Screening surface-liquid interaction

I See the Saunders Interactive General Chemistry CD-ROM, Screen 13.11, Properties of Liquids (4) Surface Tension/Capillary Action/ Viscosity. 

The main differences between adsorption from the gas phase and that from liquid phase are as follows [3]. First, adsorption from solution is essentially an exchange process, and hence, molecules adsorb not only because they are attracted by solids but also because the solution may reject them. A typical illustration is that the attachment of hydrophobic molecules on hydrophobic adsorbents from aqueous solutions is mainly driven by their aversion to the water and not by their attraction to the surface. Second, isotherms from solution may exhibit nonideality, not only because of lateral interactions among adsorbed molecules but also because of nonideality in the solution. Third, multilayer adsorption from solution is less common than from the gas phase, because of the stronger screening interaction forces in condensed fluids. 

In adsorption from solution, physisorption is far more common than chemisorption, although the latter is sometimes possible. Solute adsorption is usually restricted to a monomolecular layer, since the solid-solute interactions, although strong enough to compete successfully with solid-solvent interactions in the first adsorbed monolayer, do not do so in subsequent monolayers, because the interaction is screened by the solvent molecules. Thus, multilayer adsorption has only rarely been observed in a number of cases, and identified, when the number of adsorbate molecules exceeds the number of mono-layer molecules possible on the total adsorbent surface area. However, this analysis cannot be applied to polymer adsorption, because it is generally impossible to determine the surface area of a monomolecular layer of a polymer adsorbed flat on the solid surface. This is because the adsorbed polymer can only be anchored to the surface at a few points, with the remainder of the polymer in the form of loops and ends moving more or less freely in the liquid phase. 

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