Dispersion Of Graphene Sheets Research Articles

Graphene for flame-retarding elastomeric composite foams having strong interface

It is a great challenge to make elastomeric polymer foams antistatic, flame-retardant and mechanically robust. The challenge was addressed herein by in situ polymerizing polyvinyl alcohol, formaldehyde and graphene sheets. The graphene sheets – each in average being ∼5nm thick – had a carbon to oxygen atomic ratio of 9.8 and a Raman ID/IG of 0.03. The sheets proved to react with formaldehyde building up a strong interface for the composites, and the reaction promoted the exfoliation and dispersion of graphene sheets in the matrix. They were found to create a large number of fine pores to the composites. Graphene sheets at 0.12vol% increased the foam water retention rate from 346% to 784%. These composites had a percolation threshold of electrical conductivity at 0.023vol%. The composites reached a limiting oxygen index of 59.4, implying an exceptional self-extinguishing performance.

In situ preparation of graphene‐ZnO composites for enhanced graphite exfoliation and graphene‐nylon‐6 composite films

ABSTRACTAn effective method for the fabrication of graphene‐ZnO nanoparticle (GZN) composites has been developed. GZN composites with high electrical conductivity (18,607 S/m) are prepared in situ from graphite‐ZnO composites. The GZN composites also exhibit visible‐light absorption and enable the effective exfoliation of graphite. The presence of the ZnO nanoparticles assists the exfoliation of graphite and enables the preparation of solutions of highly dispersed and concentrated graphene sheets (2.7 mg/mL) that exhibit high electrical conductivity without reduction (40,404 S/m). A solution of graphene sheets was used to produce a graphene‐nylon‐6 film with an excellent Young's modulus (3 GPa) and a high tensile strength (109 MPa). An exclusive mechanism was proposed for the improvement of mechanical properties of the nylon‐6 composite film. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45034.

Mechanical Properties of Aluminium-Graphene Composite Synthesized by Powder Metallurgy and Hot Extrusion

The present work focuses on the development of multilayer graphene reinforced aluminium metal matrix composites by powder metallurgy followed by hot extrusion. Microstructure, grain size analysis and mechanical properties of hot extruded unreinforced aluminium and graphene reinforced aluminium composites are presented here. Microstructure shows uniform distribution of graphene throughout the matrix. Experimental results reveal significant increase in hardness as well as tensile strength of composite as compared to unreinforced aluminium. The improvements in properties are attributed to uniformly dispersed graphene sheets, an excellent interfacial bonding between graphene and aluminium matrix and grain refinement caused by the addition of graphene. Further, the strengthening mechanisms involved in the aluminum-graphene composite have been discussed. The fracture studies show the transition of ductile fracture in case of pure aluminium to brittle fracture in case of aluminium-graphene composites.

Facile synthesis of graphene sheets decorated nanoparticles and flammability of their polymer nanocomposites

Novel and facile method was developed for the synthesis of graphene based flame retardant for acrylonitrile-butadiene-styrene. Graphene has been exfoliated by using ultrasonication in maleate diphosphate as dispersant. The exfoliation media produced high quality less defected graphene layers. The graphene wrapped with maleate diphosphate was decorated with TiO2 nanoparticles with an average size of 21 nm. Polymer composites of acrylonitrile-butadiene-styrene with maleate diphosphate, graphene wrapped with maleate diphosphate and decorated ones have been synthesized with solvent blending method. The flammability properties of the polymer nanocomposites were significantly reduced. The peak heat release rate (PHRR) and total heat release (THR) of the polymer nanocomposites contains nanoparticles decorated graphene achieved 49% reduction. Also, average mass loss rate was reduced by 50% and emission of carbon dioxide was suppressed by 37%. The rate of burning of nanocomposites was found to be 12 mm/min compared to virgin polymer of 42.5 mm/min achieved 71% reduction. The effect of combining graphene and the materials was investigated. The graphene wrapped with maleate diphosphate and maleate diphosphates itself were characterized using FTIR spectroscopy. The different polymer nanocomposite materials were characterized using thermal gravimetric analysis, UL94 flame chamber and cone calorimeter. The exfoliation of graphene was elucidated by Raman spectroscopy and XRD and the dispersion of graphene sheets in maleate diphosphate and their decorated composites with nanoparticle were characterized using transmission electron microscopy.

