Structure and dynamics of two-dimensional confined water

The structure and dynamics of water under a geometric confinement is of great significance due to its importance in water flow, surface chemistry and environmental sciences. The physical properties of water at an interface or in a nanopore are often different than its bulk counterpart and can strongly depend on the fine details of the confinement. A systematic understanding of the influence of the confinement on this rich behavior was, until recently poor, because of experimental limitations to access interfacial water structures. The discovery that graphene is stable in its two dimensional form has opened new research possibilities and it has proved to be an instrumental tool for the investigation of confined water structures. Its remarkable mechanical and electronic properties combined with scanning probe techniques allowed us to directly visualize and measure water structures that are confined between graphene and a variety of supporting substrates. Information regarding the influence of the interface structure and wettability, environmental humidity, temperature, pressure and the presence of foreign species on the structure and dynamics of confined water were experimentally accessed in situ and real time with scanning probe microscopies. The observed phase behavior, phase transitions and dynamics of the confined water structures underline the complexity of the governing physical mechanisms. We found that the behavior of the water molecules heavily depends on the confinement characteristics as well as temperature and pressure, which indicates the significance of the interface in defining the geometry of the ice phase. We conclude that a general picture of the state of water under confinement cannot be drawn without considering the exact confinement details and conditions.