Dispersion Of Graphene Research Articles

Nonlinear optical limiting effect of graphene dispersions at 3.8 µm

We investigate the nonlinear optical limiting effect of novel graphene dispersions and graphene dispersions in carbon tetrachloride at a wavelength of 3.8 µm. The transmittances of graphene dispersions in carbon tetrachloride under two different concentrations (0.004 and 0.008 mg/mL) and two different solution thicknesses (10 and 20 mm) are measured. The influences of concentration and thickness on the optical limiting effect of graphene dispersion are analyzed. Theoretical analysis of the experimental data shows that the main optical limiting mechanism of the new graphene dispersions is Mie scattering. The limiting capacity coefficient of the new graphene dispersion in carbon tetrachloride reaches 0.405 and the minimum transmittance reaches 0.292 when the concentration is 0.004 mg/mL and the thickness is 20 mm. The graphene dispersions in carbon tetrachloride can be used to achieve good nonlinear optical limiting effects at the wavelength of 3.8 µm.

Investigation of mechanical properties of Al6061 with reinforcement of coconut shell ash and graphene metal matrix composites

In this research paper mainly focused on the fabrication of aluminum metal matrix composite reinforced with coconut shell ash particulates and graphene to enhance the mechanical behaviour of aluminum 6061. The coconut shell ash particulates (CSA) and graphene are reinforced with 6061 aluminum Alloy. The fabrication of aluminum metal matrix composites was prepared by adding 1.0 wt% of graphene and 10 wt% of coconut shell ash particulates in aluminum alloy by using stir casting techniques with a restricted environment. The proper reinforcement on 6061 aluminium Alloy materials plays a very important role in enhancing its mechanical and micro structural properties. The results obtained reveals that the mechanical properties were improved by adding 1.0 wt% of graphene and 10 wt% of coconut shell ash particulates such properties are tensile strength, hardness and yield strength of 6061 aluminum Alloy materials. The Micro structural analysis reveals that the proper dispersion of graphene and coconut shell ash particulates in 6061 aluminum Alloy materials. The enhanced mechanical properties were obtained by addition of 10 wt% of coconut shell ash particulates and 1.0 wt% ofgraphene.

Understanding the thermomechanical behavior of graphene-reinforced conjugated polymer nanocomposites via coarse-grained modeling.

Graphene-reinforced conjugated polymer (CP) nanocomposites are attractive for flexible and electronic devices, but their mechanical properties have been less explored at a fundamental level. Here, we present a predictive multiscale modeling framework for graphene-reinforced poly(3-alkylthiophene) (P3AT) nanocomposites via atomistically informed coarse-grained molecular dynamics simulations to investigate temperature-dependent thermomechanical properties at a molecular level. Our results reveal reduced graphene dispersion with increasing graphene loading. Nanocomposites with shorter P3AT side chains, lower temperatures, and higher graphene content exhibit stronger mechanical responses, which correlates with polymer dynamics. The elastic modulus increases linearly with the graphene content, which slightly deviates from the "Halpin-Tsai" micromechanical model prediction. Local stiffness analysis shows that graphene possesses the highest stiffness, followed by the P3AT backbone and side chains. Deformation-induced stronger chain alignment of the P3AT backbone compared to graphene may further promote conductive behavior. Our findings provide insights into the dynamical heterogeneity of nanocomposites, paving the way for understanding and predicting their thermomechanical properties.

Development and characterization of active starch-based films incorporating graphene/polydopamine/Cu2+ nanocomposite fillers

With increasing environmental awareness and food safety concern worldwide, biodegradable active food packaging gained wide attention in recent years. Starch has been regarded as one of the most potential biomaterials to produce biodegradable films. However, relatively poor functional performance of starch-based films severely limits their application as food packaging materials. Carbon-based fillers can be used to enhance the functional attributes of starch-based films, but they are often difficult to incorporate because of their poor matrix dispersibility. In this study, we developed a simple green method to improve the dispersity of graphene in starch-based films by modifying the graphene surfaces using mussel-inspired polydopamine and copper ions. Spectroscopy and morphology analyses showed the surface of graphene was successfully modified. The addition of the nanocomposites positively influenced the microstructure of the starch-based films, as well as impacting their mechanical, barrier, and thermal properties. Additionally, the composite films exhibited antibacterial activity against food borne pathogens, suggesting promising potential of the films acting as active food packaging. Overall, the method developed in this study has the potential for optimizing and endowing extra properties of starch-based films so as to increase their application in biodegradable food packaging.

