Based on the previous investigations, the interaction between hydrophobic tail of a foaming surfactant like CTAB and additive like ethanol is stronger than the one between the hydrophobic tail and water. Can this kind of interaction decrease foaming of a surfactant?
Foaming is the process of foam formation. "Foaming of surfactant" is not a correct phrase. I already answered that the main thing in the formation of foam is the strength of black films with water. This water is retained by surfactant layers on both sides. Layers of surfactants are created, including hydrophobic interaction. You can read about it in our works. Ethyl alcohol weakens hydrophobic interactions. Therefore, it acts as a defoamer.
The critical micelle concentration "CMC" of surfactants is defined as the concentration of the surfactant solution at which the molecules self- aggregate to form spherically shaped micelles. The molecular structure of surfactants is amphiphilic i.e, it consists of both nonpolar (hydrophobic, lipophilic) & polar (hydrophilic) parts.
Talking about ionic surfactants, the micelle formation is affected by the hydrophobic length and the nature of the additive . As a general rule for ionic surfactants, the CMC is halved when the length of the straight hydrocarbon chain is increased by one methylene group. Some additives contribute to CMC decrease (e.g. xylose & fructose) and some contribute to CMC increase (e.g. the presence of polar groups such OH) in the hydrophobic tail). Since this tail interacts but does not bond OH as the question implies, then its effect will not be that much. Taking into account that foaming will not be improved by the presence of ethanol & we saw that during the production of soap in an experiment done by our students each semester.
@Yuri Mirgorod
Thanks a lot, professor
Yes, I measured the surface tension values and my calculations results agree with your comments.
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