Adsorbate Layering in Narrow-Pore Materials

Yu. K. Tovbin

Karpov Research Institute of Physical Chemistry, ul. Vorontsovo pole 10, Moscow, 105064 Russia

e-mail: tovbin@cc.nifhi.ac.ru

Received January 31, 2008

Abstract—The conditions of layering of adsorbate molecules in porous systems with characteristic sizes of
from 1 to 50–100 nm are discussed. The porous systems contain both very narrow pores, in which interaction
potentials of pore walls overlap, and comparatively broad pores without overlapping of surface potentials.
Three pore size intervals are distinguished. In the first interval, no adsorbate layering occurs, the second interval
is characterized by capillary condensation with critical parameters different from their volume values, and, in
the third interval, capillary condensation conditions are almost the same as in the volume adsorbtive phase. Cri-
teria of the characteristic pore sizes of different geometries are formulated; the criteria correspond to small vol-
umes in which first-order phase transitions are absent. The boundary between the first and second pore size
regions is observed experimentally as the disappearance/appearance of hysteresis loops in adsorption-desorp-
tion isotherms measured under strictly equilibrium conditions as the size of pores decreases/increases. A non-
uniform distribution of the surface potential is shown to be responsible for the multiplicity of local regions in
porous media with their own vapor–liquid coexisting phases. The spinodal transitions in adsorption-desorption
in pores can occur between various local regions. An analysis is performed in terms of the lattice gas model
with short-range Lennard-Jones interaction of adsorbate molecules with each other and adsorbent walls.

DOI: 10.1134/S0036024408100014

Pleiades Publishing home page | journal home page | top

If you have any problems with this server, contact webmaster.