Session: Molecular Processes at Mineral-Water Interfaces:

Interactions between water and metal oxide interfaces become an increasing popular topic in recent years. In this work, we investigated the water/alumina (0001) and (1120) interfaces using classical molecular dynamics simulations. Simulated contact angles show complete wetting for both surfaces but we found that the (0001) surface is more hydrophilic than the (1120) surface by comparing the free energy of removing interfacial water. Interfacial water molecules show two major orientations, pointing to or away from the solid surface; in the former case, waters donate stronger hydrogen bonds to the surface, while in the latter they accept relatively weaker ones, generating vibrations at the 3200 cm^-1 and 3400 cm^-1, respectively, which is in agreement with vibrational sum frequency generation spectra. On the (0001) surface, the strong hydrogen bonds that water donates to the surface have a longer lifetime as well, but long lifetime hydrogen bonds on the (1120) surface are due to the limitation of surface OH motions. Interactions between both surfaces and interfacial waters promote a templating effect whereby the latter are aligned in a pattern that follows the configuration of the mineral surfaces. Finally, we compare the surface OH angle distributions and their hydrogen bond modes for the two surfaces. This work improves our microscopic insight into structure of water/alumina interfaces.

Michael Klein

Temple University

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