Application for Powder Dispersibility and Interface Characterization Using Low-field NMR

The dispersibility and wettability of the powder can be possible to measure by pulse NMR. The characteristic is being able to measure with good reproducibility in a short time without diluting. As a concrete measurement example of dispersibility, we compared with the particle size distribution measurement depending on the dispersion time on low concentration carbon nanotubes. Which was about 0.02%. Next, we compared the graphene dispersion sample from 10% to 50% by pulse-NMR and diluted sample by laser diffraction measurement. In the example of comparing the results in the diluted state have good correlation. However, in the case of different concentrations, there was no correlation. In addition, as a concrete evaluation example of wettability, surface treatment of powder was performed, and the difference in wettability to pure water and hexane were compared. Furthermore, an example was shown in which the wettability to the resin was also compared. Although it only shows simple applications, we think this valuation method has a high potential by the user’s idea.

Study of Molecular-Level Dispersion of Pristine Graphene in Aqueous Media via Polyvinyl Alcohol Coil Physisorption.

Graphene has been widely used as a nanofiller in advanced electronic devices and nanocomposite materials to achieve enhanced electronic, mechanical, and barrier properties. Adequate polymers play the role of the composite matrix and can assist in the liquid-phase exfoliation of pristine graphene without any heavy chemical modification and the detriment of the properties of graphene. This stabilization mechanism is generally attributed to the steric forces formed between the polymer-adsorbed adsorbent. However, the key influence of the polymer concentration on the maximum graphene content in the colloidal solutions is still unclear. In this study, three different molar weights of water-soluble polyvinyl alcohol (PVA) were used for graphene dispersion. The influence of the PVA concentration on the graphene dispersion was systematically studied. Based on Flory's theory, we first proposed a model to describe the polymer adsorption process in the graphene/PVA/water ternary system in the "dilute" regime and simulated the adsorption-free energy changes during this transformation. This model is in good agreement with the experimental results and explains the critical polymer concentration, Cc, allowing the optimization of the graphene/polymer ratio. This fundamental understanding of polymer physisorption on 2D materials provides a simple method for producing nanocomposites with controlled nanosheet/polymer ratios and structures, which are of great interest for energy devices and biomaterials.

Direct Evidence of the Exfoliation Efficiency and Graphene Dispersibility of Green Solvents toward Sustainable Graphene Production.

Achieving a sustainable production of pristine high-quality graphene and other layered materials at a low cost is one of the bottlenecks that needs to be overcome for reaching 2D material applications at a large scale. Liquid phase exfoliation in conjunction with N-methyl-2-pyrrolidone (NMP) is recognized as the most efficient method for both the exfoliation and dispersion of graphene. Unfortunately, NMP is neither sustainable nor suitable for up-scaling production due to its adverse impact on the environment. Here, we show the real potential of green solvents by revealing the independent contributions of their exfoliation efficiency and graphene dispersibility to the graphene yield. By experimentally separating these two factors, we demonstrate that the exfoliation efficiency of a given solvent is independent of its dispersibility. Our studies revealed that isopropanol can be used to exfoliate graphite as efficiently as NMP. Our finding is corroborated by the matching ratio between the polar and dispersive energies of graphite and that of the solvent surface tension. This direct evidence of exfoliation efficiency and dispersibility of solvents paves the way to developing a deeper understanding of the real potential of sustainable graphene manufacturing at a large scale.

Well-dispersed graphene toward robust lubrication via reorganization of sliding interface

Excellent lubrication performance of graphene lubricant is mostly attributed to the dispersion of graphene and forming of tribo-film. Herein, diethylene glycol dodecyl ether (E2C12) functionalized graphene oxide (E2C12-GO) was successfully prepared by simple esterification. The physicochemical properties of as-prepared samples were characterized by a series of characterization methods. E2C12-GO with flat edge and high-level spacing possesses high dispersion stability in PAO 20 base oil. Compared with base oil, 0.08 wt% E2C12-GO could achieve the reduction of average friction coefficient and wear rate by 30 % and 57 % at 150 N, respectively. Even with each long-term friction, E2C12-GO could still maintain the state of robust low friction coefficient. Meanwhile, the addition of E2C12-GO can significantly improve the load-bearing capacity (PB value and PD value) of base oil. The excellent tribological properties of E2C12-GO were attributed to high dispersion and high layer spacing, as well as the reorganization of sliding interface. Prospectively, the E2C12-GO shows promising potential as a multi-functional oil-based lubricating additive in industrial applications.