Silane functionalization of graphene oxide and its use as a reinforcement in bismaleimide composites

Silane-functionalized graphene oxide (GO) nanosheets were synthesized by chemically grafting γ-methacryloxypropyltrimethoxysilane (MPTS) onto GO sheets. The resulting MPTS-functionalized GO (MPTS-GO) nanosheets were characterized by Fourier transform infrared spectroscopy, energy dispersive X-ray analysis, X-ray photoelectron spectra, X-ray diffraction, and Raman spectroscopy. Bismaleimide (BMI) composites filled with GO and MPTS-GO were prepared at different filler loading levels. The study showed that the exfoliation and dispersion of graphene sheets in BMI resin were significantly improved due to the surface functionalization effect. The tensile test indicated that the MPTS-GO/BMI nanocomposites showed higher tensile strength and modulus than the neat BMI resin and GO/BMI composites. Meanwhile, the impact strength of composites was also improved. The maximum increment of the tensile strength, tensile modulus, and impact strength of MPTS-GO/BMI nanocomposites were 22.17, 33.05, and 66.64 %, respectively. The fracture surface analysis revealed that the highly dispersed MPTS-GO nanosheets could trigger large-scale plastic deformation of resin matrix.

Understanding the Stabilization of Single-Walled Carbon Nanotubes and Graphene in Ionic Surfactant Aqueous Solutions: Large-Scale Coarse-Grained Molecular Dynamics Simulation-Assisted DLVO Theory

Understanding the dispersion of single-walled carbon nanotubes (SWCNTs) and graphene in surfactant aqueous solutions is essential for processing of these materials. Herein, we develop the first theoretical framework, which combines large-scale coarse-grained (CG) molecular dynamics (MD) simulations with the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory and Langmuir isotherm, to inform the mechanisms of surfactant adsorption and induced colloidal stability. By carrying out large-scale CG-MD simulations (∼1 million CPU h), we successfully calculated the surface coverage of the widely used ionic surfactant sodium cholate (SC) on different carbon nanomaterials at experimentally realistic SC concentrations. This was accomplished by simultaneously simulating SC micellization and adsorption in one simulation box. Our theoretical framework further allows us to quantify the surface electric potential and the potential energy barrier height that maintains colloidal stability of dispersed SWCNTs or graphene sheets ...

Water Dispersible Graphene Sheets Produced from Unassembled Graphene–Polyaniline Nanohybrids

We present an efficient process for producing water dispersible graphene sheets from unassembled graphene–polyaniline nanohybrids. The result of atomic force microscopy reveals that over 80% of thus-prepared graphitic sheets are single layers with typical thickness of approximately 0.8 nm. The proportion of modifying molecules in the product is found to be as low as 3.0 wt.%, as determined by elemental analysis. Along with its fascinating water dispersibility and remarkably high electrical conductivity, such material is anticipated to be very promising for use in graphene-based nanoelectronics and high-performance composites.

An effective non-covalent grafting approach to functionalize individually dispersed reduced graphene oxide sheets with high grafting density, solubility and electrical conductivity.

Polymer-functionalized reduced graphene oxide (polymer-FG), produced as individually dispersed graphene sheets, offers new possibilities for the production of nanomaterials that are useful for a broad range of potential applications. Although non-covalent functionalization has produced graphene with good dispersibility and a relatively complete conjugated network, there are few reports related to the effective functionalization of reduced graphene oxide (RGO) using a simple, general method. Herein, we report a facile and effective approach for the preparation of polymer-FG from a non-covalently functionalized pyrene-terminal polymer in benzoyl alcohol (BnOH). This aromatic alcohol (BnOH) was used as the liquid medium for the dispersion of graphene oxide (GO) with a pyrene-terminal polymer, and as an effective reductant; this makes the synthesis procedure convenient and the production of polymer-FG easily scalable because the conversion of GO to RGO and the non-covalent functionalization proceed simultaneously. The resulting polymer-FG sheets show organo-dispersibility, high electrical conductivity and good processability, and have a similar grafting density comparable to covalently made materials, thus making them promising candidates for applications such as electrochemical devices, nanomaterials and polymer nanocomposites. Hence, this work provides a general methodology for preparing individually dispersed graphene sheets with desirable properties.

