Nylon-6/Graphene composites modified through polymeric modification of graphene

The covalent functionalization of graphene oxide (GO) with poly(vinyl alcohol) (PVA) via ester linkages (GO-es-PVA) as well as the characterization of modified graphene based Nylon-6 (PA6) composite prepared by solution mixing techniques was examined. The anchoring of PVA chains on GO sheets was confirmed by XPS and FTIR measurements. The resulting functionalized sample became soluble in formic acid, allowing solution-phase processing for preparation of PA6/GO composites. Answering to the efficient polymer-chain grafting, a homogeneously dispersion of GO sheets in PA6 matrix and a dramatic improvement of interface adhesion between nanosheets and matrix were observed in PA6/GO-es-PVA composites by SEM and TEM. The depressed crystallization of PA6 chains in PA6/GO-es-PVA composites was investigated by their DSC and XRD results.     

Graphene fluoride: a stable stoichiometric graphene derivative and its chemical conversion to graphene

Stoichoimetric graphene fluoride monolayers are obtained in a single step by the liquid-phase exfoliation of graphite fluoride with sulfolane. Comparative quantum-mechanical calculations reveal that graphene fluoride is the most thermodynamically stable of five studied hypothetical graphene derivatives; graphane, graphene fluoride, bromide, chloride, and iodide. The graphene fluoride is transformed into graphene via graphene iodide, a spontaneously decomposing intermediate. The calculated bandgaps of graphene halides vary from zero for graphene bromide to 3.1 eV for graphene fluoride. It is possible to design the electronic properties of such two-dimensional crystals.     

Mechanical strain and electric-field modulation of graphene transistors integrated on MEMS cantilevers

Journal of Materials Science - This work proposes a structure which allows characterization of graphene monolayers under combined electric field and mechanical strain modulation. Our approach is...     

Graphene/thermoplastic polyurethane nanocomposites: Surface modification of graphene through oxidation,polyvinyl pyrrolidone coating and reduction

Herein, oxidation, polyvinyl pyrrolidone (PVP) coating and reduction are used to modify the surface of graphene in thermoplastic polyurethane (TPU)/graphene nanocomposites. It is demonstrated that graphene could be easily dispersed in TPU with PVP absorbed on reduced graphene oxide (RGO) as stabilizer during reduction. In the stress–strain curves for these composites containing GO, PVP coated GO (GO/PVP) and reduced GO/PVP (RGO/PVP) as filler, PVP coating and reduction can largely enhance the stress in low modulus region. It is thought to largely related with enhanced interfacial interaction between filler and matrix and healing of graphene structure during reduction. Consequently, the modulus of TPU/GO/PVP and TPU/RGO/PVP is significantly increased. Meanwhile, an electrical percolation threshold of 0.35 wt.% is obtained for TPU/RGO/PVP. Comparing with the results in literature, the filler surface modification used in this study has created nanocomposites with a good balance between electrical conductivity and mechanical properties.     

Graphene oxide and lipid membranes: interactions and nanocomposite structures

We have investigated the interaction between graphene oxide and lipid membranes, using both supported lipid membranes and supported liposomes. Also, the reverse situation, where a surface coated with graphene oxide was exposed to liposomes in solution, was studied. We discovered graphene oxide-induced rupture of preadsorbed liposomes and the formation of a nanocomposite, bio-nonbio multilayer structure, consisting of alternating graphene oxide monolayers and lipid membranes. The assembly process was monitored in real time by two complementary surface analytical techniques (the quartz crystal microbalance with dissipation monitoring technique (QCM-D) and dual polarization interferometry (DPI)), and the formed structures were imaged with atomic force microscopy (AFM). From a basic science point of view, the results point toward the importance of electrostatic interactions between graphene oxide and lipid headgroups. Implications from a more practical point of view concern structure-activity relationship for biological health/safety aspects of graphene oxide and the potential of the nanocomposite, multilayer structure as scaffolds for advanced biomolecular functions and sensing applications.     

pH responsive polymer cushions for probing membrane environment interactions

A robust and straightforward method for the preparation of lipid membranes upon dynamically responsive polymer cushions is reported. Structural characterization demonstrates that complete, well-packed membranes with tunable mobility can be constructed on the polymeric cushion. With this system, membrane conformational changes induced by cellular cytoskeleton interactions can be modeled. The membrane can be tailored to screen the cushion from changes in pH or allow rapid response to the pH environment by incorporation of protein ion channels. This elementary system offers a means to replicate the conformational changes that occur with the cellular cytoskeleton and has great potential for fundamental biophysical studies of membrane properties and membrane-protein interactions decoupled from the underlying solid support.     

