Phase equilibria of absorbed liquids and the structure of porous media

The phase equilibria of water within porous silica has been studied by proton and deuteron magnetic resonance. Proton signal amplitude as a function of filling factor was measured. These protons arise from the proton-deuterium equilibrium that is established between the liquid and the absorbed layer on the pore wall. The results for temperatures below 0°C show a maximum as a function of filling factor, Θ. This suggests that the pores fill from either a surface layer or from the crevices and interstices into the center. Another experiment used cryoporometry to study the size of crystals formed within the pores as a function of Θ and leads to the same conclusion.