Highly conductive and dispersible graphene and its application in P3HT-based solar cells.

A simple reduction method without the need for high-temperature annealing is proposed for highly conductive and dispersible graphene sheets. This method consists of the grafting of graphene oxide (GO) with 1-pyrenecarboxylic acid (PCA) and the exothermic reduction of the PCA-grafted GO, followed by an endothermic decarboxylation with refluxing hot water. The PCA-grafted reduced graphene oxide (PCA-rGO) has a high conductivity of ~1.52 × 10(5) S m(-1). Upon incorporating the rGO-PCA in active and electron transport layers of organic solar cells, compared to P3HT-only devices (0.18%) a 16-fold increase in the power conversion efficiency (2.85%) is obtained, attributed to a substantial increase in the short-circuit current density from 0.017 to 12.09 mA cm(-2).

Graphene/Polyaniline nanocomposite as electrode material for membrane capacitive deionization

Capacitive deionization (CDI) is a novel ion removal technology that uses static electrical force to drive ions to the charged electrode and stores the ions into porous structure of the electrode. Graphene and graphene nanocomposites are considered promising materials for electrodes because of its good conductivity and extraordinarily high specific surface area. Graphene/Polyaniline nanocomposite was chosen that aims to increase the ion-electrosorption capacitance of graphene. In this work, graphene nanosheets were obtained by reducing oxidized graphite flasks. Graphene/Polyaniline (G/PANI) nanocomposites were synthesized by chemical polymerization of aniline in the presence of dispersed graphene sheets. The morphology and electrochemical property of the composite were characterized. The ion removal performance of the composite was determined by using a membrane capacitive deionization (CDI) bench-scale system.

Electrical properties of poly(arylene ether nitrile)/graphene nanocomposites prepared by in situ thermal reduction route

In order to obtain highly flexible polymer composites with high dielectric performance, novel poly(arylene ether nitrile) (PEN)/graphene nanocomposites were prepared by a two-step method, involving facile solution-casting for dispersing graphene oxide and followed by thermal reduction of dispersed graphene oxide at 200 °C for 2 h. The results showed that the in situ thermal reduction method can help to fabricate PEN-based nanocomposites with homogenously dispersed graphene sheets and give rise to a 236 % increase of the dielectric constant between 160 °C and 200 °C of from 10.43 to 24.65 at 50 Hz. As a result of the formation of an alternative multilayered structure of PEN and graphene sheets, a typical percolation transition was observed as the content of the graphene oxide increased. The conductivity and dielectric constant followed the percolation threshold power law, yielding a percolation threshold (f c ) of 0.014. The corresponding critical exponent was calculated as μ = t(t + s)− 1 = 0.83, which was in good agreement with the experimental data of μ = 0.81 as f graphene = 0.013. This type of PEN/graphene composite with low percolation threshold can be potentially applied as novel dielectric materials.

Non-linear temperature variation of resistivity in graphene/silicate glass nanocomposite

Graphene/glass nanocomposite was synthesized by gelation of the glass in a solution with dispersed graphene sheets. Electrical transport measurements were carried out on pellets formed by cold pressing of composite powders. Resistivity showed a nonlinear increase as a function of temperature in the range 300–400 K. This has been explained as arising due to the phonon spectra of the glass affecting the movement of electrons in graphene. Raman studies confirmed the presence of phonons in the silicate glass phase. The dielectric relaxation spectra of the composites at different temperatures are consistent with the above mechanism of the electron–glass phonon interaction.

