[pcm81]

I read the wiki article about surfactants. https://en.wikipedia.org/wiki/Surfactant

My question is rather theoretical but should be pretty straight forward.

The question is: Given some organic compound, say grease or oil, would a surfactant with tail made of the same carbon chain as the "given" compound (or parts of that compound) be the ideal surfactant for that compound or will there be a law of diminishing returns vs the length of the carbon chains in the given compound, resulting in "best" surfactant tail being something other than that compound?

I realize that the "head" of the surfactant will contribute to how "ideal" it may be for a particular combination of solute (organic compound) and solvent (water or some other substance).

It seems to me the design of an "ideal" surfactant should try to optimize several criteria:
1. Surfactant needs to have hydrophobic chain that can enter and bond to the target solute
2. Surfactant needs to have a hydrophilic head that needs to have strong attraction to solvent.
3. Surfactant needs to be the smallest possible molecule that meets criteria 1 and 2, in order to increase the total number of molecules of surfactant per gram of it.

One of the most common surfactants is sodium stearate, which seems to me to have a rather long carbon chain... Which is what got me thinking and wondering about the effect of length of the carbon chain and if chains made from solute would be the ideal match for that material?

I guess a long carbon chain can get partially embedded into solute with its hydrophilic head sticking far out from solute, being pulled by solvent reasonably far away from the boundary of solute to solvent.

But also, a carbon chain which can easily enter solute can just as easily be pulled out, rather than pulling solute with it...

Years ago the basic chemistry taught me that "like dissolves like" but it did not go deep enough to teach me about what makes 2 organic compounds mix best vs not at all... And it seems "mixing" of the organic compounds is the key here, since organic tail of the surfactant has to mix into the solute.

Thanks ahead

[Enthalpy]

I would add:

4. made from cheap and abundant resource.

because we just spill surfactants on the floor before rinsing them to the sewage. Fats, vegetable oils and soda are cheap enough for that. Starting from crude oil, coal, butane, sugar, starch... would demand costly processing. Are there alternative sources? Maybe myrcene can get a hydrophilic head with a limited effort, similar to the production of maleic anhydride, or by Diels-Alder with maleic anhydride, followed by neutralisation. Or styrene, cyclopentadiene - there are few such commodities, all needing more processing than a fat. Maybe an aromatic surfactant emulsionates an aromatic hydrocarbon better and justifies the cost?

For high-tech uses, other surfactants are possible. I saw papers about "micro-emulsions" with ethanol or butanol as a surfactant.