The Kinetic Properties Of Alloy Solid-liquid Interfaces, The Structure And Stability Of Nano Systems: A Molecular Dynamics Study

The properties of interfaces play a central role in the structure, stability and kinetic properties of multi-phase systems. The thesis explores the kinetic properties of alloy solid-liquid interfaces, the surface effect on cluster structures, as well as the structural deformation and instability of an elastic tube driven by the interfacial free energies of an infiltrated liquid droplet. In particular, the first chapter of the thesis reviews the fundamentals related to the interface kinetics and thermodynamics. The third chapter introduces our research on the kinetic properties of alloy solid-liquid interfaces. The fourth chapter describes our results on the infiltrated liquid driven structural deformation and instability of an elastic tube. The structural phase dia-gram and a universal structural model are introduced in chapter five and chapter six, respectively. Molecular dynamics is introduced in chapter two.Key findings of the thesis are as following:(1) The molecular dynamics simulations is applied in the study of rapid solidifi-cation kinetics in a binary alloy system. Temperature gradients are found around the interface area during the solidification process, this phenomenon has never been re-ported before, it is of extremely importance in determining the correct supercooling temperature. A first quantitative relationship between growth velocity and partition coefficient is obtained, and the discontinuity change of the partition coefficient is observed. For the first time, the presence of appreciable solute drag is obtained in the simulations. Significant anisotropy of kinetic coefficient as well as partition coefficient are validated.(2) The capillary-induced structural deformation of an elastic circular tube par-tially filled by a liquid is studied by combining theoretical analysis and molecular dynamics simulations. The analysis shows that, associated with the deformation, there is a well-defined length scale (elasto-capillary length), which exhibits a scal-ing relationship with the characteristic length of the tube, regardless of the inter-action details. We validate this scaling relationship for a carbon nanotube partially filled by liquid iron.(3) The effect of the equilibrium pair separation on the evolution of cluster structures is investigated. The computational results demonstrate that the poten-tial with large equilibrium pair separation stabilizes decahedra and close-packed structures, while disordered structures appear for the potential with small equilib-rium pair separation. The icosahedral clusters are dominated in the middle range of equilibrium pair separation. For the small size clusters (N<24) the dominated structural motif is the polytetrahedra, which is almost independent of the details of the potential.(4) Two structural parameters are quantitatively defined to describe the defor-mation and the interface effect of clusters. Based on these two parameters, universal scaling law is found for different clusters (including geometric closed-shell struc-tures, non-closed-shell structures and metastable clusters) under certain structural motif, regardless of the interaction details. The evolution of the two structural pa-rameters can be understood by employing two basic structure units. Through ex-tending Wulff's construction, a universal energetic model for pair potential clusters is fomulated. The predicated'phase diagram'by this model is in good agreement with previous results.