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On the hydrogen bonding structure at the aqueous interface of ammonium-substituted mica: A molecular dynamics simulation

L. Narasimhan 1 Andrey G. Kalinichev 1
1 SUBATECH - Radiochimie
SUBATECH - Laboratoire SUBATECH Nantes
Abstract : Molecular dynamics (MD) computer simulations were performed for an aqueous film of 3nm thickness adsorbed at the (001) surface of ammonium-substituted muscovite mica. The results provide a detailed picture of the near-surface structure and topological characteristics of the interfacial hydrogen bonding network. The effects of D/H isotopic substitution in N(H/D)4+ on the dynamics and consequently on the convergence of the structural properties have also been explored. Unlike many earlier simulations, a much larger surface area representing 72 crystallographic unit cells was used, which allowed for a more realistic representation of the substrate surface with a more disordered distribution of Al/Si isomorphic substitutions in muscovite. The results clearly demonstrate that under ambient conditions both interfacial ammonium ions and the very first layer of water molecules are H-bonded only to the basal surface of muscovite, but do not form H-bonds with each other. As the distance from the surface increases, the H-bonds donated to the surface by both N(H/D)4+ and H2O are gradually replaced by the H-bonds to the neighboring water molecules, with the ammonia ions experiencing one reorientational transition region, while the H2O molecules experiencing three such distinct consecutive transitions. The hydrated N(H/D)4+ ions adsorb almost exclusively as inner-sphere surface complexes with the preferential coordination to the basal bridging oxygen atoms surrounding the Al/Si substitutions.
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L. Narasimhan, Andrey G. Kalinichev. On the hydrogen bonding structure at the aqueous interface of ammonium-substituted mica: A molecular dynamics simulation. Zeitschrift fur Naturforschung a, Verlag der Zeitschrift Fuer Naturforschung, 2013, 68, pp.91-100. ⟨10.5560/ZNA.2012-0101⟩. ⟨in2p3-00768710⟩

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