It's common knowledge that surfactant molecules get adsorbed at the interface of air - water; question is how do they affect the hydrogen bonding style that exists there? Especially concerning the hydrophobic head of say soap molecules at the water surface. How do they modify the surface of water in which they exist?
Depending on the concentration and structure the surfactant monolayer consists of the following: gaseous, liquid-expended, liquid-expended/liquid-condensed (LE/LC),, liquid-condensed. LE/LC is most investigated monolaer phase transition in the literature. The order of this transition has been subgect of a long debate. The dispute could finalty the resolved by direct optical of phase coexistense at the water serface, provoting this transition to be of first order. Such a phase change on the surface corresponds to a phase transition in the volume of water, which is described in our work.Mirgorod Yu.A., Dolenko T.A. Liquid Polyamorphous Transition and Self-Оrganization in Aqueous Solutions of Ionic surfactant.// DOI:10.1021/acs.langmuir.5b00479.2015.
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That's meanly drived by the combined effects of thermodinamic, looking for equilibrium and the molecular structure that produce a moving of the surfactant molecules and a physical displacement of the water molecules from surface. For a deeply information, you can consulted some pharmacy books like "Remington: The science and practice of pharmacy" or "Pharmaceutics:The science of dosage forms" M.E.Aulton
Several types of forces such as electrostatic, covalent, hydrophobic and hydrogen bonding of various species are involved in adsorption of surfactants at the interface. Depending upon the polarity of surfactant head group, force of interaction occur. there are two effects applied simultaneously hydrophobic effect and hydrophilic nature of head group/medium. This effect promote to break the structured water and after monolayer formation aggregation of surfactant molecule takes place.
Journal of Colloid and Interface Science 291 (2005) 570–576
Since surfactants molecules are amphiphillic, the polar head group is oriented to the aqueous medium while the long hydrophobic tails point away from the water. Addition of surfactants to water causes the surfactant molecules to align on the surface of water as mentioned above, forming a monolayer. Further addition of surfactants causes the molecules to aggregate into clusters called micelles. This takes place at a concentration called the critical micelle concentration (CMC), which varies with the type and nature of the surfactant molecule
Thank you all for the helpful answers and comments, plus the sources of useful literature.
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