Simulations Of Operating System And Driving Process On Micro/nano Scale

A macroscopic object or a long-term process consists of a number of components(even small to atoms)which can be taken as systems.With the development of science and technology,computer simulation will become an important assistant tool for the study of microscopic structure and behavior of material.To observe every detail on the atomic scale has been the dream of people.In order to observe the details of system or process clearly,researchers focus on achievement of the whole system or process simulation.Generally,a small-scale system with the characteristics of simple operation can be simulated by the classical molecular dynamics method.However,for a complex system or a long-time process,molecular dynamics cannot be carried out based on the limitation of its calculation ability.How to keep the key details of the process and close to the actual process on the calculation scale is the key point to solve the problem..This thesis regarded micro/nano scale as cutting point,and simulated the system and process,respectively.We carried out the system research on the deformation behavior and mechanism of FCC Ag nanowire upon the tensile loading by using molecular dynamics.It could be the theoretical foundation to build nano mechanical device with high strength;On the other hand,we took the example of common gas chromatography analysis,and simulated the separation process by random walk in confined space.It aims to reveal the diffusion and separation mechanism of particles to be separated in the chromatographic column,so as to provide guidance and reference for the optimization of separation conditions and the improvement of chromatographic column.The specific contents include the following parts:1.Investigation on the tensile deformation mechanism of the faceted single Ag nanowireThe faceted Ag nanowire is composed of several square frustums with the same size.The simulations of the deformation behavior of the faceted Ag nanowire are performed.The effect of the square frustum height,the temperature and the stretching rate on the elastic deformation,the initial plastic deformation and the fracture behavior are investigated.The simulation results show that the surface morphology is the dominant controlling factor of the faceted nanowire.Different from the brittle fracture mode of other nanowires,the fracture mode of the faceted nanowire is mainly influenced by the temperature and the tensile rate.It is easy to exhibit the brittle fracture behavior at low temperature.In addition,two kinds of models of the external line defect and the inner void defect were designed for the faceted nanowire,and the effect of defect size on the yield stress was studied.The results show that the void defect more easily affects the yield behavior of the faceted nanowire than the line defect.2.Investigation on the tensile deformation mechanism of the twin Ag nanowire The tensile deformation behavior of<111>crystal orientation twin Ag nanowire was studied by molecular dynamics method.Firstly,the different twin boundary density can weaken or strengthen the nanowire by comparing with the strength of the single crystal nanowire.And it is found that the ultimate stress can exponentially rise with the increase of reciprocal of twin lamellar thickness.Secondly,the sectional area and the length of the twinned nanowire were also considered.The results show that the large twin area helps to improve the strength.However,the change of the length has little effect on the strength.Lastly,the faceted twinned nanowire was designed.Comparing with the square twin with the same size,we found that the introduction of{111} surface can further strengthen the nanowire,but it is less effective than twin boundary.3.Simulation of particle diffusion process in a GC packing columnIn order to thoroughly understand the influence of particle diffusion on chromatographic dynamics,the diffusion of the particles to be separated in a GC packing column was dynamically simulated by using random walk in confined space on micro scale.The effects of filling rate and arrangement of stationary phase,column pressure as well as column length on chromatographic dynamics are investigated.The results show that short column and high filling rate are conductive to improve column efficiency,but arrangement of stationary phase has little effect.The particles to be separated normally show basic diffusion characteristics,and their axial dispersion behaviors are more apparent with the increase of column pressure.4.Simulation of particle separation process in a GC open tubular columnThe interaction between the particle and the barriers is described by the adsorption model.The simulation of the whole separation process in a GC open tubular column is realized by the dynamically tracing the trajectories of the particles.Firstly,the establishment of the separation model is described,and the method of determining the simulation conditions is found by means of inter restricted relationship of simulation parameters.According to the part of experimental data and Kovats Retention Indices,the functions of adsorption step number and temperature as well as the carbon number were established respectively,so as to explore the separation method of the homologues under different temperature and pressure conditions.The separations of alkanes and alcohols are simulated,and the results show that this method can accurately predict the retention time and describe the basic characteristics of chromatographic peak.