Liquid adsorption, physisorption mechanisms

Physisorption arises from the van der Waals forces, and these forces also condense gas molecules into their liquid state. Thus, in principle, there is no reason to stop upon completion of a monolayer during physisorption. Indeed, the formation of multi-layers, which are basically liquid in nature, is very common in physisorption experiments. Brunauer, Emmett and Teller developed a theory in 1938 to describe physisorption, where the adsorbate thickness exceeds a monolayer, and this isotherm equation is known by the initials of the authors (B.E.T.). The original derivation of the B.E.T. equation is an extension of Langmuir s treatment of monolayer adsorption from kinetic arguments. Later, in 1946, Hill derived this equation from statistical mechanics. In the B.E.T. isotherm, it is assumed that ... 

In the mesoporous range for MCM-41, each steps of the water adsorption mechanism are well identified by neutron diffraction the physisorption of the first molecules on the rough MCM-41 wall, then the whole filling of the MCM-41 mesopore by water molecules. The usual molecular water organisation is measured (confined liquid phase, confined nanociystallites of cubic ice). The confinement effect, the displacement of the whole water phase diagram towards the low temperature side is quantifi decreasing the MCM-41 pore size increases the temperature displacement. 

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