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Many researches have shown that nanotwinned structure and graphene reinforcing phase can improve the mechanical properties of aluminum (Al) metal, but the synergistic effect of the two on nanoindentation mechanical response of Al matrix composites is rarely reported. In this research, based on molecular dynamics simulations, the nanoindentation mechanical properties and microscopic deformation mechanisms of graphene/nanotwinned Al matrix composites are studied. The effect of the inclination angle and spacing of the twin boundaries (TBs), the insertion position of the graphene sheet, the graphene coating and the layer number of the graphene sheet on the nanoindentation mechanical properties of the Al matrix composites is analyzed. The nanoindentation mechanical properties of nanotwinned Al strongly depend on the inclination angle of TBs, and the dislocation slip modes mainly includes three types: hard mode I (dislocation pile-up penetration mode), soft mode I (partial dislocation parallel twin boundary slip mode) and hard mode II (dislocation limited slip mode). Moreover, as the twin boundary spacing increases, the dislocation slip mode starts to weaken until the nanoindentation mechanical properties are insensitive to the twin inclination orientation. The insertion of the graphene sheet weakens the indentation mechanical properties of the nanotwinned Al matrix composite, which is attributed to the interaction of the graphene with the dislocations and the subsequent absorption of part of them. The weakening effect depends on the distance between the graphene/Al interface and the plastic zone. What's more, graphene coating can improve the indentation mechanical properties of composites. In addition to the load bearing effect of graphene in the elastic stage, this strengthening effect is also attributed to the combined action of graphene and TBs in the plastic stage, which makes the dense dislocation network widely distributed around the indentation of graphene coating and induces the interfacial strain hardening. [ABSTRACT FROM AUTHOR]

Based on the Lennard-Jones potential function, a theoretical model of atoms/ions interaction with finite-size (doped) graphene is presented to investigate the mechanical behaviors of atoms/ions adsorption and migration on the surface of finite-size boron, nitrogen and boron nitride doped graphene. The results show that boron, nitrogen and boron nitride doping can change the interaction between atoms/ions and graphene, and the type, position and domain size of doping elements have significant effects on the adsorption sites and adsorption energy of atoms/ions. The stable adsorption sites, adsorption heights and adsorption energy of atoms/ions on the surface of doped graphene can be controlled by regulating the doping elements. Meanwhile, boron, nitrogen and boron nitride doping can affect the energy period and energy barrier of atoms/ions migration on graphene surface. The proper design of boron, nitrogen and boron nitride doping position, size and distribution can effectively control the atom/ion migration behavior on graphene surface. This research work can provide a theoretical reference for atoms/ions carriers, molecular sieves and ion battery electrodes based on doped graphene and graphene heterostructures. [ABSTRACT FROM AUTHOR]

In drug delivery systems, graphene materials are promising drug carriers. Drug molecules are loaded on graphene through π-π interaction between graphene and benzene ring structure, which is widely found in organic drug molecules. Then the drug molecules are released under different conditions, such as different environmental pH, at lesion site. In the application, the adsorption and desorption between benzene ring structure in drug molecules and graphene play a key role. Herein, an experimental method for measuring the adhesion force between a single phenyl and graphene is proposed, and the adsorption and desorption mechanical properties of a benzene ring structure on graphene surface at different environmental pH are firstly measured. The experimental results show that the adhesion force decreases with the increase of environmental pH. Moreover, molecular dynamics simulations show that the influence of pH on adhesion force is mainly realized by changing the electrostatic potential distribution on graphene surface, and the interaction force between a single benzene and graphene changes from attractive to repulsive with the increase of environmental alkalinity. In addition, a molecular dynamics model for the dynamic adsorption and desorption capacities of benzene molecules on graphene surface at different quantity of ions is established. Benzene molecules can achieve full adsorption on the surface of graphene when there are 10 and 20 hydrogen ions. And benzene molecules can achieve full desorption on the surface of graphene when there are 10 and 20 hydroxide ions. [Display omitted] [ABSTRACT FROM AUTHOR]

