Yinlu Sun

Effective Brownian Ratchet Separation by a Combination of Molecular Filtering and a Self-Spreading Lipid Bilayer System

A new molecular manipulation method in the self-spreading lipid bilayer membrane by combining Brownian ratchet and molecular filtering effects is reported. The newly designed ratchet obstacle was developed to effectively separate dye-lipid molecules. The self-spreading lipid bilayer acted as both a molecular transport system and a manipulation medium. By controlling the size and shape of ratchet obstacles, we achieved a significant increase in the separation angle for dye-lipid molecules compared to that with the previous ratchet obstacle. A clear difference was observed between the experimental results and the simple random walk simulation that takes into consideration only the geometrical effect of the ratchet obstacles. This difference was explained by considering an obstacle-dependent local decrease in molecular diffusivity near the obstacles, known as the molecular filtering effect at nanospace. Our experimental findings open up a novel controlling factor in the Brownian ratchet manipulation that allow the efficient separation of molecules in the lipid bilayer based on the combination of Brownian ratchet and molecular filtering effects.

Investigation on the mechanical behaviour of faceted Ag nanowires

Using molecular-dynamic (MD) simulation, we investigated the mechanical response of faceted silver nanowires (NWs) to tensile deformations. The investigation considers different frustum heights, temperatures and 3D void effects to study the yield elasticity, incipient plasticity and ductility of the faceted NWs. The embedded-atom-method (EAM) potential is employed to describe the atomic interactions. To identify the defect evolution and deformation mechanism, the centrosymmetry parameter is implemented in our self-developed programme. A detailed discussion of surface-dominated deformation behaviour has been presented. It is found that the faceted NWs show brittle breaking behaviour in low temperature, which has never been reported in other NWs. This temperature-dependent breaking mode, as reported in this paper, might be useful in avoiding certain deformation mechanisms of metallic NWs in future.

Simulation for diffusion behaviour of molecules in nanopattern-supported lipid bilayers based on random walk theory

In both the scientific and the technological approach, molecular manipulation with microscopic obstacles is of great importance. Recently, the application of a self-spreading lipid bilayer has attracted growing interest for its ability to transport any molecule in any desired direction. In this paper, we propose a new model, which imitates a self-spreading lipid bilayer on a substrate with metallic nanobarriers, to simulate the diffusion behaviours of molecules within it based on the random walk (RW) theory. The barriers are designed as Jones Tsais experiments. The barriers length, width, spacing, gap and interaction energy with molecules are investigated in this paper. The mean square displacement and diffusion coefficients (D) were calculated based on our simulation results. The results show that our simulation is consistent with the experiments. Comparing with the experimental techniques, this simulation work has improved the time- and space-resolution. Furthermore, it can simulate in rather long time-scale. Our RW models are expected to provide theoretical foundation for single molecular observation of hop diffusion in a lipid bilayer with metallic nanogates.

A study on the effects of twin boundaries and surface morphology on deformation behaviours of silver nanowires

Nanoscale twin boundaries (TBs) and surface morphology play a significant role in the yield behaviour of nanowires (NWs). However, few studies have directly compared their effects on the mechanical response of metal NWs. In this article, the mechanical properties of three 〈1 1 1〉 silver NWs with a diameter of 12.2 nm are studied using molecular dynamics simulations. The 〈1 1 1〉 silver NWs are single crystalline rectangular NWs (SCNW), twinned rectangular NWs (TRNW) and faceted twinned NWs (FTNW), respectively. Comparing SCNW and the twinned NWs, we found that a superior combination of higher strength and elasticity was achieved in the twinned NWs by introducing the TBs in elastic region. Then, we also found that the yield strain of FTNW have a strong dependence on TB spacing. Furthermore, a comparison of the incipient plastic deformation between TRNW and FTNW has been made by monitoring defects evolution. To identify the defects evolution, a centrosymmetry parameter was defined and implemented in the self-developed program. And we also compared the effect of TB and surface morphology on mechanical response of three silver NWs. In general, it can be concluded that TBs significantly influence the mechanical properties of metallic NWs and it is more essential than surface morphology.

Theoretical simulation of chromatographic separation based on random diffusion in the restricted space

The diffusion behavior of particles in the chromatography is a fundamental issue of chromatographic dynamics. The understanding of the diffusion behaviors is particularly critical to optimize the operation conditions, improve the chromatographic performance and design a new separation device. Many of the present simulations focus on chromatographic thermodynamics, and very few aim at the overall diffusion and separation process. In order to dynamically trace the trajectory of the diffusing particles and to perform simulations of the whole chromatographic process, we have developed a model based on the framework of random walk in the restricted space and performed the simulation of a single particle diffusion in the gas chromatography. The simulation parameters were determined by comparing with the experimental data. The elution profiles of n-alkanes under different flow rates were accurately simulated with the method. The results show that the relative difference between the measures and the simulations are less than 2% and 10% for the retention time and the peak width, respectively. The simulation method shows great significance for the optimization of separation conditions and the development of novel technologies of chromatographic separation.

Twin boundary spacing-dependent deformation behaviours of twinned silver nanowires

Twin boundary spacing (TBS) plays a significant role in the yield behaviour of twinned nanowires (NWs). However, few studies have shown an overall view of the effects on the mechanical response of twinned silver NWs under tensile loading. In this article, the mechanical properties of 〈111〉-oriented NWs with different TBSs are studied using molecular dynamics simulations. In elastic region, it is found that the addition of twin boundaries (TBs) to crystalline NWs can not only cause strengthening but also softening effect, which depending on the ST/SF (the ratio of the total area of TBs to the area of lateral free surfaces). Furthermore, our simulation results show that the evolution of reduced number of different types of atoms in twinned Ag NWs has a strong dependence on TBS. For twinned NWs with larger TBSs, the dislocation–TB interaction dominates the plastic deformation process. While for twinned NWs with smaller TBSs, shear banding is activated as the incipient plastic deformation, leading to the atoms clustering into disorder near the surfaces. The study will be helpful to the further understanding of TB-related mechanical properties of nanomaterials.