Surface Of Graphene Nanoplatelets Research Articles

Nacre-like GNP/Epoxy composites: Reinforcement efficiency vis-à-vis graphene content

Nanocomposites based on the biomimetic brick and mortar architecture are gathering great attention recently due to the outstanding properties of the natural analogues. Thanks to the very high in-plane orientation of nanoplatelets and the low matrix content, these materials exhibit good mechanical performance combined with excellent functional properties based on the nanoplatelets characteristics. Key feature of these materials is the presence of a regular nanostructure that consists of alternated nanoplatelet and matrix layers. Such architecture is commonly attained by means of bottom-up manufacturing processes able to control the alternation of the two phases at the nanoscale. This differs markedly from the top-down manufacturing processes, which are suitable for an industrial scale up but fail to meet the expected requirements. In the present work, nacre-like graphene nanoplatelets (GNPs)/epoxy films at different filler content have been prepared by a top-down manufacturing technology and their mechanical properties in tension have been experimentally evaluated. The elastic modulus has been found to exhibit a maximum between 53 and 67 vol% filler content and then it starts dropping at higher loadings. This was attributed to the depletion of the polymeric matrix which disrupts the continuity of the matrix layer thus inducing incomplete GNP surface coverage. As a result, the effective area for stress-transfer is considerably reduced and this impairs the reinforcement efficiency. In order to explain this behaviour, a model is proposed for predicting the stress transfer characteristics in brick and mortar systems by paying attention to possible non-uniform matrix distribution over the nanoplatelets. The proposed analysis captures well the observed effects and paves the way for the development and further improvement of this new class of engineering materials.

Graphene-mediated electrospray cooling for discrete heat sources in microslits

Efficient and targeted cooling of small discrete heat sources located in a confined gap, such as a microslit, is challenging. In this study, we demonstrate by using electrospray technique, the charged droplets can be effectively transported within a microslit – consisting of a top substrate and a bottom substrate – and subsequently deposited on the heated spots located within it; up to approximately 28% cooling enhancement can be obtained, and, increases to approximately 67% cooling enhancement when the surface of the heated electrode (representing a heated spot) is coated with graphene nanoplatelets (GNPs), which can be attributed to the fast water permeation. Specifically, two heated electrodes are located within the microslit – one on the top substrate (top electrode) and one on the bottom substrate (bottom electrode) – and induced convection within the microslit. We observe that majority of the charged droplets are dragged by the convection and deposited mostly on the top heated electrode, indicating that near the heated electrodes, drag force exerted on the charged droplets is significant. Interestingly, by applying the GNPs coating only on one heated electrode, for the positively charged droplets, we observe a reduction in the cooling enhancement when the top electrode is coated with GNPs. This can be attributed to the positively charged GNPs surface repels the positively charged droplets. On the other hand, for negatively charged droplets, we observe a reduction in cooling enhancement when the bottom electrode is coated with GNPs. This can be attributed to the positively charged GNPs surface attracts the negatively charged droplets. These findings are crucial for the design of an effective cooling system, particularly for the targeted cooling of small heat sources within microslit.

The effect of polymeric surfactant content on the mechanical properties of Al/GNP nanocomposites

Graphene nanoplatelets (GNPs) are ideal reinforcements for improving the mechanical properties of aluminum-based matrices due to their outstanding properties. However, it essentially depends on their uniform dispersion in the matrix. In this study, the challenge of uniform dispersion of graphene was performed by functionalizing the non-covalent surface and sonication of GNPs applying non-ionic polymeric ethyl cellulose (EC) surfactant, in which a colloidal mixture was provided with Al powder and graphene, followed by sintering at 620 °C and consolidation. The density and mechanical properties of nanocomposite specimens were investigated and compared with a non-surfactant-assisted Al/GNP nanocomposite. The results showed that GNPs/Al specimen prepared by 1.5% (wt/vol) of surfactant and 0.5 wt% GNPs showed the highest hardness and reduced wear rate compared to non-surfactant-assisted Al/GNPs sample. Besides, the GNPs content was investigated and the optimum amount was found to be 0.5 wt%.