The superb mechanical properties make graphene an ideal candidate material for impact protection. Combining molecular dynamics simulations and theoretical analyses, the deformation and failure modes, energy absorption of single-layer graphene under ballistic impact are investigated. According to numerical and theoretical results, the expression for residual velocity of projectile after impact is given. The dependence of deformation and failure modes, energy absorption mechanisms, specific penetration energy (SPE) on impact velocity is analyzed. The results show that during low-velocity impact, there are conical deformation region (CDR), star-like crack and monoatomic carbon chain in graphene. Energy absorption mechanisms of graphene are mainly local deformation and fracture. With increasing impact velocity, the size of CDR decreases. The star-like crack gradually transforms into circular hole. When impact velocity is high enough, carbon atoms within projectile projection area in graphene will be ejected in the form of debris. The kinetic energy (KE) loss of projectile is converted into KE of debris carbon atoms and fracture energy of carbon bonds. Besides, it is also found that SPE (dominant factors are deformation of conical region and KE increments) exhibits a decreasing–increasing trend with increasing impact velocity. When impact velocity is the same, SPE decreases with increasing projectile diameter. [Display omitted] • Energy absorption of graphene under ballistic impact is studied by MD simulations. • The expression for residual velocity of rigid projectile after impact is given. • The dependence of deformation and failure modes on impact velocity is discussed. • Energy absorption mechanism of graphene during impact process is analyzed. • The effect of impact velocity on specific penetration energy is studied. [ABSTRACT FROM AUTHOR]

In field of drug delivery, graphene is a potential material as drug carrier due to its large specific surface area and excellent chemical stability. Many kinds of drug molecules can be adsorbed on graphene surface through single or multiple benzene ring structures in drug molecules. Graphene loaded with drug molecules needs to be transported to the lesion site through blood. The content of water molecules in blood accounts for 92%. Therefore, the influence of water molecule on adsorption performance cannot be ignored. Here, the influence and mechanism of water molecule on the adsorption properties between benzene molecule and graphene is studied. The adsorption models of benzene molecule on graphene surface in vacuum and water environments are established, respectively. The adhesion energy, adhesion force and stable adsorption position of benzene molecule in two environments are analyzed by molecular dynamics simulation and potential function theory. Moreover, a model of preadsorption of a single water molecule on graphene surface is further presented, which explains the reason of the difference in adsorption performance in vacuum and water environment from the perspective of energy. The preadsorption of water molecule on graphene surface promotes the adsorption of benzene molecule. [Display omitted] [ABSTRACT FROM AUTHOR]

• Compressive properties of 3D graphene are studied by theory and MD simulations. • The unified constitutive relations of three kinds of 3D graphene are derived. • Compressive deformation mechanisms of three kinds of 3D graphene are discussed. • The configuration-property relationships of 3D graphene are elucidated. • Energy absorption capacities of three kinds of 3D graphene are analyzed. Combining molecular dynamics (MD) simulations and continuum modeling, the uniaxial in-plane compressive properties of honeycomb three-dimensional (h3D), triangle-like 3D (t3D) and non-equilateral hexagon 3D (nh3D) graphene are investigated to elucidate configuration-property relationships, and the constitutive relations of three kinds of 3D graphene are derived to evaluate the compressive mechanical properties. Based on theoretical and MD simulation results, it is found that the compressive stress-strain responses of 3D graphene can be divided into five stages. The compressive mechanical properties and deformation mechanisms of each stage are different. When 3D graphene is compressed, graphene sidewalls undergo rotations, bending and buckling deformations, collapses. Because graphene sidewalls of h3D graphene are prone to undergo buckling deformations, there is large locking strain in h3D graphene. For t3D and nh3D graphene, their high plateau stress is attributed to unique configurations. Moreover, we also find that with increasing graphene sidewall width, Young's modulus and plateau stress of 3D graphene gradually decrease. In addition to the above investigations, the energy absorption mechanisms and compression-unloading stress-strain curves of 3D graphene are also studied. It is found that there are extraordinary compression-recovery properties and energy absorption capacities in 3D graphene. Finally, the selection criteria of 3D graphene are proposed. [Display omitted] [ABSTRACT FROM AUTHOR]

Many studies have shown that both the nanotwinned structure and the graphene reinforcing phase can improve the mechanical properties of aluminum, but the synergistic effect of the two on the strengthening and toughening mechanisms of aluminum matrix composites has rarely been reported. In this work, the mechanical properties and microscopic deformation mechanisms of graphene/nanotwinned aluminum matrix composites under uniaxial tensile load are studied by molecular dynamics simulations. The effects of the distribution patterns of graphene and twin boundaries (TBs), their angles and the number of graphene layers on the mechanical behaviors of graphene/nanotwinned aluminum matrix composites are analyzed. It is found that the synergistic effect of TBs and graphene results in secondary reinforcement of aluminum matrix composites in the plastic stage, resulting in enhanced strength and toughness. Moreover, the elastic modulus, strength and toughness of graphene/nanotwinned aluminum matrix composites increase linearly with the number of graphene layers. By analyzing the microscopic deformation and dislocation evolution of aluminum matrix composites, the mechanisms of dislocation derivation and propagation induced by graphene and TBs are explored. In addition, it is found that there is a competition between graphene and TBs for the dislocation evolution, and the graphene can weaken the dislocation blocking effect of TBs. Finally, it is proved that the angle between graphene and TBs will weaken the mechanical properties of the composites. The effect of the TB angle on the mechanical properties of graphene/nanotwinned aluminum matrix composites is discussed in three cases, depending on the stress-strain curve and the microstructure deformation mechanism. • The effect of graphene and TBs on mechanical properties of Al-matrix is studied. • The influence of distribution patterns and layer number of graphene is analyzed. • The effect of the inclination angle of TBs and graphene is considered. • The mechanisms of dislocation derivation and propagation is explored. [ABSTRACT FROM AUTHOR]

