Properties Of Graphene Sheets Research Articles

Strain-Induced Nonlinear Frictional Behavior of Graphene Nanowall Films.

Graphene nanowall (GNW) films, a representation of three-dimensional (3D) carbon nanomaterial films, are emerging as promising candidates for applications in electric devices and composites, on account of their 3D structures and exceptional properties of graphene sheets. However, the frictional responses of GNW films, which exhibit significant influence on their performances, have seldom been reported. Herein, we reported a growth process of a GNW film by the chemical vapor deposition method and studied the frictional behavior of the GNW film for the first time. The results demonstrated the nonlinearity between the frictional force of the GNW film and normal load. Based on the structural evolution of the GNW film with normal load and frictional tests on precompressed GNW films, the influence of the strain property of the GNW film, namely, the strengthening effect, could be confirmed. The results of molecular dynamics simulations show that the bending force of GNWs in front of the tip plays a determinate role in the frictional force of the GNW film. Furthermore, the bending force is proportional to the bending contact area, which increases nonlinearly with the normal load due to the strengthening effect of the GNW film. The result suggests that the nonlinear increase of the bending contact area induced by the strengthening effect of the GNW film is the key factor that leads to its nonlinear frictional force. This study provides a novel insight into the frictional responses of GNW films, which would be beneficial for the design and application of electric devices and composites made of GNW and other 3D carbon nanomaterial films.

PEO/Graphene Composites Prepared by a Green Method

PEO/graphene composites were prepared by a simple and green method in presence of graphite oxide (GO) reduced by Vitamin C (VC) in aqueous. In this process, GO was dispersed well into PEO aqueous solution before reduction. Although the carbon content and hydrophobic properties of graphene sheets were increased during the reduction, the uncompleted reduction process could be detected and confirmed by FTIR and TGA. The residual oxygen containing groups on the surface of graphene sheets could improve the compatibility of PEO and graphene sheets in aqueous.

Research on Strain Rate Effect of the Mechanical Properties of Graphene Sheet Containing Randomly Distributed Defects

Strain rate effects on the mechanical properties of graphene sheets (GSs) contain randomly distributed defects investigated by molecular dynamics simulations, and the results have been discussed. The strain rate has a significant effect on the tensile strength, while fracture strain and failure mechanism of GSs and elastic modulus are insensitive to the strain rate. At room temperature of 300 K, GSs without defects show that brittle failure is at a low strain rate and linear hardening is at a high strain rate. The strain rate is higher, the GSs are harder. However, GSs with a large number of randomly distributed defects only show brittle failure under high temperature. The tensile strength and fracture strain increase with the strain rate increasing. The tensile strength of GSs without defects has a linear relation to the logarithm of the strain rate, but the GSs with defects do not exhibit this phenomenon because the defects are sensitive to the strain rate. The present study provides a theoretical optimization method for the preparation and performance of GSs.

Extended ADI‐FDTD for anisotropic magnetised graphene sheets

The unconditionally stable alternating-direction-implicit finite-difference time-domain (ADI-FDTD) method is extended for modelling anisotropic magnetised graphene sheets. In contrast to the conventional method for isotropic media, two additional sub-stepping calculations are applied to incorporate anisotropic medium properties. The unconditional stability of the proposed extended method is examined numerically. The method is applied to study the transmission properties of graphene sheets. Numerical results show that the proposed method is more accurate than the recently developed locally one-dimensional FDTD method.

Buckling analysis of graphene sheets using nonlocal isogeometric finite element method for NEMS applications

In this study, an isogeometric finite element approach (IGA) based on non-uniform rational B-splines (NURBS) basis function in combination with the first order shear deformation plate theory (FSDT) for buckling analysis of graphene sheet under uniaxial and biaxial compressions is investigated. To study the small scale effects on buckling analysis, the nonlocal elasticity theory is applied. Nonlocal governing equations of motion for the single-layered graphene sheet are derived from the principle of virtual displacements. The properties of graphene sheet are considered as isotropic and orthotropic plates. Numerical results of critical buckling loads are presented, and compared with other available results to reveal the efficiency and accuracy of the present IGA approach. At the end some numerical results are presented to study the effects of nonlocal parameter, different boundary conditions, different material properties, side length and aspect ratio on critical buckling loads.