Contribution of Water Molecules in the Spontaneous Release of Protein by Graphene Sheets

Applications of graphene sheets in the fields of biosensors and biomedical devices are limited by the aqueous solubility of graphene. Consequently, understanding the role of water molecules in the aggregation or dispersion of graphene in aqueous solution with a biomolecule is of vital importance to its application. Herein, protein is spontaneously released by the layer-to-layer aggregation of two single-layer graphene sheets due to van der Waals force between the sheets. The properties of water molecules, including density and dynamics, are discussed in detail. The dynamic behavior of aggregation of graphene sheets is triggered by the dynamics of water molecules. To stabilize dispersed graphene sheets in aqueous solution, the density of water molecules between the graphene sheets should be larger than 0.83 g cm(-3), and graphene modified by hydroxyl groups could be a good choice. The stability of a model protein on the graphene sheet is studied to investigate the biological compatibility of graphene sheets. To be a material with good biocompatibility, graphene should be functionalized by hydrophilic groups. The results presented herein could be helpful in the research and application of graphene sheets in the fields of biomaterials, biosensors, and biomedical devices.

The production of a melt-spun functionalized graphene/poly(ε-caprolactam) nanocomposite fiber

Abstract An in situ polymerization technique was used to develop localized polymers grafted onto the surface of dispersed pristine graphene sheets. A 4-substituted benzoic acid monomer was grafted to the surface of expanded graphene by ‘‘ Direct Friedel–Crafts ” acylation. The chains of poly(e-caprolactam) (PA6) that were grafted on the functionalized graphene (FG) were prepared by in situ polymerization of e-caprolactam in the presence of FG. Nanocomposite fibers with different loadings of FG were melt-spun with a piston spinning machine and a hot-roller drawing machine. FG is evenly distributed in the nanocomposite. A significant mechanical property increase of FG/PA6 nanocomposite is obtained at a low FG loading; e.g., a 65% improvement of tensile strength and a 290% improvement of Young’s modulus compared to a pure PA6 fiber is achieved at a FG loading of 0.1 wt.%. The compatibility of FG and PA6 in the nanocomposite fiber improves the thermal stability of the polymer matrix. This functionalization method paves the way for the facile fabrication of graphene-based nanocomposite fibers without disrupting the primary structures of the graphene.

Polyelectrolyte-Induced Dispersion of Graphene Sheets in the Hybrid AgCl/PDDA/Graphene Nanocomposites

Cationic polyelectrolyte poly(diallyldimethylammonium chloride) (PDDA) was used to stabilize graphene sheets in the self-assembly of AgCl/PDDA/Graphene heterostructure. The resultant AgCl/PDDA/Graphene nanocomposites were characterized by Scanning electron microscopy, Atomic force microscopy and X-ray photoelectron spectroscopy. The results showed that AgCl nanoparticles with sizes of 500 nm uniformly positioned on the PDDA stabilized graphene sheets surface. This work presents a facile and environmentally friendly approach to the synthesis of AgCl/PDDA/Graphene and opens up a new possibility for preparing graphene-based nanomaterials for large-scale applications.

Graphene reinforced biodegradable poly(3-hydroxybutyrate-co-4-hydroxybutyrate) nano-composites

Novel biodegradable poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (PHBV)/graphene nanocomposites were prepared by solution casting. The thermal properties, crystallization behavior, microstructure, and fracture morphology of the composites were investigated. Scanning electron microscope (SEM) results show that graphene layers are homoge- neously dispersed in the polymer matrix. X-ray diffraction (XRD) and dynamic scanning calorimetry (DSC) studies show that the well dispersed graphene sheets act as nucleating agent for crystallization. Consequently, the mechanical properties of the composites have been substantially improved as evident from dynamic mechanical and static tensile tests. Differen- tial thermal analysis (DTA) showed an increase in temperature of maximum degradation. Soil degradation tests of PHBV/graphene nanocomposites showed that presence of graphene doesn't interfere in its biodegradability.