Advanced hierarchical hybrid nanostructures of polar, conductive and catalytic chemical traps/carbon with rationally tailored components, structures, and chemistries are important in determining the performance of lithium-sulfur (Li–S) batteries. Herein we propose a facile strategy to prepare 3D-structured CNF@graphene-CoSe (CNF@G L -CoSe) cable/sheath heterostructure with the in-situ formed CoSe as a catalyst for graphene-like carbon growth and Se as a catalyst promoter. The architecture integrates high electrical conductivity, effective ion transport, notable polysulfide entrapment, and polysulfide redox kinetics, availing lithium/sulfur conversion when applied as an interlayer in a Li–S battery. As expected, the battery delivered a low decay of 0.053% per cycle over 700 cycles at 1 C. The capacity even remained 649.4 and 524.5 mA h g−1 at 4 and 6 C, respectively. Furthermore, an areal capacity of about 3 mA h cm−2 at 0.1 C after long-term tests can still maintain with sulfur loading of 4.5 mg cm−2. A facile effective strategy to prepare 3D-structured CNF@graphene-CoSe cable/sheath heterostructure with the in situ formed CoSe as a catalyst for graphene-like carbon growth and Se as a catalyst promoter, achieving significant enhancement in electrochemical performance of Li–S batteries. [Display omitted] • In situ constructing CNF@graphene-CoSe cable/sheath heterostructure. • CoSe catalyzes the growth of graphene sheath and Se as a catalyst promoter. • Synergism of conductivity, absorption and catalysis. • Enabling excellent performance as an interlayer. [ABSTRACT FROM AUTHOR]

[Display omitted] • The pH effect of adhesion force of benzene on graphene is quantitatively studied. • The edge effect of adhesion force is confirmed by experiment. • The potential function method is used to reveal the mechanism of pH effect. • The edge effect is explained by the vdW and electrostatic interaction. Graphene materials, as drug carriers, play an important role in the specific drug delivery system. The drug molecules with aromatic structures can be adsorbed on the surface of graphene in vitro through π-π stacking interaction and released directionally at the lesion under special temperature and pH-value environment. This paper proposes a new experimental method and theoretical model for the purpose to study the effect and mechanism of environmental pH and edge of graphene on the adsorption mechanical properties between graphene and benzene. The experimental results based on atomic force microscope show that the acidic environment is more conducive to the adsorption of benzene on the surface of graphene than the alkaline environment. The adsorption performance of benzene at the center of graphene is better than that at the edge. Moreover, based on experimental results, mechanisms of pH effect and edge effect are revealed by potential function theory. The pH effect is influenced by the change of electrostatic interaction in different pH environments. In addition, edge effect is mainly dominated by van der Waals interaction. This study solves the problem of specific influence mechanism of pH on π-π stacking interaction using mechanical means for the first time, and shows that graphene as a drug carrier has strong pH response characteristics and great application potential. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) graphene possesses a variety of excellent properties. It is worth using 2D graphene as building block to construct novel three-dimensional (3D) graphene which "inherits" superb performance of 2D graphene. Combining theoretical calculations and finite element method (FEM) based on molecular structural mechanics, the effects of graphene sidewall width, junction structure, in-plane domain size and in-plane overall shape on the elastic properties of zigzag honeycomb 3D graphene and three types of triangle-like 3D graphene are investigated, and the analytical expressions for Young's modulus of triangle-like 3D graphene are derived. The results of FEM are consistent with those of theoretical method. It is found that as graphene sidewall width increases, in-plane/out-of-plane Young's moduli of the above-mentioned 3D graphene first decrease and then tend to stabilize. For the armchair and zigzag triangle-like 3D graphene (sidewall width remains unchanged) with rectangular in-plane overall shape, the Young's modulus will vary with in-plane domain size. These results show that the elastic properties of 3D graphene are strongly dependent on structural size. In addition, junction structure has little influence on the elastic properties of 3D graphene. • A novel triangle-like 3D graphene containing sp3-sp3 carbon bond is constructed. • The size-dependent Young's modulus of triangle-like 3D graphene is investigated. • Analytical expressions of Young's modulus of triangle-like 3D graphene are derived. • The influencing factors for elastic properties of 3D graphene are studied by FEM. [ABSTRACT FROM AUTHOR]

