  Direct observations of the surface and shape of model nano-colloidal gels
associated with measurements of the spatial distribution of water content
during drying show that air starts to significantly penetrate the sample when
the material stops shrinking. We show that whether the material fractures or
not during desiccation, as air penetrates the porous body, the water saturation
decreases but remains almost homogeneous throughout the sample. This
air-invasion is at the origin of another type of fracture due to capillary
effects, these results provide a new insight in the liquid dynamics at the
nano-scale. PACS number(s): 47.56.+r, 68.03.Fg, 81.40.Np