Influence of graphene content and nickel decoration on the microstructural and mechanical characteristics of the Cu/Sn–Ag–Cu/Cu soldered joint

In this research article, lead-free nanocomposite soldering is assessed by using the eutectic composition of Sn-3.5Ag-0.7Cu (SAC, wt%) solder alloy as the matrix and graphene nanoplatelets (GNPs) as the reinforcing agent. Powders of these materials are mixed in a mechanical milling system, then compacted, and sintered before application. The effects of GNPs content with different amounts of 0.05, 0.1, and 0.2wt% are examined to prepare nanocomposite solders as compared to the SAC solder alloy. Furthermore, to improve the metallurgical compatibility between the graphene and SAC solder matrix, the surface of GNPs was decorated by nickel particles using electroless plating techniques before incorporation. After that, the solderability of these prepared lead-free nanocomposite solders is investigated on the copper substrate. As the main result, the formation of the intermetallic compound (IMC) layers at the interface between the Cu-substrate and solder material was found very determinative to control the mechanical performance of soldered joints during lap-shear testing. The content of GNPs and Ni-coating modification strongly affected the morphology and growth of IMC layers at the interface. By increasing the amount of GNPs up to ∼0.2wt% and using Ni-coating, the growth of IMC layers was considerably suppressed, leading to a significant improvement of the joint strength up to ∼27%, despite a reduction of ∼50% of the ductility. Furthermore, isothermal aging at 150°C up to 100h resulted in a remarkable increase in the shear strength (∼45%) and elongation to failure (∼19.9%) through controlling the growth of the IMC layers at the interface.

Congo Red Dye Degradation by Graphene Nanoplatelets/Doped Bismuth Ferrite Nanoparticle Hybrid Catalysts under Dark and Light Conditions

The continuously growing need for clean water has increased research looking for new and efficient ways to treat wastewater. Due to its magnetic properties, Bismuth ferrite, a photo-catalyst, has introduced a novel field of photo-catalysis where the photo-catalytic material could easily be separated from the aqueous solution after wastewater treatment. Herein, a new type of photo-catalysts, composed of Gadolinium (Gd) and Tin (Sn), co-doped Bismuth Ferrite deposited over graphene nanoplatelet surface have been synthesized using a two-step method. In first step, Gd (fixed concentration 10%) and Sn (5%, 15%, 20% and 25%) were doped inside bismuth ferrite (BFO) host using sol-gel method (namely the BGFSO nanoparticles, abbreviated for Gd and Sn doped BFO). In the second step, BGFSO nanoparticles were introduced onto GNPs using co-precipitation method (namely the BGFSO/GNP nanohybrids). The x-ray photoelectron spectroscopy confirmed the chemical bonding between co-doped BFO and GNP sheets via oxy and hydroxyl groups. The photocatalytic activities of the nanohybrids under both, visible light and dark conditions have been increased, and the maximum degradation activity (74%) of organic dye Congo-red (CR) is obtained for 25% Sn-doped BGFSO/GNP nanohybrid. The photocatalytic activity may be attributed to enhanced adsorption capability, electron storage properties of graphene and the presence of oxygen-rich species inside nanohybrids. Based on the current overgrowing population and need for clean water, these materials present versatile potential as catalysts for wastewater treatment.

Calculations of factors that affect thermal conductivity in epoxy composites with hybrid carbon nanotube and graphene nano platelet

Carbon Nanotubes (CNTs) and Graphene Nano Platelets (GNPs) had been used to enhance the thermal conductivity of the epoxy composites and show a synergistic effect. Complex service conditions also put forward the requirements for the structural design of the composites to get better performance. Researches should be done to further understand the mechanism of enhancement in composites and find ways to assist the design and optimization of the structure. In this research, epoxy composites with CNTs, GNPs and hybrid CNTs-GNPs (5:2) were prepared, whose total content of fillers was kept constant at 0.4 vol%. Test of specific surface area shew the hybrid fillers had less aggregation and the composites with hybrid fillers had the highest thermal conductivity. Observing the microstructure of the composites, CNTs were absorbed on the surface of GNPs, forming a cross-network which could improve aggregation and provide channels for the heat. A series of finite element models were established using scripts to find the factors that affect the forming of network and heat flow. A parameter was created to reflect the distribution of the fillers: distance of non-network(DNN). Positions, orientations, ratios, shapes, and sizes are all factors. The effect of angles depends on the relative positions of the fillers. A proper bending degree of CNTs would have better enhancement. The vertical-structure network was created manually and heat flux on the network was shown: GNPs expanded the area of network for the acceptance and release of heat. CNTs provide efficient channels for the multidirectional heat flow. The combination of the geometry expanded the influence region of the network.