Promoted photoinduced charge separation and directional electron transfer over dispersible xanthene dyes sensitized graphene sheets for efficient solar H2 evolution

Directional electron transfer and effective charge separation facilitated by graphene sheets have provided an inspiring approach to enhance the efficiencies of photoelectric conversion and photocatalysis. Herein, we demonstrated the feasibility of constructing a high-performance of the dye-sensitized H2 evolution system using dispersible graphene sheets as both efficient electron transfer carrier and catalyst scaffold. Among the xanthene dyes sensitized H2 evolution catalysts in this study, photocatalyst of Rose Bengal (RB) sensitized graphene decorated with Pt is the most active one and exhibits the highest apparent quantum efficiency (AQE) of 18.5% at wavelength of 550 nm and rather long-term stability for H2 evolution. Dispersible graphene sheets can not only capture electrons from the excited dye and then transfer them to the decorated catalysts efficiently for improving charge separation with a small energy loss, but also afford large interfaces for highly dispersing catalyst nanoparticles with more active sites, thereby significantly enhancing the H2 evolution efficiency than graphite oxide (GO) and multiwall carbon nanotubes (MWCNTs). This work proposes a potential strategy to develop efficient photocatalytic systems for solar-energy-conversion and provides a new insight into mechanistic study of photoinduced electron transfer by effective synergetic combination of dispersible graphene sheets with an efficient dye and a H2 evolution catalyst.

Facile synthesis of graphene hybrid tube-like structure for simultaneous detection of ascorbic acid, dopamine, uric acid and tryptophan

In the present work, a tube-like structure of graphene hybrid as modifier to fabricate electrode for simultaneous detection of ascorbic acid (AA), dopamine (DA), uric acid (UA) and tryptophan (Trp) was reported. The hybrid was synthesized by a simple method based on graphene sheets (GS) and 3,4,9,10-perylenetetracarboxylic acid (PTCA) via π–π stacking interaction under ultrasonic condition. The combination of GS and PTCA could effectively improve the dispersion of GS, owing to PTCA with the carboxylic-functionalized interface. Comparing with pure GS or PTCA modified electrode, GS–PTCA displayed high catalytic activity and selectivity toward the oxidation of AA, DA, UA, and Trp. Moreover, cyclic voltammetry, different pulse voltammetry and scanning electron microscopy were employed to characterize the sensors. The experiment results showed that the linear response range for simultaneous detection of AA, DA, UA, and Trp were 20–420μM, 0.40–374μM, 4–544μM and 0.40–138μM, respectively, and the detection limits were 5.60μM, 0.13μM, 0.92μM and 0.06μM (S/N=3). Importantly, the proposed method offers promise for simple, rapid, selective and cost-effective analysis of small biomolecules.

Effect of Graphene Modification on Thermo-Mechanical and Microwave Absorption Properties of Polystyrene/Graphene Nanocomposites

In the present study the effect of graphene percentage and graphene modification on the microwave absorption properties of the polystyrene/graphene nanocomposites was studied in detail. Acid modified graphene was prepared by the mixed acid route. Polystyrene/graphene nanocomposites with various percentages of graphene and modified graphene were prepared by solution mixing process. The dispersion of graphene sheets in the polystyrene matrix was analyzed by TEM and SEM and found to be uniform for the 1%, 2 wt% of graphene and 1 wt% of modified graphene loading. Microwave absorption of modified graphene containing nanocomposite was found to be superior among the nanocomposites. Incorporation of 1 wt% of ferrite particles enhanced the microwave absorption of the nanocomposite above all the nanocomposites, in the whole range of X-band, due to the effective cancellation of both electrical and magnetic components of the microwave. Incorporation of graphene enhanced the thermal and mechanical properties of the nanocomposites.

Large-scale preparation of graphene sheets and their easy incorporation with other nanomaterials

Graphene dispersions with concentrations up to 0.5 mg/mL were produced by dispersion in N,N-dimethylformamide with the aid of polyacrylic acid. Graphene oxide could also be dispersed with even higher concentration (17 mg/mL), and this advantage was used for the large-scale synthesis of graphene. The good dispersion of graphene sheets also facilitated the preparation of a new hybrid material of graphene and Fe3O4 nanoparticles, which exhibited interesting magnetic properties.