Example
Consider liquid, its vapors and the solute as a two-phase two-component system. Let the properties of the vapor be represented by []' and the properties of the liquid phase by []".
(1) represents solvent and
(2) represents solute.
If the solute is non-volatile (surfactants are usually non-volatile), then . Further, since concentration of solvent in vapor phase is very small compared to that in the bulk liquid phase, we have .
From the above discussion we have
If we consider the bulk solubility of the surfactant to be small then
This is a limiting case implying that all the surfactant has gone to the surface.
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