Electrochemical behaviour of graphene and alumina whisker co-reinforced copper matrix composites

ABSTRACT This study prepared copper (Cu) matrix composites with different graphene contents (0∼1.0 wt-%) and an equal amount of alumina (Al2O3) whisker by vacuum hot pressing sintering. The microstructures of the Cu/C and Cu/Al2O3 interfaces were characterised. The electrochemical corrosion behaviour of the composites was evaluated to study the influence of graphene content on the corrosion performance of the Cu matrix composites. The results showed that incorporating uniformly dispersed graphene with a small amount (∼0.25 wt-%) enables close integration with the Cu matrix, slows down the corrosion rate, and increases the impedance of the composites, thus effectively improving the corrosion resistance of Cu matrix composites. With an increase in graphene content (∼1.0 wt-%), defects tend to generate, leading to the formation of multiple corrosive microcell cavities in the composite, thus accelerating the corrosion of the composite. The Gr/Cu-0.25 composite exhibited better corrosion resistance in acidic, neutral, and alkaline corrosive solutions.

Static and dynamic mechanical thermoanalyses of cement paste with highly dispersed graphene oxide

This study investigated the static mechanical properties of cement pastes with highly dispersed graphene oxide (GO), performed a dynamic mechanical thermoanalysis (DMTA), and studied the microstructure of cement pastes after exposure to high temperatures (105, 200, 300, 450, 600, and 750 °C). First, GO was uniformly dispersed in the cement paste with the aid of polycarboxylate-based superplasticizers. Generally, the incorporation of dispersed GO can enhance the residual compressive strengths of the cement pastes. For pastes with 0.04% GO (by weight) exposed to temperatures of 105, 200, 300, 450, 600, and 750 °C, the strengths are 14.84%, 4.83%, 13.35%, 15.71%, 11.91%, and 64.49% higher than that of pastes without GO, respectively. The DMTA results reveal that cement pastes with 0.04% GO have a high storage modulus and low loss factors in the temperature range of 25–350 °C, which improve their thermal resistance. Moreover, the addition of dispersed GO refines the pore structure and decreases the total porosity at high temperatures by suppressing the coarsening of the pore structure of cement pastes.

High-Performance Corrosion-Resistant Polymer/Graphene Nanomaterials for Biomedical Relevance

Initially, pristine polymers were used to develop corrosion-resistant coatings. Later, the trend shifted to the use of polymeric nanocomposites in anti-corrosion materials. In this regard, graphene has been identified as an important corrosion-resistant nanomaterial. Consequently, polymer/graphene nanocomposites have been applied for erosion protection applications. Among polymers, conducting polymers (polyaniline, polypyrrole, polythiophene, etc.) and nonconducting polymers (epoxy, poly(methyl methacrylate), etc.) have been used as matrices for anticorrosion graphene nanocomposites. The corrosion-resistant polymer/graphene nanocomposites have found several important applications in biomedical fields such as biocompatible materials, biodegradable materials, bioimplants, tissue engineering, and drug delivery. The biomedical performance of the nanomaterials depends on the graphene dispersion and interaction with the polymers and living systems. Future research on the anti-corrosion polymer/graphene nanocomposite is desirable to perceive further advanced applications in the biomedical arenas.

Sulfonated cobalt phthalocyanine-stabilized graphene: Ultrasonic exfoliation and application in anticorrosion of aluminum

Aqueous phase exfoliation (APE) has become a promising method of the graphene preparation. However, it still has some disadvantages, such as low yield and the influence of residual stabilizer on its application. Herein we report a method of the graphene preparation via APE of graphite assisted by sulfonated cobalt phthalocyanine (CoPcS) as the stabilizer. A high yield of graphene can be obtained at low concentration of CoPcS. The yield was 3.2 % in single exploitation, and the total yield reached to 7.3 % after three cycles of exfoliation. The sizes of the prepared graphene sheets were in micron level, and the percentage of few-layer graphene (<5) reached 93 %. The π-π interaction of graphene with CoPcS, as well as the repulsive interaction between negatively charged CoPcS ions, played a crucial role in stabilizing the graphene dispersion. The as-exfoliated graphene powder served directly as a filler in the epoxy coating on the surface of aluminum to improve the protection performance of the coating. A simple, cost-effective, and potential avenue has been provided to product and utilize high-quality graphene materials.