Plasmonic waves of graphene on a conducting substrate

The properties of plasmonic waves of graphene on a conducting substrate are discussed based on the classical electrodynamics and linearized hydrodynamic model. General expressions are given and illustrated graphically for the dispersion relation, power flow, energy density and energy transport velocity of the plasmonic waves. The numerical results show that acoustic plasmon mode of the system has a group velocity that can be made arbitrarily close to the graphene Fermi velocity by tuning the graphene–metal distance or graphene sheet carrier density.     

Nitrogen-doped carbon nanotube arrays grown on graphene substrate

Nitrogen-doped carbon nanotube (N-doped CNT) arrays have been synthesized on graphene substrate by chemical vapor deposition process, in which iron nanoparticles (NPs) assembled on the graphene sheet were generated in situ from the reduction of Fe₃O₄ NPs/reduced graphene oxide (RGO) and were used as catalyst. The morphology and structure of the N-doped CNT arrays were investigated by field emission scanning electron microscope and high-resolution transmission electron microscope. The N-doped CNTs were bamboo-shaped and the density can be controlled by modulating the density of catalyst NPs on RGO sheets. The concentration and incorporation of nitrogen were studied by elemental analysis, X-ray photoelectron spectroscope and Raman analysis, and the results showed that the nitrogen content was around 3 wt.%. Because of the good conductivity of graphene structure, N-doped CNT arrays grown on graphene substrate may be promising candidates as noble metal-free electrodes for oxygen reduction reaction in the future.     

Defective graphene as a high-efficiency Raman enhancement substrate

Pristine graphene (PG) has been demonstrated to be an excellent substrate for Raman enhancement, which is called graphene-enhanced Raman scattering. However, the chemically inert and hydrophobic surface of PG hinders the adsorption of molecules especially in aqueous solutions, and consequently limits the Raman enhanced efficiency. Here, we synthesized defective graphene (DG) films by chemical vapor deposition on Au, which has a defect density of ∼2.0 × 10¹¹ cm⁻². The DG shows a much better wettability than PG towards dye solution. Combining with the strong adsorption ability of defects to molecules, DG shows greatly enhanced efficiency than PG with perfect lattice. For example, the detection limit for rhodamine B can reach 2 × 10⁻⁹ M for DG while it is on the order of 10⁻⁷ M for PG. In addition, DG has high enhancement uniformity and the Au substrate can be reused after electrochemical bubbling transfer. These advantages suggest the great potential of the DG grown on Au for practical applications in environmental monitoring.     

Graphene growth at the interface between Ni catalyst layer and SiO2/Si substrate

Graphene was synthesized deliberately at the interface between Ni film and SiO2/Si substrate as well as on top surface of Ni film using chemical vapor deposition (CVD) which is suitable for large-scale and low-cost synthesis of graphene. The carbon atom injected at the top surface of Ni film can penetrate and reach to the Ni/SiO2 interface for the formation of graphene. Once we have the graphene in between Ni film and SiO2/Si substrate, the substrate spontaneously provides insulating SiO2 layer and we may easily get graphene/SiO2/Si structure simply by discarding Ni film. This growth of graphene at the interface can exclude graphene transfer step for electronic application. Raman spectroscopy and optical microscopy show that graphene was successfully synthesized at the back of Ni film and the coverage of graphene varies with temperature and time of synthesis. The coverage of graphene at the interface depends on the amount of carbon atoms diffused into the back of Ni film.     

Micro/nanoscale spatial resolution temperature probing for the interfacial thermal characterization of epitaxial graphene on 4H-SiC

Limited internal phonon coupling and transfer within graphene in the out-of-plane direction significantly affects graphene-substrate interfacial phonon coupling and scattering, and leads to unique interfacial thermal transport phenomena. Through the simultaneous characterization of graphene and SiC Raman peaks, it is possible, for the first time, to distinguish the temperature of a graphene layer and its adjacent 4H-SiC substrate. The thermal probing resolution reaches the nanometer scale with the graphene (≈1.12 nm) and is on the micrometer scale (≈12 μm) within SiC next to the interface. A very high thermal resistance at the interface of 5.30 (-0.46) (+0.46) x 10(-5) Km2 W(-1) is observed by using a Raman frequency method under surface Joule heating. This value is much higher than those from molecular dynamics predictions of 7.01(-1.05) (+1.05) x 10(-1) and 8.47(-0.75) (+0.75) x 10(-10) Km2 w(-1) for surface heat fluxes of 3 × 10(9) and 1 × 10(9) and 1 x 10(10) W m(-2) , respectively. This analysis shows that the measured anomalous thermal contact resistance stems from the thermal expansion mismatch between graphene and SiC under Joule heating. This mismatch leads to interface delamination/separation and significantly enhances local phonon scattering. An independent laser-heating experiment conducted under the same conditions yielded a higher interfacial thermal resistance of 1.01(-0.59) (+1.23) x 10(-4) Km2 W(-1). Furthermore, the peak width method of Raman thermometry is also employed to evaluate the interfacial thermal resistance. The results are 3.52 × 10(-5) and 8.57 × 10(-5) K m2 W(-1) for Joule-heating and laser-heating experiments, respectively, confirming the anomalous thermal resistance between graphene and SiC. The difference in the results from the frequency and peak-width methods is caused by the thermal stress generated in the heating processes.     

