Hydration structure of water confined between mica surfaces

We report further molecular dynamics simulations on the structure of bound hydration layers under extreme confinement between mica surfaces. We find that the liquid phase of water is maintained down to 2 monolayer (ML) thick, whereas the structure of the K(+) ion hydration shell is close to the bulk structure even under D = 0.92 nm confinement. Unexpectedly, the density of confined water remains approximately the bulk value or less, whereas the diffusion of water molecules decreases dramatically. Further increase in confinement leads to a transition to a bilayer ice, whose density is much less than that of ice Ih due to the formation of a specific hydrogen-bonding network.