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, 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 enthalpy of phase change and the equilibrium vapour pressure, as indicated by equations