Mechanically Strong and Electrically Conductive Polyethylene Oxide/Few-Layer Graphene/Cellulose Nanofibrils Nanocomposite Films

In this work, a cellulose nanofibrils (CNFs)/few-layer graphene (FLG) hybrid is mechanically stripped from bamboo pulp and expanded graphene (EG) using a grinder. This strategy is scalable and environmentally friendly for high-efficiency exfoliation and dispersion of graphene in an aqueous medium. The in situ-generated CNFs play a key role in this process, acting as a "green" dispersant. Next, the obtained CNFs-FLG is used as a functional filler in a polyoxyethylene (PEO) matrix. When the composition of CNFs-FLG is 50 wt.%, the resultant PEO/CNFs-FLG nanocomposite film exhibits a Young's modulus of 1.8 GPa and a tensile strength of 25.7 MPa, showing 480% and 260% enhancement as compared to those of the pure PEO film, respectively. Remarkably, the incorporation of CNFs-FLG also provides the nanocomposite films with a stunning electrical conductivity (72.6 S/m). These attractive features make PEO/CNFs-FLG nanocomposite films a promising candidate for future electronic devices.

Curcuma longa L. Rhizome Extract as a Poly(vinyl chloride)/Graphene Nanocomposite Green Modifier.

In this work, a method to increase the dispersion of graphene (GN) in the matrix of rigid poly(vinyl chloride) (PVC) by using a natural plant extract from Curcuma longa L. (CE) is proposed. Currently, despite the increasing number of reports on the improvement of GN dispersion in PVC blends, still there is a need to find environmentally friendly and economical dispersion stabilizers. We proposed a stabilizer that can be easily obtained from a plant offering thermal stability and high effectiveness. PVC/GN nanocomposites stabilized with the proposed extract were investigated by SEM, AFM (structure), TGA, and Congo red test (thermal properties). Additionally, static and dynamic mechanical properties and electrical resistivity were measured. The use of CE as a graphene dispersant improved its dispersion in the PVC matrix, influenced tensile properties, increased the storage modulus and glass transition temperature, and extended the thermal stability time of nanocomposites. In this work, a CE extract is proposed as an efficient eco-friendly additive for the production of nanocomposites with an improved homogeneity of a nanofiller in the matrix and promising characteristics.

Fractal structures of PA6/POE blend nanocomposites and their dynamic properties

We investigate the effect of minor phase rheological properties and compatibilizer on the phase morphology and graphene 3D structure in polyamide-6 (PA6)/polyolefin elastomer (POE) blends. It is revealed that in blends containing low viscosity (LV) POE, graphene is better dispersed facilitating its localization at the interface. In the blend containing high viscosity (HV) POE with poor graphene dispersion, large graphene aggregates are observed inside the POE phase with less interfacial coverage. Interestingly, graphene induces a co-continuous morphology and electrical and rheological percolation in both systems, although at a lower graphene content for the LV system. The LV system exhibits a more interconnected morphology, while in the HV system we observe a compact fractal-like POE structure with a lower degree of interconnectivity. Our morphological observation suggests that co-continuous morphology in the LV system is dominated by sheet formation, while in the HV system it is dominated by coalescence between moderately elongated domains. Fractal analysis of the graphene 3D network (based on the rheological characterization) is correlated with the higher degree of connectivity of the graphene 3D structure in the LV system. The 2D fractal dimension of the POE phase (host phase for graphene) is in line with the fractal dimension of the graphene flocs, indicating that the graphene flocs influence the blend morphology. The addition of compatibilizer to the HV system did not result in improved electrical properties.

Shear deformation behavior and failure mechanisms of graphene reinforced Sn-based solder joints bonded by transient current

Graphene as a reinforcement is expected to improve the shear strength of solder joint. However, little is known about the deformation behavior and mechanisms of composite solder joints. In this study, sandwich joints are prepared using graphene nanosheets-reinforced Sn-Ag-Cu composite solder (GNSs/SAC) by transient current bonding technology in order to obtain dispersed graphene. Interrupted shear tests combined with orientation image microscopy are conducted at different strain to observe the morphology and crystal orientation evolution of solder joints in situ. Some twins rotate, and the orientation begins to spread during shear, while the orientation of large Sn grain shows a minimal change. Cracks tend to initiate and propagate along the boundary. The failure mechanisms of the solder joint is determined. Molecular dynamics results show that the strain concentration at the boundary. Continuous shear tests show that the shear strength was improved by approximately 50.7% with the addition of 0.1 wt% graphene. Based on microstructure analysis and calculation, load transfer is identified as the dominant strengthening mechanism for GNSs/SAC alloys, followed by Orowan system. Graphene does not refine the grain size of solder joints, and dislocation multiplication from thermal mismatch does not strengthen them.

Graphene/Polymer Nanocomposites: Preparation, Mechanical Properties, and Application.