Titanium carbide coating on graphene nanoplatelets

Titanium carbide was formed on graphene nanoplatelets (GNPs) using potassium hexa-fluorotitanate (K2TiF6) salt in the presence of pure aluminium. K2TiF6 - GNPs mixture with titanium to carbon ratio of 5:1 was heated at a high temperature of 900 °C for 1 h under argon atmosphere. Energy dispersive spectroscopy indicated the presence of elemental titanium on the surface of GNPs, while the presence of titanium carbide was verified by X-ray diffraction. Scanning electron microscopy confirmed the morphology of titanium carbide-coated nanoplatelets embedded in aluminium melt. Thermal characterisation was carried out by differential scanning calorimetry to identify the reaction kinetics and products of the reactions. This facile process to coat titanium carbide on GNPs offers a possibility to reduce the wettability issues of GNPs in the aluminium matrix and enhance the dispersion with an opportunity to prepare hybrid aluminium matrix composites. The present study deals with in-situ synthesis of titanium carbide on GNPs, which aims to prepare nano-reinforced hybrid reinforcement aluminium matrix composite.

High-performance epoxy-based adhesives modified with functionalized graphene nanoplatelets and triblock copolymers

In this study, a high-performance epoxy-based adhesive was developed by adding graphene nanoplatelets (GNPs) and phase-separated triblock copolymers (BCPs) to enhance the lap shear strength of the adhesive joints. The GNPs were functionalized using an ultrasonicated ozonolysis (USO) method so as to achieve a homogeneous and stable dispersion in the epoxy matrix. The USO treated GNPs (OZ-GNPs) were incorporated into epoxy resin at different weight fractions using a 3-roll mill technique. Both poly(methyl methacrylate)-poly(butyl acrylate)-poly(methyl methacrylate) (MAM) and poly(styrene)-poly(butadiene)-poly(methyl methacrylate) (SBM) BCPs were mixed separately as toughening agents. Single lap shear joints were prepared by bonding aluminium sheets using the developed adhesives to study the lap shear strength of the joints. A significant improvement in the lap shear strength was observed for the hybrid epoxy system with GNPs and BCP. Adding 1.0 wt% OZ-GNPs into 10 wt% SBM modified epoxy adhesive resulted in the lap shear strength increase by 129%, compared to that of the unmodified epoxy. Raman spectroscopy and scanning electron microscope (SEM) studies found that the USO treatment facilitated the stable dispersions and improved epoxy bonding due to the oxygen functional groups introduced onto the GNP surfaces. Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and thermogravimetric analyzer (TGA) studies showed that the GNPs and BCPs were well bonded with epoxy resin without compromising the thermal stability. To better understand the influence of GNPs and BCPs on the lap shear strength, the fracture surfaces of the joints were studied using SEM. The fracture images showed that the BCPs formed different nanostructures in the epoxy matrix and the resulting nanostructures activated different toughening mechanisms that were responsible for the improvement in the lap shear strength, while the OZ-GNPs increased the joint strength by stiffening the matrix.

Graphene Nanoplatelets-Based Aptamer Biochip for the Detection of Lipocalin-2

An electrochemical label-free aptasensor platform was developed by using amine-functionalized aptamer that was incorporated onto screen-printed carbon electrode (SPCE) modified with graphene nanoplatelets (GNPs) for the detection of lipocalin-2 (LCN-2) protein. The aptamers were covalently bound to the GNPs surface via 1-Ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) and $N$ -hydroxysuccinimide (NHS) chemistry and were used as the molecular recognition element for the target protein. Successful interaction between aptamer and LCN-2 protein was ascertained via electrochemical probe, ferro-, and ferri-cyanide {Fe(CN)63−/4−} and monitored by means of square wave voltammetry (SWV) whilst layer-by-layer fabrication study was done using cyclic voltammetry (CV). The developed LCN-2 aptasensor achieved sub-picomolar detection of the protein, with the detection limit determined as 0.07 pg ml−1, and a dynamic linear range of 0.1 to 10 pg ml−1. Fabricated aptasensor successfully demonstrated high selectivity, stability, and reproducibility as well as displaying potential for the in vitro detection of LCN-2 in real serum samples.

