Water Structure on Mica Surfaces: Investigating the Effect of Cations

We studied thin films of water at the mica-air interface using infrared spectroscopy and molecular dynamics simulations. We investigate the influence of ions on interfacial water by exchanging the naturally occurring K+ ion with H+/Na+, Ca2+, and Mg2+. The experiments do not show a difference in the bulk structure (i. e. in the infrared spectra), but indicate that water is more strongly attracted to the Mg2+ mica. The simulations reveal that the cation-water interactions significantly influence the microscopic arrangement of water on mica. Our results indicate that the divalent cations result in strong water-mica interactions, which leads to longer hydrogen bond lifetimes and larger hydrogen bonded clusters of interfacial water molecules. These results have implications for surface-mediated processes such as heterogeneous ice nucleation, protein assembly and catalysis.