Molecular Structure, Diffusion Dynamics and Hydration Energetics of Non-Confined Water and Water at Mineral Surfaces

242 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2004.Molecular dynamics (MD) computational modeling studies of the structure, dynamics and energetics of water at surfaces and in nano-confined spaces provide greatly increased, atomistically detailed understanding of the effects of surface structure and composition on the structural ordering, hydrogen bond organization, interfacial transport and hydration energetics of H2O molecules. Interaction between water and solid surfaces and changes in the structural and dynamical behavior resulting from local electric fields, geometric confinement, different bonding geometries and different surface structures can substantially affect the properties of both phases in the near surface region. These interactions are of significant interest in geochemistry, materials technological and biology in cases where the aqueous phase is strongly perturbed by the surface and continuum models of the fluid fail to adequately capture surface effects. MD methods are, thus, rapidly developing as important tools for predicting and understanding the interaction of aqueous solutions with rocks, sediments, soils and other natural and synthetic materials. This thesis presents the results of a series of MD studies designed to evaluate the effects of the crystal structure, structural charge, and surface charge distribution of the substrate on ordering and local structure of near-surface water, its hydrogen bond network, diffusive dynamics and energetics. Results for brucite [Mg(OH)2], gibbsite [Al(OH)3], and hydrotalcite [Mg2Al(OH)6Cl·2H2O] will illustrate these effects for hydroxide phases, and results for talc [Mg3Si 4O10(OH)2] and muscovite [KAl2(Si 3Al)O10(OH)2] those for silicates. Topics highlighted include the transition from the first layer of surface water to bulk water, interlayer hydration energetics, the low-frequency vibrational dynamics of nano-confined species, confined 2-dimensional ice and its melting, and the structure of the 10A phase (a potential water reservoir in the earth's mantle). Results are discussed in terms of computed density profiles, orientational ordering statistics, two-dimensional radial distribution functions, a tetrahedral order parameter, structural details of the H-bonding network, diffusive dynamics, and hydration energetics.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD