Real-space visualization of intercalated water phases at the hydrophobic graphene interface with atomic force microscopy

The phase behavior of water is a topic of perpetual interest due to its remarkable anomalous properties and importance to biology, material science, geoscience, nanoscience, etc. It is predicted confined water at interface can exist in large amounts of crystalline or amorphous states. However, the experimental evidence of coexistence of liquid water phases at interface is still insufficient. Here, a special folding few-layers graphene film was elaborate prepared to form a hydrophobic/hydrophobic interface, which can provide a suited platform to study the structure and properties of confined liquid water. The real-space visualization of intercalated water layers phases at the folding interface is obtained using advanced atomic force microscopy (AFM). The folding graphene interface displays complicated internal interfacial characteristics. The intercalated water molecules present themselves as two phases, low-density liquid (LDL, solid-like) and high-density liquid (HDL, liquid-like), according to their specific mechanical properties taken in two multifrequency-AFM (MF-AFM) modes. Furthermore, the water molecules structural evolution is demonstrated in a series of continuous MF-AFM measurements. The work preliminary confirms the existence of two liquid phases of water in real space and will inspire further experimental work to deeply understanding their liquid dynamics behavior.