Search

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]

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]

One way to increase the ductility of metallic glasses is to induce heterogeneous microstructures, as for example in nanoglasses and crystal-glass composites. The heterogeneities have important consequences not only on the development of shear bands, but also on the structural relaxations in the glass phase. Experiments using dynamic mechanical spectroscopy (DMS) have been conducted, but an atomic-scale picture is still lacking. Here we apply DMS within molecular dynamics simulations to a classical CuZr metallic glass to study how structural relaxations and mechanical energy dissipation are affected by different microstructures, including nanoglasses, crystal-glass nanolaminates and glasses with spherical crystalline inclusions. We find that in a fully glassy system, not only the fraction but also the spatial homogeneity of "hard" icosahedral environments matter. When hard crystalline particles are introduced, the storage modulus simply results from volumetric averages consistent with the classical Voigt and Reuss bounds. On the other hand, loss moduli are much more complex and can be smaller or larger than in a pure glass depending on the microstructure and loading condition. Atomistic processes leading to these evolutions are discussed and remaining open questions are highlighted. [Display omitted] [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]

Soil and ground water pollution by heavy metal is an identified global environment concern. Montmorillonite is widely adopted as an adsorbent used in retardation of heavy metals due to its excellent adsorption capacity, conveniency, and stability. However, the adsorption mechanism of heavy metal ions in the interlayer and nanopore of montmorillonite needs to be further studied. The classical grand canonical monte carlo (GCMC) and molecular dynamics (MD) simulations were performed to quantify the structural and dynamic properties of heavy metal ions in the interlayer and nanopore of montmorillonite (MMT). Two layer charge densities of MMT, two cation concentrations, and three typical heavy metal ions (Pb2+, Ba2+, and Cs+) were considered. With the increase of layer charge density, outer-sphere adsorption (OSA) was transformed into inner-sphere adsorption (ISA) for three heavy metal ions. The adsorption quantity increased with the increase of layer charge density and cation concentration. The calculated diffusion coefficients of three heavy metal caions in montmorillonite was bulk solution > nanopore > interlayer. The results and adsorption mechanism are helpful for understanding the natural processes of heavy metal ions in environment and developing more efficient remediation materials. [Display omitted] • Outer-sphere adsorption occurred for Pb2 + and Ba2 + on low-charge montmorillonite surface. • The adsorption capacity of high-charge montmorillonite was stronger than low-charge montmorillonite. • Higher cation concentration increases adsorption quantity but doesn't change adsorption pattern. • The mobility of cations in montmorillonite follow the order of interlayer < nanopore < solution. [ABSTRACT FROM AUTHOR]