Is Polyethylene glycol 400 (PEG 400) really a non-ionic surfactant? When PEG 400 dissolved in water, is it only decrease the surface tension of water or it can also form micelle and it has a CMC (critical micelle concentration)?
PEG only slightly lowers surface tension in comparison to surfactants. To be a surfactant compound needs to have hydrophilic and hydrophobic compartments. In PEG we have only CH2-CH2-O units which are hydrophilic. Therefore increasing H2O/PEG ratio these units will gradually hydrate without any agglomerate formation.
https://www.researchgate.net/publication/241013746_The_use_of_methyl_orange_for_the_characterization_of_micelles_in_aqueous_nonionic_surfactant_solutions
Article The use of methyl orange for the characterization of micelle...
Thanks for all of your answers, especially Professor Titus Sobisch. I test PEG 400 and it is found that it decrease surface tension of water from 71 mN/m to 65.66 mN/m at 3000 ppm and T=303 K. So, according to your idea and my experimental results, it does not show interfacial/surface activity, so it is not a surfactant. It is just a soluble polymer in water.
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