Molecular Dynamics Simulations For Micropore/Surface And Complex Fluids

Molecular dynamics simulation plays an important role in chemical engineering and material science in recent years. It can simulate equilibrium structure and dynamics properties of fluids under extreme conditions such as supercritical fluids and supercooled fluids. Behaviors of confined fluids in micropores or on amorphous surfaces can also be obtained by molecular dynamics simulations, which are difficult by direct access to experimental measurement. Moreover, molecular dynamics simulation is a powerful tool in investigating the hydrogen bonding structure of aqueous solutions at a molecular level. In this thesis, several complicated systems are studied by molecular dynamics simulation. 1. Structure property and diffusion behaviors of dense carbon dioxide confined in a series of clay slit pores are studied. The structural and dynamics properties of the dense carbon dioxide are important in material synthesis and adsorptive separation. This study will assist in understanding the mechanism and process in the intercalation of functional molecules into clay mineral and the containment removal from clay sediment by using supercritical carbon dioxide. It is observed that the confined CO2 fluids form obvious layers near the clay surface. The density profile and structure of carbon dioxide vary with pore width and only the fluids in the contact layer show long-range order. Near the clay surface the oxygen atoms of carbon dioxide form a solid-like structure. The self-diffusion coefficient and the orientation correlation time are calculated to investigate the detail behaviors of confined carbon dioxide. 2. Molecular dynamics simulations are performed to study the behaviors of dense carbon dioxide on amorphous silica surface. Silica is used extensively as semiconductor material in electronic industry and the application of dense carbon dioxide on microelectronics processing are attractive for its special physical chemistry properties. Thus, the studies of structure and dynamics properties of dense carbon dioxide on silica surface are required in order to develop the process. From the simulation, the carbon dioxide molecules form a high density layer in the proximity of the silica surfaces. The density profile and the free energy profile of carbon dioxide have a "mirror symmetry", where the high density coincides with the free energy well. The diffusion coefficients of carbon dioxide near the silica surface are anisotropic. The translational diffusivities of the carbon dioxide at the silica surface are hindered and the rotational diffusivities are enhanced compared to bulk fluids. The residence time of carbon dioxide near the silica surface is almost five times the size of that in middle layer. 3. The structure and diffusion properties of ethanol/water mixtures are studied by molecular dynamics simulation. The physical chemistry properties of the alcohol solutions play important roles in theoretical study and technological application involving mass transfer, and the solution structure behaviors is very fundamental to understand the mixture diffusion phenomenon. Analyzing the local structure by the O-O and O-H radial distribution functions obtained from the simulation, the ethanol-ethanol hydrogen bonding structures are broken as the water concentration increases. The strong correlations between ethanol and water molecules lead to an enhancement in the ethanol-water structure with ethanol concentration increasing. The simulated self-diffusion coefficients of water and ethanol under different concentrations are larger than the experimental data. The self-diffusion coefficient of water is described by the combining contribution of the "bound"and "free"water molecules. The mutual diffusion coefficients obtained by the MD simulation are in fair agreement with the experimental data in the ethanol/water mixture. The effects of concentration and microstructure of mixtures on the diffusion coefficient are investigated by the simulation data.