Alignment of polymer based magnetic composites in magnetic field

Composite films made of graphene nanoplatelets (GNP) and magnetite Fe3O4 nanoparticles have been prepared with and without magnetic field. Poly(3,4-ethylenedioxythiophene):polystyrenesulfonic acid (PEDOT:PSS) was used as a stabilizing polymer matrix. Film morphology was found to depend strongly on the presence of magnetic field, i.e. more porous structure of GNP- Fe3O4 is formed in magnetic field. Thin films formed without magnetic field have activation character of conductivity, while thin films formed in magnetic field have metallic conductivity. Thus, the magnetic field acting during film formation in these composites results in semiconductor-metal transition. DFT calculations show that at low distance between GNP surface and nanoparticle strong interaction between them can be observed.

Multiscale modeling of carbon fiber- graphene nanoplatelet-epoxy hybrid composites using a reactive force field

Numerous research efforts have been focused on developing lightweight epoxy-based composite materials that rival expensive metal alloys in aerospace structural components. Due to their high specific stiffness and strength, carbon fiber (CF)/graphene nanoplatelet (GNP)/epoxy hybrid composites are excellent candidates for this purpose. The objective of this study is to develop a multiscale modeling approach to predict the effective mechanical properties of a CF/GNP/epoxy composite material. The work-flow of this study involves molecular dynamics (MD) simulation with a reactive force field to predict the structure and behavior of the GNP/epoxy material at the molecular level and micromechanics to predict the mechanical properties of the CF/GNP/epoxy hybrid composite at the bulk level. The study provides evidence of an alignment behavior of phenyl rings in epoxy with the planar GNP surface at the interphase region. The results also indicate the validity of using a reactive force field as they compare well with experiment.

Surface Decoration and Dispersibility of Graphene Nanoplatelets in Aqueous Surfactant Solution

Preparing highly homogeneous and stable aqueous graphene nanoplatelets (GNPs) suspension plays a significant role in practical applications. To achieve good dispersion for the GNPs, a method utilizing ultrasonic processing and dispersants was employed. In this study, four dispersants, including gum arabic (GA), polyvinylpyrrolidone (PVP), polyoxyethylene (40) nonylphenylether (Igepal, CO890) and cetyltrimethyl ammonium bromide (CTAB), were used individually and in combination at given concentrations for dispersing the GNPs in aqueous solution. The dispersing performance for GNPs suspension was characterized by standing test and UV-vis absorbance. The maximum achievable dispersing status for GNPs in aqueous solution was demonstrated by optical microscope and transmission electron microscopy (TEM) from both macro and micro aspects. Some experimental results demonstrated that the best dispersion was achieved with CTAB addition of 0.3 g/L, meaning that the optimum concentration ratio of GNPs to CTAB was 1:3. In addition, the dispersing mechanism was also assessed using Fourier transform Infrared (FTIR) spectroscopy. The CTAB molecules were adsorbed on the surface of GNPs, which prevented aggregation of GNPs by electrostatic repulsion.

Transmittance and Reflectance Effects during Thermal Diffusivity Measurements of GNP Samples with the Flash Method.

Thermal diffusivity of GNPs (graphene nano-platelets) is an important thermo-physical property as it is useful to predict the material behavior in many heat transfer applications. GNP samples were pressed at different loads to obtain different densities, and then thermal diffusivity was measured with the flash method. All samples were coated with a thin layer (~1 µm) of colloidal graphite (Aquadag®) on both sides to reduce reflectance of their surfaces and consequently increase the emissivity. Carrying out measurements on both samples with and without coating, a difference between the two series of measurements was found: This is attributed to a non-negligible transmittance of the uncoated samples due to the porosity of GNPs. Furthermore, assuming a spatial distribution of the light within the samples according to the Lambert-Bougert-Beer law, the extinction coefficient of GNP at different densities has been evaluated processing experimental data with a nonlinear least square regression, (NL-LSF, nonlinear least square fitting), whose model contains the extinction coefficient as unknown. The proposed method represents a further improvement of thermal diffusivity data processing, crucial to calculate the extinction coefficient when data with and without coating are available; or to correct biased thermal diffusivity data when the extinction coefficient is already known. Moreover, reflectance effects have been highlighted comparing asymptotic temperature reached during the tests on coated and uncoated samples at different densities. In fact, the decrease of asymptotic temperature of the uncoated samples gives the percentage of the light reflected and consequently an estimate of the reflectance of the GNP surface.