Although polymers are very important and vastly used materials, their physical properties are limited. Therefore, they are reinforced with fillers to relieve diverse restrictions and expand their application areas. The exceptional properties of graphene make it an interesting material with huge potential for application in various industries and devices. The interfacial interaction between graphene and the polymer matrix improved the uniform graphene dispersion in the polymer matrix, enhancing the general nanocomposite performance. Therefore, graphene functionalization is essential to enhance the interfacial interaction, maintain excellent properties, and obstruct graphene agglomeration. Many studies have reported that graphene/polymer nanocomposites have exceptional properties that enable diverse applications. The use of graphene/polymer nanocomposites is expected to increase sustainably and to transform from a basic to an advanced material to offer optimum solutions to industry and consumers.

Promising Supercapacitive and Photocatalytic Performances of TiO2 Nanotubes Loaded with Graphene: Insight on the Quantitative Chatacterisation by EIS

In the present work, graphene (Gr) was successfully electrodeposited on TiO2 nanotubes (TiNT) by electrochemical deposition from dispersed graphene. Graphene was produced by electrochemical exfoliation of pure (P) graphite sheet and 5B pencil cores in sulfate-containing electrolytes. The electrochemical capacitance performance of Gr/TiNT electrodes was investigated by galvanostatic charge-discharge, electrochemical impedance spectroscopy and cyclic voltammetry techniques. The results demonstrate that Gr/TiNT electrodes are a promising candidate for supercapacitive applications, as they perform better than TiNT alone. Electrochemical impedance spectroscopy is among the most commonly applied approaches for characterizing electrodes for energy applications. The effects of oxygen functional groups are so evaluated in accordance with the parameters derived from the impedance spectra, with the aim of providing insight into the effects of oxygen functional groups in the energy storage process. Oxygen functional groups lowered the surface conductivity of the materials and hindered ions from reaching the pores, resulting in the decrease of the capacitive performance. Moreover, PGr/TiNT electrode have proven to be much more effective photocatalyst than TiNT alone. PGr/TiNT showed a two-fold increase in photocatalytic efficiency under visible light.

Water-based chitosan/reduced graphene oxide ink for extrusion printing of a disposable amperometric glucose sensor

Recently, developing appropriate printing techniques and conductive inks has received considerable attention in the field of (bio)sensors. Extrusion printing technology is an interesting alternative to conventional screen-printing for making flexible and disposable electronics due to its special features such as, direct printing, easy control of design, and manufacturing processes. Moreover, fabricating highly dispersed and stable graphene inks with appropriate conductivity and printability is always a challenge in (bio)sensors. Here, a water-based chitosan/reduced graphene oxide (CS/rGO) ink was obtained using extrusion printing to make conductive electrodes on paper. CS/GO ratio of 0.2 showed the best stability, electrochemical performance and hydrophilicity (water contact angle of 85° ± 6). The resulting sensor was a simple two-electrode device based on the chronoamperometry technique, representing a good potential for detecting glucose in the linear range of 0.5 to 4 mM and with a limit of detection (LOD) of 0.45 mM (S/N = 3). Furthermore, this non-enzymatic sensor showed proper selectivity against interfering substances, as well as an excellent stability during 28 days (2.9% response fall). Ultimately, the developed conductive ink can be considered as an innovative material with high stability and dispersivity of rGO for the future studies on disposable (bio)sensors and flexible electronics.

Investigation of the corrosion resistance of graphene-nickel composite micro-parts

Nickel-based microparts possess a short lifetime owing to their rapid dissolution in corrosive environments. To mitigate this phenomenon, composite microparts of graphene/Ni were prepared using UV-LIGA technology; their corrosion behavior was examined in acid, alkali, and salt solutions as well as after subjecting them to heat-treatment processes. The microstructures were investigated with scanning electron microscopy (SEM), x-ray diffraction (XRD), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). Corrosion resistances were characterized through various electrochemical tests and compared with those of pure Ni microparts. The results demonstrate that the surface oxidation layer (i.e.,the protective layer) of the microparts was readily destroyed in NaCl and H2SO4 solutions without the formation of a passivation film; however, a passivation film was formed in the NaOH solution. The corrosion rates of graphene/Ni in NaCl, NaOH, and H2SO4 corrosion solutions were reduced by 73%, 22%, and 84%, respectively, relative to those of pure Ni microparts. This can be primarily attributed to the homogeneous dispersion of graphene in the Ni matrix, which refined the grain size, and the impermeability and chemical stability of graphene, which lengthened the diffusion path of the corrosive medium. In addition, heat treatment of the graphene/Ni microparts at 200 °C increased the corrosion resistance by a factor of nearly one with little change in microhardness, which can be attributed to the removal of internal stress and the increased proportion of CSL grain boundares. Corrosion occurred at the interface between nickel and graphene, lengthening the corrosion path.