  Water molecules play a fundamental role in the physics of slow crack
propagation in glasses. It is commonly understood that, during
stress-corrosion, water molecules that move in the crack cavity effectively
reduce the bond strength at the strained crack tip and, thus, support crack
propagation. Yet the details of the environmental condition at the crack tip in
moist air are not well determined. In a previous work, we reported direct
evidence of the presence of a 100 nm long liquid condensate at the crack tip in
fused silica glass during very slow crack propagation (10^-9 to 10^-10 m/s).
These observations are based on in-situ AFM phase imaging techniques applied on
DCDC glass specimens in controlled atmosphere. Here, we discuss the physical
origin of the AFM phase contrast between the liquid condensate and the glass
surface in relation to tip-sample adhesion induced by capillary bridges. We
then report new experimental data on the water condensation length increase
with relative humidity in the atmosphere. The measured condensation lengths
were much larger than what predicted using the Kelvin equation and expected
geometry of the crack tip.
