There exist many thermodynamic models and experiments to explain the behaviors of water molecules in bulk liquid, ice, at charged interfaces, etc... And then there is also a couple of thermodynamic models for micellization in the liquid phase. However, the behavior of water before and after the adsorption of surfactant molecules at the solid/liquid interface has not been well discussed. Notice that this discussion only limits to the general idea in terms of thermodynamic terms explaining whether or why water lets the surfactant occupy the adsorption sites. The structural behavior of interfacial water may be too specific and requires other techniques to find out.
The thermodynamics of surfactant solutions at the interface between the phases solution - solid is well developed. This science is called thermodynamics of adsorption at liquid-solid interface.
Yuri Mirgorod Thanks. Most of the articles/books I have read describe the adsorption phenomenon in terms of amphiphile molecular states with all the thermodynamic models trying to explain the adsorption at equilibrium in that direction. However, let's think about this way, the surfactant molecule does not "adsorb" to the interface by itself, but rather the hydrogen bonding restoration "squeezes" the C-H to the interface to minimize the surface tension. In fact, this is true, and water should be described carefully in a thermodynamic way.
Thong Ly
There is such a theory and it is called the hydrophobic effect. When surfactant dissolves in water, some of the molecules are in water, and some of the others are adsorbed at the interface. When the interface is completely filled with a monomolecular surfactant layer, the formation of micelles begins. There are no more water molecules at the interface. The thermodynamics of adsorption has been developed, but as you rightly state, the role of water is not visible.
We are investigating the role of water. See the review and our other articles on my profile
Article Liquid Polyamorphous Transition and Self-Organization in Aqu...
Surfactants and other molecules are "pushed" out of the water to the interface and into micelles. The Gibbs energy of the pushing (adsorption) process is equal to the Gibbs energy of the formation of a cavity of the size of the surfactant. Similarly, for micelle formation. Adsorption is visible and thermodynamics of adsorption is developed, and the role of water is not visible.
The role of water in the adsorption and micelle formation of surfactants is of great importance. Surfactant micelles are studied as models of hydrophobic interaction processes in biological cells. The intermolecular interaction of water has quantum effects.
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