Graphene resist interlacing process for versatile fabrication of free-standing graphene

We present a graphene resist interlacing process (GRIP) to sandwich graphene between polymer lines in a cloth-like fashion, making it more accessible for experiments and applications. We demonstrate the handling of large-area graphene in this way. Here, GRIP is used to fabricate supports for transmission electron microscopy. These supports improve the imaging quality of nanoparticles, as we show by comparison to imaging on standard lacey carbon supports.     

Graphene for reducing bubble defects and enhancing mechanical properties of graphene/cellulose acetate composite films

In this study, we have demonstrated a strategy by which graphene was used to reduce the bubble defects and enhance the mechanical properties in graphene/cellulose acetate (Gr/CA) composite films. Mono- and multilayer graphene flakes were successfully prepared in the water–acetone mixtures by a jet cavitation method. Moreover, outstanding enhancement of mechanical properties of Gr/CA composite films were obtained at relatively low concentration of graphene flakes. Young’s modulus of these composite films increased linearly with the graphene flakes loading, due to the significantly high surface area of graphene and strong interactions between graphene flake and CA. Furthermore, three-dimensional channel formed by graphene flakes could increase the degassing speed and reduce the negative effects of bubbles. The Gr/CA composite has excellent mechanical properties and, more importantly, it is a natural and environmentally friendly polymer composite.     

Electron-electron interactions in monolayer graphene quantum capacitors

We demonstrate the effects of electron-electron （e-e） interactions in monolayer graphene quantum capacitors. Ultrathin yttrium oxide showed excellent per-formance as the dielectric layer in top-gate device geometry. The structure and dielectric constant of the yttrium oxide layers have been carefully studied. The inverse compressibility retrieved from the quantum capacitance agreed fairly well with the theoretical predictions for the e--e interactions in monolayer graphene at different temperatures. We found that electron-hole puddles played a significant role in the low-density carrier region in graphene. By considering the temperature-dependent charge fluctuation, we established a model to explain the round-off effect originating from the e-e interactions in monolayer graphene near the Dirac point.     

Synthesis of graphene on SiC substrate via Ni-silicidation reactions

In this work, the features of graphene layers are studied with the aim of preparing the thinnest layers possible. The graphene layers were prepared by the annealing of Ni/SiC structures. The main advantage of this process is a relatively low temperature compared with the method of graphene epitaxial growth on SiC and short annealing times compared with the chemical vapor deposition method. We prepared graphene layers from several Ni/SiC structures in which the Ni layer thickness ranged from 1 to 200 nm. The parameters of the annealing process (temperature, rate of temperature increase, annealing time) were modified during the experiments. The formed graphene layers were analyzed by means of Raman spectroscopy. From the spectra, the basic parameters of graphene, such as the number of carbon layers and crystallinity, were determined. The annealing of the Ni(200 nm)/SiC structure at 1080 °C for 10 s, produced graphene in the form of 3-4 carbon monolayers. The value was verified by X-ray Photoelectron Spectroscopy (XPS). Good agreement was achieved in the results obtained using Raman spectroscopy and XPS.     

Electrophoretic-deposited novel ternary silk fibroin/graphene oxide/hydroxyapatite nanocomposite coatings on titanium substrate for orthopedic applications

The combination of graphene oxide (GO) with robust mechanical property, silk fibroin (SF) with fascinating biological effects and hydroxyapatite (HA) with superior osteogenic activity is a competitive approach to make novel coatings for orthopedic applications. Herein, the feasibility of depositing ternary SF/GO/HA nanocomposite coatings on Ti substrate was firstly verified by exploiting electrophoretic nanotechnology, with SF being used as both a charging additive and a dispersion agent. The surface morphology, microstructure and composition, in vitro hemocompatibility and in vitro cytocompatibility of the resulting coatings were investigated by SEM, Raman, FTIR spectra and biocompatibility tests. Results demonstrated that GO, HA and SF could be co-deposited with a uniform, smooth thin-film morphology. The hemolysis rate analysis and the platelet adhesion test indicated good blood compatibility of the coatings. The human osteosarcoma MG63 cells displayed well adhesion and proliferation behaviors on the prepared coatings, with enhanced ALP activities. The present study suggested that SF/GO/HA nanocomposite coatings could be a promising candidate for the surface functionalization of biomaterials, especially as orthopedic implant coating.