Nucleate pool boiling enhancement by ultrafast water permeation in graphene-nanostructure

Nucleate boiling efficiency can be significantly enhanced using the nanostructured graphene surface. The wettability of the graphene nanoplatelets (GNPs) coated surface is tunable using thermal curing process. The uncured GNPs surface is hydrophobic in nature while the cured GNPs surface manifests a hydrophilic characteristic and the latter performs better than the former in the nucleate boiling regime. Ultimately the ultrafast water permeation property of the cured GNPs enhances the efficiency of nucleate pool boiling, leading to a maximum enhancement of 151% in the boiling heat transfer coefficient and 154% in the vapor mass flow rate. The boiling performance of the uncured GNPs surface is also enhanced despite its hydrophobicity. Hence, the enhancement in boiling is not solely attributed to the surface wettability. The enhancement is attributed to the fascinating ultrafast water permeation property of graphene on top of its nanoporous structure. The unimpeded fast water transport within the nanochannel-network of GNPs facilitates the fast absorption of latent heat of vaporization by the water molecules, leading to a substantial increase in the nucleation, growth and departure of vapor bubbles. We propose a new explanation on the role of graphene coating on nucleate pool boiling enhancement. This study provides important insights into the effects of ultrafast water permeation property of graphene on the nucleate boiling heat transfer.

Tribological Behavior of Solid-State Processed Al-1100/GNP Surface Nanocomposites

Graphene nanoplatelets (GNPs) were infused onto aluminum alloy (Al-1100) surface by a solid-state processing technique to form surface nanocomposites which enrich the mechanical and tribological properties of the aluminum (Al) surface. Electrical resistance heating which locally softens the Al surface, followed by hot pressing, mechanically impregnates and embeds GNPs onto the Al substrate. It was observed that the GNPs mainly occupy the grain boundaries in the matrix during subsequent solidification which leads to strengthening of the matrix through various mechanisms. A detailed tribological study was carried out, and it was found that the wear rate and coefficient of friction decreases by > 85%. Least wear depth in nanoscratch testing was obtained at processing parameters 2200 A and 0.5 s, which could be identified as the optimum current/time combination. The microhardness and Young’s modulus results also show an improvement > 200%, corroborating the tribological studies.

Studies on the secondary modification of SBS modified asphalt by the application of octadecyl amine grafted graphene nanoplatelets as modifier

Modified asphalt prepared via graphene nanoplatelets (GNPs) incorporation to styrene-butadiene-styrene (SBS) possesses enhanced high temperature performance and mechanical properties but the approach suffers from poor compatibility of the components. In this study, octadecyl amine (ODA) was grafted onto the surface of GNPs resulting in ODA-GNPs composite via covalent bonding method. GNPs and ODA-GNPs composites were applied as modifiers to SBS for modified asphalt preparation. Specific amount of ODA-GNPs incorporation improved ductility, softening point and penetration while DSR, MSCR and segregation experiment showed enhancement in viscoelastic, high temperature rutting resistance performance and compatibility of the SBS modified asphalt. Textural characterization of asphalt samples using FT-IR, XRD, SEM and AFM revealed the successful grafting of ODA onto GNPs surface resulting in increased interplanar spacing of GNPs. ODA grafted onto the surface of GNPs enhanced its lipophilicity in asphalt, leading to better particles dispersion. The present methodology using ODA-GNPs composite for the preparation of modified asphalt with enhanced mechanical properties, temperature resistance and viscosity, can be deemed as an efficient approach on industrial level applications.

