Molecular Simulation Of Hydration Layer On Quartz Surface In Water

Hydration layers play a very important role in many fields such as biology,material science and engineering, environmental science and engineering, etc. Inmineral processing, it strongly affects mineral flotation and dispersion. By improve thehydrophilic property of the mineral surface, the thickness of hydration layer and thehydration repulsion force is higher, mineral is been scattered in a stable state.Therefore studying the properties of hydration layer on mineral is significant formineral flotation and dispersion. Numerous experimental approaches have been carriedout to understand the hydration layers on mineral surfaces in water. However, due tothe limitation in space and time, the have not revealed all the behavior of hydrationlayers.As a method to study complex microcosmic system, molecular simulation notonly can obtain the dynamic trajectory of atoms but also can research the microcosmicdetails of atomic motion. With small scales in both time and space, molecularsimulation might obtain the details on the microscopic information of the hydrationlayers which can’t been observed by experimental approaches. This paper attempts touse molecular dynamic simulation method to research the hydration layer on quartz(001) surface, the result show that the water molecules in hydration layers have ahigher density and the lower the coefficient of the self diffusion. The coefficients of theself diffusion in two directions both parallel to the surface are similar and much higherthan it in direction perpendicular to the surface. It indicates that hindrance to watermolecules motion in the direction perpendicular to the surface is bigger than it in thedirection parallel to surface.The hydration layer on before hydration and hydration (001) α-quartz surface hasbeen studied by the molecular simulation method. The results indicate that thehydration layer on the hydration surface of the α-quartz is1nm, the maximum densityis1.45g/cm3, the diffusion coefficient is small, there are a large number of hydrogenbonds formed between the–OH groups on the surface and water; but hydration layer on the before hydration surface is thinner only0.4nm and the density is smaller, themaximum density is1.24g/cm3, the diffusion coefficient is larger, there is a vacuumformed between the surface layer and water instead of hydrogen bond.The different quartz surfaces in different alkali condition have been built, and themolecular dynamic simulation of water on these surfaces has been done. The resultsshow in alkali condition, the density of hydration layer on surface is1.5227g/cm3larger it in no alkali condition is1.5134g/cm3. It indicates that the alkali condition isbenefit to form the hydration layer on quartz surface.The molecular dynamic simulation of water on the negatively charged quartzsurface and electrically neutral quartz surface, show that the density of hydration layeron the negatively charged surface is higher, but the coefficient of the self diffusion islower. It demonstrates that compared with the electrically neutral surface, with chargeis better to form hydration layer.