understanding and controlling the assembly behavior of GO has become an important subject of research. In this Research News article the surface activity of GO and how it can be employed to create two-dimensional assemblies over large areas is discussed.
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Using high resolution transmission electron microscopy, we identify the specific atomic scale features in chemically derived graphene monolayers that originate from the oxidation-reduction treatment of graphene. The layers are found to comprise defect-free graphene areas with sizes of a few nanometers interspersed with defect areas dominated by clustered pentagons and heptagons. Interestingly, all carbon atoms in these defective areas are bonded to three neighbors maintaining a planar sp(2)-configuration, which makes them undetectable by spectroscopic techniques. Furthermore, we observe that they introduce significant in-plane distortions and strain in the surrounding lattice.
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Small start-up companies are making large volumes of graphene, the world's thinnest material, for applications such as composites and electrodes.
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Graphene sheets were produced through chemical exfoliation of natural graphite flake and hydrazine conversion. Subsequently, graphene sheets were assembled into a thin film, and microscale liquid droplets were placed onto the film surface for measurement of wettability and contact angle. It is found that a graphene oxide sheet is hydrophilic and a graphene sheet is hydrophobic. Isolated graphene layers seem more difficult to wet in comparison to graphite, and low adhesion work was found in the graphene-liquid interface. Approximation of solid-liquid interfacial energy with the equation of state theory was applied to determine the graphene surface energy. The results indicate that surface energy of graphene and graphene oxide is 46.7 and 62.1 mJ/m2, respectively, while natural graphite flake shows a surface free energy of 54.8 mJ/m2 at room temperature. These results will provide valuable guidance for the design and manufacturing of graphene-based biomaterials, medical instruments, structural composites, electronics, and renewable energy devices.
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Graphene is a wonder material with many superlatives to its name. It is the thinnest known material in the universe and the strongest ever measured. Its charge carriers exhibit giant intrinsic mobility, have zero effective mass, and can travel for micrometers without scattering at room temperature. Graphene can sustain current densities six orders of magnitude higher than that of copper, shows record thermal conductivity and stiffness, is impermeable to gases, and reconciles such conflicting qualities as brittleness and ductility. Electron transport in graphene is described by a Dirac-like equation, which allows the investigation of relativistic quantum phenomena in a benchtop experiment. This review analyzes recent trends in graphene research and applications, and attempts to identify future directions in which the field is likely to develop.
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Problems associated with large-scale pattern growth of graphene constitute one of the main obstacles to using this material in device applications. Recently, macroscopic-scale graphene films were prepared by two-dimensional assembly of graphene sheets chemically derived from graphite crystals and graphene oxides. However, the sheet resistance of these films was found to be much larger than theoretically expected values. Here we report the direct synthesis of large-scale graphene films using chemical vapour deposition on thin nickel layers, and present two different methods of patterning the films and transferring them to arbitrary substrates. The transferred graphene films show very low sheet resistance of approximately 280 Omega per square, with approximately 80 per cent optical transparency. At low temperatures, the monolayers transferred to silicon dioxide substrates show electron mobility greater than 3,700 cm(2) V(-1) s(-1) and exhibit the half-integer quantum Hall effect, implying that the quality of graphene grown by chemical vapour deposition is as high as mechanically cleaved graphene. Employing the outstanding mechanical properties of graphene, we also demonstrate the macroscopic use of these highly conducting and transparent electrodes in flexible, stretchable, foldable electronics.
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The electronic properties of graphene, such as high charge carrier concentrations and mobilities, make it a promising candidate for next-generation nanoelectronic devices. In particular, electrons and holes can undergo ballistic transport on the sub-micrometre scale in graphene and do not suffer from the scale limitations of current MOSFET technologies. However, it is still difficult to produce single-layer samples of graphene and bulk processing has not yet been achieved, despite strenuous efforts to develop a scalable production method. Here, we report a versatile solution-based process for the large-scale production of single-layer chemically converted graphene over the entire area of a silicon/SiO(2) wafer. By dispersing graphite oxide paper in pure hydrazine we were able to remove oxygen functionalities and restore the planar geometry of the single sheets. The chemically converted graphene sheets that were produced have the largest area reported to date (up to 20 x 40 microm), making them far easier to process. Field-effect devices have been fabricated by conventional photolithography, displaying currents that are three orders of magnitude higher than previously reported for chemically produced graphene. The size of these sheets enables a wide range of characterization techniques, including optical microscopy, scanning electron microscopy and atomic force microscopy, to be performed on the same specimen.
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A monolayer of ultrathin sheets of highly hydrophobic graphene nanosheets was prepared on a large area substrate via self-assembly at the liquid-liquid interface. Driven by the minimization of interfacial energy these planar shaped graphene nanosheets produce a close packed monolayer structure at the liquid-liquid interface. This monolayer film shows high electrical conductivity of more than 1000 S/cm and an optical transmission of more than 70% at a wavelength of 550 nm. Interfacial self-assembly of these nanosheets demonstrates a promising route for the application of this novel material in optoelectronics applications.
  • P De Gennes
  • P.-G Brochard-Wyart
  • F Quéré
P. de Gennes, P.-G. Brochard-Wyart, F. Quéré, D. Capillarity and Wetting Phenomena; Springer: New York, 2003.
Two-Dimensional Nanosheets Produced by Liquid Exfoliation of Layered Materials
  • J N Coleman
  • M Latya
  • A O'neill
  • S D Bergin
  • P J King
  • U Khan
  • K Young
  • A Gaucher
  • S De
  • R J Smith
Coleman, J. N.; Latya, M.; O'Neill, A.; Bergin, S. D.; King, P. J.; Khan, U.; Young, K.; Gaucher, A.; De, S.; Smith, R. J.; et al. Two-Dimensional Nanosheets Produced by Liquid Exfoliation of Layered Materials. Science 2011, 331, 568-571.