I am reviewing some literature for my thesis; I found in one article that NaCl salt drastically increases the CMC of carboxy betaine (Cocamidopropyl betaine). Is there any molecular-level explanation I should follow?
I know it is not true for ionic surfactants, but non-ionic and zwitterionic surfactants follow the 'salt-in' or 'salt-out' effect.
Article Effect of Sodium Chloride on the Surface and Wetting Propert...
Virendrakumar Patel
It would be nice if you wrote a link to this effect.
Hello Virendrakumar Patel
maybe this discussion at https://www.researchgate.net/post/How_does_salt_influences_CMC_and_micelle_formation is of use.
one should mention, that this effect usually will be practically irrelevant, as betains are used as minor compounds in practical formulations beside other surfactants. Adding electrolyes the amphotheric complex will be weaker and character shifts more to real zwitterionic I assume.
For micellization, betaines and sulfobetaines behave more like nonionic surfactants than ionic surfactants with added electrolyes, provided they are in the zwitterionic state. At low pH they will be cationic and far more susceptible to electrolyte effects...
See Weers et al. Effect of intramolecular charge separation distance on the solution properties of betaines and sulfobetaines. Langmuir 1991, 7:854-867.
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