Phase behavior of capillary bridges: towards nanoscale water phase diagram.

Water capillary bridges often condense at contact spots between small particles or asperities. The capillary adhesion force caused by these bridges is a major component of the attractive adhesion force, and thus it significantly affects the nanotribological performance of contacting surfaces. Recent atomic force microscope (AFM) measurements indicate that phase behavior of water in these tiny bridges may be different from macroscale water behavior. In particular, a metastable state with a deeply negative pressure, boiling at low temperatures, and ice at room temperature have been reported. Understanding these effects can lead to a modification of the traditional water phase diagram by creating a scale-dependent or nanoscale phase diagram.