Nanoscopic friction as a probe of local phase transitions

We study nanoscopic friction forces between an atomic force microscope tip and a glass sample. We show how and why it is possible to tune friction forces in a predictable way by changing either the sample temperature, or the humidity in the experimental chamber. We relate the friction behavior to confined water phase transitions. We find that the water gas-liquid phase diagram is the same at the macroscopic scale as at the nanoscopic tip-sample contact.