  The disjoining pressure isotherm in foam films is theoretically studied and
an important contribution of adsorption is discovered. On the basis of the
interfacial thermodynamics an adsorption disjoining pressure component is
derived, which is repulsive and exponentially decaying by the film thickness.
Expressions for its magnitude and decay length are derived in terms of
well-known thermodynamic characteristics such as the partial Gibbs elasticity
and adsorption length. Several adsorption isotherms are considered and the
corresponding adsorption disjoining pressure components are calculated. An
important coupling between the interfacial layer phases and wetting transitions
is discussed as well.
