Wetting and capillary phenomena of water on mica

The structure of water films on mica was locally modified by contact with the tip of an atomic force microscope (AFM) in a humid environment. The subsequent evolution of the film was studied by noncontact scanning polarization force microscopy. At high relative humidity (>20%), capillary condensation caused water to form droplets and two-dimensional islands around the contact point. The droplets evaporated in a short period of time, but the islands remained for much longer periods (hours). At low relative humidity (>20%), the tip contact produced a circular depression in the local polarizability. None of these structures could be observed in contact AFM images which revealed only the usual atomically flat mica surface.