Interfacial topography and properties of graphene sheets on different reconstructed silicon surfaces

Graphene growth on a substrate has been widely investigated due to its broad application potential. Previous studies have found that the properties of graphene depend on its underlying substrate and their interaction. However, the dynamic behavior of the interfacial structure as a function of temperature has not been investigated, as well as the interfacial structure related to its mechanical properties. In this work, molecular dynamics has been employed to study the topographic characteristics and intrinsic mechanical properties of graphene when attached to a reconstructed silicon surface. The fitness between the interfacial structures plays an important role in stabilizing the attached graphene and forming pattern. The degree of planarity of the attached graphene determines the magnitude of the residual stress, while temperature affects atomic bonding and varies this residual stress. Findings suggest that the different pairings between graphene and surface structures significantly affects the topographic characteristics, residual stress, and interaction strength of the graphene sheet, which would further change the electronic properties of its application.

Interfacial adhesion properties of graphene sheet on nanoscale corrugated surface: a molecular dynamics simulation study

Adhesive contacts between graphene sheet (GS) and corrugated substrates made of an ordered array of atomic pillars with variable geometries were investigated by molecular dynamics simulations. Depending on the height and interval distance of the pillars, GS can conformably coat the surface, partially adhere, or remain flat on top of the pillars. The relationship between the geometries of the pillar and the final adhesion configurations of GS was partially established. A critical adsorption energy was determined to achieve stable adsorption configuration of GS on corrugated substrates made of ordered pillar arrays. Besides the geometries of pillars, the effects of initial coating angle of GS were also considered as an important factor that affects the final adsorption configuration. We observed two interesting morphologies of GS, ‘I shape’ and ‘L shape’, which were determined by the initial coating angles.

Back Cover: Engineering the Electrochemical Capacitive Properties of Graphene Sheets in Ionic-Liquid Electrolytes by Correct Selection of Anions (ChemSusChem 11/2014)

Back Cover: Engineering the Electrochemical Capacitive Properties of Graphene Sheets in Ionic-Liquid Electrolytes by Correct Selection of Anions (ChemSusChem 11/2014)

Ab-initio study of planar strain on electronic structure properties of graphene sheets with nanoholes

We use an ab-initio method to calculate the electronic structure properties of graphene with several kinds of nanoholes features (topological defects) in presence of planar strain distributions. Calculations are performed by using first-principles method in framework of the density functional theory as implemented in VASP software. Generalized gradient approximation is considered for the exchange-correlation functional. By applying a full spin polarized description to the system, we demonstrate that the nanoholes (antidot lattice) create the magnetic moment, which change with different intensity of the planar strain on the sheet. Magnetic nature of these intrinsic carbon defects suggests that it is important to understand their role in recently observed magnetism in graphene systems with periodic nanoholes.

DIRAC EQUATION ON A CURVED (2+1)-DIMENSIONAL HYPERSURFACE

Interest on (2+1)-dimensional electron systems has increased considerably after the realization of novel properties of graphene sheets, in which the behavior of electrons is effectively described by relativistic equations. Having this fact in mind, the following problem is studied in this work: when a spin-1/2 particle is constrained to move on a curved surface, is it possible to describe this particle without giving reference to the dimensions external to the surface? As a special case of this, a relativistic spin-1/2 particle which is constrained to move on a (2+1)-dimensional hypersurface of the (3+1)-dimensional Minkowskian spacetime is considered, and an effective Dirac equation for this particle is derived using the so-called thin layer method. Some of the results are compared with those obtained in a previous work by Burgess and Jensen.

Finite element modelling of nano-structured materials

A finite element model is developed to study the mechanical behaviour of nano-structured materials. The model serves as a link between computational chemistry and solid mechanics by substituting discrete molecular structures with an equivalent-continuum model. As an important example with direct application to the development and characterisation of single-walled carbon nanotubes, the model has been applied to determine the effective stiffness of a graphene sheet. Two different load cases have been studied showing the capabilities of the developed model in predicting the mechanical properties of graphene sheet under varying loading conditions.