The layered metal phosphorus trichalcogenides (MPTs) are a newly emerging van der Waals material family with bandgaps ranging from 1.3 to 3.5 eV, which are promising candidates for optoelectronic devices. By using the excited multiple energy levels of FePSe3, a high‐performance FePSe3 photodetector, which shows tunable response speed in the range of ultraviolet (UV) to near‐infrared (NIR), is designed. The FePSe3 photodetector exhibits a high photoresponsivity of 236.18 A·W−1 under 532 nm laser illumination (laser power density P = 1 mW cm−2). The properties of FePSe3 can be modulated by oxygen plasma treatment, which transfer to oxygen‐doped FePSe3 (FePSe3‐O). Moreover, the speed of the FePSe3‐O photodetector can be improved more than 240 times compared to the intrinsic FePSe3 photodetector under NIR illumination (λ = 808 nm). In addition, the FePSe3‐graphene heterojunction can significantly improve the photoresponsivity and simultaneously prolong the response time of the device due to the FePSe3/graphene interfacial barrier. These results suggest that intrinsic, doped FePSe3 and its heterojunction can be used as multifunctional photodetectors with tunable response speeds. [ABSTRACT FROM AUTHOR]

The negative Poisson's ratio (NPR) of graphene is studied via molecular dynamics (MD) simulations when epoxy groups are orderly arranged on its surface. When two epoxy groups are located on the same side of the zigzag bridge in a representative cell of graphene, a ripple area appears on the graphene surface. A truss structure model of the ripple is presented to reveal the nature of the NPR phenomenon due to the de-wrinkling effect during stretching. Based on this, the wrinkle region is defined as a periodic distribution unit, and it is evenly distributed along the X- and Y-direction in the 5 nm × 5 nm graphene, then it is found that graphene exhibits a remarkable negative Poisson's ratio phenomenon. In addition, the results show that the oxygen atoms proportion of graphene significantly influence its NPR, and the NPR is the most remarkable when the proportion of oxygen atoms is 4.2 %. [Display omitted] • NPR of graphene caused by epoxy group was studied by theoretical and MD method. • A truss structure model was presented to reveal the nature of NPR phenomenon. • The designed graphene containing epoxy groups exhibits remarkable NPR phenomenon. • NPR of graphene containing epoxy groups depends on the proportion of oxygen atoms. • GO with 4.2 % oxygen atoms has the most remarkable NPR. [ABSTRACT FROM AUTHOR]

The Poisson's ratio of the in-plane pristine armchair and zigzag graphene under uniaxial tensile loading is studied by molecular dynamics simulations, which indicates that Poisson's ratio strongly depends on the tensile strain. At the critical strain, the Poisson's ratio will transform from positive to negative, and the critical strain of the zigzag is far less than that of armchair. The study on the representative cell of graphene shows that the intrinsic nature of strain-induced negative Poisson's ratio (NPR) is the competition between the variation rates of bond length and bond angle. Meanwhile, the critical strain that induces NPR has significant size effects, which depends on the proportion of representative cells at the width boundary in the whole graphene. What's more, 5-8-5 defect has a significant effect on the NPR phenomenon of graphene. By introducing 5-8-5 defects into in-plane graphene, the critical strain value that induces NPR can be effectively regulated by adjusting the distribution modes and percentage of defects. The distributions of 5-8-5 defects adjacent to each other in the X-direction and Y-direction can significantly reduce the critical strain value. Furthermore, by increasing the percentage of 5-8-5 defects in graphene, the critical strain value can be reduced to about 50%, and the 5-ring defect plays a vital role in reducing the critical strain value. Based on this, a penta-graphene consisting entirely of 5-rings is constructed, and its Poisson's ratio is studied. The results confirm that the critical strain that induces NPR is 0. In a word, the NPR of in-plane pristine graphene can be induced by tensile strain, 5-8-5 defects can regulate the critical strain value of NPR, and penta-graphene is a perfect NPR material. [Display omitted] • Poisson's ratio will transform positive to negative at critical strain. • NPR originates from competition between the variation rates of bond length and bond angle. • The critical strain that induces NPR of graphene has significant size effects. • The distributions and percentage of 5-8-5 defects significantly reduce the critical strain. • The critical strain that induces NPR for a penta-graphene consisting entirely of 5-rings is 0. [ABSTRACT FROM AUTHOR]