2. Adsorption, capillarity

Two fundamental mechanisms help to "bind" a fluid to a porous matrix. These are, respectively, capillarity and adsorption .

In the latter case, the vapor molecules are chemically or physically attached to the inner surface of the pores in the form of a film. The molecular films thus formed are then in equilibrium with the vapour under conditions that are sometimes very different from conventional thermodynamic conditions, with the effect of modifying the phase-change enthalpy and equilibrium vapour pressure, as indicated by the equations and