Two dimensional ice has been confirmed to play a ubiquitous role in many physical processes like surface wetting, antifreezing, adhesion, friction, etc. Though many work has been done on investigating two-dimensional ice on various solid surfaces, the geometry and thermodynamics of ice formation in salt solutions at the solid-liquid interface are still less understood, due to the complex interactions between salt ions, water molecules, and solid surfaces.

Motivated by such a challenge, a research team led by Prof. CHEN Jige at Shanghai Advanced Research Institute (SARI) of the Chinese Academy of Sciences reported a systematic study of the two-dimensional rhombic ice formation process from various aqueous solutions at ambient temperature under strong compressed confinement of graphene.

The research results were published as a Letter in Physical Review E.

The classical molecular dynamics simulation (MD) shows that two rhombic ice phases grow from the aqueous salt solutions by applying continuous external compression in the confined graphene layers.

The rhombic ice phases possess identical geometry and thermodynamic properties such as the configuration entropy, tetrahedral order parameter, and hydrogen bond number, but with different projections of the oxygen atoms against solid surface symmetry.

The density functional theory (DFT) calculation reveals that the rhombic ice phase relates to the stable and metastable arrangements of water molecules. The rhombic ice formation is a general phenomenon in different aqueous solutions like NaCl, LiCl, KCl, CaCl₂ , MgCl₂ , and AlCl₃ solutions, etc.

The result indicates salt ions and the hydration shell of water molecules around salt ions would heavily contribute to the ice formation process. It is thus particular important in practical applications since salt ions are commonly present in our liquid environment.

The result further enlightens our understanding of the ordered geometry of water molecules and the complex hydrated structures on the solid surface. 

Contact: CHEN Jige

Shanghai Advanced Research Institute

Email:chenjg@sari.ac.cn