Salt-Water System under Diamond Confinement

Abstract

Deriving inspiration from the salinity of ice VII inclusions in excavated diamonds, we explore the phase behavior of quasi-two-dimensional salt water in diamond nanoconfinement via molecular dynamics simulations. We construct the compression-limit phase diagram for several slit widths over a wide range of gigapascal-high lateral pressures. We observe the assembly of solid-like amorphous monolayer, bilayer, and trilayer phases, distinct from the ordered structures found in both pure bulk water and quasi-two-dimensional confined water. The underlying mechanism of dehydration, caused by the disruptive presence of ions, and the concomitant destruction of the long-range order of the encapsulating water hydrogen-bond network are critically analyzed. Orientational analyses of the constrained salt-water system reveal ties to interlayer water hydrogen bonding and the preferential arrangement of ion and water layers. Our results offer fresh insight into the formation and structural characteristics of the phases exhibited by nanoconfined salt water.