Graphene-Based Materials for the Fast Removal of Cytokines from Blood Plasma.

There is a range of medical conditions, which include acute organ failure, bacterial and viral infection, and sepsis, that result in overactivation of the inflammatory response of the organism and release of proinflammatory cytokines into the bloodstream. Fast removal of these cytokines from blood circulation could offer a potentially efficient treatment of such conditions. This study aims at the development and assessment of novel biocompatible graphene-based adsorbents for blood purification from proinflammatory cytokines. These graphene-based materials were chosen on the basis of their surface accessibility for small molecules further facilitated by the interlayer porosity, which is comparable to the size of the cytokine molecules to be adsorbed. Our preliminary results show that graphene nanoplatelets (GnP) exhibit high adsorption capacity, but they cannot be used in direct contact with blood due to the risk of small carbon particle release into the bloodstream. Granulation of GnP using poly(tetrafluoroethylene) as a binder eliminated an undesirable nanoparticle release without affecting the GnP surface accessibility for the cytokine molecules. The efficiency of proinflammatory cytokine removal was shown using a specially designed flow-through system. So far, GnP proved to be among the fastest acting and most efficient sorbents for cytokine removal identified to date, outperforming porous activated carbons and porous polymers.

Enhancement of thermal conductivity of Ba(OH)2 · 8H2O phase change material by graphene nanoplatelets

Ba(OH)2 · 8H2O /graphene nanoplatelets composite phase change materials were prepared in this paper. It can be found that Ba(OH)2 · 8H2O is able to be dispersed evenly on the surface of graphene nanoplatelets by scanning electron microscope. Further, relevant tests showed that the thermal conductivity of composite phase change materials can be improved by graphene nanoplatelets. The thermal conductivity growth rate of the composite phase change material with 1.5 wt% graphene nanoplatelets is the largest, which is 51.36%. The melting and solidification thermal cycling tests of composite phase change materials with graphene nanoplatelets showed that the supercooling degree and the heat storage time of Ba(OH)2 · 8H2O can be effectively reduced. According to the DSC tests, the melting point and the phase change enthalpy of Ba(OH)2 · 8H2O composite phase change materials are almost invariable after the graphene nanoplatelets is added. The excellent heat storage property is also maintained.

Graphene Nanoplatelet and Reduced Graphene Oxide Functionalized by Ionic Liquid for CO2 Capture

An ionic liquid (IL) [P66614][Triz] with a low regeneration temperature was loaded on a graphene nanoplatelet (GNP) and reduced graphene oxide (RGO) to accelerate the CO2 absorption rate. High-resolution transmission electron microscopy (HRTEM) patterns showed that GNP was composed of a regular “honeycomb” lattice, but a regular lattice structure was not observed for RGO as a result of the functional group on it. The CO2 absorption capacity (63.6 mg of CO2/g of IL) and absorption peak rate (22.4 mg of CO2 g–1 of IL min–1) of IL loaded on GNP were increased by 8.2 and 72.3%, respectively, compared to those of neat IL. The supported IL performed better because [P66614][Triz] was oriented in a favorable dispersion as a result of the negative ζ potential of the GNP surface. In contrast, the CO2 absorption rate of RGO–20% IL (mass ratio of RGO/IL = 4:1) was lower than that of IL, which could be attributed to the hydrogen bond between surface oxygen functional groups and IL. 13C nuclear magnetic resonance and M...

STUDY ON SYNTHESIS OF MnFe2O4/GNPs COMPOSITE AND APPLICATION ON HEAVY METAL REMOVAL

Nowadays, composite materials between mixed-metal oxides and graphene are widely studied due to their multiple applications on different fields. MnFe2O4 is a magnetic material which has the ability to absorb toxic heavy metal in water. Graphene nanoplatelets (GNPs) with about 10 layers, is one of type of graphene. GNPs was used as matrix for the fine distribution of metal oxide nanoparticles. Surface area for the absorption process can be increased. Composite was synthesized using solvothermal method, in which mixed-metal oxide nanoparticles were directly formed in-situ from precursor salts onto GNPs surface. Synthesized material was analyzed using XRD, SEM and EDX methods to determine its properties. Heavy metal absorption capacity was also studied and showed good results.